diff --git a/compiler/rustc_ast/src/mut_visit.rs b/compiler/rustc_ast/src/mut_visit.rs
index 90d31d4801f92..024d9687f3119 100644
--- a/compiler/rustc_ast/src/mut_visit.rs
+++ b/compiler/rustc_ast/src/mut_visit.rs
@@ -28,7 +28,7 @@ pub trait ExpectOne<A: Array> {
 
 impl<A: Array> ExpectOne<A> for SmallVec<A> {
     fn expect_one(self, err: &'static str) -> A::Item {
-        assert!(self.len() == 1, err);
+        assert!(self.len() == 1, "{}", err);
         self.into_iter().next().unwrap()
     }
 }
diff --git a/compiler/rustc_data_structures/src/lib.rs b/compiler/rustc_data_structures/src/lib.rs
index 36d261fb737ce..5880bbd3de44e 100644
--- a/compiler/rustc_data_structures/src/lib.rs
+++ b/compiler/rustc_data_structures/src/lib.rs
@@ -13,6 +13,7 @@
 #![feature(unboxed_closures)]
 #![feature(generator_trait)]
 #![feature(fn_traits)]
+#![feature(int_bits_const)]
 #![feature(min_specialization)]
 #![feature(auto_traits)]
 #![feature(nll)]
diff --git a/compiler/rustc_error_codes/src/error_codes/E0463.md b/compiler/rustc_error_codes/src/error_codes/E0463.md
index e46938c607d34..d0cd1b1dcb75b 100644
--- a/compiler/rustc_error_codes/src/error_codes/E0463.md
+++ b/compiler/rustc_error_codes/src/error_codes/E0463.md
@@ -11,3 +11,24 @@ extern crate cake_is_a_lie; // error: can't find crate for `cake_is_a_lie`
 You need to link your code to the relevant crate in order to be able to use it
 (through Cargo or the `-L` option of rustc example). Plugins are crates as
 well, and you link to them the same way.
+
+## Common causes
+
+- The crate is not present at all. If using Cargo, add it to `[dependencies]`
+  in Cargo.toml.
+- The crate is present, but under a different name. If using Cargo, look for
+  `package = ` under `[dependencies]` in Cargo.toml.
+
+## Common causes for missing `std` or `core`
+
+- You are cross-compiling for a target which doesn't have `std` prepackaged.
+  Consider one of the following:
+  + Adding a pre-compiled version of std with `rustup target add`
+  + Building std from source with `cargo build -Z build-std`
+  + Using `#![no_std]` at the crate root, so you won't need `std` in the first
+    place.
+- You are developing the compiler itself and haven't built libstd from source.
+  You can usually build it with `x.py build library/std`. More information
+  about x.py is available in the [rustc-dev-guide].
+
+[rustc-dev-guide]: https://rustc-dev-guide.rust-lang.org/building/how-to-build-and-run.html#building-the-compiler
diff --git a/compiler/rustc_errors/src/lib.rs b/compiler/rustc_errors/src/lib.rs
index e184e929b0745..aa88233209940 100644
--- a/compiler/rustc_errors/src/lib.rs
+++ b/compiler/rustc_errors/src/lib.rs
@@ -901,7 +901,7 @@ impl HandlerInner {
 
     fn span_bug(&mut self, sp: impl Into<MultiSpan>, msg: &str) -> ! {
         self.emit_diag_at_span(Diagnostic::new(Bug, msg), sp);
-        panic!(ExplicitBug);
+        panic::panic_any(ExplicitBug);
     }
 
     fn emit_diag_at_span(&mut self, mut diag: Diagnostic, sp: impl Into<MultiSpan>) {
@@ -955,7 +955,7 @@ impl HandlerInner {
 
     fn bug(&mut self, msg: &str) -> ! {
         self.emit_diagnostic(&Diagnostic::new(Bug, msg));
-        panic!(ExplicitBug);
+        panic::panic_any(ExplicitBug);
     }
 
     fn delay_as_bug(&mut self, diagnostic: Diagnostic) {
diff --git a/compiler/rustc_hir/src/hir.rs b/compiler/rustc_hir/src/hir.rs
index 1c16dc026670b..58bcd37478a73 100644
--- a/compiler/rustc_hir/src/hir.rs
+++ b/compiler/rustc_hir/src/hir.rs
@@ -2057,6 +2057,28 @@ pub enum PrimTy {
 }
 
 impl PrimTy {
+    /// All of the primitive types
+    pub const ALL: [Self; 17] = [
+        // any changes here should also be reflected in `PrimTy::from_name`
+        Self::Int(IntTy::I8),
+        Self::Int(IntTy::I16),
+        Self::Int(IntTy::I32),
+        Self::Int(IntTy::I64),
+        Self::Int(IntTy::I128),
+        Self::Int(IntTy::Isize),
+        Self::Uint(UintTy::U8),
+        Self::Uint(UintTy::U16),
+        Self::Uint(UintTy::U32),
+        Self::Uint(UintTy::U64),
+        Self::Uint(UintTy::U128),
+        Self::Uint(UintTy::Usize),
+        Self::Float(FloatTy::F32),
+        Self::Float(FloatTy::F64),
+        Self::Bool,
+        Self::Char,
+        Self::Str,
+    ];
+
     pub fn name_str(self) -> &'static str {
         match self {
             PrimTy::Int(i) => i.name_str(),
@@ -2078,6 +2100,33 @@ impl PrimTy {
             PrimTy::Char => sym::char,
         }
     }
+
+    /// Returns the matching `PrimTy` for a `Symbol` such as "str" or "i32".
+    /// Returns `None` if no matching type is found.
+    pub fn from_name(name: Symbol) -> Option<Self> {
+        let ty = match name {
+            // any changes here should also be reflected in `PrimTy::ALL`
+            sym::i8 => Self::Int(IntTy::I8),
+            sym::i16 => Self::Int(IntTy::I16),
+            sym::i32 => Self::Int(IntTy::I32),
+            sym::i64 => Self::Int(IntTy::I64),
+            sym::i128 => Self::Int(IntTy::I128),
+            sym::isize => Self::Int(IntTy::Isize),
+            sym::u8 => Self::Uint(UintTy::U8),
+            sym::u16 => Self::Uint(UintTy::U16),
+            sym::u32 => Self::Uint(UintTy::U32),
+            sym::u64 => Self::Uint(UintTy::U64),
+            sym::u128 => Self::Uint(UintTy::U128),
+            sym::usize => Self::Uint(UintTy::Usize),
+            sym::f32 => Self::Float(FloatTy::F32),
+            sym::f64 => Self::Float(FloatTy::F64),
+            sym::bool => Self::Bool,
+            sym::char => Self::Char,
+            sym::str => Self::Str,
+            _ => return None,
+        };
+        Some(ty)
+    }
 }
 
 #[derive(Debug, HashStable_Generic)]
diff --git a/compiler/rustc_index/src/bit_set/tests.rs b/compiler/rustc_index/src/bit_set/tests.rs
index 6cc3e9427d1a7..c11b98e77aa58 100644
--- a/compiler/rustc_index/src/bit_set/tests.rs
+++ b/compiler/rustc_index/src/bit_set/tests.rs
@@ -1,6 +1,7 @@
 use super::*;
 
 extern crate test;
+use std::hint::black_box;
 use test::Bencher;
 
 #[test]
@@ -364,3 +365,36 @@ fn union_hybrid_sparse_full_small_domain(b: &mut Bencher) {
         sparse.union(&dense);
     })
 }
+
+#[bench]
+fn bench_insert(b: &mut Bencher) {
+    let mut bs = BitSet::new_filled(99999usize);
+    b.iter(|| {
+        black_box(bs.insert(black_box(100u32)));
+    });
+}
+
+#[bench]
+fn bench_remove(b: &mut Bencher) {
+    let mut bs = BitSet::new_filled(99999usize);
+    b.iter(|| {
+        black_box(bs.remove(black_box(100u32)));
+    });
+}
+
+#[bench]
+fn bench_iter(b: &mut Bencher) {
+    let bs = BitSet::new_filled(99999usize);
+    b.iter(|| {
+        bs.iter().map(|b: usize| black_box(b)).for_each(drop);
+    });
+}
+
+#[bench]
+fn bench_intersect(b: &mut Bencher) {
+    let mut ba: BitSet<u32> = BitSet::new_filled(99999usize);
+    let bb = BitSet::new_filled(99999usize);
+    b.iter(|| {
+        ba.intersect(black_box(&bb));
+    });
+}
diff --git a/compiler/rustc_lint/src/context.rs b/compiler/rustc_lint/src/context.rs
index 8bd9dad785c4b..58a9064b9195b 100644
--- a/compiler/rustc_lint/src/context.rs
+++ b/compiler/rustc_lint/src/context.rs
@@ -39,6 +39,7 @@ use rustc_session::SessionLintStore;
 use rustc_span::lev_distance::find_best_match_for_name;
 use rustc_span::{symbol::Symbol, MultiSpan, Span, DUMMY_SP};
 use rustc_target::abi::LayoutOf;
+use tracing::debug;
 
 use std::cell::Cell;
 use std::slice;
@@ -336,6 +337,20 @@ impl LintStore {
         }
     }
 
+    /// True if this symbol represents a lint group name.
+    pub fn is_lint_group(&self, lint_name: Symbol) -> bool {
+        debug!(
+            "is_lint_group(lint_name={:?}, lint_groups={:?})",
+            lint_name,
+            self.lint_groups.keys().collect::<Vec<_>>()
+        );
+        let lint_name_str = &*lint_name.as_str();
+        self.lint_groups.contains_key(&lint_name_str) || {
+            let warnings_name_str = crate::WARNINGS.name_lower();
+            lint_name_str == &*warnings_name_str
+        }
+    }
+
     /// Checks the name of a lint for its existence, and whether it was
     /// renamed or removed. Generates a DiagnosticBuilder containing a
     /// warning for renamed and removed lints. This is over both lint
diff --git a/compiler/rustc_lint/src/levels.rs b/compiler/rustc_lint/src/levels.rs
index 18cd25e5d2aa3..1fc2bd0916757 100644
--- a/compiler/rustc_lint/src/levels.rs
+++ b/compiler/rustc_lint/src/levels.rs
@@ -5,7 +5,7 @@ use rustc_ast::attr;
 use rustc_ast::unwrap_or;
 use rustc_ast_pretty::pprust;
 use rustc_data_structures::fx::FxHashMap;
-use rustc_errors::{struct_span_err, Applicability};
+use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder};
 use rustc_hir as hir;
 use rustc_hir::def_id::{CrateNum, LOCAL_CRATE};
 use rustc_hir::{intravisit, HirId};
@@ -17,11 +17,15 @@ use rustc_middle::lint::{
 };
 use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::TyCtxt;
-use rustc_session::lint::{builtin, Level, Lint, LintId};
+use rustc_session::lint::{
+    builtin::{self, FORBIDDEN_LINT_GROUPS},
+    Level, Lint, LintId,
+};
 use rustc_session::parse::feature_err;
 use rustc_session::Session;
 use rustc_span::symbol::{sym, Symbol};
 use rustc_span::{source_map::MultiSpan, Span, DUMMY_SP};
+use tracing::debug;
 
 use std::cmp;
 
@@ -51,6 +55,7 @@ pub struct LintLevelsBuilder<'s> {
     id_to_set: FxHashMap<HirId, u32>,
     cur: u32,
     warn_about_weird_lints: bool,
+    store: &'s LintStore,
 }
 
 pub struct BuilderPush {
@@ -59,13 +64,14 @@ pub struct BuilderPush {
 }
 
 impl<'s> LintLevelsBuilder<'s> {
-    pub fn new(sess: &'s Session, warn_about_weird_lints: bool, store: &LintStore) -> Self {
+    pub fn new(sess: &'s Session, warn_about_weird_lints: bool, store: &'s LintStore) -> Self {
         let mut builder = LintLevelsBuilder {
             sess,
             sets: LintLevelSets::new(),
             cur: 0,
             id_to_set: Default::default(),
             warn_about_weird_lints,
+            store,
         };
         builder.process_command_line(sess, store);
         assert_eq!(builder.sets.list.len(), 1);
@@ -120,36 +126,75 @@ impl<'s> LintLevelsBuilder<'s> {
             if let (Level::Forbid, old_src) =
                 self.sets.get_lint_level(id.lint, self.cur, Some(&specs), &self.sess)
             {
-                let mut diag_builder = struct_span_err!(
-                    self.sess,
-                    src.span(),
-                    E0453,
-                    "{}({}) incompatible with previous forbid",
-                    level.as_str(),
-                    src.name(),
+                // Backwards compatibility check:
+                //
+                // We used to not consider `forbid(lint_group)`
+                // as preventing `allow(lint)` for some lint `lint` in
+                // `lint_group`. For now, issue a future-compatibility
+                // warning for this case.
+                let id_name = id.lint.name_lower();
+                let fcw_warning = match old_src {
+                    LintLevelSource::Default => false,
+                    LintLevelSource::Node(symbol, _, _) => self.store.is_lint_group(symbol),
+                    LintLevelSource::CommandLine(symbol, _) => self.store.is_lint_group(symbol),
+                };
+                debug!(
+                    "fcw_warning={:?}, specs.get(&id) = {:?}, old_src={:?}, id_name={:?}",
+                    fcw_warning, specs, old_src, id_name
                 );
-                diag_builder.span_label(src.span(), "overruled by previous forbid");
-                match old_src {
-                    LintLevelSource::Default => {
-                        diag_builder.note(&format!(
-                            "`forbid` lint level is the default for {}",
-                            id.to_string()
-                        ));
-                    }
-                    LintLevelSource::Node(_, forbid_source_span, reason) => {
-                        diag_builder.span_label(forbid_source_span, "`forbid` level set here");
-                        if let Some(rationale) = reason {
-                            diag_builder.note(&rationale.as_str());
+
+                let decorate_diag_builder = |mut diag_builder: DiagnosticBuilder<'_>| {
+                    diag_builder.span_label(src.span(), "overruled by previous forbid");
+                    match old_src {
+                        LintLevelSource::Default => {
+                            diag_builder.note(&format!(
+                                "`forbid` lint level is the default for {}",
+                                id.to_string()
+                            ));
+                        }
+                        LintLevelSource::Node(_, forbid_source_span, reason) => {
+                            diag_builder.span_label(forbid_source_span, "`forbid` level set here");
+                            if let Some(rationale) = reason {
+                                diag_builder.note(&rationale.as_str());
+                            }
+                        }
+                        LintLevelSource::CommandLine(_, _) => {
+                            diag_builder.note("`forbid` lint level was set on command line");
                         }
                     }
-                    LintLevelSource::CommandLine(_, _) => {
-                        diag_builder.note("`forbid` lint level was set on command line");
-                    }
+                    diag_builder.emit();
+                };
+                if !fcw_warning {
+                    let diag_builder = struct_span_err!(
+                        self.sess,
+                        src.span(),
+                        E0453,
+                        "{}({}) incompatible with previous forbid",
+                        level.as_str(),
+                        src.name(),
+                    );
+                    decorate_diag_builder(diag_builder);
+                } else {
+                    self.struct_lint(
+                        FORBIDDEN_LINT_GROUPS,
+                        Some(src.span().into()),
+                        |diag_builder| {
+                            let diag_builder = diag_builder.build(&format!(
+                                "{}({}) incompatible with previous forbid",
+                                level.as_str(),
+                                src.name(),
+                            ));
+                            decorate_diag_builder(diag_builder);
+                        },
+                    );
                 }
-                diag_builder.emit();
 
