Auto merge of #54980 - zackmdavis:and_the_case_of_the_universal_call, r=oli-obk

structured suggestion for E0223 ambiguous associated type

(routine (and when are we going to be done finding these, anyway?) but something that stuck out to me while glancing at #54970)

r? @estebank

Author: bors

Diff for: src/librustc_typeck/astconv.rs

@@ -30,7 +30,7 @@ use std::slice;
 use require_c_abi_if_variadic;
 use util::common::ErrorReported;
 use util::nodemap::FxHashMap;
-use errors::{FatalError, DiagnosticId};
+use errors::{Applicability, FatalError, DiagnosticId};
 use lint;
 
 use std::iter;
@@ -1092,11 +1092,12 @@ impl<'o, 'gcx: 'tcx, 'tcx> dyn AstConv<'gcx, 'tcx>+'o {
                                         trait_str: &str,
                                         name: &str) {
         struct_span_err!(self.tcx().sess, span, E0223, "ambiguous associated type")
-            .span_label(span, "ambiguous associated type")
-            .note(&format!("specify the type using the syntax `<{} as {}>::{}`",
-                           type_str, trait_str, name))
-            .emit();
-
+            .span_suggestion_with_applicability(
+                span,
+                "use fully-qualified syntax",
+                format!("<{} as {}>::{}", type_str, trait_str, name),
+                Applicability::HasPlaceholders
+            ).emit();
     }
 
     // Search for a bound on a type parameter which includes the associated item

Diff for: src/test/ui/associated-types/associated-types-in-ambiguous-context.stderr

@@ -2,25 +2,19 @@ error[E0223]: ambiguous associated type
   --> $DIR/associated-types-in-ambiguous-context.rs:16:36
    |
 LL | fn get<T:Get,U:Get>(x: T, y: U) -> Get::Value {}
-   |                                    ^^^^^^^^^^ ambiguous associated type
-   |
-   = note: specify the type using the syntax `<Type as Get>::Value`
+   |                                    ^^^^^^^^^^ help: use fully-qualified syntax: `<Type as Get>::Value`
 
 error[E0223]: ambiguous associated type
   --> $DIR/associated-types-in-ambiguous-context.rs:25:10
    |
 LL | type X = std::ops::Deref::Target;
-   |          ^^^^^^^^^^^^^^^^^^^^^^^ ambiguous associated type
-   |
-   = note: specify the type using the syntax `<Type as std::ops::Deref>::Target`
+   |          ^^^^^^^^^^^^^^^^^^^^^^^ help: use fully-qualified syntax: `<Type as std::ops::Deref>::Target`
 
 error[E0223]: ambiguous associated type
   --> $DIR/associated-types-in-ambiguous-context.rs:21:23
    |
 LL |     fn grab(&self) -> Grab::Value;
-   |                       ^^^^^^^^^^^ ambiguous associated type
-   |
-   = note: specify the type using the syntax `<Type as Grab>::Value`
+   |                       ^^^^^^^^^^^ help: use fully-qualified syntax: `<Type as Grab>::Value`
 
 error: aborting due to 3 previous errors
 

Diff for: src/test/ui/did_you_mean/bad-assoc-ty.stderr

@@ -44,33 +44,25 @@ error[E0223]: ambiguous associated type
   --> $DIR/bad-assoc-ty.rs:11:10
    |
 LL | type A = [u8; 4]::AssocTy;
-   |          ^^^^^^^^^^^^^^^^ ambiguous associated type
-   |
-   = note: specify the type using the syntax `<[u8; _] as Trait>::AssocTy`
+   |          ^^^^^^^^^^^^^^^^ help: use fully-qualified syntax: `<[u8; _] as Trait>::AssocTy`
 
 error[E0223]: ambiguous associated type
   --> $DIR/bad-assoc-ty.rs:15:10
    |
 LL | type B = [u8]::AssocTy;
-   |          ^^^^^^^^^^^^^ ambiguous associated type
-   |
-   = note: specify the type using the syntax `<[u8] as Trait>::AssocTy`
+   |          ^^^^^^^^^^^^^ help: use fully-qualified syntax: `<[u8] as Trait>::AssocTy`
 
