Fix incorrect suggestion for undeclared hrtb lifetimes in where clauses.

fixes rust-lang#122714

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -7,6 +7,7 @@ use crate::ty::fast_reject::SimplifiedType;
 use crate::{errors, path_names_to_string};
 use crate::{Module, ModuleKind, ModuleOrUniformRoot};
 use crate::{PathResult, PathSource, Segment};
+use ast::HasNodeId;
 use rustc_hir::def::Namespace::{self, *};
 
 use rustc_ast::ptr::P;
@@ -17,6 +18,7 @@ use rustc_ast::{
 };
 use rustc_ast_pretty::pprust::where_bound_predicate_to_string;
 use rustc_data_structures::fx::FxHashSet;
+use rustc_data_structures::fx::FxIndexSet;
 use rustc_errors::{
     codes::*, pluralize, struct_span_code_err, Applicability, Diag, ErrorGuaranteed, MultiSpan,
     SuggestionStyle,
@@ -31,7 +33,7 @@ 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;
 
@@ -2711,8 +2713,12 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
         self.suggest_introducing_lifetime(
             &mut err,
             Some(lifetime_ref.ident.name.as_str()),
-            |err, _, span, message, suggestion| {
-                err.span_suggestion(span, message, suggestion, Applicability::MaybeIncorrect);
+            |err, _, span, message, suggestion, span_suggs| {
+                err.multipart_suggestion_verbose(
+                    message,
+                    std::iter::once((span, suggestion)).chain(span_suggs.iter().cloned()).collect(),
+                    Applicability::MaybeIncorrect,
+                );
                 true
             },
         );
@@ -2723,13 +2729,20 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
         &self,
         err: &mut Diag<'_>,
         name: Option<&str>,
-        suggest: impl Fn(&mut Diag<'_>, bool, Span, Cow<'static, str>, String) -> bool,
+        suggest: impl Fn(
+            &mut Diag<'_>,
+            bool,
+            Span,
+            Cow<'static, str>,
+            String,
+            &Vec<(Span, 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
@@ -2758,11 +2771,58 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
                             | LifetimeBinderKind::PolyTrait
                             | LifetimeBinderKind::WhereBound
                     );
+
+                    let mut rm_inner_binders: FxIndexSet<Span> = Default::default();
                     let (span, sugg) = if span.is_empty() {
+                        let mut binder_idents: FxIndexSet<Ident> = Default::default();
+                        binder_idents.insert(if let Some(name) = name {
+                            Ident::from_str(name)
+                        } else {
+                            Ident::from_str("'a")
+                        });
+
+                        // We need to special treat binders in following situation:
+                        // Change `T: for<'a> Trait<T> + 'b` to `for<'a, 'b> T: Trait<T> + 'b`
+                        // T: for<'a> Trait<T> + 'b
+                        //    ^^^^^^^  remove existing inner binder `for<'a>`
+                        // for<'a, 'b> T: Trait<T> + 'b
+                        // ^^^^^^^^^^^  suggest outer binder `for<'a, 'b>`
+                        if let LifetimeBinderKind::WhereBound = kind
+                            && let Some(ast::WherePredicate::BoundPredicate(
+                                ast::WhereBoundPredicate { bounded_ty, bounds, .. },
+                            )) = self.diag_metadata.current_where_predicate
+                            && bounded_ty.node_id() == node_id
+                        {
+                            for bound in bounds {
+                                let ast::GenericBound::Trait(poly_trait_ref, _) = bound else {
+                                    continue;
+                                };
+                                rm_inner_binders.insert(
+                                    poly_trait_ref
+                                        .span
+                                        .with_hi(poly_trait_ref.trait_ref.path.span.lo()),
+                                );
+                                poly_trait_ref.bound_generic_params.iter().for_each(|v| {
+                                    binder_idents.insert(v.ident);
+                                });
+                            }
+                        }
+
+                        let len = binder_idents.len();
+                        let binders_sugg = binder_idents.into_iter().enumerate().fold(
+                            "".to_string(),
+                            |mut binders, (i, x)| {
+                                binders += x.as_str();
+                                if i != len - 1 {
+                                    binders += ", ";
+                                }
+                                binders
+                            },
+                        );
                         let sugg = format!(
                             "{}<{}>{}",
                             if higher_ranked { "for" } else { "" },
-                            name.unwrap_or("'a"),
+                            format!("{}", binders_sugg),
                             if higher_ranked { " " } else { "" },
                         );
                         (span, sugg)
@@ -2777,24 +2837,39 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
                         let sugg = format!("{}, ", name.unwrap_or("'a"));
                         (span, sugg)
                     };
+
                     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 = suggest(
+                            err,
+                            true,
+                            span,
+                            message,
+                            sugg,
+                            &if rm_inner_binders.len() > 0 {
+                                rm_inner_binders
+                                    .into_iter()
+                                    .map(|v| (v, "".to_string()))
+                                    .collect::<Vec<_>>()
+                            } else {
+                                vec![]
+                            },
+                        );
                         err.note_once(
                             "for more information on higher-ranked polymorphism, visit \
                              https://doc.rust-lang.org/nomicon/hrtb.html",
                         );
                     } else if let Some(name) = name {
                         let message =
                             Cow::from(format!("consider introducing lifetime `{name}` here"));
-                        should_continue = suggest(err, false, span, message, sugg);
+                        should_continue = suggest(err, false, span, message, sugg, &vec![]);
                     } else {
                         let message = Cow::from("consider introducing a named lifetime parameter");
-                        should_continue = suggest(err, false, span, message, sugg);
+                        should_continue = suggest(err, false, span, message, sugg, &vec![]);
                     }
                 }
                 LifetimeRibKind::Item | LifetimeRibKind::ConstParamTy => break,
@@ -3030,7 +3105,7 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
                 self.suggest_introducing_lifetime(
                     err,
                     None,
-                    |err, higher_ranked, span, message, intro_sugg| {
+                    |err, higher_ranked, span, message, intro_sugg, _| {
                         err.multipart_suggestion_verbose(
                             message,
                             std::iter::once((span, intro_sugg))
@@ -3158,7 +3233,7 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
                             self.suggest_introducing_lifetime(
                                 err,
                                 None,
-                                |err, higher_ranked, span, message, intro_sugg| {
+                                |err, higher_ranked, span, message, intro_sugg, _| {
                                     err.multipart_suggestion_verbose(
                                         message,
                                         std::iter::once((span, intro_sugg))
@@ -3306,7 +3381,6 @@ 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/associated-inherent-types/issue-109299.stderr

