Auto merge of #104437 - matthiaskrgr:rollup-n5jdg9v, r=matthiaskrgr

Rollup of 9 pull requests

Successful merges:

 - #103439 (Show note where the macro failed to match)
 - #103734 (Adjust stabilization version to 1.65.0 for wasi fds)
 - #104148 (Visit attributes of trait impl items during AST validation)
 - #104241 (Move most of unwind's build script to lib.rs)
 - #104258 (Deduce closure signature from a type alias `impl Trait`'s supertraits)
 - #104296 (Walk types more carefully in `ProhibitOpaqueTypes` visitor)
 - #104309 (Slightly improve error message for invalid identifier)
 - #104316 (Simplify suggestions for errors in generators.)
 - #104339 (Add `rustc_deny_explicit_impl`)

Failed merges:

 - #103484 (Add `rust` to `let_underscore_lock` example)

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

Author: bors

Diff for: compiler/rustc_ast_passes/src/ast_validation.rs

@@ -1051,6 +1051,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 
                     walk_list!(this, visit_assoc_item, items, AssocCtxt::Impl);
                 });
+                walk_list!(self, visit_attribute, &item.attrs);
                 return; // Avoid visiting again.
             }
             ItemKind::Impl(box Impl {
@@ -1168,7 +1169,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                 });
                 walk_list!(self, visit_assoc_item, items, AssocCtxt::Trait);
                 walk_list!(self, visit_attribute, &item.attrs);
-                return;
+                return; // Avoid visiting again
             }
             ItemKind::Mod(unsafety, ref mod_kind) => {
                 if let Unsafe::Yes(span) = unsafety {

Diff for: compiler/rustc_error_codes/src/error_codes/E0322.md

@@ -1,4 +1,5 @@
-The `Sized` trait was implemented explicitly.
+A built-in trait was implemented explicitly. All implementations of the trait
+are provided automatically by the compiler.
 
 Erroneous code example:
 

Diff for: compiler/rustc_error_messages/locales/en-US/parser.ftl

@@ -384,3 +384,6 @@ parser_fn_ptr_with_generics = function pointer types may not have generic parame
         [true] the
         *[false] a
     } `for` parameter list
+
+parser_invalid_identifier_with_leading_number = expected identifier, found number literal
+    .label = identifiers cannot start with a number

Diff for: compiler/rustc_expand/src/mbe/macro_parser.rs

@@ -76,6 +76,7 @@ pub(crate) use ParseResult::*;
 use crate::mbe::{macro_rules::Tracker, KleeneOp, TokenTree};
 
 use rustc_ast::token::{self, DocComment, Nonterminal, NonterminalKind, Token};
+use rustc_ast_pretty::pprust;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::sync::Lrc;
 use rustc_errors::ErrorGuaranteed;
@@ -86,6 +87,7 @@ use rustc_span::symbol::MacroRulesNormalizedIdent;
 use rustc_span::Span;
 use std::borrow::Cow;
 use std::collections::hash_map::Entry::{Occupied, Vacant};
+use std::fmt::Display;
 
 /// A unit within a matcher that a `MatcherPos` can refer to. Similar to (and derived from)
 /// `mbe::TokenTree`, but designed specifically for fast and easy traversal during matching.
@@ -96,7 +98,7 @@ use std::collections::hash_map::Entry::{Occupied, Vacant};
 ///
 /// This means a matcher can be represented by `&[MatcherLoc]`, and traversal mostly involves
 /// simply incrementing the current matcher position index by one.
-#[derive(Debug)]
+#[derive(Debug, PartialEq, Clone)]
 pub(crate) enum MatcherLoc {
     Token {
         token: Token,
@@ -129,6 +131,46 @@ pub(crate) enum MatcherLoc {
     Eof,
 }
 
