Unrolled build for rust-lang#122591

Rollup merge of rust-lang#122591 - gurry:122162-impl-type-binding-suggestion, r=fmease

Suggest using type args directly instead of equality constraint

When type arguments are written erroneously using an equality constraint we suggest specifying them directly without the equality constraint.

Fixes rust-lang#122162

Changes the diagnostic in the issue from:
```rust
error[E0229]: associated type bindings are not allowed here
9 | impl std::cmp::PartialEq<Rhs = T> for S {
  |                          ^^^^^^^ associated type not allowed here
  |
```
to
```rust
error[E0229]: associated type bindings are not allowed here
9 | impl std::cmp::PartialEq<Rhs = T> for S {
  |                          ^^^^^^^ associated type not allowed here
  |
help: to use `T` as a generic argument specify it directly
  |
  |      impl std::cmp::PartialEq<T> for S {
  |                               ~
```

compiler/rustc_hir_analysis/src/hir_ty_lowering/errors.rs

@@ -17,6 +17,7 @@ use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_infer::traits::FulfillmentError;
 use rustc_middle::query::Key;
+use rustc_middle::ty::GenericParamDefKind;
 use rustc_middle::ty::{self, suggest_constraining_type_param};
 use rustc_middle::ty::{AdtDef, Ty, TyCtxt, TypeVisitableExt};
 use rustc_middle::ty::{Binder, TraitRef};
@@ -1200,12 +1201,12 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
 /// Emits an error regarding forbidden type binding associations
 pub fn prohibit_assoc_item_binding(
     tcx: TyCtxt<'_>,
-    span: Span,
-    segment: Option<(&hir::PathSegment<'_>, Span)>,
+    binding: &hir::TypeBinding<'_>,
+    segment: Option<(DefId, &hir::PathSegment<'_>, Span)>,
 ) -> ErrorGuaranteed {
-    tcx.dcx().emit_err(AssocTypeBindingNotAllowed {
-        span,
-        fn_trait_expansion: if let Some((segment, span)) = segment
+    let mut err = tcx.dcx().create_err(AssocTypeBindingNotAllowed {
+        span: binding.span,
+        fn_trait_expansion: if let Some((_, segment, span)) = segment
             && segment.args().parenthesized == hir::GenericArgsParentheses::ParenSugar
         {
             Some(ParenthesizedFnTraitExpansion {
@@ -1215,7 +1216,109 @@ pub fn prohibit_assoc_item_binding(
         } else {
             None
         },
-    })
+    });
+
+    // Emit a suggestion to turn the assoc item binding into a generic arg
+    // if the relevant item has a generic param whose name matches the binding name;
+    // otherwise suggest the removal of the binding.
+    if let Some((def_id, segment, _)) = segment
+        && segment.args().parenthesized == hir::GenericArgsParentheses::No
+        && let hir::TypeBindingKind::Equality { term } = binding.kind
+    {
+        // Suggests removal of the offending binding
+        let suggest_removal = |e: &mut Diag<'_>| {
+            let bindings = segment.args().bindings;
+            let args = segment.args().args;
+            let binding_span = binding.span;
+
+            // Compute the span to remove based on the position
+            // of the binding. We do that as follows:
+            //  1. Find the index of the binding in the list of bindings
+            //  2. Locate the spans preceding and following the binding.
+            //     If it's the first binding the preceding span would be
+            //     that of the last arg
+            //  3. Using this information work out whether the span
+            //     to remove will start from the end of the preceding span,
+            //     the start of the next span or will simply be the
+            //     span encomassing everything within the generics brackets
+
+            let Some(binding_index) = bindings.iter().position(|b| b.hir_id == binding.hir_id)
+            else {
+                bug!("a type binding exists but its HIR ID not found in generics");
+            };
+
+            let preceding_span = if binding_index > 0 {
+                Some(bindings[binding_index - 1].span)
+            } else {
+                args.last().map(|a| a.span())
+            };
+
+            let next_span = if binding_index < bindings.len() - 1 {
+                Some(bindings[binding_index + 1].span)
+            } else {
+                None
+            };
+
+            let removal_span = match (preceding_span, next_span) {
+                (Some(prec), _) => binding_span.with_lo(prec.hi()),
+                (None, Some(next)) => binding_span.with_hi(next.lo()),
+                (None, None) => {
+                    let Some(generics_span) = segment.args().span_ext() else {
+                        bug!("a type binding exists but generic span is empty");
+                    };
+
+                    generics_span
+                }
+            };
+
+            // Now emit the suggestion
+            if let Ok(suggestion) = tcx.sess.source_map().span_to_snippet(removal_span) {
+                e.span_suggestion_verbose(
+                    removal_span,
+                    "consider removing this type binding",
+                    suggestion,
+                    Applicability::MaybeIncorrect,
+                );
+            }
+        };
+
+        // Suggest replacing the associated item binding with a generic argument.
+        // i.e., replacing `<..., T = A, ...>` with `<..., A, ...>`.
+        let suggest_direct_use = |e: &mut Diag<'_>, sp: Span| {
+            if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(sp) {
+                e.span_suggestion_verbose(
+                    binding.span,
+                    format!("to use `{snippet}` as a generic argument specify it directly"),
+                    snippet,
+                    Applicability::MaybeIncorrect,
+                );
+            }
+        };
+
+        // Check if the type has a generic param with the
+        // same name as the assoc type name in type binding
+        let generics = tcx.generics_of(def_id);
+        let matching_param =
+            generics.params.iter().find(|p| p.name.as_str() == binding.ident.as_str());
+
+        // Now emit the appropriate suggestion
+        if let Some(matching_param) = matching_param {
+            match (&matching_param.kind, term) {
+                (GenericParamDefKind::Type { .. }, hir::Term::Ty(ty)) => {
+                    suggest_direct_use(&mut err, ty.span);
+                }
+                (GenericParamDefKind::Const { .. }, hir::Term::Const(c)) => {
+                    let span = tcx.hir().span(c.hir_id);
+                    suggest_direct_use(&mut err, span);
+                }
+                _ => suggest_removal(&mut err),
+            }
+        } else {
+            suggest_removal(&mut err);
+        }
+    }
+
+    err.emit()
 }
 
