diff --git a/compiler/rustc_driver_impl/Cargo.toml b/compiler/rustc_driver_impl/Cargo.toml
index 242aa06fe3e3c..fcc0afd3488b0 100644
--- a/compiler/rustc_driver_impl/Cargo.toml
+++ b/compiler/rustc_driver_impl/Cargo.toml
@@ -50,7 +50,7 @@ rustc_trait_selection = { path = "../rustc_trait_selection" }
 rustc_ty_utils = { path = "../rustc_ty_utils" }
 serde_json = "1.0.59"
 shlex = "1.0"
-time = { version = "0.3", default-features = false, features = ["alloc", "formatting"] }
+time = { version = "0.3", default-features = false, features = ["alloc", "formatting", "parsing", "macros"] }
 tracing = { version = "0.1.35" }
 # tidy-alphabetical-end
 
diff --git a/compiler/rustc_driver_impl/messages.ftl b/compiler/rustc_driver_impl/messages.ftl
index 39462112dc287..1b69a6e2fbecc 100644
--- a/compiler/rustc_driver_impl/messages.ftl
+++ b/compiler/rustc_driver_impl/messages.ftl
@@ -1,6 +1,10 @@
 driver_impl_ice = the compiler unexpectedly panicked. this is a bug.
 driver_impl_ice_bug_report = we would appreciate a bug report: {$bug_report_url}
 driver_impl_ice_bug_report_internal_feature = using internal features is not supported and expected to cause internal compiler errors when used incorrectly
+driver_impl_ice_bug_report_outdated =
+    it seems that this compiler `{$version}` is outdated, a newer nightly should have been released in the mean time
+    .update = please consider running `rustup update nightly` to update the nightly channel and check if this problem still persists
+    .url = if the problem still persists, we would appreciate a bug report: {$bug_report_url}
 driver_impl_ice_exclude_cargo_defaults = some of the compiler flags provided by cargo are hidden
 
 driver_impl_ice_flags = compiler flags: {$flags}
diff --git a/compiler/rustc_driver_impl/src/lib.rs b/compiler/rustc_driver_impl/src/lib.rs
index ab1e37e4ac221..85be97ea24fdf 100644
--- a/compiler/rustc_driver_impl/src/lib.rs
+++ b/compiler/rustc_driver_impl/src/lib.rs
@@ -58,7 +58,7 @@ use std::str;
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::{Arc, OnceLock};
 use std::time::{Instant, SystemTime};
-use time::OffsetDateTime;
+use time::{Date, OffsetDateTime, Time};
 
 #[allow(unused_macros)]
 macro do_not_use_print($($t:tt)*) {
@@ -1369,6 +1369,9 @@ pub fn install_ice_hook(
     using_internal_features
 }
 
+const DATE_FORMAT: &[time::format_description::FormatItem<'static>] =
+    &time::macros::format_description!("[year]-[month]-[day]");
+
 /// Prints the ICE message, including query stack, but without backtrace.
 ///
 /// The message will point the user at `bug_report_url` to report the ICE.
@@ -1397,10 +1400,34 @@ fn report_ice(
         dcx.emit_err(session_diagnostics::Ice);
     }
 
-    if using_internal_features.load(std::sync::atomic::Ordering::Relaxed) {
-        dcx.emit_note(session_diagnostics::IceBugReportInternalFeature);
+    use time::ext::NumericalDuration;
+
+    // Try to hint user to update nightly if applicable when reporting an ICE.
+    // Attempt to calculate when current version was released, and add 12 hours
+    // as buffer. If the current version's release timestamp is older than
+    // the system's current time + 24 hours + 12 hours buffer if we're on
+    // nightly.
+    if let Some("nightly") = option_env!("CFG_RELEASE_CHANNEL")
+        && let Some(version) = option_env!("CFG_VERSION")
+        && let Some(ver_date_str) = option_env!("CFG_VER_DATE")
+        && let Ok(ver_date) = Date::parse(&ver_date_str, DATE_FORMAT)
+        && let ver_datetime = OffsetDateTime::new_utc(ver_date, Time::MIDNIGHT)
+        && let system_datetime = OffsetDateTime::from(SystemTime::now())
+        && system_datetime.checked_sub(36.hours()).is_some_and(|d| d > ver_datetime)
+        && !using_internal_features.load(std::sync::atomic::Ordering::Relaxed)
+    {
+        dcx.emit_note(session_diagnostics::IceBugReportOutdated {
+            version,
+            bug_report_url,
+            note_update: (),
+            note_url: (),
+        });
     } else {
-        dcx.emit_note(session_diagnostics::IceBugReport { bug_report_url });
+        if using_internal_features.load(std::sync::atomic::Ordering::Relaxed) {
+            dcx.emit_note(session_diagnostics::IceBugReportInternalFeature);
+        } else {
+            dcx.emit_note(session_diagnostics::IceBugReport { bug_report_url });
+        }
     }
 
     let version = util::version_str!().unwrap_or("unknown_version");
diff --git a/compiler/rustc_driver_impl/src/session_diagnostics.rs b/compiler/rustc_driver_impl/src/session_diagnostics.rs
index 2b31fdd77cca3..62d0da62d2a79 100644
--- a/compiler/rustc_driver_impl/src/session_diagnostics.rs
+++ b/compiler/rustc_driver_impl/src/session_diagnostics.rs
@@ -46,6 +46,17 @@ pub(crate) struct IceBugReport<'a> {
 #[diag(driver_impl_ice_bug_report_internal_feature)]
 pub(crate) struct IceBugReportInternalFeature;
 
+#[derive(Diagnostic)]
+#[diag(driver_impl_ice_bug_report_outdated)]
+pub(crate) struct IceBugReportOutdated<'a> {
+    pub version: &'a str,
+    pub bug_report_url: &'a str,
+    #[note(driver_impl_update)]
+    pub note_update: (),
+    #[note(driver_impl_url)]
+    pub note_url: (),
+}
+
 #[derive(Diagnostic)]
 #[diag(driver_impl_ice_version)]
 pub(crate) struct IceVersion<'a> {
diff --git a/compiler/rustc_errors/src/emitter.rs b/compiler/rustc_errors/src/emitter.rs
index 293d8f01e673a..57b8df52f4b79 100644
--- a/compiler/rustc_errors/src/emitter.rs
+++ b/compiler/rustc_errors/src/emitter.rs
@@ -10,7 +10,6 @@
 use rustc_span::source_map::SourceMap;
 use rustc_span::{FileLines, FileName, SourceFile, Span};
 
-use crate::error::TranslateError;
 use crate::snippet::{
     Annotation, AnnotationColumn, AnnotationType, Line, MultilineAnnotation, Style, StyledString,
 };
@@ -539,18 +538,9 @@ impl Emitter for HumanEmitter {
 /// Fatal diagnostics are forwarded to `fatal_dcx` to avoid silent
 /// failures of rustc, as witnessed e.g. in issue #89358.
 pub struct SilentEmitter {
+    pub fallback_bundle: LazyFallbackBundle,
     pub fatal_dcx: DiagCtxt,
-    pub fatal_note: String,
-}
-
-pub fn silent_translate<'a>(message: &'a DiagMessage) -> Result<Cow<'_, str>, TranslateError<'_>> {
-    match message {
-        DiagMessage::Str(msg) | DiagMessage::Translated(msg) => Ok(Cow::Borrowed(msg)),
-        DiagMessage::FluentIdentifier(identifier, _) => {
-            // Any value works here.
-            Ok(identifier.clone())
-        }
-    }
+    pub fatal_note: Option<String>,
 }
 
 impl Translate for SilentEmitter {
@@ -559,17 +549,9 @@ impl Translate for SilentEmitter {
     }
 
     fn fallback_fluent_bundle(&self) -> &FluentBundle {
-        panic!("silent emitter attempted to translate message")
-    }
-
-    // Override `translate_message` for the silent emitter because eager translation of
-    // subdiagnostics result in a call to this.
-    fn translate_message<'a>(
-        &'a self,
-        message: &'a DiagMessage,
-        _: &'a FluentArgs<'_>,
-    ) -> Result<Cow<'_, str>, TranslateError<'_>> {
-        silent_translate(message)
+        // Ideally this field wouldn't be necessary and the fallback bundle in `fatal_dcx` would be
+        // used but the lock prevents this.
+        &self.fallback_bundle
     }
 }
 