 error[E0223]: ambiguous associated type
   --> $DIR/bad-assoc-ty.rs:19:10
    |
 LL | type C = (u8)::AssocTy;
-   |          ^^^^^^^^^^^^^ ambiguous associated type
-   |
-   = note: specify the type using the syntax `<u8 as Trait>::AssocTy`
+   |          ^^^^^^^^^^^^^ help: use fully-qualified syntax: `<u8 as Trait>::AssocTy`
 
 error[E0223]: ambiguous associated type
   --> $DIR/bad-assoc-ty.rs:23:10
    |
 LL | type D = (u8, u8)::AssocTy;
-   |          ^^^^^^^^^^^^^^^^^ ambiguous associated type
-   |
-   = note: specify the type using the syntax `<(u8, u8) as Trait>::AssocTy`
+   |          ^^^^^^^^^^^^^^^^^ help: use fully-qualified syntax: `<(u8, u8) as Trait>::AssocTy`
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
   --> $DIR/bad-assoc-ty.rs:27:10
@@ -82,25 +74,19 @@ error[E0223]: ambiguous associated type
   --> $DIR/bad-assoc-ty.rs:31:19
    |
 LL | type F = &'static (u8)::AssocTy;
-   |                   ^^^^^^^^^^^^^ ambiguous associated type
-   |
-   = note: specify the type using the syntax `<u8 as Trait>::AssocTy`
+   |                   ^^^^^^^^^^^^^ help: use fully-qualified syntax: `<u8 as Trait>::AssocTy`
 
 error[E0223]: ambiguous associated type
   --> $DIR/bad-assoc-ty.rs:37:10
    |
 LL | type G = 'static + (Send)::AssocTy;
-   |          ^^^^^^^^^^^^^^^^^^^^^^^^^ ambiguous associated type
-   |
-   = note: specify the type using the syntax `<(dyn std::marker::Send + 'static) as Trait>::AssocTy`
+   |          ^^^^^^^^^^^^^^^^^^^^^^^^^ help: use fully-qualified syntax: `<(dyn std::marker::Send + 'static) as Trait>::AssocTy`
 
 error[E0223]: ambiguous associated type
   --> $DIR/bad-assoc-ty.rs:43:10
    |
 LL | type H = Fn(u8) -> (u8)::Output;
-   |          ^^^^^^^^^^^^^^^^^^^^^^ ambiguous associated type
-   |
-   = note: specify the type using the syntax `<(dyn std::ops::Fn(u8) -> u8 + 'static) as Trait>::Output`
+   |          ^^^^^^^^^^^^^^^^^^^^^^ help: use fully-qualified syntax: `<(dyn std::ops::Fn(u8) -> u8 + 'static) as Trait>::Output`
 
 error: aborting due to 15 previous errors
 

Diff for: src/test/ui/error-codes/E0223.stderr

@@ -2,9 +2,7 @@ error[E0223]: ambiguous associated type
   --> $DIR/E0223.rs:14:14
    |
 LL |     let foo: MyTrait::X;
-   |              ^^^^^^^^^^ ambiguous associated type
-   |
-   = note: specify the type using the syntax `<Type as MyTrait>::X`
+   |              ^^^^^^^^^^ help: use fully-qualified syntax: `<Type as MyTrait>::X`
 
 error: aborting due to previous error
 

Diff for: src/test/ui/impl-trait/impl_trait_projections.stderr

@@ -26,9 +26,7 @@ error[E0223]: ambiguous associated type
   --> $DIR/impl_trait_projections.rs:21:50
    |
 LL | fn projection_is_disallowed(x: impl Iterator) -> <impl Iterator>::Item {
-   |                                                  ^^^^^^^^^^^^^^^^^^^^^ ambiguous associated type
-   |
-   = note: specify the type using the syntax `<impl std::iter::Iterator as Trait>::Item`
+   |                                                  ^^^^^^^^^^^^^^^^^^^^^ help: use fully-qualified syntax: `<impl std::iter::Iterator as Trait>::Item`
 
 error: aborting due to 5 previous errors
 

Diff for: src/test/ui/issues/issue-23073.stderr

@@ -2,9 +2,7 @@ error[E0223]: ambiguous associated type
   --> $DIR/issue-23073.rs:16:17
    |
 LL |     type FooT = <<Self as Bar>::Foo>::T; //~ ERROR ambiguous associated type
-   |                 ^^^^^^^^^^^^^^^^^^^^^^^ ambiguous associated type
-   |
-   = note: specify the type using the syntax `<<Self as Bar>::Foo as Trait>::T`
+   |                 ^^^^^^^^^^^^^^^^^^^^^^^ help: use fully-qualified syntax: `<<Self as Bar>::Foo as Trait>::T`
 
