Auto merge of #96347 - estebank:issue-96292, r=compiler-errors

Erase type params when suggesting fully qualified path

When suggesting the use of a fully qualified path for a method call that
is ambiguous because it has multiple candidates, erase type params in
the resulting code, as they would result in an error when applied. We
replace them with `_` in the output to rely on inference. There might be
cases where this still produces slighlty incomplete suggestions, but it
otherwise produces many more errors in relatively common cases.

Fix #96292

1 files changed, 31 insertions, 10 deletions

diff --git a/compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs b/compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs
index a9a92fdbd64..465358de932 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs
@@ -734,22 +734,28 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                 if !impl_candidates.is_empty() && e.span.contains(span)
                     && let Some(expr) = exprs.first()
                     && let ExprKind::Path(hir::QPath::Resolved(_, path)) = expr.kind
-                    && let [path_segment] = path.segments
+                    && let [_] = path.segments
                 {
+                    let mut eraser = TypeParamEraser(self.tcx);
                     let candidate_len = impl_candidates.len();
-                    let suggestions = impl_candidates.iter().map(|candidate| {
-                        format!(
-                            "{}::{}({})",
-                            candidate, segment.ident, path_segment.ident
-                        )
-                    });
-                    err.span_suggestions(
-                        e.span,
+                    let mut suggestions: Vec<_> = impl_candidates.iter().map(|candidate| {
+                        let candidate = candidate.super_fold_with(&mut eraser);
+                        vec![
+                            (expr.span.shrink_to_lo(), format!("{}::{}(", candidate, segment.ident)),
+                            if exprs.len() == 1 {
+                                (expr.span.shrink_to_hi().with_hi(e.span.hi()), ")".to_string())
+                            } else {
+                                (expr.span.shrink_to_hi().with_hi(exprs[1].span.lo()), ", ".to_string())
+                            },
+                        ]
+                    }).collect();
+                    suggestions.sort_by(|a, b| a[0].1.cmp(&b[0].1));
+                    err.multipart_suggestions(
                         &format!(
                             "use the fully qualified path for the potential candidate{}",
                             pluralize!(candidate_len),
                         ),
-                        suggestions,
+                        suggestions.into_iter(),
                         Applicability::MaybeIncorrect,
                     );
                 }
@@ -1037,3 +1043,18 @@ impl<'tcx> TypeFolder<'tcx> for ErrTypeParamEraser<'tcx> {
         }
     }
 }
+
+/// Replace type parameters with `ty::Infer(ty::Var)` to display `_`.
+struct TypeParamEraser<'tcx>(TyCtxt<'tcx>);
+
+impl<'tcx> TypeFolder<'tcx> for TypeParamEraser<'tcx> {
+    fn tcx<'a>(&'a self) -> TyCtxt<'tcx> {
+        self.0
+    }
+    fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
+        match t.kind() {
+            ty::Param(_) | ty::Error(_) => self.tcx().mk_ty_var(ty::TyVid::from_u32(0)),
+            _ => t.super_fold_with(self),
+        }
+    }
+}