Fix incorrect suggestion for undeclared hrtb lifetimes in where clauses.

fixes #122714

Author: surechen

compiler/rustc_resolve/src/late.rs

@@ -653,6 +653,13 @@ struct DiagMetadata<'ast> {
     current_elision_failures: Vec<MissingLifetime>,
 }
 
+#[derive(Debug, Default)]
+struct RedundantPolyTraitRef {
+    poly_trait: Span,
+    trait_ref: Span,
+    generic_param_idents: Vec<Ident>,
+}
+
 struct LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
     r: &'b mut Resolver<'a, 'tcx>,
 
@@ -693,6 +700,9 @@ struct LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
 
     /// Count the number of places a lifetime is used.
     lifetime_uses: FxHashMap<LocalDefId, LifetimeUseSet>,
+
+    /// Record poly-trait-ref, only used for diagnostic.
+    with_poly_trait_ref: FxHashMap<NodeId, RedundantPolyTraitRef>,
 }
 
 /// Walks the whole crate in DFS order, visiting each item, resolving names as it goes.
@@ -1197,6 +1207,7 @@ impl<'a: 'ast, 'ast, 'tcx> Visitor<'ast> for LateResolutionVisitor<'a, '_, 'ast,
 
     fn visit_where_predicate(&mut self, p: &'ast WherePredicate) {
         debug!("visit_where_predicate {:?}", p);
+        self.record_where_bound_predicate_with_poly_trait(p);
         let previous_value = replace(&mut self.diag_metadata.current_where_predicate, Some(p));
         self.with_lifetime_rib(LifetimeRibKind::AnonymousReportError, |this| {
             if let WherePredicate::BoundPredicate(WhereBoundPredicate {
@@ -1306,6 +1317,7 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
             // errors at module scope should always be reported
             in_func_body: false,
             lifetime_uses: Default::default(),
+            with_poly_trait_ref: Default::default(),
         }
     }
 
@@ -4702,6 +4714,39 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
             });
         }
     }
+
+    fn record_where_bound_predicate_with_poly_trait(&mut self, p: &WherePredicate) {
+        if let ast::WherePredicate::BoundPredicate(ast::WhereBoundPredicate {
+            bounded_ty,
+            bounds,
+            ..
+        }) = p
+        {
+            for bound in bounds {
+                if let ast::GenericBound::Trait(
+                    ast::PolyTraitRef {
+                        span: poly_span,
+                        trait_ref: ast::TraitRef { path: ast::Path { span, .. }, .. },
+                        bound_generic_params,
+                        ..
+                    },
+                    _,
+                ) = bound
+                {
+                    let names = bound_generic_params.iter().map(|v| v.ident).collect();
+                    self.with_poly_trait_ref.insert(
+                        bounded_ty.node_id(),
+                        RedundantPolyTraitRef {
+                            poly_trait: *poly_span,
+                            trait_ref: *span,
+                            generic_param_idents: names,
+                        },
+                    );
+                    break;
+                }
+            }
+        }
+    }
 }
 
 /// Walks the whole crate in DFS order, visiting each item, counting the declared number of

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -31,7 +31,7 @@ use rustc_span::edit_distance::find_best_match_for_name;
 use rustc_span::edition::Edition;
 use rustc_span::hygiene::MacroKind;
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
-use rustc_span::Span;
+use rustc_span::{Span, DUMMY_SP};
 
 use rustc_middle::ty;
 
