Rollup of 9 pull requests

compiler/rustc_abi/src/lib.rs

@@ -427,11 +427,13 @@ pub struct Size {
     raw: u64,
 }
 
-// Safety: Ord is implement as just comparing numerical values and numerical values
-// are not changed by (de-)serialization.
 #[cfg(feature = "nightly")]
-unsafe impl StableOrd for Size {
+impl StableOrd for Size {
     const CAN_USE_UNSTABLE_SORT: bool = true;
+
+    // `Ord` is implemented as just comparing numerical values and numerical values
+    // are not changed by (de-)serialization.
+    const THIS_IMPLEMENTATION_HAS_BEEN_TRIPLE_CHECKED: () = ();
 }
 
 // This is debug-printed a lot in larger structs, don't waste too much space there

compiler/rustc_ast/src/ast.rs

@@ -2126,7 +2126,8 @@ pub struct BareFnTy {
     pub ext: Extern,
     pub generic_params: ThinVec<GenericParam>,
     pub decl: P<FnDecl>,
-    /// Span of the `fn(...) -> ...` part.
+    /// Span of the `[unsafe] [extern] fn(...) -> ...` part, i.e. everything
+    /// after the generic params (if there are any, e.g. `for<'a>`).
     pub decl_span: Span,
 }
 

compiler/rustc_ast_lowering/messages.ftl

@@ -130,6 +130,9 @@ ast_lowering_never_pattern_with_guard =
 
 ast_lowering_no_precise_captures_on_apit = `use<...>` precise capturing syntax not allowed in argument-position `impl Trait`
 
+ast_lowering_no_precise_captures_on_rpitit = `use<...>` precise capturing syntax is currently not allowed in return-position `impl Trait` in traits
+    .note = currently, return-position `impl Trait` in traits and trait implementations capture all lifetimes in scope
+
 ast_lowering_previously_used_here = previously used here
 
 ast_lowering_register1 = register `{$reg1_name}`

compiler/rustc_ast_lowering/src/errors.rs

@@ -424,6 +424,14 @@ pub(crate) struct NoPreciseCapturesOnApit {
     pub span: Span,
 }
 
+#[derive(Diagnostic)]
+#[diag(ast_lowering_no_precise_captures_on_rpitit)]
+#[note]
+pub(crate) struct NoPreciseCapturesOnRpitit {
+    #[primary_span]
+    pub span: Span,
+}
+
 #[derive(Diagnostic)]
 #[diag(ast_lowering_yield_in_closure)]
 pub(crate) struct YieldInClosure {

compiler/rustc_ast_lowering/src/lib.rs

@@ -1594,6 +1594,26 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         };
         debug!(?captured_lifetimes_to_duplicate);
 
+        match fn_kind {
+            // Deny `use<>` on RPITIT in trait/trait-impl for now.
+            Some(FnDeclKind::Trait | FnDeclKind::Impl) => {
+                if let Some(span) = bounds.iter().find_map(|bound| match *bound {
+                    ast::GenericBound::Use(_, span) => Some(span),
+                    _ => None,
+                }) {
+                    self.tcx.dcx().emit_err(errors::NoPreciseCapturesOnRpitit { span });
+                }
+            }
+            None
+            | Some(
+                FnDeclKind::Fn
+                | FnDeclKind::Inherent
+                | FnDeclKind::ExternFn
+                | FnDeclKind::Closure
+                | FnDeclKind::Pointer,
+            ) => {}
+        }
+
         self.lower_opaque_inner(
             opaque_ty_node_id,
             origin,

compiler/rustc_borrowck/src/diagnostics/region_errors.rs

@@ -1151,7 +1151,9 @@ impl<'tcx> MirBorrowckCtxt<'_, '_, '_, 'tcx> {
         // Get the arguments for the found method, only specifying that `Self` is the receiver type.
         let Some(possible_rcvr_ty) = typeck_results.node_type_opt(rcvr.hir_id) else { return };
         let args = GenericArgs::for_item(tcx, method_def_id, |param, _| {
-            if param.index == 0 {
+            if let ty::GenericParamDefKind::Lifetime = param.kind {
+                tcx.lifetimes.re_erased.into()
+            } else if param.index == 0 && param.name == kw::SelfUpper {
                 possible_rcvr_ty.into()
             } else if param.index == closure_param.index {
                 closure_ty.into()
@@ -1168,7 +1170,7 @@ impl<'tcx> MirBorrowckCtxt<'_, '_, '_, 'tcx> {
             Obligation::misc(tcx, span, self.mir_def_id(), self.param_env, pred)
         }));
 