-                // Retain the forbid lint level
-                return;
+                // Retain the forbid lint level, unless we are
+                // issuing a FCW. In the FCW case, we want to
+                // respect the new setting.
+                if !fcw_warning {
+                    return;
+                }
             }
         }
         specs.insert(id, (level, src));
diff --git a/compiler/rustc_lint/src/lib.rs b/compiler/rustc_lint/src/lib.rs
index 6f44436e2a010..638b73c27a8d7 100644
--- a/compiler/rustc_lint/src/lib.rs
+++ b/compiler/rustc_lint/src/lib.rs
@@ -55,8 +55,8 @@ mod late;
 mod levels;
 mod methods;
 mod non_ascii_idents;
+mod non_fmt_panic;
 mod nonstandard_style;
-mod panic_fmt;
 mod passes;
 mod redundant_semicolon;
 mod traits;
@@ -81,8 +81,8 @@ use builtin::*;
 use internal::*;
 use methods::*;
 use non_ascii_idents::*;
+use non_fmt_panic::NonPanicFmt;
 use nonstandard_style::*;
-use panic_fmt::PanicFmt;
 use redundant_semicolon::*;
 use traits::*;
 use types::*;
@@ -169,7 +169,7 @@ macro_rules! late_lint_passes {
                 ClashingExternDeclarations: ClashingExternDeclarations::new(),
                 DropTraitConstraints: DropTraitConstraints,
                 TemporaryCStringAsPtr: TemporaryCStringAsPtr,
-                PanicFmt: PanicFmt,
+                NonPanicFmt: NonPanicFmt,
             ]
         );
     };
diff --git a/compiler/rustc_lint/src/non_fmt_panic.rs b/compiler/rustc_lint/src/non_fmt_panic.rs
new file mode 100644
index 0000000000000..e98297b692c92
--- /dev/null
+++ b/compiler/rustc_lint/src/non_fmt_panic.rs
@@ -0,0 +1,197 @@
+use crate::{LateContext, LateLintPass, LintContext};
+use rustc_ast as ast;
+use rustc_errors::{pluralize, Applicability};
+use rustc_hir as hir;
+use rustc_middle::ty;
+use rustc_parse_format::{ParseMode, Parser, Piece};
+use rustc_span::{sym, symbol::kw, InnerSpan, Span, Symbol};
+
+declare_lint! {
+    /// The `non_fmt_panic` lint detects `panic!(..)` invocations where the first
+    /// argument is not a formatting string.
+    ///
+    /// ### Example
+    ///
+    /// ```rust,no_run
+    /// panic!("{}");
+    /// panic!(123);
+    /// ```
+    ///
+    /// {{produces}}
+    ///
+    /// ### Explanation
+    ///
+    /// In Rust 2018 and earlier, `panic!(x)` directly uses `x` as the message.
+    /// That means that `panic!("{}")` panics with the message `"{}"` instead
+    /// of using it as a formatting string, and `panic!(123)` will panic with
+    /// an `i32` as message.
+    ///
+    /// Rust 2021 always interprets the first argument as format string.
+    NON_FMT_PANIC,
+    Warn,
+    "detect single-argument panic!() invocations in which the argument is not a format string",
+    report_in_external_macro
+}
+
+declare_lint_pass!(NonPanicFmt => [NON_FMT_PANIC]);
+
+impl<'tcx> LateLintPass<'tcx> for NonPanicFmt {
+    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'tcx>) {
+        if let hir::ExprKind::Call(f, [arg]) = &expr.kind {
+            if let &ty::FnDef(def_id, _) = cx.typeck_results().expr_ty(f).kind() {
+                if Some(def_id) == cx.tcx.lang_items().begin_panic_fn()
+                    || Some(def_id) == cx.tcx.lang_items().panic_fn()
+                    || Some(def_id) == cx.tcx.lang_items().panic_str()
+                {
+                    if let Some(id) = f.span.ctxt().outer_expn_data().macro_def_id {
+                        if cx.tcx.is_diagnostic_item(sym::std_panic_2015_macro, id)
+                            || cx.tcx.is_diagnostic_item(sym::core_panic_2015_macro, id)
+                        {
+                            check_panic(cx, f, arg);
+                        }
+                    }
+                }
+            }
+        }
+    }
+}
+
+fn check_panic<'tcx>(cx: &LateContext<'tcx>, f: &'tcx hir::Expr<'tcx>, arg: &'tcx hir::Expr<'tcx>) {
+    if let hir::ExprKind::Lit(lit) = &arg.kind {
+        if let ast::LitKind::Str(sym, _) = lit.node {
+            // The argument is a string literal.
+            check_panic_str(cx, f, arg, &sym.as_str());
+            return;
+        }
+    }
+
+    // The argument is *not* a string literal.
+
+    let (span, panic) = panic_call(cx, f);
+
+    cx.struct_span_lint(NON_FMT_PANIC, arg.span, |lint| {
+        let mut l = lint.build("panic message is not a string literal");
+        l.note("this is no longer accepted in Rust 2021");
+        if span.contains(arg.span) {
+            l.span_suggestion_verbose(
+                arg.span.shrink_to_lo(),
+                "add a \"{}\" format string to Display the message",
+                "\"{}\", ".into(),
+                Applicability::MaybeIncorrect,
+            );
+            if panic == sym::std_panic_macro {
+                l.span_suggestion_verbose(
+                    span.until(arg.span),
+                    "or use std::panic::panic_any instead",
+                    "std::panic::panic_any(".into(),
+                    Applicability::MachineApplicable,
+                );
+            }
+        }
+        l.emit();
+    });
+}
+
+fn check_panic_str<'tcx>(
+    cx: &LateContext<'tcx>,
+    f: &'tcx hir::Expr<'tcx>,
+    arg: &'tcx hir::Expr<'tcx>,
+    fmt: &str,
+) {
+    if !fmt.contains(&['{', '}'][..]) {
+        // No brace, no problem.
+        return;
+    }
+
+    let fmt_span = arg.span.source_callsite();
+
+    let (snippet, style) = match cx.sess().parse_sess.source_map().span_to_snippet(fmt_span) {
+        Ok(snippet) => {
+            // Count the number of `#`s between the `r` and `"`.
+            let style = snippet.strip_prefix('r').and_then(|s| s.find('"'));
+            (Some(snippet), style)
+        }
+        Err(_) => (None, None),
+    };
+
+    let mut fmt_parser =
+        Parser::new(fmt.as_ref(), style, snippet.clone(), false, ParseMode::Format);
+    let n_arguments = (&mut fmt_parser).filter(|a| matches!(a, Piece::NextArgument(_))).count();
+
+    let (span, _) = panic_call(cx, f);
+
+    if n_arguments > 0 && fmt_parser.errors.is_empty() {
+        let arg_spans: Vec<_> = match &fmt_parser.arg_places[..] {
+            [] => vec![fmt_span],
+            v => v.iter().map(|span| fmt_span.from_inner(*span)).collect(),
+        };
+        cx.struct_span_lint(NON_FMT_PANIC, arg_spans, |lint| {
+            let mut l = lint.build(match n_arguments {
+                1 => "panic message contains an unused formatting placeholder",
+                _ => "panic message contains unused formatting placeholders",
+            });
+            l.note("this message is not used as a format string when given without arguments, but will be in Rust 2021");
+            if span.contains(arg.span) {
+                l.span_suggestion(
+                    arg.span.shrink_to_hi(),
+                    &format!("add the missing argument{}", pluralize!(n_arguments)),
+                    ", ...".into(),
+                    Applicability::HasPlaceholders,
+                );
+                l.span_suggestion(
+                    arg.span.shrink_to_lo(),
+                    "or add a \"{}\" format string to use the message literally",
+                    "\"{}\", ".into(),
+                    Applicability::MachineApplicable,
+                );
+            }
+            l.emit();
+        });
+    } else {
+        let brace_spans: Option<Vec<_>> =
+            snippet.filter(|s| s.starts_with('"') || s.starts_with("r#")).map(|s| {
+                s.char_indices()
+                    .filter(|&(_, c)| c == '{' || c == '}')
+                    .map(|(i, _)| fmt_span.from_inner(InnerSpan { start: i, end: i + 1 }))
+                    .collect()
+            });
+        let msg = match &brace_spans {
+            Some(v) if v.len() == 1 => "panic message contains a brace",
+            _ => "panic message contains braces",
+        };
+        cx.struct_span_lint(NON_FMT_PANIC, brace_spans.unwrap_or(vec![span]), |lint| {
+            let mut l = lint.build(msg);
+            l.note("this message is not used as a format string, but will be in Rust 2021");
+            if span.contains(arg.span) {
+                l.span_suggestion(
+                    arg.span.shrink_to_lo(),
+                    "add a \"{}\" format string to use the message literally",
+                    "\"{}\", ".into(),
+                    Applicability::MachineApplicable,
+                );
+            }
+            l.emit();
+        });
+    }
+}
+
+fn panic_call<'tcx>(cx: &LateContext<'tcx>, f: &'tcx hir::Expr<'tcx>) -> (Span, Symbol) {
+    let mut expn = f.span.ctxt().outer_expn_data();
+
+    let mut panic_macro = kw::Empty;
+
+    // Unwrap more levels of macro expansion, as panic_2015!()
+    // was likely expanded from panic!() and possibly from
+    // [debug_]assert!().
+    for &i in
+        &[sym::std_panic_macro, sym::core_panic_macro, sym::assert_macro, sym::debug_assert_macro]
+    {
+        let parent = expn.call_site.ctxt().outer_expn_data();
+        if parent.macro_def_id.map_or(false, |id| cx.tcx.is_diagnostic_item(i, id)) {
+            expn = parent;
+            panic_macro = i;
+        }
+    }
+
+    (expn.call_site, panic_macro)
+}
diff --git a/compiler/rustc_lint/src/panic_fmt.rs b/compiler/rustc_lint/src/panic_fmt.rs
deleted file mode 100644
index 4a6aca72acbbe..0000000000000
--- a/compiler/rustc_lint/src/panic_fmt.rs
+++ /dev/null
@@ -1,155 +0,0 @@
-use crate::{LateContext, LateLintPass, LintContext};
-use rustc_ast as ast;
-use rustc_errors::{pluralize, Applicability};
-use rustc_hir as hir;
-use rustc_middle::ty;
-use rustc_parse_format::{ParseMode, Parser, Piece};
-use rustc_span::{sym, InnerSpan};
-
-declare_lint! {
-    /// The `panic_fmt` lint detects `panic!("..")` with `{` or `}` in the string literal.
-    ///
-    /// ### Example
-    ///
-    /// ```rust,no_run
-    /// panic!("{}");
-    /// ```
-    ///
-    /// {{produces}}
-    ///
-    /// ### Explanation
-    ///
-    /// In Rust 2018 and earlier, `panic!("{}")` panics with the message `"{}"`,
-    /// as a `panic!()` invocation with a single argument does not use `format_args!()`.
-    /// Rust 2021 interprets this string as format string, which breaks this.
-    PANIC_FMT,
-    Warn,
-    "detect braces in single-argument panic!() invocations",
-    report_in_external_macro
-}
-
-declare_lint_pass!(PanicFmt => [PANIC_FMT]);
-
-impl<'tcx> LateLintPass<'tcx> for PanicFmt {
-    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'tcx>) {
-        if let hir::ExprKind::Call(f, [arg]) = &expr.kind {
-            if let &ty::FnDef(def_id, _) = cx.typeck_results().expr_ty(f).kind() {
-                if Some(def_id) == cx.tcx.lang_items().begin_panic_fn()
-                    || Some(def_id) == cx.tcx.lang_items().panic_fn()
-                {
-                    check_panic(cx, f, arg);
-                }
-            }
-        }
-    }
-}
-
-fn check_panic<'tcx>(cx: &LateContext<'tcx>, f: &'tcx hir::Expr<'tcx>, arg: &'tcx hir::Expr<'tcx>) {
-    if let hir::ExprKind::Lit(lit) = &arg.kind {
-        if let ast::LitKind::Str(sym, _) = lit.node {
-            let mut expn = f.span.ctxt().outer_expn_data();
-            if let Some(id) = expn.macro_def_id {
-                if cx.tcx.is_diagnostic_item(sym::std_panic_2015_macro, id)
-                    || cx.tcx.is_diagnostic_item(sym::core_panic_2015_macro, id)
-                {
-                    let fmt = sym.as_str();
-                    if !fmt.contains(&['{', '}'][..]) {
-                        return;
-                    }
-
-                    let fmt_span = arg.span.source_callsite();
-
-                    let (snippet, style) =
-                        match cx.sess().parse_sess.source_map().span_to_snippet(fmt_span) {
-                            Ok(snippet) => {
-                                // Count the number of `#`s between the `r` and `"`.
-                                let style = snippet.strip_prefix('r').and_then(|s| s.find('"'));
-                                (Some(snippet), style)
-                            }
-                            Err(_) => (None, None),
-                        };
-
-                    let mut fmt_parser =
-                        Parser::new(fmt.as_ref(), style, snippet.clone(), false, ParseMode::Format);
-                    let n_arguments =
-                        (&mut fmt_parser).filter(|a| matches!(a, Piece::NextArgument(_))).count();
-
-                    // Unwrap more levels of macro expansion, as panic_2015!()
-                    // was likely expanded from panic!() and possibly from
-                    // [debug_]assert!().
-                    for &assert in &[
-                        sym::std_panic_macro,
-                        sym::core_panic_macro,
-                        sym::assert_macro,
-                        sym::debug_assert_macro,
-                    ] {
-                        let parent = expn.call_site.ctxt().outer_expn_data();
-                        if parent
-                            .macro_def_id
-                            .map_or(false, |id| cx.tcx.is_diagnostic_item(assert, id))
-                        {
-                            expn = parent;
-                        }
-                    }
-
-                    if n_arguments > 0 && fmt_parser.errors.is_empty() {
-                        let arg_spans: Vec<_> = match &fmt_parser.arg_places[..] {
-                            [] => vec![fmt_span],
-                            v => v.iter().map(|span| fmt_span.from_inner(*span)).collect(),
-                        };
-                        cx.struct_span_lint(PANIC_FMT, arg_spans, |lint| {
-                            let mut l = lint.build(match n_arguments {
-                                1 => "panic message contains an unused formatting placeholder",
-                                _ => "panic message contains unused formatting placeholders",
-                            });
-                            l.note("this message is not used as a format string when given without arguments, but will be in a future Rust edition");
-                            if expn.call_site.contains(arg.span) {
-                                l.span_suggestion(
-                                    arg.span.shrink_to_hi(),
-                                    &format!("add the missing argument{}", pluralize!(n_arguments)),
-                                    ", ...".into(),
-                                    Applicability::HasPlaceholders,
-                                );
-                                l.span_suggestion(
-                                    arg.span.shrink_to_lo(),
-                                    "or add a \"{}\" format string to use the message literally",
-                                    "\"{}\", ".into(),
-                                    Applicability::MachineApplicable,
-                                );
-                            }
-                            l.emit();
-                        });
-                    } else {
-                        let brace_spans: Option<Vec<_>> = snippet
-                            .filter(|s| s.starts_with('"') || s.starts_with("r#"))
-                            .map(|s| {
-                                s.char_indices()
-                                    .filter(|&(_, c)| c == '{' || c == '}')
-                                    .map(|(i, _)| {
-                                        fmt_span.from_inner(InnerSpan { start: i, end: i + 1 })
-                                    })
-                                    .collect()
-                            });
-                        let msg = match &brace_spans {
-                            Some(v) if v.len() == 1 => "panic message contains a brace",
-                            _ => "panic message contains braces",
-                        };
-                        cx.struct_span_lint(PANIC_FMT, brace_spans.unwrap_or(vec![expn.call_site]), |lint| {
-                            let mut l = lint.build(msg);
-                            l.note("this message is not used as a format string, but will be in a future Rust edition");
-                            if expn.call_site.contains(arg.span) {
-                                l.span_suggestion(
-                                    arg.span.shrink_to_lo(),
-                                    "add a \"{}\" format string to use the message literally",
-                                    "\"{}\", ".into(),
-                                    Applicability::MachineApplicable,
-                                );
-                            }
-                            l.emit();
-                        });
-                    }
-                }
-            }
-        }
-    }
-}
diff --git a/compiler/rustc_lint_defs/src/builtin.rs b/compiler/rustc_lint_defs/src/builtin.rs
index 4337600384008..da62ad3a6b1cd 100644
--- a/compiler/rustc_lint_defs/src/builtin.rs
+++ b/compiler/rustc_lint_defs/src/builtin.rs
@@ -5,10 +5,48 @@
 //! compiler code, rather than using their own custom pass. Those
 //! lints are all available in `rustc_lint::builtin`.
 
