Don't suggest impl Trait in path position

Author: jieyouxu

compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs

@@ -162,10 +162,18 @@ fn fmt_printer<'a, 'tcx>(infcx: &'a InferCtxt<'tcx>, ns: Namespace) -> FmtPrinte
         let mut infcx_inner = infcx.inner.borrow_mut();
         let ty_vars = infcx_inner.type_variables();
         let var_origin = ty_vars.var_origin(ty_vid);
-        if let TypeVariableOriginKind::TypeParameterDefinition(name, _) = var_origin.kind
+        if let TypeVariableOriginKind::TypeParameterDefinition(name, def_id) = var_origin.kind
             && !var_origin.span.from_expansion()
         {
-            Some(name)
+            let generics = infcx.tcx.generics_of(infcx.tcx.parent(def_id));
+            let idx = generics.param_def_id_to_index(infcx.tcx, def_id).unwrap();
+            let generic_param_def = generics.param_at(idx as usize, infcx.tcx);
+            if let ty::GenericParamDefKind::Type { synthetic: true, .. } = generic_param_def.kind
+            {
+                None
+            } else {
+                Some(name)
+            }
         } else {
             None
         }

tests/ui/inference/need_type_info/issue-113264-incorrect-impl-trait-in-path-suggestion.rs

@@ -0,0 +1,12 @@
+trait T {}
+
+struct S {}
+
+impl S {
+    fn owo(&self, _: Option<&impl T>) {}
+}
+
+fn main() {
+    (S {}).owo(None)
+    //~^ ERROR type annotations needed
+}

tests/ui/inference/need_type_info/issue-113264-incorrect-impl-trait-in-path-suggestion.stderr

@@ -0,0 +1,14 @@
+error[E0282]: type annotations needed
+  --> $DIR/issue-113264-incorrect-impl-trait-in-path-suggestion.rs:10:16
+   |
+LL |     (S {}).owo(None)
+   |                ^^^^ cannot infer type of the type parameter `T` declared on the enum `Option`
+   |
+help: consider specifying the generic argument
+   |
+LL |     (S {}).owo(None::<&_>)
+   |                    ++++++
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0282`.