-        if ocx.select_all_or_error().is_empty() {
+        if ocx.select_all_or_error().is_empty() && count > 0 {
             diag.span_suggestion_verbose(
                 tcx.hir().body(*body).value.peel_blocks().span.shrink_to_lo(),
                 "dereference the return value",

compiler/rustc_data_structures/src/stable_hasher.rs

@@ -238,12 +238,21 @@ pub trait ToStableHashKey<HCX> {
 /// The associated constant `CAN_USE_UNSTABLE_SORT` denotes whether
 /// unstable sorting can be used for this type. Set to true if and
 /// only if `a == b` implies `a` and `b` are fully indistinguishable.
-pub unsafe trait StableOrd: Ord {
+pub trait StableOrd: Ord {
     const CAN_USE_UNSTABLE_SORT: bool;
+
+    /// Marker to ensure that implementors have carefully considered
+    /// whether their `Ord` implementation obeys this trait's contract.
+    const THIS_IMPLEMENTATION_HAS_BEEN_TRIPLE_CHECKED: ();
 }
 
-unsafe impl<T: StableOrd> StableOrd for &T {
+impl<T: StableOrd> StableOrd for &T {
     const CAN_USE_UNSTABLE_SORT: bool = T::CAN_USE_UNSTABLE_SORT;
+
+    // Ordering of a reference is exactly that of the referent, and since
+    // the ordering of the referet is stable so must be the ordering of the
+    // reference.
+    const THIS_IMPLEMENTATION_HAS_BEEN_TRIPLE_CHECKED: () = ();
 }
 
 /// This is a companion trait to `StableOrd`. Some types like `Symbol` can be
@@ -290,8 +299,12 @@ macro_rules! impl_stable_traits_for_trivial_type {
             }
         }
 
-        unsafe impl $crate::stable_hasher::StableOrd for $t {
+        impl $crate::stable_hasher::StableOrd for $t {
             const CAN_USE_UNSTABLE_SORT: bool = true;
+
+            // Encoding and decoding doesn't change the bytes of trivial types
+            // and `Ord::cmp` depends only on those bytes.
+            const THIS_IMPLEMENTATION_HAS_BEEN_TRIPLE_CHECKED: () = ();
         }
     };
 }
@@ -327,8 +340,12 @@ impl<CTX> HashStable<CTX> for Hash128 {
     }
 }
 
-unsafe impl StableOrd for Hash128 {
+impl StableOrd for Hash128 {
     const CAN_USE_UNSTABLE_SORT: bool = true;
+
+    // Encoding and decoding doesn't change the bytes of `Hash128`
+    // and `Ord::cmp` depends only on those bytes.
+    const THIS_IMPLEMENTATION_HAS_BEEN_TRIPLE_CHECKED: () = ();
 }
 
 impl<CTX> HashStable<CTX> for ! {
@@ -392,8 +409,12 @@ impl<T1: HashStable<CTX>, T2: HashStable<CTX>, CTX> HashStable<CTX> for (T1, T2)
     }
 }
 
-unsafe impl<T1: StableOrd, T2: StableOrd> StableOrd for (T1, T2) {
+impl<T1: StableOrd, T2: StableOrd> StableOrd for (T1, T2) {
     const CAN_USE_UNSTABLE_SORT: bool = T1::CAN_USE_UNSTABLE_SORT && T2::CAN_USE_UNSTABLE_SORT;
+
+    // Ordering of tuples is a pure function of their elements' ordering, and since
+    // the ordering of each element is stable so must be the ordering of the tuple.
+    const THIS_IMPLEMENTATION_HAS_BEEN_TRIPLE_CHECKED: () = ();
 }
 
 impl<T1, T2, T3, CTX> HashStable<CTX> for (T1, T2, T3)
@@ -410,9 +431,13 @@ where
     }
 }
 