+// ignore-tidy-filelength
+
 use crate::{declare_lint, declare_lint_pass};
 use rustc_span::edition::Edition;
 use rustc_span::symbol::sym;
 
+declare_lint! {
+    /// The `forbidden_lint_groups` lint detects violations of
+    /// `forbid` applied to a lint group. Due to a bug in the compiler,
+    /// these used to be overlooked entirely. They now generate a warning.
+    ///
+    /// ### Example
+    ///
+    /// ```rust
+    /// #![forbid(warnings)]
+    /// #![deny(bad_style)]
+    ///
+    /// fn main() {}
+    /// ```
+    ///
+    /// {{produces}}
+    ///
+    /// ### Recommended fix
+    ///
+    /// If your crate is using `#![forbid(warnings)]`,
+    /// we recommend that you change to `#![deny(warnings)]`.
+    ///
+    /// ### Explanation
+    ///
+    /// Due to a compiler bug, applying `forbid` to lint groups
+    /// previously had no effect. The bug is now fixed but instead of
+    /// enforcing `forbid` we issue this future-compatibility warning
+    /// to avoid breaking existing crates.
+    pub FORBIDDEN_LINT_GROUPS,
+    Warn,
+    "applying forbid to lint-groups",
+    @future_incompatible = FutureIncompatibleInfo {
+        reference: "issue #81670 <https://github.com/rust-lang/rust/issues/81670>",
+        edition: None,
+    };
+}
+
 declare_lint! {
     /// The `ill_formed_attribute_input` lint detects ill-formed attribute
     /// inputs that were previously accepted and used in practice.
@@ -2888,6 +2926,7 @@ declare_lint_pass! {
     /// Does nothing as a lint pass, but registers some `Lint`s
     /// that are used by other parts of the compiler.
     HardwiredLints => [
+        FORBIDDEN_LINT_GROUPS,
         ILLEGAL_FLOATING_POINT_LITERAL_PATTERN,
         ARITHMETIC_OVERFLOW,
         UNCONDITIONAL_PANIC,
diff --git a/compiler/rustc_middle/src/lint.rs b/compiler/rustc_middle/src/lint.rs
index 0bdccf7b5f073..ca73481b21699 100644
--- a/compiler/rustc_middle/src/lint.rs
+++ b/compiler/rustc_middle/src/lint.rs
@@ -5,7 +5,10 @@ use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_errors::{DiagnosticBuilder, DiagnosticId};
 use rustc_hir::HirId;
-use rustc_session::lint::{builtin, Level, Lint, LintId};
+use rustc_session::lint::{
+    builtin::{self, FORBIDDEN_LINT_GROUPS},
+    Level, Lint, LintId,
+};
 use rustc_session::{DiagnosticMessageId, Session};
 use rustc_span::hygiene::MacroKind;
 use rustc_span::source_map::{DesugaringKind, ExpnKind, MultiSpan};
@@ -89,7 +92,12 @@ impl LintLevelSets {
         // If we're about to issue a warning, check at the last minute for any
         // directives against the warnings "lint". If, for example, there's an
         // `allow(warnings)` in scope then we want to respect that instead.
-        if level == Level::Warn {
+        //
+        // We exempt `FORBIDDEN_LINT_GROUPS` from this because it specifically
+        // triggers in cases (like #80988) where you have `forbid(warnings)`,
+        // and so if we turned that into an error, it'd defeat the purpose of the
+        // future compatibility warning.
+        if level == Level::Warn && LintId::of(lint) != LintId::of(FORBIDDEN_LINT_GROUPS) {
             let (warnings_level, warnings_src) =
                 self.get_lint_id_level(LintId::of(builtin::WARNINGS), idx, aux);
             if let Some(configured_warning_level) = warnings_level {
diff --git a/compiler/rustc_middle/src/util/bug.rs b/compiler/rustc_middle/src/util/bug.rs
index e79adcdb54598..791d5060fe5c7 100644
--- a/compiler/rustc_middle/src/util/bug.rs
+++ b/compiler/rustc_middle/src/util/bug.rs
@@ -3,7 +3,7 @@
 use crate::ty::{tls, TyCtxt};
 use rustc_span::{MultiSpan, Span};
 use std::fmt;
-use std::panic::Location;
+use std::panic::{panic_any, Location};
 
 #[cold]
 #[inline(never)]
@@ -32,7 +32,7 @@ fn opt_span_bug_fmt<S: Into<MultiSpan>>(
         match (tcx, span) {
             (Some(tcx), Some(span)) => tcx.sess.diagnostic().span_bug(span, &msg),
             (Some(tcx), None) => tcx.sess.diagnostic().bug(&msg),
-            (None, _) => panic!(msg),
+            (None, _) => panic_any(msg),
         }
     });
     unreachable!();
diff --git a/compiler/rustc_resolve/src/diagnostics.rs b/compiler/rustc_resolve/src/diagnostics.rs
index 9d55bafd2868e..0714d76f7448a 100644
--- a/compiler/rustc_resolve/src/diagnostics.rs
+++ b/compiler/rustc_resolve/src/diagnostics.rs
@@ -9,6 +9,7 @@ use rustc_feature::BUILTIN_ATTRIBUTES;
 use rustc_hir::def::Namespace::{self, *};
 use rustc_hir::def::{self, CtorKind, CtorOf, DefKind, NonMacroAttrKind};
 use rustc_hir::def_id::{DefId, CRATE_DEF_INDEX, LOCAL_CRATE};
+use rustc_hir::PrimTy;
 use rustc_middle::bug;
 use rustc_middle::ty::{self, DefIdTree};
 use rustc_session::Session;
@@ -718,10 +719,9 @@ impl<'a> Resolver<'a> {
                     }
                 }
                 Scope::BuiltinTypes => {
-                    let primitive_types = &this.primitive_type_table.primitive_types;
-                    suggestions.extend(primitive_types.iter().flat_map(|(name, prim_ty)| {
+                    suggestions.extend(PrimTy::ALL.iter().filter_map(|prim_ty| {
                         let res = Res::PrimTy(*prim_ty);
-                        filter_fn(res).then_some(TypoSuggestion::from_res(*name, res))
+                        filter_fn(res).then_some(TypoSuggestion::from_res(prim_ty.name(), res))
                     }))
                 }
             }
diff --git a/compiler/rustc_resolve/src/late.rs b/compiler/rustc_resolve/src/late.rs
index 9b5b793363b5b..cca40a793dd00 100644
--- a/compiler/rustc_resolve/src/late.rs
+++ b/compiler/rustc_resolve/src/late.rs
@@ -20,7 +20,7 @@ use rustc_errors::DiagnosticId;
 use rustc_hir::def::Namespace::{self, *};
 use rustc_hir::def::{self, CtorKind, DefKind, PartialRes, PerNS};
 use rustc_hir::def_id::{DefId, CRATE_DEF_INDEX};
-use rustc_hir::TraitCandidate;
+use rustc_hir::{PrimTy, TraitCandidate};
 use rustc_middle::{bug, span_bug};
 use rustc_session::lint;
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
@@ -1927,7 +1927,7 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
                     self.r.trait_map.insert(id, traits);
                 }
 
-                if self.r.primitive_type_table.primitive_types.contains_key(&path[0].ident.name) {
+                if PrimTy::from_name(path[0].ident.name).is_some() {
                     let mut std_path = Vec::with_capacity(1 + path.len());
 
                     std_path.push(Segment::from_ident(Ident::with_dummy_span(sym::std)));
@@ -2121,13 +2121,9 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
             // The same fallback is used when `a` resolves to nothing.
             PathResult::Module(ModuleOrUniformRoot::Module(_)) | PathResult::Failed { .. }
                 if (ns == TypeNS || path.len() > 1)
-                    && self
-                        .r
-                        .primitive_type_table
-                        .primitive_types
-                        .contains_key(&path[0].ident.name) =>
+                    && PrimTy::from_name(path[0].ident.name).is_some() =>
             {
-                let prim = self.r.primitive_type_table.primitive_types[&path[0].ident.name];
+                let prim = PrimTy::from_name(path[0].ident.name).unwrap();
                 PartialRes::with_unresolved_segments(Res::PrimTy(prim), path.len() - 1)
             }
             PathResult::Module(ModuleOrUniformRoot::Module(module)) => {
diff --git a/compiler/rustc_resolve/src/late/diagnostics.rs b/compiler/rustc_resolve/src/late/diagnostics.rs
index 927535b72bdb5..d2a693a568828 100644
--- a/compiler/rustc_resolve/src/late/diagnostics.rs
+++ b/compiler/rustc_resolve/src/late/diagnostics.rs
@@ -1212,8 +1212,8 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
             // Add primitive types to the mix
             if filter_fn(Res::PrimTy(PrimTy::Bool)) {
                 names.extend(
-                    self.r.primitive_type_table.primitive_types.iter().map(|(name, prim_ty)| {
-                        TypoSuggestion::from_res(*name, Res::PrimTy(*prim_ty))
+                    PrimTy::ALL.iter().map(|prim_ty| {
+                        TypoSuggestion::from_res(prim_ty.name(), Res::PrimTy(*prim_ty))
                     }),
                 )
             }
diff --git a/compiler/rustc_resolve/src/lib.rs b/compiler/rustc_resolve/src/lib.rs
index b19990e49b84f..2be669a1726a1 100644
--- a/compiler/rustc_resolve/src/lib.rs
+++ b/compiler/rustc_resolve/src/lib.rs
@@ -25,7 +25,7 @@ use rustc_arena::{DroplessArena, TypedArena};
 use rustc_ast::node_id::NodeMap;
 use rustc_ast::unwrap_or;
 use rustc_ast::visit::{self, Visitor};
-use rustc_ast::{self as ast, FloatTy, IntTy, NodeId, UintTy};
+use rustc_ast::{self as ast, NodeId};
 use rustc_ast::{Crate, CRATE_NODE_ID};
 use rustc_ast::{ItemKind, Path};
 use rustc_ast_lowering::ResolverAstLowering;
@@ -39,8 +39,7 @@ use rustc_hir::def::Namespace::*;
 use rustc_hir::def::{self, CtorOf, DefKind, NonMacroAttrKind, PartialRes};
 use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, LocalDefId, CRATE_DEF_INDEX};
 use rustc_hir::definitions::{DefKey, DefPathData, Definitions};
-use rustc_hir::PrimTy::{self, Bool, Char, Float, Int, Str, Uint};
-use rustc_hir::TraitCandidate;
+use rustc_hir::{PrimTy, TraitCandidate};
 use rustc_index::vec::IndexVec;
 use rustc_metadata::creader::{CStore, CrateLoader};
 use rustc_middle::hir::exports::ExportMap;
@@ -834,39 +833,6 @@ impl<'a> NameBinding<'a> {
     }
 }
 
-/// Interns the names of the primitive types.
-///
-/// All other types are defined somewhere and possibly imported, but the primitive ones need
-/// special handling, since they have no place of origin.
-struct PrimitiveTypeTable {
-    primitive_types: FxHashMap<Symbol, PrimTy>,
-}
-
-impl PrimitiveTypeTable {
-    fn new() -> PrimitiveTypeTable {
-        let mut table = FxHashMap::default();
-
-        table.insert(sym::bool, Bool);
-        table.insert(sym::char, Char);
-        table.insert(sym::f32, Float(FloatTy::F32));
-        table.insert(sym::f64, Float(FloatTy::F64));
-        table.insert(sym::isize, Int(IntTy::Isize));
-        table.insert(sym::i8, Int(IntTy::I8));
-        table.insert(sym::i16, Int(IntTy::I16));
-        table.insert(sym::i32, Int(IntTy::I32));
-        table.insert(sym::i64, Int(IntTy::I64));
-        table.insert(sym::i128, Int(IntTy::I128));
-        table.insert(sym::str, Str);
-        table.insert(sym::usize, Uint(UintTy::Usize));
-        table.insert(sym::u8, Uint(UintTy::U8));
-        table.insert(sym::u16, Uint(UintTy::U16));
-        table.insert(sym::u32, Uint(UintTy::U32));
-        table.insert(sym::u64, Uint(UintTy::U64));
-        table.insert(sym::u128, Uint(UintTy::U128));
-        Self { primitive_types: table }
-    }
-}
-
 #[derive(Debug, Default, Clone)]
 pub struct ExternPreludeEntry<'a> {
     extern_crate_item: Option<&'a NameBinding<'a>>,
@@ -912,9 +878,6 @@ pub struct Resolver<'a> {
     /// "self-confirming" import resolutions during import validation.
     unusable_binding: Option<&'a NameBinding<'a>>,
 
-    /// The idents for the primitive types.
-    primitive_type_table: PrimitiveTypeTable,
-
     /// Resolutions for nodes that have a single resolution.
     partial_res_map: NodeMap<PartialRes>,
     /// Resolutions for import nodes, which have multiple resolutions in different namespaces.
@@ -1284,8 +1247,6 @@ impl<'a> Resolver<'a> {
             last_import_segment: false,
             unusable_binding: None,
 