@@ -2,9 +2,12 @@ error[E0261]: use of undeclared lifetime name `'d`
   --> $DIR/issue-109299.rs:6:12
    |
 LL | impl Lexer<'d> {
-   |     -      ^^ undeclared lifetime
-   |     |
-   |     help: consider introducing lifetime `'d` here: `<'d>`
+   |            ^^ undeclared lifetime
+   |
+help: consider introducing lifetime `'d` here
+   |
+LL | impl<'d> Lexer<'d> {
+   |     ++++
 
 error: lifetime may not live long enough
   --> $DIR/issue-109299.rs:10:1

tests/ui/borrowck/generic_const_early_param.stderr

@@ -7,19 +7,24 @@ LL | struct DataWrapper<'static> {
 error[E0261]: use of undeclared lifetime name `'a`
   --> $DIR/generic_const_early_param.rs:6:12
    |
-LL | struct DataWrapper<'static> {
-   |                    - help: consider introducing lifetime `'a` here: `'a,`
-LL |
 LL |     data: &'a [u8; Self::SIZE],
    |            ^^ undeclared lifetime
+   |
+help: consider introducing lifetime `'a` here
+   |
+LL | struct DataWrapper<'a, 'static> {
+   |                    +++
 
 error[E0261]: use of undeclared lifetime name `'a`
   --> $DIR/generic_const_early_param.rs:11:18
    |
 LL | impl DataWrapper<'a> {
-   |     -            ^^ undeclared lifetime
-   |     |
-   |     help: consider introducing lifetime `'a` here: `<'a>`
+   |                  ^^ undeclared lifetime
+   |
+help: consider introducing lifetime `'a` here
+   |
+LL | impl<'a> DataWrapper<'a> {
+   |     ++++
 
 warning: the feature `generic_const_exprs` is incomplete and may not be safe to use and/or cause compiler crashes
   --> $DIR/generic_const_early_param.rs:1:12

tests/ui/const-generics/generic_const_exprs/unresolved_lifetimes_error.stderr

@@ -1,10 +1,13 @@
 error[E0261]: use of undeclared lifetime name `'a`
   --> $DIR/unresolved_lifetimes_error.rs:5:13
    |
-LL | fn foo() -> [(); {
-   |       - help: consider introducing lifetime `'a` here: `<'a>`
 LL |     let a: &'a ();
    |             ^^ undeclared lifetime
+   |
+help: consider introducing lifetime `'a` here
+   |
+LL | fn foo<'a>() -> [(); {
+   |       ++++
 