@@ -2718,10 +2718,11 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
         suggest: impl Fn(&mut Diag<'_>, bool, Span, Cow<'static, str>, String) -> bool,
     ) {
         let mut suggest_note = true;
+
         for rib in self.lifetime_ribs.iter().rev() {
             let mut should_continue = true;
             match rib.kind {
-                LifetimeRibKind::Generics { binder: _, span, kind } => {
+                LifetimeRibKind::Generics { binder: node_id, span, kind } => {
                     // Avoid suggesting placing lifetime parameters on constant items unless the relevant
                     // feature is enabled. Suggest the parent item as a possible location if applicable.
                     if let LifetimeBinderKind::ConstItem = kind
@@ -2750,14 +2751,43 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
                             | LifetimeBinderKind::PolyTrait
                             | LifetimeBinderKind::WhereBound
                     );
-                    let (span, sugg) = if span.is_empty() {
+
+                    let (span, sugg, rm_poly_trait_span) = if span.is_empty() {
+                        let (generic_params, poly_trait_span, trait_ref_span) =
+                            if let Some(with_poly_trait_ref) =
+                                self.with_poly_trait_ref.get(&node_id)
+                                && higher_ranked
+                            {
+                                let generic_params = with_poly_trait_ref
+                                    .generic_param_idents
+                                    .iter()
+                                    .fold("".to_string(), |mut generic_params, x| {
+                                        generic_params += x.as_str();
+                                        generic_params += ", ";
+                                        generic_params
+                                    });
+                                (
+                                    generic_params,
+                                    with_poly_trait_ref.poly_trait,
+                                    with_poly_trait_ref.trait_ref,
+                                )
+                            } else {
+                                ("".to_string(), DUMMY_SP, DUMMY_SP)
+                            };
+
+                        let rm_poly_trait_span = if generic_params.is_empty() {
+                            DUMMY_SP
+                        } else {
+                            poly_trait_span.with_hi(trait_ref_span.lo())
+                        };
+
                         let sugg = format!(
                             "{}<{}>{}",
                             if higher_ranked { "for" } else { "" },
-                            name.unwrap_or("'a"),
+                            format!("{}{}", generic_params, name.unwrap_or("'a")),
                             if higher_ranked { " " } else { "" },
                         );
-                        (span, sugg)
+                        (span, sugg, rm_poly_trait_span)
                     } else {
                         let span = self
                             .r
@@ -2767,15 +2797,30 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
                             .span_through_char(span, '<')
                             .shrink_to_hi();
                         let sugg = format!("{}, ", name.unwrap_or("'a"));
-                        (span, sugg)
+                        (span, sugg, DUMMY_SP)
                     };
+
                     if higher_ranked {
                         let message = Cow::from(format!(
                             "consider making the {} lifetime-generic with a new `{}` lifetime",
                             kind.descr(),
                             name.unwrap_or("'a"),
                         ));
-                        should_continue = suggest(err, true, span, message, sugg);
+                        should_continue = if !rm_poly_trait_span.is_dummy() {
+                            // For poly-trait-ref like `for<'a> Trait<T>` in
+                            // `T: for<'a> Trait<T> + 'b { }`.
+                            // We should merge the higher-ranked lifetimes: existed `for<'a>` and suggestion `for<'b>`
+                            // or will get err:
+                            // `[E0316] nested quantification of lifetimes`.
+                            err.multipart_suggestion_verbose(
+                                message,
+                                vec![(span, sugg), (rm_poly_trait_span, "".to_string())],
+                                Applicability::MaybeIncorrect,
+                            );
+                            false
+                        } else {
+                            suggest(err, true, span, message.clone(), sugg.clone())
+                        };
                         err.note_once(
                             "for more information on higher-ranked polymorphism, visit \
                              https://doc.rust-lang.org/nomicon/hrtb.html",
@@ -3298,7 +3343,6 @@ fn mk_where_bound_predicate(
     poly_trait_ref: &ast::PolyTraitRef,
     ty: &Ty,
 ) -> Option<ast::WhereBoundPredicate> {
-    use rustc_span::DUMMY_SP;
     let modified_segments = {
         let mut segments = path.segments.clone();
         let [preceding @ .., second_last, last] = segments.as_mut_slice() else {

tests/ui/generics/generic-higher-ranked-lifetime-issue-122714.fixed

@@ -0,0 +1,8 @@
+//@ run-rustfix
+
+#![allow(dead_code)]
+
+trait Trait<T>
+  where for<'a, 'b> T: Trait<T> + 'b { } //~ ERROR use of undeclared lifetime name `'b`
+
+fn main() {}

tests/ui/generics/generic-higher-ranked-lifetime-issue-122714.rs

@@ -0,0 +1,8 @@
+//@ run-rustfix
+
+#![allow(dead_code)]
+
+trait Trait<T>
+  where T: for<'a> Trait<T> + 'b { } //~ ERROR use of undeclared lifetime name `'b`
+
+fn main() {}

tests/ui/generics/generic-higher-ranked-lifetime-issue-122714.stderr

@@ -0,0 +1,16 @@
+error[E0261]: use of undeclared lifetime name `'b`
+  --> $DIR/generic-higher-ranked-lifetime-issue-122714.rs:6:31
+   |
+LL |   where T: for<'a> Trait<T> + 'b { }
+   |                               ^^ undeclared lifetime
+   |
+   = note: for more information on higher-ranked polymorphism, visit https://doc.rust-lang.org/nomicon/hrtb.html
+help: consider making the bound lifetime-generic with a new `'b` lifetime
+   |
+LL -   where T: for<'a> Trait<T> + 'b { }
+LL +   where for<'a, 'b> T: Trait<T> + 'b { }
+   |
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0261`.