-            primitive_type_table: PrimitiveTypeTable::new(),
-
             partial_res_map: Default::default(),
             import_res_map: Default::default(),
             label_res_map: Default::default(),
@@ -1994,9 +1955,9 @@ impl<'a> Resolver<'a> {
         }
 
         if ns == TypeNS {
-            if let Some(prim_ty) = self.primitive_type_table.primitive_types.get(&ident.name) {
+            if let Some(prim_ty) = PrimTy::from_name(ident.name) {
                 let binding =
-                    (Res::PrimTy(*prim_ty), ty::Visibility::Public, DUMMY_SP, ExpnId::root())
+                    (Res::PrimTy(prim_ty), ty::Visibility::Public, DUMMY_SP, ExpnId::root())
                         .to_name_binding(self.arenas);
                 return Some(LexicalScopeBinding::Item(binding));
             }
diff --git a/compiler/rustc_resolve/src/macros.rs b/compiler/rustc_resolve/src/macros.rs
index d0adee2429d9a..d76db7c645abc 100644
--- a/compiler/rustc_resolve/src/macros.rs
+++ b/compiler/rustc_resolve/src/macros.rs
@@ -21,6 +21,7 @@ use rustc_expand::expand::{AstFragment, Invocation, InvocationKind};
 use rustc_feature::is_builtin_attr_name;
 use rustc_hir::def::{self, DefKind, NonMacroAttrKind};
 use rustc_hir::def_id;
+use rustc_hir::PrimTy;
 use rustc_middle::middle::stability;
 use rustc_middle::ty;
 use rustc_session::lint::builtin::{SOFT_UNSTABLE, UNUSED_MACROS};
@@ -796,12 +797,10 @@ impl<'a> Resolver<'a> {
                         }
                         result
                     }
-                    Scope::BuiltinTypes => {
-                        match this.primitive_type_table.primitive_types.get(&ident.name).cloned() {
-                            Some(prim_ty) => ok(Res::PrimTy(prim_ty), DUMMY_SP, this.arenas),
-                            None => Err(Determinacy::Determined),
-                        }
-                    }
+                    Scope::BuiltinTypes => match PrimTy::from_name(ident.name) {
+                        Some(prim_ty) => ok(Res::PrimTy(prim_ty), DUMMY_SP, this.arenas),
+                        None => Err(Determinacy::Determined),
+                    },
                 };
 
                 match result {
diff --git a/compiler/rustc_serialize/src/lib.rs b/compiler/rustc_serialize/src/lib.rs
index ea04e7bb44b3b..53c3adcc20c02 100644
--- a/compiler/rustc_serialize/src/lib.rs
+++ b/compiler/rustc_serialize/src/lib.rs
@@ -17,6 +17,7 @@ Core encoding and decoding interfaces.
 #![feature(min_specialization)]
 #![feature(vec_spare_capacity)]
 #![feature(core_intrinsics)]
+#![feature(int_bits_const)]
 #![feature(maybe_uninit_slice)]
 #![feature(new_uninit)]
 #![cfg_attr(test, feature(test))]
diff --git a/compiler/rustc_serialize/tests/leb128.rs b/compiler/rustc_serialize/tests/leb128.rs
index 3e2aab5125ab7..a2bcf2c251d7a 100644
--- a/compiler/rustc_serialize/tests/leb128.rs
+++ b/compiler/rustc_serialize/tests/leb128.rs
@@ -1,3 +1,4 @@
+#![feature(int_bits_const)]
 #![feature(maybe_uninit_slice)]
 #![feature(maybe_uninit_uninit_array)]
 
diff --git a/compiler/rustc_session/src/filesearch.rs b/compiler/rustc_session/src/filesearch.rs
index 3a757e5f0075d..47f14fa6b7a74 100644
--- a/compiler/rustc_session/src/filesearch.rs
+++ b/compiler/rustc_session/src/filesearch.rs
@@ -113,6 +113,8 @@ pub fn make_target_lib_path(sysroot: &Path, target_triple: &str) -> PathBuf {
     sysroot.join(&relative_target_lib_path(sysroot, target_triple))
 }
 
+// This function checks if sysroot is found using env::args().next(), and if it
+// is not found, uses env::current_exe() to imply sysroot.
 pub fn get_or_default_sysroot() -> PathBuf {
     // Follow symlinks.  If the resolved path is relative, make it absolute.
     fn canonicalize(path: PathBuf) -> PathBuf {
@@ -123,15 +125,51 @@ pub fn get_or_default_sysroot() -> PathBuf {
         fix_windows_verbatim_for_gcc(&path)
     }
 
-    match env::current_exe() {
-        Ok(exe) => {
-            let mut p = canonicalize(exe);
-            p.pop();
-            p.pop();
-            p
+    // Use env::current_exe() to get the path of the executable following
+    // symlinks/canonicalizing components.
+    fn from_current_exe() -> PathBuf {
+        match env::current_exe() {
+            Ok(exe) => {
+                let mut p = canonicalize(exe);
+                p.pop();
+                p.pop();
+                p
+            }
+            Err(e) => panic!("failed to get current_exe: {}", e),
+        }
+    }
+
+    // Use env::args().next() to get the path of the executable without
+    // following symlinks/canonicalizing any component. This makes the rustc
+    // binary able to locate Rust libraries in systems using content-addressable
+    // storage (CAS).
+    fn from_env_args_next() -> Option<PathBuf> {
+        match env::args_os().next() {
+            Some(first_arg) => {
+                let mut p = PathBuf::from(first_arg);
+
+                // Check if sysroot is found using env::args().next() only if the rustc in argv[0]
+                // is a symlink (see #79253). We might want to change/remove it to conform with
+                // https://www.gnu.org/prep/standards/standards.html#Finding-Program-Files in the
+                // future.
+                if fs::read_link(&p).is_err() {
+                    // Path is not a symbolic link or does not exist.
+                    return None;
+                }
+
+                p.pop();
+                p.pop();
+                let mut libdir = PathBuf::from(&p);
+                libdir.push(find_libdir(&p).as_ref());
+                if libdir.exists() { Some(p) } else { None }
+            }
+            None => None,
         }
-        Err(e) => panic!("failed to get current_exe: {}", e),
     }
+
+    // Check if sysroot is found using env::args().next(), and if is not found,
+    // use env::current_exe() to imply sysroot.
+    from_env_args_next().unwrap_or(from_current_exe())
 }
 
 // The name of the directory rustc expects libraries to be located.
diff --git a/library/alloc/src/lib.rs b/library/alloc/src/lib.rs
index 0a1ecced49abc..a49979fb7aa18 100644
--- a/library/alloc/src/lib.rs
+++ b/library/alloc/src/lib.rs
@@ -102,6 +102,7 @@
 #![feature(fn_traits)]
 #![feature(fundamental)]
 #![feature(inplace_iteration)]
+#![feature(int_bits_const)]
 #![feature(lang_items)]
 #![feature(layout_for_ptr)]
 #![feature(maybe_uninit_ref)]
diff --git a/library/alloc/tests/lib.rs b/library/alloc/tests/lib.rs
index 9c7343e8cbf5a..dd98f806451d8 100644
--- a/library/alloc/tests/lib.rs
+++ b/library/alloc/tests/lib.rs
@@ -17,6 +17,7 @@
 #![feature(binary_heap_retain)]
 #![feature(inplace_iteration)]
 #![feature(iter_map_while)]
+#![feature(int_bits_const)]
 #![feature(vecdeque_binary_search)]
 #![feature(slice_group_by)]
 #![feature(vec_extend_from_within)]
diff --git a/library/core/src/macros/panic.md b/library/core/src/macros/panic.md
index a02e74d5e5a4d..6e502426df906 100644
--- a/library/core/src/macros/panic.md
+++ b/library/core/src/macros/panic.md
@@ -10,22 +10,23 @@ tests. `panic!` is closely tied with the `unwrap` method of both
 `panic!` when they are set to [`None`] or [`Err`] variants.
 
 This macro is used to inject panic into a Rust thread, causing the thread to
-panic entirely. Each thread's panic can be reaped as the [`Box`]`<`[`Any`]`>` type,
-and the single-argument form of the `panic!` macro will be the value which
-is transmitted.
+panic entirely. This macro panics with a string and uses the [`format!`] syntax
+for building the message.
+
+Each thread's panic can be reaped as the [`Box`]`<`[`Any`]`>` type,
+which contains either a `&str` or `String` for regular `panic!()` invocations.
+To panic with a value of another other type, [`panic_any`] can be used.
 
 [`Result`] enum is often a better solution for recovering from errors than
 using the `panic!` macro. This macro should be used to avoid proceeding using
 incorrect values, such as from external sources. Detailed information about
 error handling is found in the [book].
 
-The multi-argument form of this macro panics with a string and has the
-[`format!`] syntax for building a string.
-
 See also the macro [`compile_error!`], for raising errors during compilation.
 