+impl MatcherLoc {
+    pub(super) fn span(&self) -> Option<Span> {
+        match self {
+            MatcherLoc::Token { token } => Some(token.span),
+            MatcherLoc::Delimited => None,
+            MatcherLoc::Sequence { .. } => None,
+            MatcherLoc::SequenceKleeneOpNoSep { .. } => None,
+            MatcherLoc::SequenceSep { .. } => None,
+            MatcherLoc::SequenceKleeneOpAfterSep { .. } => None,
+            MatcherLoc::MetaVarDecl { span, .. } => Some(*span),
+            MatcherLoc::Eof => None,
+        }
+    }
+}
+
+impl Display for MatcherLoc {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            MatcherLoc::Token { token } | MatcherLoc::SequenceSep { separator: token } => {
+                write!(f, "`{}`", pprust::token_to_string(token))
+            }
+            MatcherLoc::MetaVarDecl { bind, kind, .. } => {
+                write!(f, "meta-variable `${bind}")?;
+                if let Some(kind) = kind {
+                    write!(f, ":{}", kind)?;
+                }
+                write!(f, "`")?;
+                Ok(())
+            }
+            MatcherLoc::Eof => f.write_str("end of macro"),
+
+            // These are not printed in the diagnostic
+            MatcherLoc::Delimited => f.write_str("delimiter"),
+            MatcherLoc::Sequence { .. } => f.write_str("sequence start"),
+            MatcherLoc::SequenceKleeneOpNoSep { .. } => f.write_str("sequence end"),
+            MatcherLoc::SequenceKleeneOpAfterSep { .. } => f.write_str("sequence end"),
+        }
+    }
+}
+
 pub(super) fn compute_locs(matcher: &[TokenTree]) -> Vec<MatcherLoc> {
     fn inner(
         tts: &[TokenTree],
@@ -398,6 +440,10 @@ impl TtParser {
         }
     }
 
+    pub(super) fn has_no_remaining_items_for_step(&self) -> bool {
+        self.cur_mps.is_empty()
+    }
+
     /// Process the matcher positions of `cur_mps` until it is empty. In the process, this will
     /// produce more mps in `next_mps` and `bb_mps`.
     ///

Diff for: compiler/rustc_expand/src/mbe/macro_rules.rs

@@ -337,7 +337,7 @@ fn expand_macro<'cx>(
         return result;
     }
 
-    let Some((token, label)) = tracker.best_failure else {
+    let Some((token, label, remaining_matcher)) = tracker.best_failure else {
         return tracker.result.expect("must have encountered Error or ErrorReported");
     };
 
@@ -351,6 +351,12 @@ fn expand_macro<'cx>(
 
     annotate_doc_comment(&mut err, sess.source_map(), span);
 
+    if let Some(span) = remaining_matcher.span() {
+        err.span_note(span, format!("while trying to match {remaining_matcher}"));
+    } else {
+        err.note(format!("while trying to match {remaining_matcher}"));
+    }
+
     // Check whether there's a missing comma in this macro call, like `println!("{}" a);`
     if let Some((arg, comma_span)) = arg.add_comma() {
         for lhs in lhses {
@@ -379,17 +385,22 @@ fn expand_macro<'cx>(
 }
 
 /// The tracker used for the slow error path that collects useful info for diagnostics.
-struct CollectTrackerAndEmitter<'a, 'cx> {
+struct CollectTrackerAndEmitter<'a, 'cx, 'matcher> {
     cx: &'a mut ExtCtxt<'cx>,
+    remaining_matcher: Option<&'matcher MatcherLoc>,
     /// Which arm's failure should we report? (the one furthest along)
-    best_failure: Option<(Token, &'static str)>,
+    best_failure: Option<(Token, &'static str, MatcherLoc)>,
     root_span: Span,
     result: Option<Box<dyn MacResult + 'cx>>,
 }
 
-impl<'a, 'cx, 'matcher> Tracker<'matcher> for CollectTrackerAndEmitter<'a, 'cx> {
-    fn before_match_loc(&mut self, _parser: &TtParser, _matcher: &'matcher MatcherLoc) {
-        // Empty for now.
+impl<'a, 'cx, 'matcher> Tracker<'matcher> for CollectTrackerAndEmitter<'a, 'cx, 'matcher> {
+    fn before_match_loc(&mut self, parser: &TtParser, matcher: &'matcher MatcherLoc) {
+        if self.remaining_matcher.is_none()
+            || (parser.has_no_remaining_items_for_step() && *matcher != MatcherLoc::Eof)
+        {
+            self.remaining_matcher = Some(matcher);
+        }
     }
 