-unsafe impl<T1: StableOrd, T2: StableOrd, T3: StableOrd> StableOrd for (T1, T2, T3) {
+impl<T1: StableOrd, T2: StableOrd, T3: StableOrd> StableOrd for (T1, T2, T3) {
     const CAN_USE_UNSTABLE_SORT: bool =
         T1::CAN_USE_UNSTABLE_SORT && T2::CAN_USE_UNSTABLE_SORT && T3::CAN_USE_UNSTABLE_SORT;
+
+    // Ordering of tuples is a pure function of their elements' ordering, and since
+    // the ordering of each element is stable so must be the ordering of the tuple.
+    const THIS_IMPLEMENTATION_HAS_BEEN_TRIPLE_CHECKED: () = ();
 }
 
 impl<T1, T2, T3, T4, CTX> HashStable<CTX> for (T1, T2, T3, T4)
@@ -431,13 +456,15 @@ where
     }
 }
 
-unsafe impl<T1: StableOrd, T2: StableOrd, T3: StableOrd, T4: StableOrd> StableOrd
-    for (T1, T2, T3, T4)
-{
+impl<T1: StableOrd, T2: StableOrd, T3: StableOrd, T4: StableOrd> StableOrd for (T1, T2, T3, T4) {
     const CAN_USE_UNSTABLE_SORT: bool = T1::CAN_USE_UNSTABLE_SORT
         && T2::CAN_USE_UNSTABLE_SORT
         && T3::CAN_USE_UNSTABLE_SORT
         && T4::CAN_USE_UNSTABLE_SORT;
+
+    // Ordering of tuples is a pure function of their elements' ordering, and since
+    // the ordering of each element is stable so must be the ordering of the tuple.
+    const THIS_IMPLEMENTATION_HAS_BEEN_TRIPLE_CHECKED: () = ();
 }
 
 impl<T: HashStable<CTX>, CTX> HashStable<CTX> for [T] {
@@ -530,8 +557,12 @@ impl<CTX> HashStable<CTX> for str {
     }
 }
 
-unsafe impl StableOrd for &str {
+impl StableOrd for &str {
     const CAN_USE_UNSTABLE_SORT: bool = true;
+
+    // Encoding and decoding doesn't change the bytes of string slices
+    // and `Ord::cmp` depends only on those bytes.
+    const THIS_IMPLEMENTATION_HAS_BEEN_TRIPLE_CHECKED: () = ();
 }
 
 impl<CTX> HashStable<CTX> for String {
@@ -541,10 +572,12 @@ impl<CTX> HashStable<CTX> for String {
     }
 }
 
-// Safety: String comparison only depends on their contents and the
-// contents are not changed by (de-)serialization.
-unsafe impl StableOrd for String {
+impl StableOrd for String {
     const CAN_USE_UNSTABLE_SORT: bool = true;
+
+    // String comparison only depends on their contents and the
+    // contents are not changed by (de-)serialization.
+    const THIS_IMPLEMENTATION_HAS_BEEN_TRIPLE_CHECKED: () = ();
 }
 
 impl<HCX> ToStableHashKey<HCX> for String {
@@ -570,9 +603,11 @@ impl<CTX> HashStable<CTX> for bool {
     }
 }
 
-// Safety: sort order of bools is not changed by (de-)serialization.
-unsafe impl StableOrd for bool {
+impl StableOrd for bool {
     const CAN_USE_UNSTABLE_SORT: bool = true;
+
+    // sort order of bools is not changed by (de-)serialization.
+    const THIS_IMPLEMENTATION_HAS_BEEN_TRIPLE_CHECKED: () = ();
 }
 
 impl<T, CTX> HashStable<CTX> for Option<T>
@@ -590,9 +625,11 @@ where
     }
 }
 
-// Safety: the Option wrapper does not add instability to comparison.
-unsafe impl<T: StableOrd> StableOrd for Option<T> {
+impl<T: StableOrd> StableOrd for Option<T> {
     const CAN_USE_UNSTABLE_SORT: bool = T::CAN_USE_UNSTABLE_SORT;
+
+    // the Option wrapper does not add instability to comparison.
+    const THIS_IMPLEMENTATION_HAS_BEEN_TRIPLE_CHECKED: () = ();
 }
 
 impl<T1, T2, CTX> HashStable<CTX> for Result<T1, T2>

compiler/rustc_hir/src/hir_id.rs

@@ -165,10 +165,12 @@ impl ItemLocalId {
     pub const INVALID: ItemLocalId = ItemLocalId::MAX;
 }
 