 [ounwrap]: Option::unwrap
 [runwrap]: Result::unwrap
+[`panic_any`]: ../std/panic/fn.panic_any.html
 [`Box`]: ../std/boxed/struct.Box.html
 [`Any`]: crate::any::Any
 [`format!`]: ../std/macro.format.html
@@ -42,6 +43,6 @@ program with code `101`.
 # #![allow(unreachable_code)]
 panic!();
 panic!("this is a terrible mistake!");
-panic!(4); // panic with the value of 4 to be collected elsewhere
 panic!("this is a {} {message}", "fancy", message = "message");
+std::panic::panic_any(4); // panic with the value of 4 to be collected elsewhere
 ```
diff --git a/library/core/src/num/int_macros.rs b/library/core/src/num/int_macros.rs
index 96affd17cc520..8fdd7c9e5d7fb 100644
--- a/library/core/src/num/int_macros.rs
+++ b/library/core/src/num/int_macros.rs
@@ -32,9 +32,10 @@ macro_rules! int_impl {
         /// # Examples
         ///
         /// ```
+        /// #![feature(int_bits_const)]
         #[doc = concat!("assert_eq!(", stringify!($SelfT), "::BITS, ", stringify!($BITS), ");")]
         /// ```
-        #[stable(feature = "int_bits_const", since = "1.51.0")]
+        #[unstable(feature = "int_bits_const", issue = "76904")]
         pub const BITS: u32 = $BITS;
 
         /// Converts a string slice in a given base to an integer.
diff --git a/library/core/src/num/uint_macros.rs b/library/core/src/num/uint_macros.rs
index aee424b9b1392..9fccf3f72ce1a 100644
--- a/library/core/src/num/uint_macros.rs
+++ b/library/core/src/num/uint_macros.rs
@@ -32,9 +32,10 @@ macro_rules! uint_impl {
         /// # Examples
         ///
         /// ```
+        /// #![feature(int_bits_const)]
         #[doc = concat!("assert_eq!(", stringify!($SelfT), "::BITS, ", stringify!($BITS), ");")]
         /// ```
-        #[stable(feature = "int_bits_const", since = "1.51.0")]
+        #[unstable(feature = "int_bits_const", issue = "76904")]
         pub const BITS: u32 = $BITS;
 
         /// Converts a string slice in a given base to an integer.
diff --git a/library/core/tests/lib.rs b/library/core/tests/lib.rs
index 26dbcb8569b43..bc0e3e059c917 100644
--- a/library/core/tests/lib.rs
+++ b/library/core/tests/lib.rs
@@ -70,6 +70,7 @@
 #![feature(partition_point)]
 #![feature(once_cell)]
 #![feature(unsafe_block_in_unsafe_fn)]
+#![feature(int_bits_const)]
 #![feature(nonzero_leading_trailing_zeros)]
 #![feature(const_option)]
 #![feature(integer_atomics)]
diff --git a/library/panic_unwind/src/lib.rs b/library/panic_unwind/src/lib.rs
index 99a0c67fc11b9..9ce9c477ec0f0 100644
--- a/library/panic_unwind/src/lib.rs
+++ b/library/panic_unwind/src/lib.rs
@@ -18,6 +18,7 @@
     issue_tracker_base_url = "https://github.com/rust-lang/rust/issues/"
 )]
 #![feature(core_intrinsics)]
+#![feature(int_bits_const)]
 #![feature(lang_items)]
 #![feature(nll)]
 #![feature(panic_unwind)]
diff --git a/library/std/src/ffi/os_str.rs b/library/std/src/ffi/os_str.rs
index 21060182d60bc..c9c8f68cd9cce 100644
--- a/library/std/src/ffi/os_str.rs
+++ b/library/std/src/ffi/os_str.rs
@@ -826,7 +826,7 @@ impl OsStr {
     /// assert!(!OsString::from("Ferrös").eq_ignore_ascii_case("FERRÖS"));
     /// ```
     #[unstable(feature = "osstring_ascii", issue = "70516")]
-    pub fn eq_ignore_ascii_case<S: ?Sized + AsRef<OsStr>>(&self, other: &S) -> bool {
+    pub fn eq_ignore_ascii_case<S: AsRef<OsStr>>(&self, other: S) -> bool {
         self.inner.eq_ignore_ascii_case(&other.as_ref().inner)
     }
 }
diff --git a/library/std/src/sys/wasi/ext/fs.rs b/library/std/src/sys/wasi/ext/fs.rs
index 4f7cf6018d90f..a8da003d550ac 100644
--- a/library/std/src/sys/wasi/ext/fs.rs
+++ b/library/std/src/sys/wasi/ext/fs.rs
@@ -514,3 +514,11 @@ pub fn symlink<P: AsRef<Path>, U: AsRef<Path>>(
         .fd()
         .symlink(osstr2str(old_path.as_ref().as_ref())?, osstr2str(new_path.as_ref().as_ref())?)
 }
+
+/// Create a symbolic link.
+///
+/// This is a convenience API similar to [`std::os::unix::fs::symlink`] and
+/// [`std::os::windows::fs::symlink_file`] and [`symlink_dir`](std::os::windows::fs::symlink_dir).
+pub fn symlink_path<P: AsRef<Path>, U: AsRef<Path>>(old_path: P, new_path: U) -> io::Result<()> {
+    crate::sys::fs::symlink(old_path.as_ref(), new_path.as_ref())
+}
diff --git a/library/term/src/terminfo/parm/tests.rs b/library/term/src/terminfo/parm/tests.rs
index b975bd2d19882..1cc0967c8f42e 100644
--- a/library/term/src/terminfo/parm/tests.rs
+++ b/library/term/src/terminfo/parm/tests.rs
@@ -77,15 +77,15 @@ fn test_comparison_ops() {
     for &(op, bs) in v.iter() {
         let s = format!("%{{1}}%{{2}}%{}%d", op);
         let res = expand(s.as_bytes(), &[], &mut Variables::new());
-        assert!(res.is_ok(), res.unwrap_err());
+        assert!(res.is_ok(), "{}", res.unwrap_err());
         assert_eq!(res.unwrap(), vec![b'0' + bs[0]]);
         let s = format!("%{{1}}%{{1}}%{}%d", op);
         let res = expand(s.as_bytes(), &[], &mut Variables::new());
-        assert!(res.is_ok(), res.unwrap_err());
+        assert!(res.is_ok(), "{}", res.unwrap_err());
         assert_eq!(res.unwrap(), vec![b'0' + bs[1]]);
         let s = format!("%{{2}}%{{1}}%{}%d", op);
         let res = expand(s.as_bytes(), &[], &mut Variables::new());
-        assert!(res.is_ok(), res.unwrap_err());
+        assert!(res.is_ok(), "{}", res.unwrap_err());
         assert_eq!(res.unwrap(), vec![b'0' + bs[2]]);
     }
 }
@@ -95,13 +95,13 @@ fn test_conditionals() {
     let mut vars = Variables::new();
     let s = b"\\E[%?%p1%{8}%<%t3%p1%d%e%p1%{16}%<%t9%p1%{8}%-%d%e38;5;%p1%d%;m";
     let res = expand(s, &[Number(1)], &mut vars);
-    assert!(res.is_ok(), res.unwrap_err());
+    assert!(res.is_ok(), "{}", res.unwrap_err());
     assert_eq!(res.unwrap(), "\\E[31m".bytes().collect::<Vec<_>>());
     let res = expand(s, &[Number(8)], &mut vars);
-    assert!(res.is_ok(), res.unwrap_err());
+    assert!(res.is_ok(), "{}", res.unwrap_err());
     assert_eq!(res.unwrap(), "\\E[90m".bytes().collect::<Vec<_>>());
     let res = expand(s, &[Number(42)], &mut vars);
-    assert!(res.is_ok(), res.unwrap_err());
+    assert!(res.is_ok(), "{}", res.unwrap_err());
     assert_eq!(res.unwrap(), "\\E[38;5;42m".bytes().collect::<Vec<_>>());
 }
 
diff --git a/library/test/src/tests.rs b/library/test/src/tests.rs
index 99e12c973c4a2..f0586d510dbdb 100644
--- a/library/test/src/tests.rs
+++ b/library/test/src/tests.rs
@@ -199,7 +199,7 @@ fn test_should_panic_bad_message() {
 fn test_should_panic_non_string_message_type() {
     use crate::tests::TrFailedMsg;
     fn f() {
-        panic!(1i32);
+        std::panic::panic_any(1i32);
     }
     let expected = "foobar";
     let failed_msg = format!(
diff --git a/src/bootstrap/test.rs b/src/bootstrap/test.rs
index f0e33be757d16..d9132f20d85b3 100644
--- a/src/bootstrap/test.rs
+++ b/src/bootstrap/test.rs
@@ -1880,8 +1880,7 @@ impl Step for RemoteCopyLibs {
         builder.info(&format!("REMOTE copy libs to emulator ({})", target));
         t!(fs::create_dir_all(builder.out.join("tmp")));
 
-        let server =
-            builder.ensure(tool::RemoteTestServer { compiler: compiler.with_stage(0), target });
+        let server = builder.ensure(tool::RemoteTestServer { compiler, target });
 
         // Spawn the emulator and wait for it to come online
         let tool = builder.tool_exe(Tool::RemoteTestClient);
diff --git a/src/test/ui-fulldeps/issue-15149.rs b/src/test/ui-fulldeps/issue-15149.rs
index c80628aabc83f..c7ef5ad70a114 100644
--- a/src/test/ui-fulldeps/issue-15149.rs
+++ b/src/test/ui-fulldeps/issue-15149.rs
@@ -50,7 +50,7 @@ fn test() {
                                                       .output().unwrap();
 
     assert!(child_output.status.success(),
-            format!("child assertion failed\n child stdout:\n {}\n child stderr:\n {}",
-                    str::from_utf8(&child_output.stdout).unwrap(),
-                    str::from_utf8(&child_output.stderr).unwrap()));
+            "child assertion failed\n child stdout:\n {}\n child stderr:\n {}",
+            str::from_utf8(&child_output.stdout).unwrap(),
+            str::from_utf8(&child_output.stderr).unwrap());
 }
diff --git a/src/test/ui/consts/const-eval/const_panic.rs b/src/test/ui/consts/const-eval/const_panic.rs
index e9d66477d60a5..8ae8376ae4a6f 100644
--- a/src/test/ui/consts/const-eval/const_panic.rs
+++ b/src/test/ui/consts/const-eval/const_panic.rs
@@ -1,4 +1,5 @@
 #![feature(const_panic)]
+#![allow(non_fmt_panic)]
 #![crate_type = "lib"]
 
 const MSG: &str = "hello";
diff --git a/src/test/ui/consts/const-eval/const_panic.stderr b/src/test/ui/consts/const-eval/const_panic.stderr
index 713be5b662d54..74907a0b49518 100644
--- a/src/test/ui/consts/const-eval/const_panic.stderr
+++ b/src/test/ui/consts/const-eval/const_panic.stderr
@@ -1,10 +1,10 @@
 error: any use of this value will cause an error
-  --> $DIR/const_panic.rs:6:15
+  --> $DIR/const_panic.rs:7:15
    |
 LL | const Z: () = std::panic!("cheese");
    | --------------^^^^^^^^^^^^^^^^^^^^^-
    |               |
-   |               the evaluated program panicked at 'cheese', $DIR/const_panic.rs:6:15
+   |               the evaluated program panicked at 'cheese', $DIR/const_panic.rs:7:15
    |
    = note: `#[deny(const_err)]` on by default
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
@@ -12,108 +12,108 @@ LL | const Z: () = std::panic!("cheese");
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: any use of this value will cause an error
-  --> $DIR/const_panic.rs:10:16
+  --> $DIR/const_panic.rs:11:16
    |
 LL | const Z2: () = std::panic!();
    | ---------------^^^^^^^^^^^^^-
    |                |
-   |                the evaluated program panicked at 'explicit panic', $DIR/const_panic.rs:10:16
+   |                the evaluated program panicked at 'explicit panic', $DIR/const_panic.rs:11:16
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: any use of this value will cause an error
-  --> $DIR/const_panic.rs:14:15
+  --> $DIR/const_panic.rs:15:15
    |
 LL | const Y: () = std::unreachable!();
    | --------------^^^^^^^^^^^^^^^^^^^-
    |               |
-   |               the evaluated program panicked at 'internal error: entered unreachable code', $DIR/const_panic.rs:14:15
+   |               the evaluated program panicked at 'internal error: entered unreachable code', $DIR/const_panic.rs:15:15
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: any use of this value will cause an error
-  --> $DIR/const_panic.rs:18:15
+  --> $DIR/const_panic.rs:19:15
    |
 LL | const X: () = std::unimplemented!();
    | --------------^^^^^^^^^^^^^^^^^^^^^-
    |               |
-   |               the evaluated program panicked at 'not implemented', $DIR/const_panic.rs:18:15
+   |               the evaluated program panicked at 'not implemented', $DIR/const_panic.rs:19:15
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: any use of this value will cause an error
-  --> $DIR/const_panic.rs:22:15
+  --> $DIR/const_panic.rs:23:15
    |
 LL | const W: () = std::panic!(MSG);
    | --------------^^^^^^^^^^^^^^^^-
    |               |
-   |               the evaluated program panicked at 'hello', $DIR/const_panic.rs:22:15
+   |               the evaluated program panicked at 'hello', $DIR/const_panic.rs:23:15
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: any use of this value will cause an error
-  --> $DIR/const_panic.rs:26:20
+  --> $DIR/const_panic.rs:27:20
    |
 LL | const Z_CORE: () = core::panic!("cheese");
    | -------------------^^^^^^^^^^^^^^^^^^^^^^-
    |                    |
-   |                    the evaluated program panicked at 'cheese', $DIR/const_panic.rs:26:20
+   |                    the evaluated program panicked at 'cheese', $DIR/const_panic.rs:27:20
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: any use of this value will cause an error
-  --> $DIR/const_panic.rs:30:21
+  --> $DIR/const_panic.rs:31:21
    |
 LL | const Z2_CORE: () = core::panic!();
    | --------------------^^^^^^^^^^^^^^-
    |                     |
-   |                     the evaluated program panicked at 'explicit panic', $DIR/const_panic.rs:30:21
+   |                     the evaluated program panicked at 'explicit panic', $DIR/const_panic.rs:31:21
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: any use of this value will cause an error
-  --> $DIR/const_panic.rs:34:20
+  --> $DIR/const_panic.rs:35:20
    |
 LL | const Y_CORE: () = core::unreachable!();
    | -------------------^^^^^^^^^^^^^^^^^^^^-
    |                    |
-   |                    the evaluated program panicked at 'internal error: entered unreachable code', $DIR/const_panic.rs:34:20
+   |                    the evaluated program panicked at 'internal error: entered unreachable code', $DIR/const_panic.rs:35:20
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: any use of this value will cause an error
-  --> $DIR/const_panic.rs:38:20
+  --> $DIR/const_panic.rs:39:20
    |
 LL | const X_CORE: () = core::unimplemented!();
    | -------------------^^^^^^^^^^^^^^^^^^^^^^-
    |                    |
-   |                    the evaluated program panicked at 'not implemented', $DIR/const_panic.rs:38:20
+   |                    the evaluated program panicked at 'not implemented', $DIR/const_panic.rs:39:20
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: any use of this value will cause an error
-  --> $DIR/const_panic.rs:42:20
+  --> $DIR/const_panic.rs:43:20
    |
 LL | const W_CORE: () = core::panic!(MSG);
    | -------------------^^^^^^^^^^^^^^^^^-
    |                    |
-   |                    the evaluated program panicked at 'hello', $DIR/const_panic.rs:42:20
+   |                    the evaluated program panicked at 'hello', $DIR/const_panic.rs:43:20
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
diff --git a/src/test/ui/drop/dynamic-drop-async.rs b/src/test/ui/drop/dynamic-drop-async.rs
index a952fe8e76e81..cb6d58a23d936 100644
--- a/src/test/ui/drop/dynamic-drop-async.rs
+++ b/src/test/ui/drop/dynamic-drop-async.rs
@@ -82,7 +82,7 @@ impl Allocator {
         self.cur_ops.set(self.cur_ops.get() + 1);
 
         if self.cur_ops.get() == self.failing_op {
-            panic!(InjectedFailure);
+            panic::panic_any(InjectedFailure);
         }
     }
 }
diff --git a/src/test/ui/drop/dynamic-drop.rs b/src/test/ui/drop/dynamic-drop.rs
index ddccee20e12a6..e28bedb982dd9 100644
--- a/src/test/ui/drop/dynamic-drop.rs
+++ b/src/test/ui/drop/dynamic-drop.rs
@@ -46,7 +46,7 @@ impl Allocator {
         self.cur_ops.set(self.cur_ops.get() + 1);
 
         if self.cur_ops.get() == self.failing_op {
-            panic!(InjectedFailure);
+            panic::panic_any(InjectedFailure);
         }
 
         let mut data = self.data.borrow_mut();
@@ -67,7 +67,7 @@ impl<'a> Drop for Ptr<'a> {
         self.1.cur_ops.set(self.1.cur_ops.get() + 1);
 
         if self.1.cur_ops.get() == self.1.failing_op {
-            panic!(InjectedFailure);
+            panic::panic_any(InjectedFailure);
         }
     }
 }
diff --git a/src/test/ui/fmt/format-args-capture.rs b/src/test/ui/fmt/format-args-capture.rs
index 4e3fa9a3c589a..d5886a13558c6 100644
--- a/src/test/ui/fmt/format-args-capture.rs
+++ b/src/test/ui/fmt/format-args-capture.rs
