Auto merge of rust-lang#120157 - matthiaskrgr:rollup-f0p3wkk, r=matthiaskrgr

Rollup of 10 pull requests

Successful merges:

 - rust-lang#103730 (Added NonZeroXxx::from_mut(_unchecked)?)
 - rust-lang#113142 (optimize EscapeAscii's Display  and CStr's Debug)
 - rust-lang#118799 (Stabilize single-field offset_of)
 - rust-lang#119613 (Expose Obligations created during type inference.)
 - rust-lang#119752 (Avoid ICEs in trait names without `dyn`)
 - rust-lang#120132 (Teach tidy about line/col information for malformed features)
 - rust-lang#120135 (SMIR: Make the remaining "private" fields actually private)
 - rust-lang#120148 (`single_use_lifetimes`: Don't suggest deleting lifetimes with bounds)
 - rust-lang#120150 (Stabilize `round_ties_even`)
 - rust-lang#120155 (Don't use `ReErased` to detect type test promotion failed)

r? `@ghost`
`@rustbot` modify labels: rollup

Author: bors

Diff for: compiler/rustc_borrowck/src/region_infer/mod.rs

@@ -18,7 +18,7 @@ use rustc_middle::mir::{
 };
 use rustc_middle::traits::ObligationCause;
 use rustc_middle::traits::ObligationCauseCode;
-use rustc_middle::ty::{self, RegionVid, Ty, TyCtxt, TypeFoldable, TypeVisitableExt};
+use rustc_middle::ty::{self, RegionVid, Ty, TyCtxt, TypeFoldable};
 use rustc_mir_dataflow::points::DenseLocationMap;
 use rustc_span::Span;
 
@@ -1145,6 +1145,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         }
 
         let ty = ty.fold_with(&mut OpaqueFolder { tcx });
+        let mut failed = false;
 
         let ty = tcx.fold_regions(ty, |r, _depth| {
             let r_vid = self.to_region_vid(r);
@@ -1160,15 +1161,18 @@ impl<'tcx> RegionInferenceContext<'tcx> {
                 .filter(|&u_r| !self.universal_regions.is_local_free_region(u_r))
                 .find(|&u_r| self.eval_equal(u_r, r_vid))
                 .map(|u_r| ty::Region::new_var(tcx, u_r))
-                // In the case of a failure, use `ReErased`. We will eventually
-                // return `None` in this case.
-                .unwrap_or(tcx.lifetimes.re_erased)
+                // In case we could not find a named region to map to,
+                // we will return `None` below.
+                .unwrap_or_else(|| {
+                    failed = true;
+                    r
+                })
         });
 
         debug!("try_promote_type_test_subject: folded ty = {:?}", ty);
 
         // This will be true if we failed to promote some region.
-        if ty.has_erased_regions() {
+        if failed {
             return None;
         }
 

Diff for: compiler/rustc_error_codes/src/error_codes/E0795.md

@@ -3,7 +3,7 @@ Invalid argument for the `offset_of!` macro.
 Erroneous code example:
 
 ```compile_fail,E0795
-#![feature(offset_of, offset_of_enum)]
+#![feature(offset_of_enum, offset_of_nested)]
 
 let x = std::mem::offset_of!(Option<u8>, Some);
 ```
@@ -16,7 +16,7 @@ The offset of the contained `u8` in the `Option<u8>` can be found by specifying
 the field name `0`:
 
 ```
-#![feature(offset_of, offset_of_enum)]
+#![feature(offset_of_enum, offset_of_nested)]
 
 let x: usize = std::mem::offset_of!(Option<u8>, Some.0);
 ```

Diff for: compiler/rustc_feature/src/unstable.rs

@@ -549,7 +549,9 @@ declare_features! (
     /// casts in safe Rust to `dyn Trait` for such a `Trait` is also forbidden.
     (unstable, object_safe_for_dispatch, "1.40.0", Some(43561)),
     /// Allows using enums in offset_of!
-    (unstable, offset_of_enum, "1.75.0", Some(106655)),
+    (unstable, offset_of_enum, "1.75.0", Some(120141)),
+    /// Allows using multiple nested field accesses in offset_of!
+    (unstable, offset_of_nested, "CURRENT_RUSTC_VERSION", Some(120140)),
     /// Allows using `#[optimize(X)]`.
     (unstable, optimize_attribute, "1.34.0", Some(54882)),
     /// Allows macro attributes on expressions, statements and non-inline modules.