     fn after_arm(&mut self, result: &NamedParseResult) {
@@ -398,8 +409,16 @@ impl<'a, 'cx, 'matcher> Tracker<'matcher> for CollectTrackerAndEmitter<'a, 'cx>
                 unreachable!("should not collect detailed info for successful macro match");
             }
             Failure(token, msg) => match self.best_failure {
-                Some((ref best_token, _)) if best_token.span.lo() >= token.span.lo() => {}
-                _ => self.best_failure = Some((token.clone(), msg)),
+                Some((ref best_token, _, _)) if best_token.span.lo() >= token.span.lo() => {}
+                _ => {
+                    self.best_failure = Some((
+                        token.clone(),
+                        msg,
+                        self.remaining_matcher
+                            .expect("must have collected matcher already")
+                            .clone(),
+                    ))
+                }
             },
             Error(err_sp, msg) => {
                 let span = err_sp.substitute_dummy(self.root_span);
@@ -415,9 +434,9 @@ impl<'a, 'cx, 'matcher> Tracker<'matcher> for CollectTrackerAndEmitter<'a, 'cx>
     }
 }
 
-impl<'a, 'cx> CollectTrackerAndEmitter<'a, 'cx> {
+impl<'a, 'cx> CollectTrackerAndEmitter<'a, 'cx, '_> {
     fn new(cx: &'a mut ExtCtxt<'cx>, root_span: Span) -> Self {
-        Self { cx, best_failure: None, root_span, result: None }
+        Self { cx, remaining_matcher: None, best_failure: None, root_span, result: None }
     }
 }
 

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

@@ -691,6 +691,10 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         rustc_allow_incoherent_impl, AttributeType::Normal, template!(Word), ErrorFollowing, @only_local: true,
         "#[rustc_allow_incoherent_impl] has to be added to all impl items of an incoherent inherent impl."
     ),
+    rustc_attr!(
+        rustc_deny_explicit_impl, AttributeType::Normal, template!(Word), ErrorFollowing, @only_local: false,
+        "#[rustc_deny_explicit_impl] enforces that a trait can have no user-provided impls"
+    ),
     rustc_attr!(
         rustc_has_incoherent_inherent_impls, AttributeType::Normal, template!(Word), ErrorFollowing,
         "#[rustc_has_incoherent_inherent_impls] allows the addition of incoherent inherent impls for \

Diff for: compiler/rustc_hir_analysis/src/coherence/mod.rs

@@ -5,10 +5,11 @@
 // done by the orphan and overlap modules. Then we build up various
 // mappings. That mapping code resides here.
 
-use rustc_errors::struct_span_err;
+use rustc_errors::{error_code, struct_span_err};
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::{self, TyCtxt, TypeVisitable};
+use rustc_span::sym;
 use rustc_trait_selection::traits;
 
 mod builtin;
@@ -39,61 +40,26 @@ fn enforce_trait_manually_implementable(
     impl_def_id: LocalDefId,
     trait_def_id: DefId,
 ) {
-    let did = Some(trait_def_id);
-    let li = tcx.lang_items();
     let impl_header_span = tcx.def_span(impl_def_id);
 
-    // Disallow *all* explicit impls of `Pointee`, `DiscriminantKind`, `Sized` and `Unsize` for now.
-    if did == li.pointee_trait() {
-        struct_span_err!(
+    // Disallow *all* explicit impls of traits marked `#[rustc_deny_explicit_impl]`
+    if tcx.has_attr(trait_def_id, sym::rustc_deny_explicit_impl) {
+        let trait_name = tcx.item_name(trait_def_id);
+        let mut err = struct_span_err!(
             tcx.sess,
             impl_header_span,
             E0322,
-            "explicit impls for the `Pointee` trait are not permitted"
-        )
-        .span_label(impl_header_span, "impl of `Pointee` not allowed")
-        .emit();
-        return;
-    }
-
-    if did == li.discriminant_kind_trait() {
-        struct_span_err!(
-            tcx.sess,
-            impl_header_span,
-            E0322,
-            "explicit impls for the `DiscriminantKind` trait are not permitted"
-        )
-        .span_label(impl_header_span, "impl of `DiscriminantKind` not allowed")
-        .emit();
-        return;
-    }
-
-    if did == li.sized_trait() {
-        struct_span_err!(
-            tcx.sess,
-            impl_header_span,
-            E0322,
-            "explicit impls for the `Sized` trait are not permitted"
-        )
-        .span_label(impl_header_span, "impl of `Sized` not allowed")
-        .emit();
-        return;
-    }
-
-    if did == li.unsize_trait() {
-        struct_span_err!(
-            tcx.sess,
-            impl_header_span,
-            E0328,
-            "explicit impls for the `Unsize` trait are not permitted"
-        )
-        .span_label(impl_header_span, "impl of `Unsize` not allowed")
-        .emit();
-        return;
-    }
+            "explicit impls for the `{trait_name}` trait are not permitted"
+        );
+        err.span_label(impl_header_span, format!("impl of `{trait_name}` not allowed"));
+
+        // Maintain explicit error code for `Unsize`, since it has a useful
+        // explanation about using `CoerceUnsized` instead.
+        if Some(trait_def_id) == tcx.lang_items().unsize_trait() {
+            err.code(error_code!(E0328));
+        }
 