@@ -31,7 +31,7 @@ fn panic_with_single_argument_does_not_get_formatted() {
     // RFC #2795 suggests that this may need to change so that captured arguments are formatted.
     // For stability reasons this will need to part of an edition change.
 
-    #[allow(panic_fmt)]
+    #[allow(non_fmt_panic)]
     let msg = std::panic::catch_unwind(|| {
         panic!("{foo}");
     }).unwrap_err();
diff --git a/src/test/ui/lint/forbid-group-group-1.rs b/src/test/ui/lint/forbid-group-group-1.rs
new file mode 100644
index 0000000000000..80f7db4e56036
--- /dev/null
+++ b/src/test/ui/lint/forbid-group-group-1.rs
@@ -0,0 +1,13 @@
+// Check what happens when we forbid a smaller group but
+// then allow a superset of that group.
+
+#![forbid(nonstandard_style)]
+
+// FIXME: Arguably this should be an error, but the WARNINGS group is
+// treated in a very special (and rather ad-hoc) way and
+// it fails to trigger.
+#[allow(warnings)]
+fn main() {
+    let A: ();
+    //~^ ERROR should have a snake case name
+}
diff --git a/src/test/ui/lint/forbid-group-group-1.stderr b/src/test/ui/lint/forbid-group-group-1.stderr
new file mode 100644
index 0000000000000..fd425e5f74e6f
--- /dev/null
+++ b/src/test/ui/lint/forbid-group-group-1.stderr
@@ -0,0 +1,15 @@
+error: variable `A` should have a snake case name
+  --> $DIR/forbid-group-group-1.rs:11:9
+   |
+LL |     let A: ();
+   |         ^ help: convert the identifier to snake case: `a`
+   |
+note: the lint level is defined here
+  --> $DIR/forbid-group-group-1.rs:4:11
+   |
+LL | #![forbid(nonstandard_style)]
+   |           ^^^^^^^^^^^^^^^^^
+   = note: `#[forbid(non_snake_case)]` implied by `#[forbid(nonstandard_style)]`
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/lint/forbid-group-group-2.rs b/src/test/ui/lint/forbid-group-group-2.rs
new file mode 100644
index 0000000000000..b12fd72da7494
--- /dev/null
+++ b/src/test/ui/lint/forbid-group-group-2.rs
@@ -0,0 +1,26 @@
+// Check what happens when we forbid a bigger group but
+// then deny a subset of that group.
+
+#![forbid(warnings)]
+#![deny(forbidden_lint_groups)]
+
+#[allow(nonstandard_style)]
+//~^ ERROR incompatible with previous
+//~| WARNING previously accepted by the compiler
+//~| ERROR incompatible with previous
+//~| WARNING previously accepted by the compiler
+//~| ERROR incompatible with previous
+//~| WARNING previously accepted by the compiler
+//~| ERROR incompatible with previous
+//~| WARNING previously accepted by the compiler
+//~| ERROR incompatible with previous
+//~| WARNING previously accepted by the compiler
+//~| ERROR incompatible with previous
+//~| WARNING previously accepted by the compiler
+//~| ERROR incompatible with previous
+//~| WARNING previously accepted by the compiler
+//~| ERROR incompatible with previous
+//~| WARNING previously accepted by the compiler
+//~| ERROR incompatible with previous
+//~| WARNING previously accepted by the compiler
+fn main() {}
diff --git a/src/test/ui/lint/forbid-group-group-2.stderr b/src/test/ui/lint/forbid-group-group-2.stderr
new file mode 100644
index 0000000000000..214e949c11a74
--- /dev/null
+++ b/src/test/ui/lint/forbid-group-group-2.stderr
@@ -0,0 +1,115 @@
+error: allow(nonstandard_style) incompatible with previous forbid
+  --> $DIR/forbid-group-group-2.rs:7:9
+   |
+LL | #![forbid(warnings)]
+   |           -------- `forbid` level set here
+...
+LL | #[allow(nonstandard_style)]
+   |         ^^^^^^^^^^^^^^^^^ overruled by previous forbid
+   |
+note: the lint level is defined here
+  --> $DIR/forbid-group-group-2.rs:5:9
+   |
+LL | #![deny(forbidden_lint_groups)]
+   |         ^^^^^^^^^^^^^^^^^^^^^
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
+
+error: allow(nonstandard_style) incompatible with previous forbid
+  --> $DIR/forbid-group-group-2.rs:7:9
+   |
+LL | #![forbid(warnings)]
+   |           -------- `forbid` level set here
+...
+LL | #[allow(nonstandard_style)]
+   |         ^^^^^^^^^^^^^^^^^ overruled by previous forbid
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
+
+error: allow(nonstandard_style) incompatible with previous forbid
+  --> $DIR/forbid-group-group-2.rs:7:9
+   |
+LL | #![forbid(warnings)]
+   |           -------- `forbid` level set here
+...
+LL | #[allow(nonstandard_style)]
+   |         ^^^^^^^^^^^^^^^^^ overruled by previous forbid
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
+
+error: allow(nonstandard_style) incompatible with previous forbid
+  --> $DIR/forbid-group-group-2.rs:7:9
+   |
+LL | #![forbid(warnings)]
+   |           -------- `forbid` level set here
+...
+LL | #[allow(nonstandard_style)]
+   |         ^^^^^^^^^^^^^^^^^ overruled by previous forbid
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
+
+error: allow(nonstandard_style) incompatible with previous forbid
+  --> $DIR/forbid-group-group-2.rs:7:9
+   |
+LL | #![forbid(warnings)]
+   |           -------- `forbid` level set here
+...
+LL | #[allow(nonstandard_style)]
+   |         ^^^^^^^^^^^^^^^^^ overruled by previous forbid
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
+
+error: allow(nonstandard_style) incompatible with previous forbid
+  --> $DIR/forbid-group-group-2.rs:7:9
+   |
+LL | #![forbid(warnings)]
+   |           -------- `forbid` level set here
+...
+LL | #[allow(nonstandard_style)]
+   |         ^^^^^^^^^^^^^^^^^ overruled by previous forbid
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
+
+error: allow(nonstandard_style) incompatible with previous forbid
+  --> $DIR/forbid-group-group-2.rs:7:9
+   |
+LL | #![forbid(warnings)]
+   |           -------- `forbid` level set here
+...
+LL | #[allow(nonstandard_style)]
+   |         ^^^^^^^^^^^^^^^^^ overruled by previous forbid
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
+
+error: allow(nonstandard_style) incompatible with previous forbid
+  --> $DIR/forbid-group-group-2.rs:7:9
+   |
+LL | #![forbid(warnings)]
+   |           -------- `forbid` level set here
+...
+LL | #[allow(nonstandard_style)]
+   |         ^^^^^^^^^^^^^^^^^ overruled by previous forbid
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
+
+error: allow(nonstandard_style) incompatible with previous forbid
+  --> $DIR/forbid-group-group-2.rs:7:9
+   |
+LL | #![forbid(warnings)]
+   |           -------- `forbid` level set here
+...
+LL | #[allow(nonstandard_style)]
+   |         ^^^^^^^^^^^^^^^^^ overruled by previous forbid
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
+
+error: aborting due to 9 previous errors
+
diff --git a/src/test/ui/lint/forbid-group-member.rs b/src/test/ui/lint/forbid-group-member.rs
new file mode 100644
index 0000000000000..6f1b2e9f66812
--- /dev/null
+++ b/src/test/ui/lint/forbid-group-member.rs
@@ -0,0 +1,19 @@
+// Check what happens when we forbid a group but
+// then allow a member of that group.
+//
+// check-pass
+
+#![forbid(unused)]
+
+#[allow(unused_variables)]
+//~^ WARNING incompatible with previous forbid
+//~| WARNING previously accepted
+//~| WARNING incompatible with previous forbid
+//~| WARNING previously accepted
+//~| WARNING incompatible with previous forbid
+//~| WARNING previously accepted
+//~| WARNING incompatible with previous forbid
+//~| WARNING previously accepted
+fn main() {
+    let a: ();
+}
diff --git a/src/test/ui/lint/forbid-group-member.stderr b/src/test/ui/lint/forbid-group-member.stderr
new file mode 100644
index 0000000000000..c818d7ff60605
--- /dev/null
+++ b/src/test/ui/lint/forbid-group-member.stderr
@@ -0,0 +1,51 @@
+warning: allow(unused_variables) incompatible with previous forbid
+  --> $DIR/forbid-group-member.rs:8:9
+   |
+LL | #![forbid(unused)]
+   |           ------ `forbid` level set here
+LL | 
+LL | #[allow(unused_variables)]
+   |         ^^^^^^^^^^^^^^^^ overruled by previous forbid
+   |
+   = note: `#[warn(forbidden_lint_groups)]` on by default
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
+
+warning: allow(unused_variables) incompatible with previous forbid
+  --> $DIR/forbid-group-member.rs:8:9
+   |
+LL | #![forbid(unused)]
+   |           ------ `forbid` level set here
+LL | 
+LL | #[allow(unused_variables)]
+   |         ^^^^^^^^^^^^^^^^ overruled by previous forbid
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
+
+warning: allow(unused_variables) incompatible with previous forbid
+  --> $DIR/forbid-group-member.rs:8:9
+   |
+LL | #![forbid(unused)]
+   |           ------ `forbid` level set here
+LL | 
+LL | #[allow(unused_variables)]
+   |         ^^^^^^^^^^^^^^^^ overruled by previous forbid
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
+
+warning: allow(unused_variables) incompatible with previous forbid
+  --> $DIR/forbid-group-member.rs:8:9
+   |
+LL | #![forbid(unused)]
+   |           ------ `forbid` level set here
+LL | 
+LL | #[allow(unused_variables)]
+   |         ^^^^^^^^^^^^^^^^ overruled by previous forbid
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
+
+warning: 4 warnings emitted
+
diff --git a/src/test/ui/lint/forbid-member-group.rs b/src/test/ui/lint/forbid-member-group.rs
new file mode 100644
index 0000000000000..3279029a9cbc3
--- /dev/null
+++ b/src/test/ui/lint/forbid-member-group.rs
@@ -0,0 +1,12 @@
+// Check what happens when we forbid a member of
+// a group but then allow the group.
+
+#![forbid(unused_variables)]
+
+#[allow(unused)]
+//~^ ERROR incompatible with previous forbid
+//~| ERROR incompatible with previous forbid
+//~| ERROR incompatible with previous forbid
+fn main() {
+    let a: ();
+}
diff --git a/src/test/ui/lint/forbid-member-group.stderr b/src/test/ui/lint/forbid-member-group.stderr
new file mode 100644
index 0000000000000..1d8ab4d5edb0c
--- /dev/null
+++ b/src/test/ui/lint/forbid-member-group.stderr
@@ -0,0 +1,30 @@
+error[E0453]: allow(unused) incompatible with previous forbid
+  --> $DIR/forbid-member-group.rs:6:9
+   |
+LL | #![forbid(unused_variables)]
+   |           ---------------- `forbid` level set here
+LL | 
+LL | #[allow(unused)]
+   |         ^^^^^^ overruled by previous forbid
+
+error[E0453]: allow(unused) incompatible with previous forbid
+  --> $DIR/forbid-member-group.rs:6:9
+   |
+LL | #![forbid(unused_variables)]
+   |           ---------------- `forbid` level set here
+LL | 
+LL | #[allow(unused)]
+   |         ^^^^^^ overruled by previous forbid
+
+error[E0453]: allow(unused) incompatible with previous forbid
+  --> $DIR/forbid-member-group.rs:6:9
+   |
+LL | #![forbid(unused_variables)]
+   |           ---------------- `forbid` level set here
+LL | 
+LL | #[allow(unused)]
+   |         ^^^^^^ overruled by previous forbid
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0453`.
diff --git a/src/test/ui/lint/issue-70819-dont-override-forbid-in-same-scope.rs b/src/test/ui/lint/issue-70819-dont-override-forbid-in-same-scope.rs
index f725304cf29d4..05d7d924c8fab 100644
--- a/src/test/ui/lint/issue-70819-dont-override-forbid-in-same-scope.rs
+++ b/src/test/ui/lint/issue-70819-dont-override-forbid-in-same-scope.rs
@@ -14,14 +14,17 @@
 
 // compile-flags: -Z deduplicate-diagnostics=yes
 
+#![forbid(forbidden_lint_groups)]
+
 fn forbid_first(num: i32) -> i32 {
     #![forbid(unused)]
     #![deny(unused)]
     //~^ ERROR: deny(unused) incompatible with previous forbid
+    //~| WARNING being phased out
+    //~| ERROR: deny(unused) incompatible with previous forbid
+    //~| WARNING being phased out
     #![warn(unused)]
-    //~^ ERROR: warn(unused) incompatible with previous forbid
     #![allow(unused)]
-    //~^ ERROR: allow(unused) incompatible with previous forbid
 
     num * num
 }
diff --git a/src/test/ui/lint/issue-70819-dont-override-forbid-in-same-scope.stderr b/src/test/ui/lint/issue-70819-dont-override-forbid-in-same-scope.stderr
index 9f107411c102a..475410cecffa3 100644
--- a/src/test/ui/lint/issue-70819-dont-override-forbid-in-same-scope.stderr
+++ b/src/test/ui/lint/issue-70819-dont-override-forbid-in-same-scope.stderr
@@ -1,29 +1,29 @@
-error[E0453]: deny(unused) incompatible with previous forbid
-  --> $DIR/issue-70819-dont-override-forbid-in-same-scope.rs:19:13
+error: deny(unused) incompatible with previous forbid
+  --> $DIR/issue-70819-dont-override-forbid-in-same-scope.rs:21:13
    |
 LL |     #![forbid(unused)]
    |               ------ `forbid` level set here
 LL |     #![deny(unused)]
    |             ^^^^^^ overruled by previous forbid
+   |
+note: the lint level is defined here
+  --> $DIR/issue-70819-dont-override-forbid-in-same-scope.rs:17:11
+   |
+LL | #![forbid(forbidden_lint_groups)]
+   |           ^^^^^^^^^^^^^^^^^^^^^
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
 
-error[E0453]: warn(unused) incompatible with previous forbid
+error: deny(unused) incompatible with previous forbid
   --> $DIR/issue-70819-dont-override-forbid-in-same-scope.rs:21:13
    |
 LL |     #![forbid(unused)]
    |               ------ `forbid` level set here
-...
-LL |     #![warn(unused)]
+LL |     #![deny(unused)]
    |             ^^^^^^ overruled by previous forbid
-
-error[E0453]: allow(unused) incompatible with previous forbid
-  --> $DIR/issue-70819-dont-override-forbid-in-same-scope.rs:23:14
    |
-LL |     #![forbid(unused)]
-   |               ------ `forbid` level set here
-...
-LL |     #![allow(unused)]
-   |              ^^^^^^ overruled by previous forbid
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
 
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0453`.
diff --git a/src/test/ui/lint/issue-80988.rs b/src/test/ui/lint/issue-80988.rs
new file mode 100644
index 0000000000000..16a041928db73
--- /dev/null
+++ b/src/test/ui/lint/issue-80988.rs
@@ -0,0 +1,16 @@
+// Regression test for #80988
+//
+// check-pass
+
+#![forbid(warnings)]
+
+#[deny(warnings)]
+//~^ WARNING incompatible with previous forbid
+//~| WARNING being phased out
+//~| WARNING incompatible with previous forbid
+//~| WARNING being phased out
+//~| WARNING incompatible with previous forbid
+//~| WARNING being phased out
+//~| WARNING incompatible with previous forbid
+//~| WARNING being phased out
+fn main() {}
diff --git a/src/test/ui/lint/issue-80988.stderr b/src/test/ui/lint/issue-80988.stderr
new file mode 100644
index 0000000000000..4cae11f97c0fb
--- /dev/null
+++ b/src/test/ui/lint/issue-80988.stderr
@@ -0,0 +1,51 @@
+warning: deny(warnings) incompatible with previous forbid
+  --> $DIR/issue-80988.rs:7:8
+   |
+LL | #![forbid(warnings)]
+   |           -------- `forbid` level set here
+LL | 
+LL | #[deny(warnings)]
+   |        ^^^^^^^^ overruled by previous forbid
+   |
+   = note: `#[warn(forbidden_lint_groups)]` on by default
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
+
+warning: deny(warnings) incompatible with previous forbid
+  --> $DIR/issue-80988.rs:7:8
+   |
+LL | #![forbid(warnings)]
+   |           -------- `forbid` level set here
+LL | 
+LL | #[deny(warnings)]
+   |        ^^^^^^^^ overruled by previous forbid
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
+
+warning: deny(warnings) incompatible with previous forbid
+  --> $DIR/issue-80988.rs:7:8
+   |
+LL | #![forbid(warnings)]
+   |           -------- `forbid` level set here
+LL | 
+LL | #[deny(warnings)]
+   |        ^^^^^^^^ overruled by previous forbid
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
+
+warning: deny(warnings) incompatible with previous forbid