Diff for: compiler/rustc_hir_analysis/src/astconv/lint.rs

@@ -78,14 +78,17 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
     fn maybe_lint_impl_trait(&self, self_ty: &hir::Ty<'_>, diag: &mut Diagnostic) -> bool {
         let tcx = self.tcx();
         let parent_id = tcx.hir().get_parent_item(self_ty.hir_id).def_id;
-        let (hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(sig, generics, _), .. })
-        | hir::Node::TraitItem(hir::TraitItem {
-            kind: hir::TraitItemKind::Fn(sig, _),
-            generics,
-            ..
-        })) = tcx.hir_node_by_def_id(parent_id)
-        else {
-            return false;
+        let (sig, generics, owner) = match tcx.hir_node_by_def_id(parent_id) {
+            hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(sig, generics, _), .. }) => {
+                (sig, generics, None)
+            }
+            hir::Node::TraitItem(hir::TraitItem {
+                kind: hir::TraitItemKind::Fn(sig, _),
+                generics,
+                owner_id,
+                ..
+            }) => (sig, generics, Some(tcx.parent(owner_id.to_def_id()))),
+            _ => return false,
         };
         let Ok(trait_name) = tcx.sess.source_map().span_to_snippet(self_ty.span) else {
             return false;
@@ -94,6 +97,11 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         let is_object_safe = match self_ty.kind {
             hir::TyKind::TraitObject(objects, ..) => {
                 objects.iter().all(|o| match o.trait_ref.path.res {
+                    Res::Def(DefKind::Trait, id) if Some(id) == owner => {
+                        // When we're dealing with a recursive trait, we don't want to downgrade
+                        // the error, so we consider them to be object safe always. (#119652)
+                        true
+                    }
                     Res::Def(DefKind::Trait, id) => tcx.check_is_object_safe(id),
                     _ => false,
                 })
@@ -122,7 +130,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     ],
                     Applicability::MachineApplicable,
                 );
-            } else {
+            } else if diag.is_error() {
                 // We'll emit the object safety error already, with a structured suggestion.
                 diag.downgrade_to_delayed_bug();
             }
@@ -148,8 +156,10 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             }
             if !is_object_safe {
                 diag.note(format!("`{trait_name}` it is not object safe, so it can't be `dyn`"));
-                // We'll emit the object safety error already, with a structured suggestion.
-                diag.downgrade_to_delayed_bug();
+                if diag.is_error() {
+                    // We'll emit the object safety error already, with a structured suggestion.
+                    diag.downgrade_to_delayed_bug();
+                }
             } else {
                 let sugg = if let hir::TyKind::TraitObject([_, _, ..], _, _) = self_ty.kind {
                     // There are more than one trait bound, we need surrounding parentheses.

Diff for: compiler/rustc_hir_typeck/src/expr.rs

@@ -3246,6 +3246,18 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     ) -> Ty<'tcx> {
         let container = self.to_ty(container).normalized;
 
+        if let Some(ident_2) = fields.get(1)
+            && !self.tcx.features().offset_of_nested
+        {
+            rustc_session::parse::feature_err(
+                &self.tcx.sess,
+                sym::offset_of_nested,
+                ident_2.span,
+                "only a single ident or integer is stable as the field in offset_of",
+            )
+            .emit();
+        }
+
         let mut field_indices = Vec::with_capacity(fields.len());
         let mut current_container = container;
         let mut fields = fields.into_iter();