@@ -580,7 +562,9 @@ impl Emitter for SilentEmitter {
 
     fn emit_diagnostic(&mut self, mut diag: DiagInner) {
         if diag.level == Level::Fatal {
-            diag.sub(Level::Note, self.fatal_note.clone(), MultiSpan::new());
+            if let Some(fatal_note) = &self.fatal_note {
+                diag.sub(Level::Note, fatal_note.clone(), MultiSpan::new());
+            }
             self.fatal_dcx.emit_diagnostic(diag);
         }
     }
diff --git a/compiler/rustc_errors/src/lib.rs b/compiler/rustc_errors/src/lib.rs
index 0a6d66f52dad0..0caa8fa9e8abe 100644
--- a/compiler/rustc_errors/src/lib.rs
+++ b/compiler/rustc_errors/src/lib.rs
@@ -63,7 +63,7 @@ use emitter::{is_case_difference, DynEmitter, Emitter};
 use registry::Registry;
 use rustc_data_structures::fx::{FxHashSet, FxIndexMap, FxIndexSet};
 use rustc_data_structures::stable_hasher::{Hash128, StableHasher};
-use rustc_data_structures::sync::Lock;
+use rustc_data_structures::sync::{Lock, Lrc};
 use rustc_data_structures::AtomicRef;
 use rustc_lint_defs::LintExpectationId;
 use rustc_span::source_map::SourceMap;
@@ -606,29 +606,54 @@ impl DiagCtxt {
     }
 
     pub fn new(emitter: Box<DynEmitter>) -> Self {
-        Self {
-            inner: Lock::new(DiagCtxtInner {
-                flags: DiagCtxtFlags { can_emit_warnings: true, ..Default::default() },
-                err_guars: Vec::new(),
-                lint_err_guars: Vec::new(),
-                delayed_bugs: Vec::new(),
-                deduplicated_err_count: 0,
-                deduplicated_warn_count: 0,
-                emitter,
-                must_produce_diag: false,
-                has_printed: false,
-                suppressed_expected_diag: false,
-                taught_diagnostics: Default::default(),
-                emitted_diagnostic_codes: Default::default(),
-                emitted_diagnostics: Default::default(),
-                stashed_diagnostics: Default::default(),
-                future_breakage_diagnostics: Vec::new(),
-                check_unstable_expect_diagnostics: false,
-                unstable_expect_diagnostics: Vec::new(),
-                fulfilled_expectations: Default::default(),
-                ice_file: None,
-            }),
+        Self { inner: Lock::new(DiagCtxtInner::new(emitter)) }
+    }
+
+    pub fn make_silent(&mut self, fallback_bundle: LazyFallbackBundle, fatal_note: Option<String>) {
+        self.wrap_emitter(|old_dcx| {
+            Box::new(emitter::SilentEmitter {
+                fallback_bundle,
+                fatal_dcx: DiagCtxt { inner: Lock::new(old_dcx) },
+                fatal_note,
+            })
+        });
+    }
+
+    fn wrap_emitter<F>(&mut self, f: F)
+    where
+        F: FnOnce(DiagCtxtInner) -> Box<DynEmitter>,
+    {
+        // A empty type that implements `Emitter` so that a `DiagCtxtInner` can be constructed
+        // to temporarily swap in place of the real one, which will be used in constructing
+        // its replacement.
+        struct FalseEmitter;
+
+        impl Emitter for FalseEmitter {
+            fn emit_diagnostic(&mut self, _: DiagInner) {
+                unimplemented!("false emitter must only used during `wrap_emitter`")
+            }
+
+            fn source_map(&self) -> Option<&Lrc<SourceMap>> {
+                unimplemented!("false emitter must only used during `wrap_emitter`")
+            }
         }
+
+        impl translation::Translate for FalseEmitter {
+            fn fluent_bundle(&self) -> Option<&Lrc<FluentBundle>> {
+                unimplemented!("false emitter must only used during `wrap_emitter`")
+            }
+
+            fn fallback_fluent_bundle(&self) -> &FluentBundle {
+                unimplemented!("false emitter must only used during `wrap_emitter`")
+            }
+        }
+
+        let mut inner = self.inner.borrow_mut();
+        let mut prev_dcx = DiagCtxtInner::new(Box::new(FalseEmitter));
+        std::mem::swap(&mut *inner, &mut prev_dcx);
+        let new_emitter = f(prev_dcx);
+        let mut new_dcx = DiagCtxtInner::new(new_emitter);
+        std::mem::swap(&mut *inner, &mut new_dcx);
     }
 
     /// Translate `message` eagerly with `args` to `SubdiagMessage::Eager`.
@@ -1345,6 +1370,30 @@ impl DiagCtxt {
 // `DiagCtxt::foo()` just borrows `inner` and forwards a call to
 // `DiagCtxtInner::foo`.
 impl DiagCtxtInner {
+    fn new(emitter: Box<DynEmitter>) -> Self {
+        Self {
+            flags: DiagCtxtFlags { can_emit_warnings: true, ..Default::default() },
+            err_guars: Vec::new(),
+            lint_err_guars: Vec::new(),
+            delayed_bugs: Vec::new(),
+            deduplicated_err_count: 0,
+            deduplicated_warn_count: 0,
+            emitter,
+            must_produce_diag: false,
+            has_printed: false,
+            suppressed_expected_diag: false,
+            taught_diagnostics: Default::default(),
+            emitted_diagnostic_codes: Default::default(),
+            emitted_diagnostics: Default::default(),
+            stashed_diagnostics: Default::default(),
+            future_breakage_diagnostics: Vec::new(),
+            check_unstable_expect_diagnostics: false,
+            unstable_expect_diagnostics: Vec::new(),
+            fulfilled_expectations: Default::default(),
+            ice_file: None,
+        }
+    }
+
     /// Emit all stashed diagnostics.
     fn emit_stashed_diagnostics(&mut self) -> Option<ErrorGuaranteed> {
         let mut guar = None;
diff --git a/compiler/rustc_hir_analysis/src/collect.rs b/compiler/rustc_hir_analysis/src/collect.rs
index b6e2695590c13..2cc37651ef521 100644
--- a/compiler/rustc_hir_analysis/src/collect.rs
+++ b/compiler/rustc_hir_analysis/src/collect.rs
@@ -791,7 +791,12 @@ fn convert_enum_variant_types(tcx: TyCtxt<'_>, def_id: DefId) {
 }
 
 fn find_field(tcx: TyCtxt<'_>, (def_id, ident): (DefId, Ident)) -> Option<FieldIdx> {
-    tcx.adt_def(def_id).non_enum_variant().fields.iter_enumerated().find_map(|(idx, field)| {
+    let adt = tcx.adt_def(def_id);
+    if adt.is_enum() {
+        return None;
+    }
+
+    adt.non_enum_variant().fields.iter_enumerated().find_map(|(idx, field)| {
         if field.is_unnamed() {
             let field_ty = tcx.type_of(field.did).instantiate_identity();
             let adt_def = field_ty.ty_adt_def().expect("expect Adt for unnamed field");
diff --git a/compiler/rustc_hir_analysis/src/collect/type_of/opaque.rs b/compiler/rustc_hir_analysis/src/collect/type_of/opaque.rs
index f0e998b7a0032..dcb01a117b047 100644
--- a/compiler/rustc_hir_analysis/src/collect/type_of/opaque.rs
+++ b/compiler/rustc_hir_analysis/src/collect/type_of/opaque.rs
@@ -46,9 +46,7 @@ pub(super) fn find_opaque_ty_constraints_for_impl_trait_in_assoc_type(
     for &assoc_id in tcx.associated_item_def_ids(impl_def_id) {
         let assoc = tcx.associated_item(assoc_id);
         match assoc.kind {
-            ty::AssocKind::Const | ty::AssocKind::Fn => {
-                locator.check(assoc_id.expect_local(), ImplTraitSource::AssocTy)
-            }
+            ty::AssocKind::Const | ty::AssocKind::Fn => locator.check(assoc_id.expect_local()),
             // Associated types don't have bodies, so they can't constrain hidden types
             ty::AssocKind::Type => {}
         }
@@ -182,15 +180,9 @@ struct TaitConstraintLocator<'tcx> {
     typeck_types: Vec<ty::OpaqueHiddenType<'tcx>>,
 }
 