 pub(crate) fn fn_trait_to_string(

compiler/rustc_hir_analysis/src/hir_ty_lowering/generics.rs

@@ -454,7 +454,7 @@ pub(crate) fn check_generic_arg_count(
     if gen_pos != GenericArgPosition::Type
         && let Some(b) = gen_args.bindings.first()
     {
-        prohibit_assoc_item_binding(tcx, b.span, None);
+        prohibit_assoc_item_binding(tcx, b, None);
     }
 
     let explicit_late_bound =

compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs

@@ -323,7 +323,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             ty::BoundConstness::NotConst,
         );
         if let Some(b) = item_segment.args().bindings.first() {
-            prohibit_assoc_item_binding(self.tcx(), b.span, Some((item_segment, span)));
+            prohibit_assoc_item_binding(self.tcx(), b, Some((def_id, item_segment, span)));
         }
         args
     }
@@ -620,7 +620,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             ty::BoundConstness::NotConst,
         );
         if let Some(b) = item_segment.args().bindings.first() {
-            prohibit_assoc_item_binding(self.tcx(), b.span, Some((item_segment, span)));
+            prohibit_assoc_item_binding(self.tcx(), b, Some((item_def_id, item_segment, span)));
         }
         args
     }
@@ -765,7 +765,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             constness,
         );
         if let Some(b) = trait_segment.args().bindings.first() {
-            prohibit_assoc_item_binding(self.tcx(), b.span, Some((trait_segment, span)));
+            prohibit_assoc_item_binding(self.tcx(), b, Some((trait_def_id, trait_segment, span)));
         }
         ty::TraitRef::new(self.tcx(), trait_def_id, generic_args)
     }
@@ -1544,7 +1544,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         for segment in segments {
             // Only emit the first error to avoid overloading the user with error messages.
             if let Some(b) = segment.args().bindings.first() {
-                return Err(prohibit_assoc_item_binding(self.tcx(), b.span, None));
+                return Err(prohibit_assoc_item_binding(self.tcx(), b, None));
             }
         }
 

tests/rustdoc-ui/invalid_associated_const.stderr

@@ -3,6 +3,11 @@ error[E0229]: associated type bindings are not allowed here
    |
 LL |     type A: S<C<X = 0i32> = 34>;
    |                 ^^^^^^^^ associated type not allowed here
+   |
+help: consider removing this type binding
+   |
+LL |     type A: S<C<X = 0i32> = 34>;
+   |                ~~~~~~~~~~
 
 error[E0229]: associated type bindings are not allowed here
   --> $DIR/invalid_associated_const.rs:4:17
@@ -11,6 +16,10 @@ LL |     type A: S<C<X = 0i32> = 34>;
    |                 ^^^^^^^^ associated type not allowed here
    |
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+help: consider removing this type binding
+   |
+LL |     type A: S<C<X = 0i32> = 34>;
+   |                ~~~~~~~~~~
 