Diff for: compiler/rustc_hir_typeck/src/lib.rs

@@ -60,6 +60,7 @@ use rustc_hir::{HirIdMap, Node};
 use rustc_hir_analysis::astconv::AstConv;
 use rustc_hir_analysis::check::check_abi;
 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
+use rustc_infer::traits::ObligationInspector;
 use rustc_middle::query::Providers;
 use rustc_middle::traits;
 use rustc_middle::ty::{self, Ty, TyCtxt};
@@ -139,7 +140,7 @@ fn used_trait_imports(tcx: TyCtxt<'_>, def_id: LocalDefId) -> &UnordSet<LocalDef
 
 fn typeck<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> &ty::TypeckResults<'tcx> {
     let fallback = move || tcx.type_of(def_id.to_def_id()).instantiate_identity();
-    typeck_with_fallback(tcx, def_id, fallback)
+    typeck_with_fallback(tcx, def_id, fallback, None)
 }
 
 /// Used only to get `TypeckResults` for type inference during error recovery.
@@ -149,14 +150,28 @@ fn diagnostic_only_typeck<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> &ty::T
         let span = tcx.hir().span(tcx.local_def_id_to_hir_id(def_id));
         Ty::new_error_with_message(tcx, span, "diagnostic only typeck table used")
     };
-    typeck_with_fallback(tcx, def_id, fallback)
+    typeck_with_fallback(tcx, def_id, fallback, None)
 }
 
-#[instrument(level = "debug", skip(tcx, fallback), ret)]
+/// Same as `typeck` but `inspect` is invoked on evaluation of each root obligation.
+/// Inspecting obligations only works with the new trait solver.
+/// This function is *only to be used* by external tools, it should not be
+/// called from within rustc. Note, this is not a query, and thus is not cached.
+pub fn inspect_typeck<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    def_id: LocalDefId,
+    inspect: ObligationInspector<'tcx>,
+) -> &'tcx ty::TypeckResults<'tcx> {
+    let fallback = move || tcx.type_of(def_id.to_def_id()).instantiate_identity();
+    typeck_with_fallback(tcx, def_id, fallback, Some(inspect))
+}
+
+#[instrument(level = "debug", skip(tcx, fallback, inspector), ret)]
 fn typeck_with_fallback<'tcx>(
     tcx: TyCtxt<'tcx>,
     def_id: LocalDefId,
     fallback: impl Fn() -> Ty<'tcx> + 'tcx,
+    inspector: Option<ObligationInspector<'tcx>>,
 ) -> &'tcx ty::TypeckResults<'tcx> {
     // Closures' typeck results come from their outermost function,
     // as they are part of the same "inference environment".
@@ -178,6 +193,9 @@ fn typeck_with_fallback<'tcx>(
     let param_env = tcx.param_env(def_id);
 
     let inh = Inherited::new(tcx, def_id);
+    if let Some(inspector) = inspector {
+        inh.infcx.attach_obligation_inspector(inspector);
+    }
     let mut fcx = FnCtxt::new(&inh, param_env, def_id);
 
     if let Some(hir::FnSig { header, decl, .. }) = fn_sig {

Diff for: compiler/rustc_infer/src/infer/at.rs

@@ -90,6 +90,7 @@ impl<'tcx> InferCtxt<'tcx> {
             universe: self.universe.clone(),
             intercrate,
             next_trait_solver: self.next_trait_solver,
+            obligation_inspector: self.obligation_inspector.clone(),
         }
     }
 }

Diff for: compiler/rustc_infer/src/infer/mod.rs

@@ -13,7 +13,9 @@ use rustc_middle::infer::unify_key::{ConstVidKey, EffectVidKey};
 use self::opaque_types::OpaqueTypeStorage;
 pub(crate) use self::undo_log::{InferCtxtUndoLogs, Snapshot, UndoLog};
 