-#[derive(Debug)]
-enum ImplTraitSource {
-    AssocTy,
-    TyAlias,
-}
-
 impl TaitConstraintLocator<'_> {
     #[instrument(skip(self), level = "debug")]
-    fn check(&mut self, item_def_id: LocalDefId, source: ImplTraitSource) {
+    fn check(&mut self, item_def_id: LocalDefId) {
         // Don't try to check items that cannot possibly constrain the type.
         if !self.tcx.has_typeck_results(item_def_id) {
             debug!("no constraint: no typeck results");
@@ -242,12 +234,8 @@ impl TaitConstraintLocator<'_> {
                 continue;
             }
             constrained = true;
-            let opaque_types_defined_by = match source {
-                ImplTraitSource::AssocTy => {
-                    self.tcx.impl_trait_in_assoc_types_defined_by(item_def_id)
-                }
-                ImplTraitSource::TyAlias => self.tcx.opaque_types_defined_by(item_def_id),
-            };
+            let opaque_types_defined_by = self.tcx.opaque_types_defined_by(item_def_id);
+
             if !opaque_types_defined_by.contains(&self.def_id) {
                 self.tcx.dcx().emit_err(TaitForwardCompat {
                     span: hidden_type.span,
@@ -308,7 +296,7 @@ impl<'tcx> intravisit::Visitor<'tcx> for TaitConstraintLocator<'tcx> {
     }
     fn visit_expr(&mut self, ex: &'tcx Expr<'tcx>) {
         if let hir::ExprKind::Closure(closure) = ex.kind {
-            self.check(closure.def_id, ImplTraitSource::TyAlias);
+            self.check(closure.def_id);
         }
         intravisit::walk_expr(self, ex);
     }
@@ -316,7 +304,7 @@ impl<'tcx> intravisit::Visitor<'tcx> for TaitConstraintLocator<'tcx> {
         trace!(?it.owner_id);
         // The opaque type itself or its children are not within its reveal scope.
         if it.owner_id.def_id != self.def_id {
-            self.check(it.owner_id.def_id, ImplTraitSource::TyAlias);
+            self.check(it.owner_id.def_id);
             intravisit::walk_item(self, it);
         }
     }
@@ -324,13 +312,13 @@ impl<'tcx> intravisit::Visitor<'tcx> for TaitConstraintLocator<'tcx> {
         trace!(?it.owner_id);
         // The opaque type itself or its children are not within its reveal scope.
         if it.owner_id.def_id != self.def_id {
-            self.check(it.owner_id.def_id, ImplTraitSource::TyAlias);
+            self.check(it.owner_id.def_id);
             intravisit::walk_impl_item(self, it);
         }
     }
     fn visit_trait_item(&mut self, it: &'tcx TraitItem<'tcx>) {
         trace!(?it.owner_id);
-        self.check(it.owner_id.def_id, ImplTraitSource::TyAlias);
+        self.check(it.owner_id.def_id);
         intravisit::walk_trait_item(self, it);
     }
     fn visit_foreign_item(&mut self, it: &'tcx hir::ForeignItem<'tcx>) {
diff --git a/compiler/rustc_interface/src/interface.rs b/compiler/rustc_interface/src/interface.rs
index 3a2bbed19beff..b2ec8e5342924 100644
--- a/compiler/rustc_interface/src/interface.rs
+++ b/compiler/rustc_interface/src/interface.rs
@@ -45,9 +45,10 @@ pub struct Compiler {
 pub(crate) fn parse_cfg(dcx: &DiagCtxt, cfgs: Vec<String>) -> Cfg {
     cfgs.into_iter()
         .map(|s| {
-            let psess = ParseSess::with_silent_emitter(format!(
-                "this error occurred on the command line: `--cfg={s}`"
-            ));
+            let psess = ParseSess::with_silent_emitter(
+                vec![crate::DEFAULT_LOCALE_RESOURCE, rustc_parse::DEFAULT_LOCALE_RESOURCE],
+                format!("this error occurred on the command line: `--cfg={s}`"),
+            );
             let filename = FileName::cfg_spec_source_code(&s);
 
             macro_rules! error {
@@ -107,9 +108,10 @@ pub(crate) fn parse_check_cfg(dcx: &DiagCtxt, specs: Vec<String>) -> CheckCfg {
     let mut check_cfg = CheckCfg { exhaustive_names, exhaustive_values, ..CheckCfg::default() };
 
     for s in specs {
-        let psess = ParseSess::with_silent_emitter(format!(
-            "this error occurred on the command line: `--check-cfg={s}`"
-        ));
+        let psess = ParseSess::with_silent_emitter(
+            vec![crate::DEFAULT_LOCALE_RESOURCE, rustc_parse::DEFAULT_LOCALE_RESOURCE],
+            format!("this error occurred on the command line: `--check-cfg={s}`"),
+        );
         let filename = FileName::cfg_spec_source_code(&s);
 
         macro_rules! error {
diff --git a/compiler/rustc_lint/src/context/diagnostics.rs b/compiler/rustc_lint/src/context/diagnostics.rs
index a0aa252bcdf2f..a58a37bf3ac08 100644
--- a/compiler/rustc_lint/src/context/diagnostics.rs
+++ b/compiler/rustc_lint/src/context/diagnostics.rs
@@ -12,6 +12,43 @@ use rustc_span::edit_distance::find_best_match_for_name;
 use rustc_span::symbol::{sym, Symbol};
 use rustc_span::BytePos;
 
+const MAX_CHECK_CFG_NAMES_OR_VALUES: usize = 35;
+
+fn check_cfg_expected_note(
+    sess: &Session,
+    possibilities: &[Symbol],
+    type_: &str,
+    name: Option<Symbol>,
+    suffix: &str,
+) -> String {
+    use std::fmt::Write;
+
+    let n_possibilities = if sess.opts.unstable_opts.check_cfg_all_expected {
+        possibilities.len()
+    } else {
+        std::cmp::min(possibilities.len(), MAX_CHECK_CFG_NAMES_OR_VALUES)
+    };
+
+    let mut possibilities = possibilities.iter().map(Symbol::as_str).collect::<Vec<_>>();
+    possibilities.sort();
+
+    let and_more = possibilities.len().saturating_sub(n_possibilities);
+    let possibilities = possibilities[..n_possibilities].join("`, `");
+
+    let mut note = String::with_capacity(50 + possibilities.len());
+
+    write!(&mut note, "expected {type_}").unwrap();
+    if let Some(name) = name {
+        write!(&mut note, " for `{name}`").unwrap();
+    }
+    write!(&mut note, " are: {suffix}`{possibilities}`").unwrap();
+    if and_more > 0 {
+        write!(&mut note, " and {and_more} more").unwrap();
+    }
+
+    note
+}
+
 pub(super) fn builtin(sess: &Session, diagnostic: BuiltinLintDiag, diag: &mut Diag<'_, ()>) {
     match diagnostic {
         BuiltinLintDiag::UnicodeTextFlow(span, content) => {
@@ -286,16 +323,13 @@ pub(super) fn builtin(sess: &Session, diagnostic: BuiltinLintDiag, diag: &mut Di
                     }
                 }
                 if !possibilities.is_empty() {
-                    let mut possibilities =
-                        possibilities.iter().map(Symbol::as_str).collect::<Vec<_>>();
-                    possibilities.sort();
-                    let possibilities = possibilities.join("`, `");
-
-                    // The list of expected names can be long (even by default) and
-                    // so the diagnostic produced can take a lot of space. To avoid
-                    // cloging the user output we only want to print that diagnostic
-                    // once.
-                    diag.help_once(format!("expected names are: `{possibilities}`"));
+                    diag.help_once(check_cfg_expected_note(
+                        sess,
+                        &possibilities,
+                        "names",
+                        None,
+                        "",
+                    ));
                 }
             }
 
