Auto traits in dyn Trait + Auto are suggestable

compiler/rustc_middle/src/ty/diagnostics.rs

@@ -3,8 +3,8 @@
 use std::ops::ControlFlow;
 
 use crate::ty::{
-    visit::TypeVisitable, AliasTy, Const, ConstKind, DefIdTree, ExistentialPredicate, InferConst,
-    InferTy, Opaque, PolyTraitPredicate, Ty, TyCtxt, TypeSuperVisitable, TypeVisitor,
+    visit::TypeVisitable, AliasTy, Const, ConstKind, DefIdTree, InferConst, InferTy, Opaque,
+    PolyTraitPredicate, Ty, TyCtxt, TypeSuperVisitable, TypeVisitor,
 };
 
 use rustc_data_structures::fx::FxHashMap;
@@ -469,17 +469,6 @@ impl<'tcx> TypeVisitor<'tcx> for IsSuggestableVisitor<'tcx> {
                 }
             }
 
-            Dynamic(dty, _, _) => {
-                for pred in *dty {
-                    match pred.skip_binder() {
-                        ExistentialPredicate::Trait(_) | ExistentialPredicate::Projection(_) => {
-                            // Okay
-                        }
-                        _ => return ControlFlow::Break(()),
-                    }
-                }
-            }
-
             Param(param) => {
                 // FIXME: It would be nice to make this not use string manipulation,
                 // but it's pretty hard to do this, since `ty::ParamTy` is missing

src/test/ui/argument-suggestions/display-is-suggestable.rs

@@ -0,0 +1,8 @@
+use std::fmt::Display;
+
+fn foo(x: &(dyn Display + Send)) {}
+
+fn main() {
+    foo();
+    //~^ ERROR this function takes 1 argument but 0 arguments were supplied
+}

src/test/ui/argument-suggestions/display-is-suggestable.stderr

@@ -0,0 +1,19 @@
+error[E0061]: this function takes 1 argument but 0 arguments were supplied
+  --> $DIR/display-is-suggestable.rs:6:5
+   |
+LL |     foo();
+   |     ^^^-- an argument of type `&dyn std::fmt::Display + Send` is missing
+   |
+note: function defined here
+  --> $DIR/display-is-suggestable.rs:3:4
+   |
+LL | fn foo(x: &(dyn Display + Send)) {}
+   |    ^^^ ------------------------
+help: provide the argument
+   |
+LL |     foo(/* &dyn std::fmt::Display + Send */);
+   |        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0061`.