-    if tcx.features().unboxed_closures {
-        // the feature gate allows all Fn traits
+        err.emit();
         return;
     }
 

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

@@ -173,34 +173,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         expected_ty: Ty<'tcx>,
     ) -> (Option<ExpectedSig<'tcx>>, Option<ty::ClosureKind>) {
         match *expected_ty.kind() {
-            ty::Opaque(def_id, substs) => {
-                let bounds = self.tcx.bound_explicit_item_bounds(def_id);
-                let sig =
-                    bounds.subst_iter_copied(self.tcx, substs).find_map(|(pred, span)| match pred
-                        .kind()
-                        .skip_binder()
-                    {
-                        ty::PredicateKind::Projection(proj_predicate) => self
-                            .deduce_sig_from_projection(
-                                Some(span),
-                                pred.kind().rebind(proj_predicate),
-                            ),
-                        _ => None,
-                    });
-
-                let kind = bounds
-                    .0
-                    .iter()
-                    .filter_map(|(pred, _)| match pred.kind().skip_binder() {
-                        ty::PredicateKind::Trait(tp) => {
-                            self.tcx.fn_trait_kind_from_lang_item(tp.def_id())
-                        }
-                        _ => None,
-                    })
-                    .fold(None, |best, cur| Some(best.map_or(cur, |best| cmp::min(best, cur))));
-                trace!(?sig, ?kind);
-                (sig, kind)
-            }
+            ty::Opaque(def_id, substs) => self.deduce_signature_from_predicates(
+                self.tcx.bound_explicit_item_bounds(def_id).subst_iter_copied(self.tcx, substs),
+            ),
             ty::Dynamic(ref object_type, ..) => {
                 let sig = object_type.projection_bounds().find_map(|pb| {
                     let pb = pb.with_self_ty(self.tcx, self.tcx.types.trait_object_dummy_self);
@@ -211,7 +186,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     .and_then(|did| self.tcx.fn_trait_kind_from_lang_item(did));
                 (sig, kind)
             }
-            ty::Infer(ty::TyVar(vid)) => self.deduce_expectations_from_obligations(vid),
+            ty::Infer(ty::TyVar(vid)) => self.deduce_signature_from_predicates(
+                self.obligations_for_self_ty(vid).map(|obl| (obl.predicate, obl.cause.span)),
+            ),
             ty::FnPtr(sig) => {
                 let expected_sig = ExpectedSig { cause_span: None, sig };
                 (Some(expected_sig), Some(ty::ClosureKind::Fn))
@@ -220,19 +197,19 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         }
     }
 
-    fn deduce_expectations_from_obligations(
+    fn deduce_signature_from_predicates(
         &self,
-        expected_vid: ty::TyVid,
+        predicates: impl DoubleEndedIterator<Item = (ty::Predicate<'tcx>, Span)>,
     ) -> (Option<ExpectedSig<'tcx>>, Option<ty::ClosureKind>) {
         let mut expected_sig = None;
         let mut expected_kind = None;
 
-        for obligation in traits::elaborate_obligations(
+        for obligation in traits::elaborate_predicates_with_span(
             self.tcx,
             // Reverse the obligations here, since `elaborate_*` uses a stack,
             // and we want to keep inference generally in the same order of
             // the registered obligations.
-            self.obligations_for_self_ty(expected_vid).rev().collect(),
+            predicates.rev(),
         ) {
             debug!(?obligation.predicate);
             let bound_predicate = obligation.predicate.kind();