@@ -338,16 +372,13 @@ pub(super) fn builtin(sess: &Session, diagnostic: BuiltinLintDiag, diag: &mut Di
             // Show the full list if all possible values for a given name, but don't do it
             // for names as the possibilities could be very long
             if !possibilities.is_empty() {
-                {
-                    let mut possibilities =
-                        possibilities.iter().map(Symbol::as_str).collect::<Vec<_>>();
-                    possibilities.sort();
-
-                    let possibilities = possibilities.join("`, `");
-                    let none = if have_none_possibility { "(none), " } else { "" };
-
-                    diag.note(format!("expected values for `{name}` are: {none}`{possibilities}`"));
-                }
+                diag.note(check_cfg_expected_note(
+                    sess,
+                    &possibilities,
+                    "values",
+                    Some(name),
+                    if have_none_possibility { "(none), " } else { "" },
+                ));
 
                 if let Some((value, value_span)) = value {
                     // Suggest the most probable if we found one
diff --git a/compiler/rustc_metadata/src/creader.rs b/compiler/rustc_metadata/src/creader.rs
index 8b48570fbbadd..0d37c0feb0c24 100644
--- a/compiler/rustc_metadata/src/creader.rs
+++ b/compiler/rustc_metadata/src/creader.rs
@@ -1132,7 +1132,13 @@ fn load_dylib(path: &Path, max_attempts: usize) -> Result<libloading::Library, S
             Err(err) => {
                 // Only try to recover from this specific error.
                 if !matches!(err, libloading::Error::LoadLibraryExW { .. }) {
-                    return Err(err.to_string());
+                    let err = format_dlopen_err(&err);
+                    // We include the path of the dylib in the error ourselves, so
+                    // if it's in the error, we strip it.
+                    if let Some(err) = err.strip_prefix(&format!(": {}", path.display())) {
+                        return Err(err.to_string());
+                    }
+                    return Err(err);
                 }
 
                 last_error = Some(err);
diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index 8357c21a3c2be..b0431ae05d395 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -344,15 +344,6 @@ rustc_queries! {
         }
     }
 
-    query impl_trait_in_assoc_types_defined_by(
-        key: LocalDefId
-    ) -> &'tcx ty::List<LocalDefId> {
-        desc {
-            |tcx| "computing the opaque types defined by `{}`",
-            tcx.def_path_str(key.to_def_id())
-        }
-    }
-
     /// Returns the list of bounds that can be used for
     /// `SelectionCandidate::ProjectionCandidate(_)` and
     /// `ProjectionTyCandidate::TraitDef`.
diff --git a/compiler/rustc_resolve/src/imports.rs b/compiler/rustc_resolve/src/imports.rs
index 0cd925c5ba6ae..6647a9a279285 100644
--- a/compiler/rustc_resolve/src/imports.rs
+++ b/compiler/rustc_resolve/src/imports.rs
@@ -8,8 +8,8 @@ use crate::errors::{
     ItemsInTraitsAreNotImportable,
 };
 use crate::Determinacy::{self, *};
-use crate::Namespace::*;
 use crate::{module_to_string, names_to_string, ImportSuggestion};
+use crate::{AmbiguityError, Namespace::*};
 use crate::{AmbiguityKind, BindingKey, ResolutionError, Resolver, Segment};
 use crate::{Finalize, Module, ModuleOrUniformRoot, ParentScope, PerNS, ScopeSet};
 use crate::{NameBinding, NameBindingData, NameBindingKind, PathResult, Used};
@@ -538,7 +538,6 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
             .chain(indeterminate_imports.iter().map(|i| (true, i)))
         {
             let unresolved_import_error = self.finalize_import(*import);
-
             // If this import is unresolved then create a dummy import
             // resolution for it so that later resolve stages won't complain.
             self.import_dummy_binding(*import, is_indeterminate);
@@ -856,7 +855,9 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
             ImportKind::Single { target_bindings, .. } => target_bindings[TypeNS].get(),
             _ => None,
         };
-        let prev_ambiguity_errors_len = self.ambiguity_errors.len();
+        let ambiguity_errors_len =
+            |errors: &Vec<AmbiguityError<'_>>| errors.iter().filter(|error| !error.warning).count();
+        let prev_ambiguity_errors_len = ambiguity_errors_len(&self.ambiguity_errors);
         let finalize = Finalize::with_root_span(import.root_id, import.span, import.root_span);
 
         // We'll provide more context to the privacy errors later, up to `len`.
@@ -870,7 +871,8 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
             ignore_binding,
         );
 
-        let no_ambiguity = self.ambiguity_errors.len() == prev_ambiguity_errors_len;
+        let no_ambiguity =
+            ambiguity_errors_len(&self.ambiguity_errors) == prev_ambiguity_errors_len;
         import.vis.set(orig_vis);
         let module = match path_res {
             PathResult::Module(module) => {
diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs
index 42c9d5e10eba1..55e1556cdf8d6 100644
--- a/compiler/rustc_session/src/options.rs
+++ b/compiler/rustc_session/src/options.rs
@@ -1565,6 +1565,8 @@ options! {
         "set options for branch target identification and pointer authentication on AArch64"),
     cf_protection: CFProtection = (CFProtection::None, parse_cfprotection, [TRACKED],
         "instrument control-flow architecture protection"),
+    check_cfg_all_expected: bool = (false, parse_bool, [UNTRACKED],
+        "show all expected values in check-cfg diagnostics (default: no)"),
     codegen_backend: Option<String> = (None, parse_opt_string, [TRACKED],
         "the backend to use"),
     collapse_macro_debuginfo: CollapseMacroDebuginfo = (CollapseMacroDebuginfo::Unspecified,
diff --git a/compiler/rustc_session/src/parse.rs b/compiler/rustc_session/src/parse.rs
index 25b5422f3225f..506bd5d5dbd81 100644
--- a/compiler/rustc_session/src/parse.rs
+++ b/compiler/rustc_session/src/parse.rs
@@ -265,14 +265,20 @@ impl ParseSess {
         }
     }
 
-    pub fn with_silent_emitter(fatal_note: String) -> Self {
-        let fallback_bundle = fallback_fluent_bundle(Vec::new(), false);
+    pub fn with_silent_emitter(locale_resources: Vec<&'static str>, fatal_note: String) -> Self {
+        let fallback_bundle = fallback_fluent_bundle(locale_resources, false);
         let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
-        let emitter =
-            Box::new(HumanEmitter::new(stderr_destination(ColorConfig::Auto), fallback_bundle));
+        let emitter = Box::new(HumanEmitter::new(
+            stderr_destination(ColorConfig::Auto),
+            fallback_bundle.clone(),
+        ));
         let fatal_dcx = DiagCtxt::new(emitter);
-        let dcx =
-            DiagCtxt::new(Box::new(SilentEmitter { fatal_dcx, fatal_note })).disable_warnings();
+        let dcx = DiagCtxt::new(Box::new(SilentEmitter {
+            fallback_bundle,
+            fatal_dcx,
+            fatal_note: Some(fatal_note),
+        }))
+        .disable_warnings();
         ParseSess::with_dcx(dcx, sm)
     }
 
diff --git a/compiler/rustc_ty_utils/src/opaque_types.rs b/compiler/rustc_ty_utils/src/opaque_types.rs
index aaf968cbb7587..c6448b4f661d7 100644
--- a/compiler/rustc_ty_utils/src/opaque_types.rs
+++ b/compiler/rustc_ty_utils/src/opaque_types.rs
@@ -33,7 +33,11 @@ enum CollectionMode {
 }
 
 impl<'tcx> OpaqueTypeCollector<'tcx> {
-    fn new(tcx: TyCtxt<'tcx>, item: LocalDefId, mode: CollectionMode) -> Self {
+    fn new(tcx: TyCtxt<'tcx>, item: LocalDefId) -> Self {
+        let mode = match tcx.def_kind(tcx.local_parent(item)) {
+            DefKind::Impl { of_trait: true } => CollectionMode::ImplTraitInAssocTypes,
+            _ => CollectionMode::TypeAliasImplTraitTransition,
+        };
         Self { tcx, opaques: Vec::new(), item, seen: Default::default(), span: None, mode }
     }
 
