Rollup merge of #101424 - compiler-errors:operator-err-sugg, r=TaKO8Ki

Adjust and slightly generalize operator error suggestion

(in no particular order)
* Stop passing around a whole extra `ProjectionPredicate`
* Add spaces around `=` in `Trait<..., Output = Ty>` suggestion
* Some code clean-ups, including
    * add `lang_item_for_op` to turn a `Op` into a `DefId`
    * avoid `SourceMap` because we don't really need to render an expr
    * Remove `TypeParamVisitor` in favor of just checking `ty.has_param_types_or_consts` -- this acts a bit differently, but shouldn't cause erroneous suggestions (actually might generalize them a bit)
* We now suggest `Output = Ty` in the `where` clause suggestion when we fail to add `Struct<T>` and `T`.

I can split this out into more PRs if needed, but they're all just miscellaneous generalizations, changes, and nitpicks I saw when messing with this operator code.

1 files changed, 14 insertions, 12 deletions

diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
index b012073f771..ecbeb9d79b1 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
@@ -25,8 +25,7 @@ use rustc_middle::hir::map;
 use rustc_middle::ty::{
     self, suggest_arbitrary_trait_bound, suggest_constraining_type_param, AdtKind, DefIdTree,
     GeneratorDiagnosticData, GeneratorInteriorTypeCause, Infer, InferTy, IsSuggestable,
-    ProjectionPredicate, ToPredicate, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperFoldable,
-    TypeVisitable,
+    ToPredicate, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperFoldable, TypeVisitable,
 };
 use rustc_middle::ty::{TypeAndMut, TypeckResults};
 use rustc_session::Limit;
@@ -174,7 +173,7 @@ pub trait InferCtxtExt<'tcx> {
         &self,
         err: &mut Diagnostic,
         trait_pred: ty::PolyTraitPredicate<'tcx>,
-        proj_pred: Option<ty::PolyProjectionPredicate<'tcx>>,
+        associated_item: Option<(&'static str, Ty<'tcx>)>,
         body_id: hir::HirId,
     );
 
@@ -467,7 +466,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
         &self,
         mut err: &mut Diagnostic,
         trait_pred: ty::PolyTraitPredicate<'tcx>,
-        proj_pred: Option<ty::PolyProjectionPredicate<'tcx>>,
+        associated_ty: Option<(&'static str, Ty<'tcx>)>,
         body_id: hir::HirId,
     ) {
         let trait_pred = self.resolve_numeric_literals_with_default(trait_pred);
@@ -604,21 +603,18 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                         trait_pred.print_modifiers_and_trait_path().to_string()
                     );
 
-                    if let Some(proj_pred) = proj_pred {
-                        let ProjectionPredicate { projection_ty, term } = proj_pred.skip_binder();
-                        let item = self.tcx.associated_item(projection_ty.item_def_id);
-
+                    if let Some((name, term)) = associated_ty {
                         // FIXME: this case overlaps with code in TyCtxt::note_and_explain_type_err.
                         // That should be extracted into a helper function.
                         if constraint.ends_with('>') {
                             constraint = format!(
-                                "{}, {}={}>",
+                                "{}, {} = {}>",
                                 &constraint[..constraint.len() - 1],
-                                item.name,
+                                name,
                                 term
                             );
                         } else {
-                            constraint.push_str(&format!("<{}={}>", item.name, term));
+                            constraint.push_str(&format!("<{} = {}>", name, term));
                         }
                     }
 
@@ -648,7 +644,13 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                     ..
                 }) if !param_ty => {
                     // Missing generic type parameter bound.
-                    if suggest_arbitrary_trait_bound(self.tcx, generics, &mut err, trait_pred) {
+                    if suggest_arbitrary_trait_bound(
+                        self.tcx,
+                        generics,
+                        &mut err,
+                        trait_pred,
+                        associated_ty,
+                    ) {
                         return;
                     }
                 }