-use crate::traits::{self, ObligationCause, PredicateObligations, TraitEngine, TraitEngineExt};
+use crate::traits::{
+    self, ObligationCause, ObligationInspector, PredicateObligations, TraitEngine, TraitEngineExt,
+};
 
 use rustc_data_structures::fx::FxIndexMap;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
@@ -334,6 +336,8 @@ pub struct InferCtxt<'tcx> {
     pub intercrate: bool,
 
     next_trait_solver: bool,
+
+    pub obligation_inspector: Cell<Option<ObligationInspector<'tcx>>>,
 }
 
 impl<'tcx> ty::InferCtxtLike for InferCtxt<'tcx> {
@@ -708,6 +712,7 @@ impl<'tcx> InferCtxtBuilder<'tcx> {
             universe: Cell::new(ty::UniverseIndex::ROOT),
             intercrate,
             next_trait_solver,
+            obligation_inspector: Cell::new(None),
         }
     }
 }
@@ -1718,6 +1723,15 @@ impl<'tcx> InferCtxt<'tcx> {
             }
         }
     }
+
+    /// Attach a callback to be invoked on each root obligation evaluated in the new trait solver.
+    pub fn attach_obligation_inspector(&self, inspector: ObligationInspector<'tcx>) {
+        debug_assert!(
+            self.obligation_inspector.get().is_none(),
+            "shouldn't override a set obligation inspector"
+        );
+        self.obligation_inspector.set(Some(inspector));
+    }
 }
 
 impl<'tcx> TypeErrCtxt<'_, 'tcx> {

Diff for: compiler/rustc_infer/src/traits/mod.rs

@@ -13,12 +13,15 @@ use std::hash::{Hash, Hasher};
 
 use hir::def_id::LocalDefId;
 use rustc_hir as hir;
+use rustc_middle::traits::query::NoSolution;
+use rustc_middle::traits::solve::Certainty;
 use rustc_middle::ty::error::{ExpectedFound, TypeError};
 use rustc_middle::ty::{self, Const, ToPredicate, Ty, TyCtxt};
 use rustc_span::Span;
 
 pub use self::ImplSource::*;
 pub use self::SelectionError::*;
+use crate::infer::InferCtxt;
 
 pub use self::engine::{TraitEngine, TraitEngineExt};
 pub use self::project::MismatchedProjectionTypes;
@@ -116,6 +119,11 @@ pub type PredicateObligations<'tcx> = Vec<PredicateObligation<'tcx>>;
 
 pub type Selection<'tcx> = ImplSource<'tcx, PredicateObligation<'tcx>>;
 
+/// A callback that can be provided to `inspect_typeck`. Invoked on evaluation
+/// of root obligations.
+pub type ObligationInspector<'tcx> =
+    fn(&InferCtxt<'tcx>, &PredicateObligation<'tcx>, Result<Certainty, NoSolution>);
+
 pub struct FulfillmentError<'tcx> {
     pub obligation: PredicateObligation<'tcx>,
     pub code: FulfillmentErrorCode<'tcx>,

Diff for: compiler/rustc_resolve/src/late/diagnostics.rs

@@ -2567,8 +2567,9 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
                     debug!(?param.ident, ?param.ident.span, ?use_span);
 
                     let elidable = matches!(use_ctxt, LifetimeCtxt::Ref);
+                    let deletion_span =
+                        if param.bounds.is_empty() { deletion_span() } else { None };
 
-                    let deletion_span = deletion_span();
                     self.r.lint_buffer.buffer_lint_with_diagnostic(
                         lint::builtin::SINGLE_USE_LIFETIMES,
                         param.id,

Diff for: compiler/rustc_span/src/symbol.rs

@@ -1153,6 +1153,7 @@ symbols! {
         offset,
         offset_of,
         offset_of_enum,
+        offset_of_nested,
         ok_or_else,
         omit_gdb_pretty_printer_section,
         on,