@@ -284,23 +288,13 @@ impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for OpaqueTypeCollector<'tcx> {
     }
 }
 
-fn impl_trait_in_assoc_types_defined_by<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    item: LocalDefId,
-) -> &'tcx ty::List<LocalDefId> {
-    let mut collector = OpaqueTypeCollector::new(tcx, item, CollectionMode::ImplTraitInAssocTypes);
-    super::sig_types::walk_types(tcx, item, &mut collector);
-    tcx.mk_local_def_ids(&collector.opaques)
-}
-
 fn opaque_types_defined_by<'tcx>(
     tcx: TyCtxt<'tcx>,
     item: LocalDefId,
 ) -> &'tcx ty::List<LocalDefId> {
     let kind = tcx.def_kind(item);
     trace!(?kind);
-    let mut collector =
-        OpaqueTypeCollector::new(tcx, item, CollectionMode::TypeAliasImplTraitTransition);
+    let mut collector = OpaqueTypeCollector::new(tcx, item);
     super::sig_types::walk_types(tcx, item, &mut collector);
     match kind {
         DefKind::AssocFn
@@ -343,6 +337,5 @@ fn opaque_types_defined_by<'tcx>(
 }
 
 pub(super) fn provide(providers: &mut Providers) {
-    *providers =
-        Providers { opaque_types_defined_by, impl_trait_in_assoc_types_defined_by, ..*providers };
+    *providers = Providers { opaque_types_defined_by, ..*providers };
 }
diff --git a/src/tools/rustfmt/src/parse/session.rs b/src/tools/rustfmt/src/parse/session.rs
index 11af986051351..60a89a5753641 100644
--- a/src/tools/rustfmt/src/parse/session.rs
+++ b/src/tools/rustfmt/src/parse/session.rs
@@ -1,9 +1,8 @@
-use std::borrow::Cow;
 use std::path::Path;
 use std::sync::atomic::{AtomicBool, Ordering};
 
 use rustc_data_structures::sync::{IntoDynSyncSend, Lrc};
-use rustc_errors::emitter::{stderr_destination, DynEmitter, Emitter, HumanEmitter};
+use rustc_errors::emitter::{stderr_destination, DynEmitter, Emitter, HumanEmitter, SilentEmitter};
 use rustc_errors::translation::Translate;
 use rustc_errors::{ColorConfig, Diag, DiagCtxt, DiagInner, Level as DiagnosticLevel};
 use rustc_session::parse::ParseSess as RawParseSess;
@@ -28,41 +27,6 @@ pub(crate) struct ParseSess {
     can_reset_errors: Lrc<AtomicBool>,
 }
 
-/// Emitter which discards every error.
-struct SilentEmitter;
-
-impl Translate for SilentEmitter {
-    fn fluent_bundle(&self) -> Option<&Lrc<rustc_errors::FluentBundle>> {
-        None
-    }
-
-    fn fallback_fluent_bundle(&self) -> &rustc_errors::FluentBundle {
-        panic!("silent emitter attempted to translate a diagnostic");
-    }
-
-    // Override `translate_message` for the silent emitter because eager translation of
-    // subdiagnostics result in a call to this.
-    fn translate_message<'a>(
-        &'a self,
-        message: &'a rustc_errors::DiagMessage,
-        _: &'a rustc_errors::translation::FluentArgs<'_>,
-    ) -> Result<Cow<'_, str>, rustc_errors::error::TranslateError<'_>> {
-        rustc_errors::emitter::silent_translate(message)
-    }
-}
-
-impl Emitter for SilentEmitter {
-    fn source_map(&self) -> Option<&Lrc<SourceMap>> {
-        None
-    }
-
-    fn emit_diagnostic(&mut self, _diag: DiagInner) {}
-}
-
-fn silent_emitter() -> Box<DynEmitter> {
-    Box::new(SilentEmitter {})
-}
-
 /// Emit errors against every files expect ones specified in the `ignore_path_set`.
 struct SilentOnIgnoredFilesEmitter {
     ignore_path_set: IntoDynSyncSend<Lrc<IgnorePathSet>>,
@@ -143,17 +107,23 @@ fn default_dcx(
         ColorConfig::Never
     };
 
-    let emitter = if hide_parse_errors {
-        silent_emitter()
+    let fallback_bundle = rustc_errors::fallback_fluent_bundle(
+        rustc_driver::DEFAULT_LOCALE_RESOURCES.to_vec(),
+        false,
+    );
+    let emitter = Box::new(
+        HumanEmitter::new(stderr_destination(emit_color), fallback_bundle.clone())
+            .sm(Some(source_map.clone())),
+    );
+
+    let emitter: Box<DynEmitter> = if hide_parse_errors {
+        Box::new(SilentEmitter {
+            fallback_bundle,
+            fatal_dcx: DiagCtxt::new(emitter),
+            fatal_note: None,
+        })
     } else {
-        let fallback_bundle = rustc_errors::fallback_fluent_bundle(
-            rustc_driver::DEFAULT_LOCALE_RESOURCES.to_vec(),
-            false,
-        );
-        Box::new(
-            HumanEmitter::new(stderr_destination(emit_color), fallback_bundle)
-                .sm(Some(source_map.clone())),
-        )
+        emitter
     };
     DiagCtxt::new(Box::new(SilentOnIgnoredFilesEmitter {
         has_non_ignorable_parser_errors: false,
@@ -232,7 +202,14 @@ impl ParseSess {
     }
 
     pub(crate) fn set_silent_emitter(&mut self) {
-        self.raw_psess.dcx = DiagCtxt::new(silent_emitter());
+        // Ideally this invocation wouldn't be necessary and the fallback bundle in
+        // `self.parse_sess.dcx` could be used, but the lock in `DiagCtxt` prevents this.
+        // See `<rustc_errors::SilentEmitter as Translate>::fallback_fluent_bundle`.
+        let fallback_bundle = rustc_errors::fallback_fluent_bundle(
+            rustc_driver::DEFAULT_LOCALE_RESOURCES.to_vec(),
+            false,
+        );
+        self.raw_psess.dcx.make_silent(fallback_bundle, None);
     }
 
     pub(crate) fn span_to_filename(&self, span: Span) -> FileName {
diff --git a/src/tools/rustfmt/tests/rustfmt/main.rs b/src/tools/rustfmt/tests/rustfmt/main.rs
index 7dcf7c8416eec..e66fad1e7fa7b 100644
--- a/src/tools/rustfmt/tests/rustfmt/main.rs
+++ b/src/tools/rustfmt/tests/rustfmt/main.rs
@@ -176,7 +176,7 @@ fn rustfmt_emits_error_on_line_overflow_true() {
 #[test]
 #[allow(non_snake_case)]
 fn dont_emit_ICE() {
-    let files = ["tests/target/issue_5728.rs", "tests/target/issue_5729.rs"];
+    let files = ["tests/target/issue_5728.rs", "tests/target/issue_5729.rs", "tests/target/issue_6082.rs"];
 