 error: aborting due to 1 previous error
 

tests/ui/const-generics/ice-unexpected-inference-var-122549.stderr

@@ -17,9 +17,12 @@ error[E0261]: use of undeclared lifetime name `'a`
   --> $DIR/ice-unexpected-inference-var-122549.rs:11:34
    |
 LL | struct ConstChunksExact<'rem, T: 'a, const N: usize> {}
-   |                         -        ^^ undeclared lifetime
-   |                         |
-   |                         help: consider introducing lifetime `'a` here: `'a,`
+   |                                  ^^ undeclared lifetime
+   |
+help: consider introducing lifetime `'a` here
+   |
+LL | struct ConstChunksExact<'a, 'rem, T: 'a, const N: usize> {}
+   |                         +++
 
 error[E0046]: not all trait items implemented, missing: `const_chunks_exact`
   --> $DIR/ice-unexpected-inference-var-122549.rs:9:1

tests/ui/const_prop/ice-type-mismatch-when-copying-112824.stderr

@@ -2,9 +2,12 @@ error[E0261]: use of undeclared lifetime name `'a`
   --> $DIR/ice-type-mismatch-when-copying-112824.rs:5:21
    |
 LL | pub struct Opcode2(&'a S);
-   |                   - ^^ undeclared lifetime
-   |                   |
-   |                   help: consider introducing lifetime `'a` here: `<'a>`
+   |                     ^^ undeclared lifetime
+   |
+help: consider introducing lifetime `'a` here
+   |
+LL | pub struct Opcode2<'a>(&'a S);
+   |                   ++++
 
 error[E0412]: cannot find type `S` in this scope
   --> $DIR/ice-type-mismatch-when-copying-112824.rs:5:24

tests/ui/error-codes/E0261.stderr

@@ -2,17 +2,23 @@ error[E0261]: use of undeclared lifetime name `'a`
   --> $DIR/E0261.rs:1:12
    |
 LL | fn foo(x: &'a str) { }
-   |       -    ^^ undeclared lifetime
-   |       |
-   |       help: consider introducing lifetime `'a` here: `<'a>`
+   |            ^^ undeclared lifetime
+   |
+help: consider introducing lifetime `'a` here
+   |
+LL | fn foo<'a>(x: &'a str) { }
+   |       ++++
 
 error[E0261]: use of undeclared lifetime name `'a`
   --> $DIR/E0261.rs:5:9
    |
-LL | struct Foo {
-   |           - help: consider introducing lifetime `'a` here: `<'a>`
 LL |     x: &'a str,
    |         ^^ undeclared lifetime
+   |
+help: consider introducing lifetime `'a` here
+   |
+LL | struct Foo<'a> {
+   |           ++++
 
 error: aborting due to 2 previous errors
 

tests/ui/generics/generic-extern-lifetime.stderr

@@ -2,9 +2,12 @@ error[E0261]: use of undeclared lifetime name `'a`
   --> $DIR/generic-extern-lifetime.rs:6:26
    |
 LL |     pub fn life2<'b>(x: &'a i32, y: &'b i32);
-   |                  -       ^^ undeclared lifetime
-   |                  |
-   |                  help: consider introducing lifetime `'a` here: `'a,`
+   |                          ^^ undeclared lifetime
+   |
+help: consider introducing lifetime `'a` here
+   |
+LL |     pub fn life2<'a, 'b>(x: &'a i32, y: &'b i32);
+   |                  +++
 
 error[E0261]: use of undeclared lifetime name `'a`
   --> $DIR/generic-extern-lifetime.rs:8:37

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

@@ -0,0 +1,28 @@
+#![allow(dead_code)]
+
+trait Trait1<T>
+  where T: for<'a> Trait1<T> + 'b { } //~ ERROR use of undeclared lifetime name `'b`
+
+trait Trait2<T>
+where
+    T: B<'b> + for<'a> A<'a>, //~ ERROR use of undeclared lifetime name `'b`
+{
+}
+
+trait Trait3<T>
+where
+    T: B<'b> + for<'a> A<'a> + 'c {}
+    //~^ ERROR use of undeclared lifetime name `'b`
+    //~| ERROR use of undeclared lifetime name `'c`
+
+trait Trait4<T>
+where
+    T: for<'a> A<'a> + 'x + for<'b> B<'b>, //~ ERROR use of undeclared lifetime name `'x`
+{
+}
+
+trait A<'a> {}
+trait B<'a> {}
+
+
+fn main() {}