 error: aborting due to 2 previous errors
 

tests/rustdoc-ui/issue-102467.stderr

@@ -3,6 +3,11 @@ error[E0229]: associated type bindings are not allowed here
    |
 LL |     type A: S<C<X = 0i32> = 34>;
    |                 ^^^^^^^^ associated type not allowed here
+   |
+help: consider removing this type binding
+   |
+LL |     type A: S<C<X = 0i32> = 34>;
+   |                ~~~~~~~~~~
 
 error[E0229]: associated type bindings are not allowed here
   --> $DIR/issue-102467.rs:7:17
@@ -11,6 +16,10 @@ LL |     type A: S<C<X = 0i32> = 34>;
    |                 ^^^^^^^^ associated type not allowed here
    |
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+help: consider removing this type binding
+   |
+LL |     type A: S<C<X = 0i32> = 34>;
+   |                ~~~~~~~~~~
 
 error: aborting due to 2 previous errors
 

tests/ui/associated-consts/issue-102335-const.stderr

@@ -3,6 +3,11 @@ error[E0229]: associated type bindings are not allowed here
    |
 LL |     type A: S<C<X = 0i32> = 34>;
    |                 ^^^^^^^^ associated type not allowed here
+   |
+help: consider removing this type binding
+   |
+LL |     type A: S<C<X = 0i32> = 34>;
+   |                ~~~~~~~~~~
 
 error[E0229]: associated type bindings are not allowed here
   --> $DIR/issue-102335-const.rs:4:17
@@ -11,6 +16,10 @@ LL |     type A: S<C<X = 0i32> = 34>;
    |                 ^^^^^^^^ associated type not allowed here
    |
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+help: consider removing this type binding
+   |
+LL |     type A: S<C<X = 0i32> = 34>;
+   |                ~~~~~~~~~~
 
 error: aborting due to 2 previous errors
 

tests/ui/associated-type-bounds/issue-102335-ty.rs

@@ -1,5 +1,11 @@
 trait T {
-    type A: S<C<i32 = u32> = ()>;
+    type A: S<C<i32 = u32> = ()>; // Just one erroneous equality constraint
+    //~^ ERROR associated type bindings are not allowed here
+    //~| ERROR associated type bindings are not allowed here
+}
+
+trait T2 {
+    type A: S<C<i32 = u32, X = i32> = ()>; // More than one erroneous equality constraints
     //~^ ERROR associated type bindings are not allowed here
     //~| ERROR associated type bindings are not allowed here
 }

tests/ui/associated-type-bounds/issue-102335-ty.stderr

@@ -1,17 +1,49 @@
 error[E0229]: associated type bindings are not allowed here
   --> $DIR/issue-102335-ty.rs:2:17
    |
-LL |     type A: S<C<i32 = u32> = ()>;
+LL |     type A: S<C<i32 = u32> = ()>; // Just one erroneous equality constraint
    |                 ^^^^^^^^^ associated type not allowed here
+   |
+help: consider removing this type binding
+   |
+LL |     type A: S<C<i32 = u32> = ()>; // Just one erroneous equality constraint
+   |                ~~~~~~~~~~~
 
 error[E0229]: associated type bindings are not allowed here
   --> $DIR/issue-102335-ty.rs:2:17
    |
-LL |     type A: S<C<i32 = u32> = ()>;
+LL |     type A: S<C<i32 = u32> = ()>; // Just one erroneous equality constraint
+   |                 ^^^^^^^^^ associated type not allowed here
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+help: consider removing this type binding
+   |
+LL |     type A: S<C<i32 = u32> = ()>; // Just one erroneous equality constraint
+   |                ~~~~~~~~~~~
+
+error[E0229]: associated type bindings are not allowed here
+  --> $DIR/issue-102335-ty.rs:8:17
+   |
+LL |     type A: S<C<i32 = u32, X = i32> = ()>; // More than one erroneous equality constraints
+   |                 ^^^^^^^^^ associated type not allowed here
+   |
+help: consider removing this type binding
+   |
+LL |     type A: S<C<i32 = u32, X = i32> = ()>; // More than one erroneous equality constraints
+   |                 ~~~~~~~~~~
+
+error[E0229]: associated type bindings are not allowed here
+  --> $DIR/issue-102335-ty.rs:8:17
+   |
+LL |     type A: S<C<i32 = u32, X = i32> = ()>; // More than one erroneous equality constraints
    |                 ^^^^^^^^^ associated type not allowed here
    |
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+help: consider removing this type binding
+   |
+LL |     type A: S<C<i32 = u32, X = i32> = ()>; // More than one erroneous equality constraints
+   |                 ~~~~~~~~~~
 
-error: aborting due to 2 previous errors
+error: aborting due to 4 previous errors
 
 For more information about this error, try `rustc --explain E0229`.