     for file in files {
         let args = [file];
diff --git a/src/tools/rustfmt/tests/target/issue_6082.rs b/src/tools/rustfmt/tests/target/issue_6082.rs
new file mode 100644
index 0000000000000..58e512c710e98
--- /dev/null
+++ b/src/tools/rustfmt/tests/target/issue_6082.rs
@@ -0,0 +1,5 @@
+macro_rules! test {
+    ($T:ident, $b:lifetime) => {
+        Box<$T<$b>>
+    };
+}
diff --git a/tests/ui/check-cfg/mix.rs b/tests/ui/check-cfg/mix.rs
index ba30bc1e69b50..69156ab67635e 100644
--- a/tests/ui/check-cfg/mix.rs
+++ b/tests/ui/check-cfg/mix.rs
@@ -74,6 +74,8 @@ fn test_cfg_macro() {
     //~^ WARNING unexpected `cfg` condition value
     //~| WARNING unexpected `cfg` condition value
     //~| WARNING unexpected `cfg` condition value
+    cfg!(target_feature = "zebra");
+    //~^ WARNING unexpected `cfg` condition value
 }
 
 fn main() {}
diff --git a/tests/ui/check-cfg/mix.stderr b/tests/ui/check-cfg/mix.stderr
index 77643f227d9d0..93333e5ef2a5b 100644
--- a/tests/ui/check-cfg/mix.stderr
+++ b/tests/ui/check-cfg/mix.stderr
@@ -245,5 +245,14 @@ LL |     cfg!(all(feature = "zebra", feature = "zebra", feature = "zebra"));
    = help: to expect this configuration use `--check-cfg=cfg(feature, values("zebra"))`
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
-warning: 26 warnings emitted
+warning: unexpected `cfg` condition value: `zebra`
+  --> $DIR/mix.rs:77:10
+   |
+LL |     cfg!(target_feature = "zebra");
+   |          ^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: expected values for `target_feature` are: `10e60`, `2e3`, `3e3r1`, `3e3r2`, `3e3r3`, `3e7`, `7e10`, `a`, `aclass`, `adx`, `aes`, `altivec`, `alu32`, `atomics`, `avx`, `avx2`, `avx512bf16`, `avx512bitalg`, `avx512bw`, `avx512cd`, `avx512dq`, `avx512er`, `avx512f`, `avx512fp16`, `avx512ifma`, `avx512pf`, `avx512vbmi`, `avx512vbmi2`, `avx512vl`, `avx512vnni`, `avx512vp2intersect`, `avx512vpopcntdq`, `bf16`, `bmi1`, `bmi2` and 186 more
+   = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
+
+warning: 27 warnings emitted
 
diff --git a/tests/ui/check-cfg/well-known-values.rs b/tests/ui/check-cfg/well-known-values.rs
index 859a36c604c6f..fa062a3fe2eae 100644
--- a/tests/ui/check-cfg/well-known-values.rs
+++ b/tests/ui/check-cfg/well-known-values.rs
@@ -6,6 +6,7 @@
 //
 //@ check-pass
 //@ compile-flags: --check-cfg=cfg() -Z unstable-options
+//@ compile-flags: -Zcheck-cfg-all-expected
 
