remove importing suggestions when there is a shadowed typo canddiate

Author: chenyukang

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -460,7 +460,7 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
             return (err, Vec::new());
         }
 
-        let (found, candidates) = self.try_lookup_name_relaxed(
+        let (found, mut candidates) = self.try_lookup_name_relaxed(
             &mut err,
             source,
             path,
@@ -473,13 +473,18 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
             return (err, candidates);
         }
 
-        let mut fallback = self.suggest_trait_and_bounds(&mut err, source, res, span, &base_error);
+        let trait_fallback =
+            self.suggest_trait_and_bounds(&mut err, source, res, span, &base_error);
 
         // if we have suggested using pattern matching, then don't add needless suggestions
         // for typos.
-        fallback |= self.suggest_typo(&mut err, source, path, following_seg, span, &base_error);
-
-        if fallback {
+        let (typo_fallback, suggested_shadowed) =
+            self.suggest_typo(&mut err, source, path, following_seg, span, &base_error);
+        if suggested_shadowed {
+            // if there is already a shadowed name, don'suggest candidates for importing
+            candidates.clear();
+        }
+        if trait_fallback || typo_fallback {
             // Fallback label.
             err.span_label(base_error.span, base_error.fallback_label);
         }
@@ -867,7 +872,7 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
         following_seg: Option<&Segment>,
         span: Span,
         base_error: &BaseError,
-    ) -> bool {
+    ) -> (bool, bool) {
         let is_expected = &|res| source.is_expected(res);
         let ident_span = path.last().map_or(span, |ident| ident.ident.span);
         let typo_sugg =
@@ -889,7 +894,7 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
                 sugg_span,
                 format!("you might have meant to refer to this {}", res.descr()),
             );
-            return true;
+            return (true, true);
         }
         let mut fallback = false;
         let typo_sugg = typo_sugg.to_opt_suggestion();
@@ -915,7 +920,7 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
                 fallback = !self.let_binding_suggestion(err, ident_span);
             }
         }
-        fallback
+        (fallback, false)
     }
 
     fn err_code_special_cases(

tests/ui/resolve/issue-120559.rs

@@ -0,0 +1,5 @@
+use std::io::Read;
+
+fn f<T: Read, U, Read>() {} //~ ERROR expected trait, found type parameter `Read`
+
+fn main() {}

tests/ui/resolve/issue-120559.stderr

@@ -0,0 +1,14 @@
+error[E0404]: expected trait, found type parameter `Read`
+  --> $DIR/issue-120559.rs:3:9
+   |
+LL | use std::io::Read;
+   |              ---- you might have meant to refer to this trait
+LL |
+LL | fn f<T: Read, U, Read>() {}
+   |         ^^^^     ---- found this type parameter
+   |         |
+   |         not a trait
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0404`.

tests/ui/span/issue-35987.stderr

@@ -8,11 +8,6 @@ LL | impl<T: Clone, Add> Add for Foo<T> {
    |                ---  ^^^ not a trait
    |                |
    |                found this type parameter
-   |
-help: consider importing this trait instead
-   |
-LL + use std::ops::Add;
-   |
 
 error: aborting due to 1 previous error