+  --> $DIR/issue-80988.rs:7:8
+   |
+LL | #![forbid(warnings)]
+   |           -------- `forbid` level set here
+LL | 
+LL | #[deny(warnings)]
+   |        ^^^^^^^^ overruled by previous forbid
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
+
+warning: 4 warnings emitted
+
diff --git a/src/test/ui/lint/issue-81218.rs b/src/test/ui/lint/issue-81218.rs
new file mode 100644
index 0000000000000..f02aa9040ebc5
--- /dev/null
+++ b/src/test/ui/lint/issue-81218.rs
@@ -0,0 +1,14 @@
+// Regression test for #81218
+//
+// check-pass
+
+#![forbid(warnings)]
+
+#[allow(unused_variables)]
+fn main() {
+    // We want to ensure that you don't get an error
+    // here. The idea is that a derive might generate
+    // code that would otherwise trigger the "unused variables"
+    // lint, but it is meant to be suppressed.
+    let x: ();
+}
diff --git a/src/test/ui/lint/outer-forbid.rs b/src/test/ui/lint/outer-forbid.rs
index d45848bf706f3..486ec3c46804f 100644
--- a/src/test/ui/lint/outer-forbid.rs
+++ b/src/test/ui/lint/outer-forbid.rs
@@ -15,11 +15,16 @@
 // compile-flags: -Z deduplicate-diagnostics=yes
 
 #![forbid(unused, non_snake_case)]
+#![forbid(forbidden_lint_groups)]
 
 #[allow(unused_variables)] //~ ERROR incompatible with previous
+//~^ ERROR incompatible with previous
+//~| WARNING this was previously accepted by the compiler
+//~| WARNING this was previously accepted by the compiler
 fn foo() {}
 
 #[allow(unused)] //~ ERROR incompatible with previous
+//~^ WARNING this was previously accepted by the compiler
 fn bar() {}
 
 #[allow(nonstandard_style)] //~ ERROR incompatible with previous
diff --git a/src/test/ui/lint/outer-forbid.stderr b/src/test/ui/lint/outer-forbid.stderr
index c012c20697e16..d69157a8bb3ad 100644
--- a/src/test/ui/lint/outer-forbid.stderr
+++ b/src/test/ui/lint/outer-forbid.stderr
@@ -1,23 +1,34 @@
-error[E0453]: allow(unused_variables) incompatible with previous forbid
-  --> $DIR/outer-forbid.rs:19:9
+error: allow(unused_variables) incompatible with previous forbid
+  --> $DIR/outer-forbid.rs:20:9
    |
 LL | #![forbid(unused, non_snake_case)]
    |           ------ `forbid` level set here
-LL | 
+...
 LL | #[allow(unused_variables)]
    |         ^^^^^^^^^^^^^^^^ overruled by previous forbid
+   |
+note: the lint level is defined here
+  --> $DIR/outer-forbid.rs:18:11
+   |
+LL | #![forbid(forbidden_lint_groups)]
+   |           ^^^^^^^^^^^^^^^^^^^^^
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
 
-error[E0453]: allow(unused) incompatible with previous forbid
-  --> $DIR/outer-forbid.rs:22:9
+error: allow(unused) incompatible with previous forbid
+  --> $DIR/outer-forbid.rs:26:9
    |
 LL | #![forbid(unused, non_snake_case)]
    |           ------ `forbid` level set here
 ...
 LL | #[allow(unused)]
    |         ^^^^^^ overruled by previous forbid
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
 
 error[E0453]: allow(nonstandard_style) incompatible with previous forbid
-  --> $DIR/outer-forbid.rs:25:9
+  --> $DIR/outer-forbid.rs:30:9
    |
 LL | #![forbid(unused, non_snake_case)]
    |                   -------------- `forbid` level set here
@@ -25,6 +36,18 @@ LL | #![forbid(unused, non_snake_case)]
 LL | #[allow(nonstandard_style)]
    |         ^^^^^^^^^^^^^^^^^ overruled by previous forbid
 
-error: aborting due to 3 previous errors
+error: allow(unused_variables) incompatible with previous forbid
+  --> $DIR/outer-forbid.rs:20:9
+   |
+LL | #![forbid(unused, non_snake_case)]
+   |           ------ `forbid` level set here
+...
+LL | #[allow(unused_variables)]
+   |         ^^^^^^^^^^^^^^^^ overruled by previous forbid
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
+
+error: aborting due to 4 previous errors
 
 For more information about this error, try `rustc --explain E0453`.
diff --git a/src/test/ui/macros/assert-macro-owned.rs b/src/test/ui/macros/assert-macro-owned.rs
index b50fe65c0150f..2846f2a1f8353 100644
--- a/src/test/ui/macros/assert-macro-owned.rs
+++ b/src/test/ui/macros/assert-macro-owned.rs
@@ -2,6 +2,8 @@
 // error-pattern:panicked at 'test-assert-owned'
 // ignore-emscripten no processes
 
+#![allow(non_fmt_panic)]
+
 fn main() {
     assert!(false, "test-assert-owned".to_string());
 }
diff --git a/src/test/ui/macros/macro-comma-behavior-rpass.rs b/src/test/ui/macros/macro-comma-behavior-rpass.rs
index c46274d59b658..fd2c590ae5fd6 100644
--- a/src/test/ui/macros/macro-comma-behavior-rpass.rs
+++ b/src/test/ui/macros/macro-comma-behavior-rpass.rs
@@ -57,7 +57,7 @@ fn writeln_1arg() {
 //
 // (Example: Issue #48042)
 #[test]
-#[allow(panic_fmt)]
+#[allow(non_fmt_panic)]
 fn to_format_or_not_to_format() {
     // ("{}" is the easiest string to test because if this gets
     // sent to format_args!, it'll simply fail to compile.
diff --git a/src/test/ui/mir/mir_drop_order.rs b/src/test/ui/mir/mir_drop_order.rs
index 2949437b1e4b6..22c804abf5cc8 100644
--- a/src/test/ui/mir/mir_drop_order.rs
+++ b/src/test/ui/mir/mir_drop_order.rs
@@ -38,7 +38,7 @@ fn main() {
     assert_eq!(get(), vec![0, 2, 3, 1]);
 
     let _ = std::panic::catch_unwind(|| {
-        (d(4), &d(5), d(6), &d(7), panic!(InjectedFailure));
+        (d(4), &d(5), d(6), &d(7), panic::panic_any(InjectedFailure));
     });
 
     // here, the temporaries (5/7) live until the end of the
diff --git a/src/test/ui/panic-brace.rs b/src/test/ui/non-fmt-panic.rs
similarity index 70%
rename from src/test/ui/panic-brace.rs
rename to src/test/ui/non-fmt-panic.rs
index 754dcc287d0f9..25c53316e1290 100644
--- a/src/test/ui/panic-brace.rs
+++ b/src/test/ui/non-fmt-panic.rs
@@ -13,19 +13,27 @@ fn main() {
     core::panic!("Hello {}"); //~ WARN panic message contains an unused formatting placeholder
     assert!(false, "{:03x} {test} bla");
     //~^ WARN panic message contains unused formatting placeholders
+    assert!(false, S);
+    //~^ WARN panic message is not a string literal
     debug_assert!(false, "{{}} bla"); //~ WARN panic message contains braces
-    panic!(C); // No warning (yet)
-    panic!(S); // No warning (yet)
+    panic!(C); //~ WARN panic message is not a string literal
+    panic!(S); //~ WARN panic message is not a string literal
+    std::panic!(123); //~ WARN panic message is not a string literal
+    core::panic!(&*"abc"); //~ WARN panic message is not a string literal
     panic!(concat!("{", "}")); //~ WARN panic message contains an unused formatting placeholder
     panic!(concat!("{", "{")); //~ WARN panic message contains braces
 
     fancy_panic::fancy_panic!("test {} 123");
     //~^ WARN panic message contains an unused formatting placeholder
 
+    fancy_panic::fancy_panic!(S);
+    //~^ WARN panic message is not a string literal
+
     // Check that the lint only triggers for std::panic and core::panic,
     // not any panic macro:
     macro_rules! panic {
         ($e:expr) => ();
     }
     panic!("{}"); // OK
+    panic!(S); // OK
 }
diff --git a/src/test/ui/panic-brace.stderr b/src/test/ui/non-fmt-panic.stderr
similarity index 52%
rename from src/test/ui/panic-brace.stderr
rename to src/test/ui/non-fmt-panic.stderr
index 93808891c3c37..45187c518c423 100644
--- a/src/test/ui/panic-brace.stderr
+++ b/src/test/ui/non-fmt-panic.stderr
@@ -1,35 +1,35 @@
 warning: panic message contains a brace
-  --> $DIR/panic-brace.rs:11:29
+  --> $DIR/non-fmt-panic.rs:11:29
    |
 LL |     panic!("here's a brace: {");
    |                             ^
    |
-   = note: `#[warn(panic_fmt)]` on by default
-   = note: this message is not used as a format string, but will be in a future Rust edition
+   = note: `#[warn(non_fmt_panic)]` on by default
+   = note: this message is not used as a format string, but will be in Rust 2021
 help: add a "{}" format string to use the message literally
    |
 LL |     panic!("{}", "here's a brace: {");
    |            ^^^^^
 
 warning: panic message contains a brace
-  --> $DIR/panic-brace.rs:12:31
+  --> $DIR/non-fmt-panic.rs:12:31
    |
 LL |     std::panic!("another one: }");
    |                               ^
    |
-   = note: this message is not used as a format string, but will be in a future Rust edition
+   = note: this message is not used as a format string, but will be in Rust 2021
 help: add a "{}" format string to use the message literally
    |
 LL |     std::panic!("{}", "another one: }");
    |                 ^^^^^
 
 warning: panic message contains an unused formatting placeholder
-  --> $DIR/panic-brace.rs:13:25
+  --> $DIR/non-fmt-panic.rs:13:25
    |
 LL |     core::panic!("Hello {}");
    |                         ^^
    |
-   = note: this message is not used as a format string when given without arguments, but will be in a future Rust edition
+   = note: this message is not used as a format string when given without arguments, but will be in Rust 2021
 help: add the missing argument
    |
 LL |     core::panic!("Hello {}", ...);
@@ -40,12 +40,12 @@ LL |     core::panic!("{}", "Hello {}");
    |                  ^^^^^
 
 warning: panic message contains unused formatting placeholders
-  --> $DIR/panic-brace.rs:14:21
+  --> $DIR/non-fmt-panic.rs:14:21
    |
 LL |     assert!(false, "{:03x} {test} bla");
    |                     ^^^^^^ ^^^^^^
    |
-   = note: this message is not used as a format string when given without arguments, but will be in a future Rust edition
+   = note: this message is not used as a format string when given without arguments, but will be in Rust 2021
 help: add the missing arguments
    |
 LL |     assert!(false, "{:03x} {test} bla", ...);
@@ -55,25 +55,97 @@ help: or add a "{}" format string to use the message literally
 LL |     assert!(false, "{}", "{:03x} {test} bla");
    |                    ^^^^^
 
+warning: panic message is not a string literal
+  --> $DIR/non-fmt-panic.rs:16:20
+   |
+LL |     assert!(false, S);
+   |                    ^
+   |
+   = note: this is no longer accepted in Rust 2021
+help: add a "{}" format string to Display the message
+   |
+LL |     assert!(false, "{}", S);
+   |                    ^^^^^
+
 warning: panic message contains braces
-  --> $DIR/panic-brace.rs:16:27
+  --> $DIR/non-fmt-panic.rs:18:27
    |
 LL |     debug_assert!(false, "{{}} bla");
    |                           ^^^^
    |
-   = note: this message is not used as a format string, but will be in a future Rust edition
+   = note: this message is not used as a format string, but will be in Rust 2021
 help: add a "{}" format string to use the message literally
    |
 LL |     debug_assert!(false, "{}", "{{}} bla");
    |                          ^^^^^
 
+warning: panic message is not a string literal
+  --> $DIR/non-fmt-panic.rs:19:12
+   |
+LL |     panic!(C);
+   |            ^
+   |
+   = note: this is no longer accepted in Rust 2021
+help: add a "{}" format string to Display the message
+   |
+LL |     panic!("{}", C);
+   |            ^^^^^
+help: or use std::panic::panic_any instead
+   |
+LL |     std::panic::panic_any(C);
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+
+warning: panic message is not a string literal
+  --> $DIR/non-fmt-panic.rs:20:12
+   |
+LL |     panic!(S);
+   |            ^
+   |
+   = note: this is no longer accepted in Rust 2021
+help: add a "{}" format string to Display the message
+   |
+LL |     panic!("{}", S);
+   |            ^^^^^
+help: or use std::panic::panic_any instead
+   |
+LL |     std::panic::panic_any(S);
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+
+warning: panic message is not a string literal
+  --> $DIR/non-fmt-panic.rs:21:17
+   |
+LL |     std::panic!(123);
+   |                 ^^^
+   |
+   = note: this is no longer accepted in Rust 2021
+help: add a "{}" format string to Display the message
+   |
+LL |     std::panic!("{}", 123);
+   |                 ^^^^^
+help: or use std::panic::panic_any instead
+   |
+LL |     std::panic::panic_any(123);
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+
+warning: panic message is not a string literal
+  --> $DIR/non-fmt-panic.rs:22:18
+   |
+LL |     core::panic!(&*"abc");
+   |                  ^^^^^^^
+   |
+   = note: this is no longer accepted in Rust 2021
+help: add a "{}" format string to Display the message
+   |
+LL |     core::panic!("{}", &*"abc");
+   |                  ^^^^^
+
 warning: panic message contains an unused formatting placeholder
-  --> $DIR/panic-brace.rs:19:12
+  --> $DIR/non-fmt-panic.rs:23:12
    |
 LL |     panic!(concat!("{", "}"));
    |            ^^^^^^^^^^^^^^^^^
    |
-   = note: this message is not used as a format string when given without arguments, but will be in a future Rust edition
+   = note: this message is not used as a format string when given without arguments, but will be in Rust 2021
 help: add the missing argument
    |
 LL |     panic!(concat!("{", "}"), ...);
@@ -84,24 +156,32 @@ LL |     panic!("{}", concat!("{", "}"));
    |            ^^^^^
 
 warning: panic message contains braces
-  --> $DIR/panic-brace.rs:20:5
+  --> $DIR/non-fmt-panic.rs:24:5
    |
 LL |     panic!(concat!("{", "{"));
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: this message is not used as a format string, but will be in a future Rust edition
+   = note: this message is not used as a format string, but will be in Rust 2021
 help: add a "{}" format string to use the message literally
    |
 LL |     panic!("{}", concat!("{", "{"));
    |            ^^^^^
 
 warning: panic message contains an unused formatting placeholder
-  --> $DIR/panic-brace.rs:22:37
+  --> $DIR/non-fmt-panic.rs:26:37
    |
 LL |     fancy_panic::fancy_panic!("test {} 123");
    |                                     ^^
    |
-   = note: this message is not used as a format string when given without arguments, but will be in a future Rust edition
+   = note: this message is not used as a format string when given without arguments, but will be in Rust 2021
+
+warning: panic message is not a string literal
+  --> $DIR/non-fmt-panic.rs:29:31
+   |
+LL |     fancy_panic::fancy_panic!(S);
+   |                               ^
+   |
+   = note: this is no longer accepted in Rust 2021
 
-warning: 8 warnings emitted
+warning: 14 warnings emitted
 
diff --git a/src/test/ui/pattern/or-pattern-macro-pat.rs b/src/test/ui/or-patterns/macro-pat.rs
similarity index 100%
rename from src/test/ui/pattern/or-pattern-macro-pat.rs
rename to src/test/ui/or-patterns/macro-pat.rs
diff --git a/src/test/ui/panics/explicit-panic-msg.rs b/src/test/ui/panics/explicit-panic-msg.rs
index 1789e2e62c8b2..bfcc12cd186bd 100644
--- a/src/test/ui/panics/explicit-panic-msg.rs
+++ b/src/test/ui/panics/explicit-panic-msg.rs
@@ -1,5 +1,6 @@
 #![allow(unused_assignments)]
 #![allow(unused_variables)]
+#![allow(non_fmt_panic)]
 
 // run-fail
 // error-pattern:wooooo
diff --git a/src/test/ui/panics/panic-macro-any-wrapped.rs b/src/test/ui/panics/panic-macro-any-wrapped.rs
index 80c87c6f32c4b..95ae6ffe8be02 100644
--- a/src/test/ui/panics/panic-macro-any-wrapped.rs
+++ b/src/test/ui/panics/panic-macro-any-wrapped.rs
@@ -2,6 +2,8 @@
 // error-pattern:panicked at 'Box<Any>'
 // ignore-emscripten no processes
 
+#![allow(non_fmt_panic)]
+
 fn main() {
     panic!(Box::new(612_i64));
 }
diff --git a/src/test/ui/panics/panic-macro-any.rs b/src/test/ui/panics/panic-macro-any.rs