 #![feature(cfg_overflow_checks)]
 #![feature(cfg_relocation_model)]
diff --git a/tests/ui/check-cfg/well-known-values.stderr b/tests/ui/check-cfg/well-known-values.stderr
index 01fc3f83f162b..86df829fe726c 100644
--- a/tests/ui/check-cfg/well-known-values.stderr
+++ b/tests/ui/check-cfg/well-known-values.stderr
@@ -1,5 +1,5 @@
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:25:5
+  --> $DIR/well-known-values.rs:26:5
    |
 LL |     clippy = "_UNEXPECTED_VALUE",
    |     ^^^^^^----------------------
@@ -11,7 +11,7 @@ LL |     clippy = "_UNEXPECTED_VALUE",
    = note: `#[warn(unexpected_cfgs)]` on by default
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:27:5
+  --> $DIR/well-known-values.rs:28:5
    |
 LL |     debug_assertions = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^^----------------------
@@ -22,7 +22,7 @@ LL |     debug_assertions = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:29:5
+  --> $DIR/well-known-values.rs:30:5
    |
 LL |     doc = "_UNEXPECTED_VALUE",
    |     ^^^----------------------
@@ -33,7 +33,7 @@ LL |     doc = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:31:5
+  --> $DIR/well-known-values.rs:32:5
    |
 LL |     doctest = "_UNEXPECTED_VALUE",
    |     ^^^^^^^----------------------
@@ -44,7 +44,7 @@ LL |     doctest = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:33:5
+  --> $DIR/well-known-values.rs:34:5
    |
 LL |     miri = "_UNEXPECTED_VALUE",
    |     ^^^^----------------------
@@ -55,7 +55,7 @@ LL |     miri = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:35:5
+  --> $DIR/well-known-values.rs:36:5
    |
 LL |     overflow_checks = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^----------------------
@@ -66,7 +66,7 @@ LL |     overflow_checks = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:37:5
+  --> $DIR/well-known-values.rs:38:5
    |
 LL |     panic = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -75,7 +75,7 @@ LL |     panic = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:39:5
+  --> $DIR/well-known-values.rs:40:5
    |
 LL |     proc_macro = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^----------------------
@@ -86,7 +86,7 @@ LL |     proc_macro = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:41:5
+  --> $DIR/well-known-values.rs:42:5
    |
 LL |     relocation_model = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -95,7 +95,7 @@ LL |     relocation_model = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:43:5
+  --> $DIR/well-known-values.rs:44:5
    |
 LL |     sanitize = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -104,7 +104,7 @@ LL |     sanitize = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:45:5
+  --> $DIR/well-known-values.rs:46:5
    |
 LL |     target_abi = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -113,7 +113,7 @@ LL |     target_abi = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:47:5
+  --> $DIR/well-known-values.rs:48:5
    |
 LL |     target_arch = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -122,7 +122,7 @@ LL |     target_arch = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:49:5
+  --> $DIR/well-known-values.rs:50:5
    |
 LL |     target_endian = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -131,7 +131,7 @@ LL |     target_endian = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:51:5
+  --> $DIR/well-known-values.rs:52:5
    |
 LL |     target_env = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -140,7 +140,7 @@ LL |     target_env = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:53:5
+  --> $DIR/well-known-values.rs:54:5
    |
 LL |     target_family = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -149,7 +149,7 @@ LL |     target_family = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:55:5
+  --> $DIR/well-known-values.rs:56:5
    |
 LL |     target_feature = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -158,7 +158,7 @@ LL |     target_feature = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:57:5
+  --> $DIR/well-known-values.rs:58:5
    |
 LL |     target_has_atomic = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -167,7 +167,7 @@ LL |     target_has_atomic = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:59:5
+  --> $DIR/well-known-values.rs:60:5
    |
 LL |     target_has_atomic_equal_alignment = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -176,7 +176,7 @@ LL |     target_has_atomic_equal_alignment = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:61:5
+  --> $DIR/well-known-values.rs:62:5
    |
 LL |     target_has_atomic_load_store = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -185,7 +185,7 @@ LL |     target_has_atomic_load_store = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:63:5
+  --> $DIR/well-known-values.rs:64:5
    |
 LL |     target_os = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -194,7 +194,7 @@ LL |     target_os = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:65:5
+  --> $DIR/well-known-values.rs:66:5
    |
 LL |     target_pointer_width = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -203,7 +203,7 @@ LL |     target_pointer_width = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:67:5
+  --> $DIR/well-known-values.rs:68:5
    |
 LL |     target_thread_local = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^^^^^----------------------
@@ -214,7 +214,7 @@ LL |     target_thread_local = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:69:5
+  --> $DIR/well-known-values.rs:70:5
    |
 LL |     target_vendor = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -223,7 +223,7 @@ LL |     target_vendor = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:71:5
+  --> $DIR/well-known-values.rs:72:5
    |
 LL |     test = "_UNEXPECTED_VALUE",
    |     ^^^^----------------------
@@ -234,7 +234,7 @@ LL |     test = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:73:5
+  --> $DIR/well-known-values.rs:74:5
    |
 LL |     unix = "_UNEXPECTED_VALUE",
    |     ^^^^----------------------
@@ -245,7 +245,7 @@ LL |     unix = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:75:5
+  --> $DIR/well-known-values.rs:76:5
    |
 LL |     windows = "_UNEXPECTED_VALUE",
    |     ^^^^^^^----------------------
@@ -256,7 +256,7 @@ LL |     windows = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `linuz`
-  --> $DIR/well-known-values.rs:81:7
+  --> $DIR/well-known-values.rs:82:7
    |
 LL | #[cfg(target_os = "linuz")] // testing that we suggest `linux`
    |       ^^^^^^^^^^^^-------
diff --git a/tests/ui/codegen/duplicated-path-in-error.rs b/tests/ui/codegen/duplicated-path-in-error.rs
new file mode 100644
index 0000000000000..cff20dd9bd639
--- /dev/null
+++ b/tests/ui/codegen/duplicated-path-in-error.rs
@@ -0,0 +1,7 @@
+//@ only-linux
+//@ compile-flags: -Zcodegen-backend=/non-existing-one.so
+
+// This test ensures that the error of the "not found dylib" doesn't duplicate
+// the path of the dylib.
+
+fn main() {}
diff --git a/tests/ui/codegen/duplicated-path-in-error.stderr b/tests/ui/codegen/duplicated-path-in-error.stderr
new file mode 100644
index 0000000000000..d0d34e2f93468
--- /dev/null
+++ b/tests/ui/codegen/duplicated-path-in-error.stderr
@@ -0,0 +1,2 @@
+error: couldn't load codegen backend /non-existing-one.so: cannot open shared object file: No such file or directory
+
diff --git a/tests/ui/imports/unresolved-seg-after-ambiguous.rs b/tests/ui/imports/unresolved-seg-after-ambiguous.rs
new file mode 100644
index 0000000000000..dcabc528a85ed
--- /dev/null
+++ b/tests/ui/imports/unresolved-seg-after-ambiguous.rs
@@ -0,0 +1,24 @@
+mod a {
+    mod b {
+        mod c {
+            pub struct E;
+        }
+
+        mod d {
+            #[derive(Debug)]
+            pub struct E;
+        }
+
+        pub use self::d::*;
+        pub use self::c::*;
+    }
+
+    pub use self::b::*;
+}
+
+use self::a::E::in_exist;
+//~^ ERROR: unresolved import `self::a::E`
+//~| WARNING: `E` is ambiguous
+//~| WARNING: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+
+fn main() {}
diff --git a/tests/ui/imports/unresolved-seg-after-ambiguous.stderr b/tests/ui/imports/unresolved-seg-after-ambiguous.stderr
new file mode 100644
index 0000000000000..9e0efd4a75f84
--- /dev/null
+++ b/tests/ui/imports/unresolved-seg-after-ambiguous.stderr
@@ -0,0 +1,32 @@
+error[E0432]: unresolved import `self::a::E`
+  --> $DIR/unresolved-seg-after-ambiguous.rs:19:14
+   |
+LL | use self::a::E::in_exist;
+   |              ^ `E` is a struct, not a module
+
+warning: `E` is ambiguous
+  --> $DIR/unresolved-seg-after-ambiguous.rs:19:14
+   |
+LL | use self::a::E::in_exist;
+   |              ^ ambiguous name
+   |
+   = 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 #114095 <https://github.com/rust-lang/rust/issues/114095>
+   = note: ambiguous because of multiple glob imports of a name in the same module
+note: `E` could refer to the struct imported here
+  --> $DIR/unresolved-seg-after-ambiguous.rs:13:17
+   |
+LL |         pub use self::c::*;
+   |                 ^^^^^^^^^^
+   = help: consider adding an explicit import of `E` to disambiguate
+note: `E` could also refer to the struct imported here
+  --> $DIR/unresolved-seg-after-ambiguous.rs:12:17
+   |
+LL |         pub use self::d::*;
+   |                 ^^^^^^^^^^
+   = help: consider adding an explicit import of `E` to disambiguate
+   = note: `#[warn(ambiguous_glob_imports)]` on by default
+
+error: aborting due to 1 previous error; 1 warning emitted
+
+For more information about this error, try `rustc --explain E0432`.
diff --git a/tests/ui/lint/use-redundant/use-redundant-issue-71450.rs b/tests/ui/lint/use-redundant/use-redundant-issue-71450.rs
new file mode 100644
index 0000000000000..d0fb3454d3f2b
--- /dev/null
+++ b/tests/ui/lint/use-redundant/use-redundant-issue-71450.rs
@@ -0,0 +1,45 @@
+//@ check-pass
+
+#![warn(unused_imports)]
+
+mod foo {
+    use std::fmt;
+
+    pub struct String;
+
+    impl String {
+        pub fn new() -> String {
+            String{}
+        }
+    }
+
+    impl fmt::Display for String {
+        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+            write!(f, "String")
+        }
+    }
+}
+
+fn main() {
+
+    {
+        use std::string::String; //~ WARNING the item `String` is imported redundantly
+        // 'String' from 'std::string::String'.
+        let s = String::new();
+        println!("{}", s);
+    }
+
+    {
+        // 'String' from 'std::string::String'.
+        let s = String::new();
+        println!("{}", s);
+    }
+
+    {
+        use foo::*;
+        // 'String' from 'foo::String'.
+        let s = String::new();
+        println!("{}", s);
+    }
+
+}
diff --git a/tests/ui/lint/use-redundant/use-redundant-issue-71450.stderr b/tests/ui/lint/use-redundant/use-redundant-issue-71450.stderr
new file mode 100644
index 0000000000000..b8832a3178371
--- /dev/null
+++ b/tests/ui/lint/use-redundant/use-redundant-issue-71450.stderr
@@ -0,0 +1,17 @@
+warning: the item `String` is imported redundantly
+  --> $DIR/use-redundant-issue-71450.rs:26:13
+   |
+LL |         use std::string::String;
+   |             ^^^^^^^^^^^^^^^^^^^
+  --> $SRC_DIR/std/src/prelude/mod.rs:LL:COL
+   |
+   = note: the item `String` is already defined here
+   |
+note: the lint level is defined here
+  --> $DIR/use-redundant-issue-71450.rs:3:9
+   |
+LL | #![warn(unused_imports)]
+   |         ^^^^^^^^^^^^^^
+
+warning: 1 warning emitted
+
diff --git a/tests/ui/lint/use-redundant/use-redundant-issue-78894.rs b/tests/ui/lint/use-redundant/use-redundant-issue-78894.rs
new file mode 100644
index 0000000000000..09c87bc37a630
--- /dev/null
+++ b/tests/ui/lint/use-redundant/use-redundant-issue-78894.rs
@@ -0,0 +1,48 @@
+//@ check-pass
+//@ edition:2018
+
+#![warn(unused_imports)]
+
+mod foo {
+    macro_rules! foo1 {
+        () => ();
+    }
+
+    pub(crate) use foo1;
+}
+
+fn main ()
+{
+    bar!();
+
+    macro_rules! bar {
+        () => ();
+    }
+
+    use bar;
+
+    mod m {
+        bar1!();
+
+        macro_rules! bar1 {
+            () => ();
+        }
+
+        use bar1;
+    }
+
+    {
+        foo::foo1!();
+    }
+
+    {
+        use foo::foo1;
+        foo1!();
+    }
+
+    {
+        use foo::foo1; //~ WARNING unused import: `foo::foo1`
+        foo::foo1!();
+    }
+
+}
diff --git a/tests/ui/lint/use-redundant/use-redundant-issue-78894.stderr b/tests/ui/lint/use-redundant/use-redundant-issue-78894.stderr
new file mode 100644
index 0000000000000..78dfe364223d4
--- /dev/null
+++ b/tests/ui/lint/use-redundant/use-redundant-issue-78894.stderr
@@ -0,0 +1,14 @@
+warning: unused import: `foo::foo1`
+  --> $DIR/use-redundant-issue-78894.rs:44:13
+   |
+LL |         use foo::foo1;
+   |             ^^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/use-redundant-issue-78894.rs:4:9
+   |
+LL | #![warn(unused_imports)]
+   |         ^^^^^^^^^^^^^^
+
+warning: 1 warning emitted
+
diff --git a/tests/ui/type-alias-impl-trait/hidden_behind_struct_field2.rs b/tests/ui/type-alias-impl-trait/hidden_behind_struct_field2.rs
index 4c881dd133086..3117060cef0d2 100644
--- a/tests/ui/type-alias-impl-trait/hidden_behind_struct_field2.rs
+++ b/tests/ui/type-alias-impl-trait/hidden_behind_struct_field2.rs
@@ -15,7 +15,7 @@ impl Trait for Bar {
     type Assoc = impl std::fmt::Debug;
     fn foo() -> Foo {
         Foo { field: () }
-        //~^ ERROR: item constrains opaque type that is not in its signature
+        //~^ ERROR: mismatched types
     }
 }
 