-// Safety: Ord is implement as just comparing the ItemLocalId's numerical
-// values and these are not changed by (de-)serialization.
-unsafe impl StableOrd for ItemLocalId {
+impl StableOrd for ItemLocalId {
     const CAN_USE_UNSTABLE_SORT: bool = true;
+
+    // `Ord` is implemented as just comparing the ItemLocalId's numerical
+    // values and these are not changed by (de-)serialization.
+    const THIS_IMPLEMENTATION_HAS_BEEN_TRIPLE_CHECKED: () = ();
 }
 
 /// The `HirId` corresponding to `CRATE_NODE_ID` and `CRATE_DEF_ID`.

compiler/rustc_hir_analysis/src/check/mod.rs

@@ -211,11 +211,18 @@ fn missing_items_err(
         .collect::<Vec<_>>()
         .join("`, `");
 
-    // `Span` before impl block closing brace.
-    let hi = full_impl_span.hi() - BytePos(1);
-    // Point at the place right before the closing brace of the relevant `impl` to suggest
-    // adding the associated item at the end of its body.
-    let sugg_sp = full_impl_span.with_lo(hi).with_hi(hi);
+    let sugg_sp = if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(full_impl_span)
+        && snippet.ends_with("}")
+    {
+        // `Span` before impl block closing brace.
+        let hi = full_impl_span.hi() - BytePos(1);
+        // Point at the place right before the closing brace of the relevant `impl` to suggest
+        // adding the associated item at the end of its body.
+        full_impl_span.with_lo(hi).with_hi(hi)
+    } else {
+        full_impl_span.shrink_to_hi()
+    };
+
     // Obtain the level of indentation ending in `sugg_sp`.
     let padding =
         tcx.sess.source_map().indentation_before(sugg_sp).unwrap_or_else(|| String::new());

compiler/rustc_infer/src/infer/error_reporting/suggest.rs

@@ -209,8 +209,10 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
             }
             (Some(ty), _) if self.same_type_modulo_infer(ty, exp_found.found) => match cause.code()
             {
-                ObligationCauseCode::Pattern { span: Some(then_span), .. } => {
-                    Some(ConsiderAddingAwait::FutureSugg { span: then_span.shrink_to_hi() })
+                ObligationCauseCode::Pattern { span: Some(then_span), origin_expr, .. } => {
+                    origin_expr.then_some(ConsiderAddingAwait::FutureSugg {
+                        span: then_span.shrink_to_hi(),
+                    })
                 }
                 ObligationCauseCode::IfExpression(box IfExpressionCause { then_id, .. }) => {
                     let then_span = self.find_block_span_from_hir_id(*then_id);

compiler/rustc_mir_build/src/build/matches/mod.rs

@@ -358,8 +358,11 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
     where
         'a: 'pat,
     {
-        // Assemble a list of candidates: there is one candidate per pattern,
-        // which means there may be more than one candidate *per arm*.
+        // Assemble the initial list of candidates. These top-level candidates
+        // are 1:1 with the original match arms, but other parts of match
+        // lowering also introduce subcandidates (for subpatterns), and will
+        // also flatten candidates in some cases. So in general a list of
+        // candidates does _not_ necessarily correspond to a list of arms.
         arms.iter()
             .copied()
             .map(|arm| {

compiler/rustc_parse/src/parser/ty.rs

@@ -608,7 +608,7 @@ impl<'a> Parser<'a> {
             self.dcx().emit_err(FnPointerCannotBeAsync { span: whole_span, qualifier: span });
         }
         // FIXME(gen_blocks): emit a similar error for `gen fn()`
-        let decl_span = span_start.to(self.token.span);
+        let decl_span = span_start.to(self.prev_token.span);
         Ok(TyKind::BareFn(P(BareFnTy { ext, safety, generic_params: params, decl, decl_span })))
     }