index ffc7114c1f5f2..d2a7ba3713a51 100644
--- a/src/test/ui/panics/panic-macro-any.rs
+++ b/src/test/ui/panics/panic-macro-any.rs
@@ -3,6 +3,7 @@
 // ignore-emscripten no processes
 
 #![feature(box_syntax)]
+#![allow(non_fmt_panic)]
 
 fn main() {
     panic!(box 413 as Box<dyn std::any::Any + Send>);
diff --git a/src/test/ui/panics/while-panic.rs b/src/test/ui/panics/while-panic.rs
index 857f65a225228..3c6ee8fa3155e 100644
--- a/src/test/ui/panics/while-panic.rs
+++ b/src/test/ui/panics/while-panic.rs
@@ -5,7 +5,7 @@
 // ignore-emscripten no processes
 
 fn main() {
-    panic!({
+    panic!("{}", {
         while true {
             panic!("giraffe")
         }
diff --git a/src/tools/clippy/clippy_lints/src/methods/mod.rs b/src/tools/clippy/clippy_lints/src/methods/mod.rs
index a17c5996293e9..4ee423b383b0f 100644
--- a/src/tools/clippy/clippy_lints/src/methods/mod.rs
+++ b/src/tools/clippy/clippy_lints/src/methods/mod.rs
@@ -2183,7 +2183,7 @@ fn lint_expect_fun_call(
         span_replace_word,
         &format!("use of `{}` followed by a function call", name),
         "try this",
-        format!("unwrap_or_else({} {{ panic!({}) }})", closure_args, arg_root_snippet),
+        format!("unwrap_or_else({} {{ panic!(\"{{}}\", {}) }})", closure_args, arg_root_snippet),
         applicability,
     );
 }
diff --git a/src/tools/clippy/clippy_lints/src/misc_early.rs b/src/tools/clippy/clippy_lints/src/misc_early.rs
index 5bc45c87874b4..84a0df92f5b43 100644
--- a/src/tools/clippy/clippy_lints/src/misc_early.rs
+++ b/src/tools/clippy/clippy_lints/src/misc_early.rs
@@ -1,4 +1,4 @@
-use crate::utils::{constants, snippet_opt, span_lint, span_lint_and_help, span_lint_and_sugg, span_lint_and_then};
+use crate::utils::{snippet_opt, span_lint, span_lint_and_help, span_lint_and_sugg, span_lint_and_then};
 use rustc_ast::ast::{
     BindingMode, Expr, ExprKind, GenericParamKind, Generics, Lit, LitFloatType, LitIntType, LitKind, Mutability,
     NodeId, Pat, PatKind, UnOp,
@@ -6,6 +6,7 @@ use rustc_ast::ast::{
 use rustc_ast::visit::FnKind;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_errors::Applicability;
+use rustc_hir::PrimTy;
 use rustc_lint::{EarlyContext, EarlyLintPass, LintContext};
 use rustc_middle::lint::in_external_macro;
 use rustc_session::{declare_lint_pass, declare_tool_lint};
@@ -264,13 +265,12 @@ impl EarlyLintPass for MiscEarlyLints {
     fn check_generics(&mut self, cx: &EarlyContext<'_>, gen: &Generics) {
         for param in &gen.params {
             if let GenericParamKind::Type { .. } = param.kind {
-                let name = param.ident.as_str();
-                if constants::BUILTIN_TYPES.contains(&&*name) {
+                if let Some(prim_ty) = PrimTy::from_name(param.ident.name) {
                     span_lint(
                         cx,
                         BUILTIN_TYPE_SHADOW,
                         param.ident.span,
-                        &format!("this generic shadows the built-in type `{}`", name),
+                        &format!("this generic shadows the built-in type `{}`", prim_ty.name()),
                     );
                 }
             }
diff --git a/src/tools/clippy/clippy_lints/src/utils/constants.rs b/src/tools/clippy/clippy_lints/src/utils/constants.rs
deleted file mode 100644
index 522932f054d89..0000000000000
--- a/src/tools/clippy/clippy_lints/src/utils/constants.rs
+++ /dev/null
@@ -1,13 +0,0 @@
-//! This module contains some useful constants.
-
-#![deny(clippy::missing_docs_in_private_items)]
-
-/// List of the built-in types names.
-///
-/// See also [the reference][reference-types] for a list of such types.
-///
-/// [reference-types]: https://doc.rust-lang.org/reference/types.html
-pub const BUILTIN_TYPES: &[&str] = &[
-    "i8", "u8", "i16", "u16", "i32", "u32", "i64", "u64", "i128", "u128", "isize", "usize", "f32", "f64", "bool",
-    "str", "char",
-];
diff --git a/src/tools/clippy/clippy_lints/src/utils/mod.rs b/src/tools/clippy/clippy_lints/src/utils/mod.rs
index ef45f9fdcd5d4..de1538233a8c3 100644
--- a/src/tools/clippy/clippy_lints/src/utils/mod.rs
+++ b/src/tools/clippy/clippy_lints/src/utils/mod.rs
@@ -8,7 +8,6 @@ pub mod author;
 pub mod camel_case;
 pub mod comparisons;
 pub mod conf;
-pub mod constants;
 mod diagnostics;
 pub mod eager_or_lazy;
 pub mod higher;
diff --git a/src/tools/clippy/tests/missing-test-files.rs b/src/tools/clippy/tests/missing-test-files.rs
index d87bb4be3c3f9..9cef7438d225c 100644
--- a/src/tools/clippy/tests/missing-test-files.rs
+++ b/src/tools/clippy/tests/missing-test-files.rs
@@ -9,14 +9,12 @@ fn test_missing_tests() {
     if !missing_files.is_empty() {
         assert!(
             false,
-            format!(
-                "Didn't see a test file for the following files:\n\n{}\n",
-                missing_files
-                    .iter()
-                    .map(|s| format!("\t{}", s))
-                    .collect::<Vec<_>>()
-                    .join("\n")
-            )
+            "Didn't see a test file for the following files:\n\n{}\n",
+            missing_files
+                .iter()
+                .map(|s| format!("\t{}", s))
+                .collect::<Vec<_>>()
+                .join("\n")
         );
     }
 }
diff --git a/src/tools/clippy/tests/ui/assertions_on_constants.rs b/src/tools/clippy/tests/ui/assertions_on_constants.rs
index 60d721c2f2049..e989de6540456 100644
--- a/src/tools/clippy/tests/ui/assertions_on_constants.rs
+++ b/src/tools/clippy/tests/ui/assertions_on_constants.rs
@@ -1,3 +1,5 @@
+#![allow(non_fmt_panic)]
+
 macro_rules! assert_const {
     ($len:expr) => {
         assert!($len > 0);
diff --git a/src/tools/clippy/tests/ui/assertions_on_constants.stderr b/src/tools/clippy/tests/ui/assertions_on_constants.stderr
index 8f09c8ce9d52a..c66fdf093f514 100644
--- a/src/tools/clippy/tests/ui/assertions_on_constants.stderr
+++ b/src/tools/clippy/tests/ui/assertions_on_constants.stderr
@@ -1,5 +1,5 @@
 error: `assert!(true)` will be optimized out by the compiler
-  --> $DIR/assertions_on_constants.rs:9:5
+  --> $DIR/assertions_on_constants.rs:11:5
    |
 LL |     assert!(true);
    |     ^^^^^^^^^^^^^^
@@ -9,7 +9,7 @@ LL |     assert!(true);
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: `assert!(false)` should probably be replaced
-  --> $DIR/assertions_on_constants.rs:10:5
+  --> $DIR/assertions_on_constants.rs:12:5
    |
 LL |     assert!(false);
    |     ^^^^^^^^^^^^^^^
@@ -18,7 +18,7 @@ LL |     assert!(false);
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: `assert!(true)` will be optimized out by the compiler
-  --> $DIR/assertions_on_constants.rs:11:5
+  --> $DIR/assertions_on_constants.rs:13:5
    |
 LL |     assert!(true, "true message");
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -27,7 +27,7 @@ LL |     assert!(true, "true message");
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: `assert!(false, "false message")` should probably be replaced
-  --> $DIR/assertions_on_constants.rs:12:5
+  --> $DIR/assertions_on_constants.rs:14:5
    |
 LL |     assert!(false, "false message");
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -36,7 +36,7 @@ LL |     assert!(false, "false message");
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: `assert!(false, msg.to_uppercase())` should probably be replaced
-  --> $DIR/assertions_on_constants.rs:15:5
+  --> $DIR/assertions_on_constants.rs:17:5
    |
 LL |     assert!(false, msg.to_uppercase());
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -45,7 +45,7 @@ LL |     assert!(false, msg.to_uppercase());
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: `assert!(true)` will be optimized out by the compiler
-  --> $DIR/assertions_on_constants.rs:18:5
+  --> $DIR/assertions_on_constants.rs:20:5
    |
 LL |     assert!(B);
    |     ^^^^^^^^^^^
@@ -54,7 +54,7 @@ LL |     assert!(B);
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: `assert!(false)` should probably be replaced
-  --> $DIR/assertions_on_constants.rs:21:5
+  --> $DIR/assertions_on_constants.rs:23:5
    |
 LL |     assert!(C);
    |     ^^^^^^^^^^^
@@ -63,7 +63,7 @@ LL |     assert!(C);
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: `assert!(false, "C message")` should probably be replaced
-  --> $DIR/assertions_on_constants.rs:22:5
+  --> $DIR/assertions_on_constants.rs:24:5
    |
 LL |     assert!(C, "C message");
    |     ^^^^^^^^^^^^^^^^^^^^^^^^
@@ -72,7 +72,7 @@ LL |     assert!(C, "C message");
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: `debug_assert!(true)` will be optimized out by the compiler
-  --> $DIR/assertions_on_constants.rs:24:5
+  --> $DIR/assertions_on_constants.rs:26:5
    |
 LL |     debug_assert!(true);
    |     ^^^^^^^^^^^^^^^^^^^^
diff --git a/src/tools/clippy/tests/ui/expect_fun_call.fixed b/src/tools/clippy/tests/ui/expect_fun_call.fixed
index f3d8a941a92bc..a756d1cf50659 100644
--- a/src/tools/clippy/tests/ui/expect_fun_call.fixed
+++ b/src/tools/clippy/tests/ui/expect_fun_call.fixed
@@ -74,12 +74,12 @@ fn main() {
             "foo"
         }
 
-        Some("foo").unwrap_or_else(|| { panic!(get_string()) });
-        Some("foo").unwrap_or_else(|| { panic!(get_string()) });
-        Some("foo").unwrap_or_else(|| { panic!(get_string()) });
+        Some("foo").unwrap_or_else(|| { panic!("{}", get_string()) });
+        Some("foo").unwrap_or_else(|| { panic!("{}", get_string()) });
+        Some("foo").unwrap_or_else(|| { panic!("{}", get_string()) });
 
-        Some("foo").unwrap_or_else(|| { panic!(get_static_str()) });
-        Some("foo").unwrap_or_else(|| { panic!(get_non_static_str(&0).to_string()) });
+        Some("foo").unwrap_or_else(|| { panic!("{}", get_static_str()) });
+        Some("foo").unwrap_or_else(|| { panic!("{}", get_non_static_str(&0).to_string()) });
     }
 
     //Issue #3839
diff --git a/src/tools/clippy/tests/ui/expect_fun_call.stderr b/src/tools/clippy/tests/ui/expect_fun_call.stderr
index a492e2df89d47..6dc796f5cee37 100644
--- a/src/tools/clippy/tests/ui/expect_fun_call.stderr
+++ b/src/tools/clippy/tests/ui/expect_fun_call.stderr
@@ -34,31 +34,31 @@ error: use of `expect` followed by a function call
   --> $DIR/expect_fun_call.rs:77:21
    |
 LL |         Some("foo").expect(&get_string());
-   |                     ^^^^^^^^^^^^^^^^^^^^^ help: try this: `unwrap_or_else(|| { panic!(get_string()) })`
+   |                     ^^^^^^^^^^^^^^^^^^^^^ help: try this: `unwrap_or_else(|| { panic!("{}", get_string()) })`
 
 error: use of `expect` followed by a function call
   --> $DIR/expect_fun_call.rs:78:21
    |
 LL |         Some("foo").expect(get_string().as_ref());
-   |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try this: `unwrap_or_else(|| { panic!(get_string()) })`
+   |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try this: `unwrap_or_else(|| { panic!("{}", get_string()) })`
 
 error: use of `expect` followed by a function call
   --> $DIR/expect_fun_call.rs:79:21
    |
 LL |         Some("foo").expect(get_string().as_str());
-   |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try this: `unwrap_or_else(|| { panic!(get_string()) })`
+   |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try this: `unwrap_or_else(|| { panic!("{}", get_string()) })`
 
 error: use of `expect` followed by a function call
   --> $DIR/expect_fun_call.rs:81:21
    |
 LL |         Some("foo").expect(get_static_str());
-   |                     ^^^^^^^^^^^^^^^^^^^^^^^^ help: try this: `unwrap_or_else(|| { panic!(get_static_str()) })`
+   |                     ^^^^^^^^^^^^^^^^^^^^^^^^ help: try this: `unwrap_or_else(|| { panic!("{}", get_static_str()) })`
 
 error: use of `expect` followed by a function call
   --> $DIR/expect_fun_call.rs:82:21
    |
 LL |         Some("foo").expect(get_non_static_str(&0));
-   |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try this: `unwrap_or_else(|| { panic!(get_non_static_str(&0).to_string()) })`
+   |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try this: `unwrap_or_else(|| { panic!("{}", get_non_static_str(&0).to_string()) })`
 
 error: use of `expect` followed by a function call
   --> $DIR/expect_fun_call.rs:86:16
diff --git a/src/tools/clippy/tests/ui/fallible_impl_from.rs b/src/tools/clippy/tests/ui/fallible_impl_from.rs
index 679f4a7dc357d..5d5af4e463297 100644
--- a/src/tools/clippy/tests/ui/fallible_impl_from.rs
+++ b/src/tools/clippy/tests/ui/fallible_impl_from.rs
@@ -36,7 +36,7 @@ impl From<Option<String>> for Invalid {
     fn from(s: Option<String>) -> Invalid {
         let s = s.unwrap();
         if !s.is_empty() {
-            panic!(42);
+            panic!("42");
         } else if s.parse::<u32>().unwrap() != 42 {
             panic!("{:?}", s);
         }
diff --git a/src/tools/clippy/tests/ui/fallible_impl_from.stderr b/src/tools/clippy/tests/ui/fallible_impl_from.stderr
index ab976b947b356..f787b30bdabc5 100644
--- a/src/tools/clippy/tests/ui/fallible_impl_from.stderr
+++ b/src/tools/clippy/tests/ui/fallible_impl_from.stderr
@@ -59,8 +59,8 @@ note: potential failure(s)
 LL |         let s = s.unwrap();
    |                 ^^^^^^^^^^
 LL |         if !s.is_empty() {
-LL |             panic!(42);
-   |             ^^^^^^^^^^^
+LL |             panic!("42");
+   |             ^^^^^^^^^^^^^
 LL |         } else if s.parse::<u32>().unwrap() != 42 {
    |                   ^^^^^^^^^^^^^^^^^^^^^^^^^
 LL |             panic!("{:?}", s);
diff --git a/src/tools/remote-test-server/src/main.rs b/src/tools/remote-test-server/src/main.rs
index d92758eb7474c..cd9d530096496 100644
--- a/src/tools/remote-test-server/src/main.rs
+++ b/src/tools/remote-test-server/src/main.rs
@@ -218,25 +218,19 @@ fn handle_run(socket: TcpStream, work: &Path, tmp: &Path, lock: &Mutex<()>, conf
     cmd.args(args);
     cmd.envs(env);
 
+    // On windows, libraries are just searched in the executable directory,
+    // system directories, PWD, and PATH, in that order. PATH is the only one
+    // we can change for this.
+    let library_path = if cfg!(windows) { "PATH" } else { "LD_LIBRARY_PATH" };
+
     // Support libraries were uploaded to `work` earlier, so make sure that's
     // in `LD_LIBRARY_PATH`. Also include our own current dir which may have
     // had some libs uploaded.
-    if cfg!(windows) {
-        // On windows, libraries are just searched in the executable directory,
-        // system directories, PWD, and PATH, in that order. PATH is the only one
-        // we can change for this.
-        cmd.env(
-            "PATH",
-            env::join_paths(
-                std::iter::once(work.to_owned())
-                    .chain(std::iter::once(path.clone()))
-                    .chain(env::split_paths(&env::var_os("PATH").unwrap())),
-            )
-            .unwrap(),
-        );
-    } else {
-        cmd.env("LD_LIBRARY_PATH", format!("{}:{}", work.display(), path.display()));
+    let mut paths = vec![work.to_owned(), path.clone()];
+    if let Some(library_path) = env::var_os(library_path) {
+        paths.extend(env::split_paths(&library_path));
     }
+    cmd.env(library_path, env::join_paths(paths).unwrap());
 
     // Some tests assume RUST_TEST_TMPDIR exists
     cmd.env("RUST_TEST_TMPDIR", tmp.to_owned());