diff --git a/tests/ui/type-alias-impl-trait/hidden_behind_struct_field2.stderr b/tests/ui/type-alias-impl-trait/hidden_behind_struct_field2.stderr
index 5c53dfa3a7500..4910e794e8d6e 100644
--- a/tests/ui/type-alias-impl-trait/hidden_behind_struct_field2.stderr
+++ b/tests/ui/type-alias-impl-trait/hidden_behind_struct_field2.stderr
@@ -1,11 +1,15 @@
-error: item constrains opaque type that is not in its signature
+error[E0308]: mismatched types
   --> $DIR/hidden_behind_struct_field2.rs:17:22
    |
+LL |     type Assoc = impl std::fmt::Debug;
+   |                  -------------------- the expected opaque type
+LL |     fn foo() -> Foo {
 LL |         Foo { field: () }
-   |                      ^^
+   |                      ^^ expected opaque type, found `()`
    |
-   = note: this item must mention the opaque type in its signature in order to be able to register hidden types
-note: this item must mention the opaque type in its signature in order to be able to register hidden types
+   = note: expected opaque type `<Bar as Trait>::Assoc`
+                found unit type `()`
+note: this item must have the opaque type in its signature in order to be able to register hidden types
   --> $DIR/hidden_behind_struct_field2.rs:16:8
    |
 LL |     fn foo() -> Foo {
@@ -13,3 +17,4 @@ LL |     fn foo() -> Foo {
 
 error: aborting due to 1 previous error
 
+For more information about this error, try `rustc --explain E0308`.
diff --git a/tests/ui/type-alias-impl-trait/hidden_behind_struct_field3.rs b/tests/ui/type-alias-impl-trait/hidden_behind_struct_field3.rs
index 1278563a92c46..c1f135994121e 100644
--- a/tests/ui/type-alias-impl-trait/hidden_behind_struct_field3.rs
+++ b/tests/ui/type-alias-impl-trait/hidden_behind_struct_field3.rs
@@ -17,7 +17,7 @@ impl Trait for Bar {
     type Assoc = impl Iterator<Item = Foo>;
     fn foo() -> Self::Assoc {
         vec![Foo { field: () }].into_iter()
-        //~^ ERROR item constrains opaque type that is not in its signature
+        //~^ ERROR mismatched types
     }
 }
 
diff --git a/tests/ui/type-alias-impl-trait/hidden_behind_struct_field3.stderr b/tests/ui/type-alias-impl-trait/hidden_behind_struct_field3.stderr
index 0570e0303c633..f10ccc0029973 100644
--- a/tests/ui/type-alias-impl-trait/hidden_behind_struct_field3.stderr
+++ b/tests/ui/type-alias-impl-trait/hidden_behind_struct_field3.stderr
@@ -1,11 +1,15 @@
-error: item constrains opaque type that is not in its signature
+error[E0308]: mismatched types
   --> $DIR/hidden_behind_struct_field3.rs:19:27
    |
+LL |     type Assoc2 = impl std::fmt::Debug;
+   |                   -------------------- the expected opaque type
+...
 LL |         vec![Foo { field: () }].into_iter()
-   |                           ^^
+   |                           ^^ expected opaque type, found `()`
    |
-   = note: this item must mention the opaque type in its signature in order to be able to register hidden types
-note: this item must mention the opaque type in its signature in order to be able to register hidden types
+   = note: expected opaque type `<Bar as Trait>::Assoc2`
+                found unit type `()`
+note: this item must have the opaque type in its signature in order to be able to register hidden types
   --> $DIR/hidden_behind_struct_field3.rs:18:8
    |
 LL |     fn foo() -> Self::Assoc {
@@ -13,3 +17,4 @@ LL |     fn foo() -> Self::Assoc {
 
 error: aborting due to 1 previous error
 
+For more information about this error, try `rustc --explain E0308`.
diff --git a/tests/ui/union/unnamed-fields/unnamed-enum-field-issue-121757.rs b/tests/ui/union/unnamed-fields/unnamed-enum-field-issue-121757.rs
new file mode 100644
index 0000000000000..5d15ec4cffdb9
--- /dev/null
+++ b/tests/ui/union/unnamed-fields/unnamed-enum-field-issue-121757.rs
@@ -0,0 +1,25 @@
+type NodeId = u32;
+struct Type<'a>(std::marker::PhantomData::<&'a ()>);
+
+type Ast<'ast> = &'ast AstStructure<'ast>;
+
+struct AstStructure<'ast> {
+//~^ ERROR struct with unnamed fields must have `#[repr(C)]` representation
+    id: NodeId,
+    _: AstKind<'ast>
+//~^ ERROR unnamed fields are not yet fully implemented [E0658]
+//~^^ ERROR unnamed fields can only have struct or union types
+}
+
+enum AstKind<'ast> {
+    ExprInt,
+    ExprLambda(Ast<'ast>),
+}
+
+fn compute_types<'tcx,'ast>(ast: Ast<'ast>) -> Type<'tcx>
+{
+    match ast.kind {}
+//~^ ERROR no field `kind` on type `&'ast AstStructure<'ast>` [E0609]
+}
+
+fn main() {}
diff --git a/tests/ui/union/unnamed-fields/unnamed-enum-field-issue-121757.stderr b/tests/ui/union/unnamed-fields/unnamed-enum-field-issue-121757.stderr
new file mode 100644
index 0000000000000..4ea910202de98
--- /dev/null
+++ b/tests/ui/union/unnamed-fields/unnamed-enum-field-issue-121757.stderr
@@ -0,0 +1,45 @@
+error[E0658]: unnamed fields are not yet fully implemented
+  --> $DIR/unnamed-enum-field-issue-121757.rs:9:5
+   |
+LL |     _: AstKind<'ast>
+   |     ^
+   |
+   = note: see issue #49804 <https://github.com/rust-lang/rust/issues/49804> for more information
+   = help: add `#![feature(unnamed_fields)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error: struct with unnamed fields must have `#[repr(C)]` representation
+  --> $DIR/unnamed-enum-field-issue-121757.rs:6:1
+   |
+LL | struct AstStructure<'ast> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^ struct `AstStructure` defined here
+   |
+note: unnamed field defined here
+  --> $DIR/unnamed-enum-field-issue-121757.rs:9:5
+   |
+LL |     _: AstKind<'ast>
+   |     ^^^^^^^^^^^^^^^^
+help: add `#[repr(C)]` to this struct
+   |
+LL + #[repr(C)]
+LL | struct AstStructure<'ast> {
+   |
+
+error: unnamed fields can only have struct or union types
+  --> $DIR/unnamed-enum-field-issue-121757.rs:9:5
+   |
+LL |     _: AstKind<'ast>
+   |     ^^^^^^^^^^^^^^^^
+
+error[E0609]: no field `kind` on type `&'ast AstStructure<'ast>`
+  --> $DIR/unnamed-enum-field-issue-121757.rs:21:15
+   |
+LL |     match ast.kind {}
+   |               ^^^^ unknown field
+   |
+   = note: available fields are: `id`, `_`
+
+error: aborting due to 4 previous errors
+
+Some errors have detailed explanations: E0609, E0658.
+For more information about an error, try `rustc --explain E0609`.