 error: aborting due to previous error
 

Diff for: src/test/ui/issues/issue-34209.stderr

@@ -2,9 +2,7 @@ error[E0223]: ambiguous associated type
   --> $DIR/issue-34209.rs:17:9
    |
 LL |         S::B{ } => { },
-   |         ^^^^ ambiguous associated type
-   |
-   = note: specify the type using the syntax `<S as Trait>::B`
+   |         ^^^^ help: use fully-qualified syntax: `<S as Trait>::B`
 
 error: aborting due to previous error
 

Diff for: src/test/ui/qualified/qualified-path-params-2.stderr

@@ -8,9 +8,7 @@ error[E0223]: ambiguous associated type
   --> $DIR/qualified-path-params-2.rs:28:10
    |
 LL | type A = <S as Tr>::A::f<u8>;
-   |          ^^^^^^^^^^^^^^^^^^^ ambiguous associated type
-   |
-   = note: specify the type using the syntax `<<S as Tr>::A as Trait>::f`
+   |          ^^^^^^^^^^^^^^^^^^^ help: use fully-qualified syntax: `<<S as Tr>::A as Trait>::f`
 
 error: aborting due to 2 previous errors
 

Diff for: src/test/ui/self/self-impl.stderr

@@ -2,17 +2,13 @@ error[E0223]: ambiguous associated type
   --> $DIR/self-impl.rs:33:16
    |
 LL |         let _: <Self>::Baz = true;
-   |                ^^^^^^^^^^^ ambiguous associated type
-   |
-   = note: specify the type using the syntax `<Bar as Trait>::Baz`
+   |                ^^^^^^^^^^^ help: use fully-qualified syntax: `<Bar as Trait>::Baz`
 
 error[E0223]: ambiguous associated type
   --> $DIR/self-impl.rs:35:16
    |
 LL |         let _: Self::Baz = true;
-   |                ^^^^^^^^^ ambiguous associated type
-   |
-   = note: specify the type using the syntax `<Bar as Trait>::Baz`
+   |                ^^^^^^^^^ help: use fully-qualified syntax: `<Bar as Trait>::Baz`
 
 error: aborting due to 2 previous errors
 

Diff for: src/test/ui/structs/struct-path-associated-type.stderr

@@ -32,9 +32,7 @@ error[E0223]: ambiguous associated type
   --> $DIR/struct-path-associated-type.rs:42:13
    |
 LL |     let s = S::A {}; //~ ERROR ambiguous associated type
-   |             ^^^^ ambiguous associated type
-   |
-   = note: specify the type using the syntax `<S as Trait>::A`
+   |             ^^^^ help: use fully-qualified syntax: `<S as Trait>::A`
 
 error[E0109]: type parameters are not allowed on this type
   --> $DIR/struct-path-associated-type.rs:43:20
@@ -46,17 +44,13 @@ error[E0223]: ambiguous associated type
   --> $DIR/struct-path-associated-type.rs:43:13
    |
 LL |     let z = S::A::<u8> {}; //~ ERROR ambiguous associated type
-   |             ^^^^^^^^^^ ambiguous associated type
-   |
-   = note: specify the type using the syntax `<S as Trait>::A`
+   |             ^^^^^^^^^^ help: use fully-qualified syntax: `<S as Trait>::A`
 
 error[E0223]: ambiguous associated type
   --> $DIR/struct-path-associated-type.rs:46:9
    |
 LL |         S::A {} => {} //~ ERROR ambiguous associated type
-   |         ^^^^ ambiguous associated type
-   |
-   = note: specify the type using the syntax `<S as Trait>::A`
+   |         ^^^^ help: use fully-qualified syntax: `<S as Trait>::A`
 
 error: aborting due to 9 previous errors
 

Diff for: src/test/ui/traits/trait-item-privacy.stderr

@@ -138,25 +138,19 @@ error[E0223]: ambiguous associated type
   --> $DIR/trait-item-privacy.rs:127:12
    |
 LL |     let _: S::A; //~ ERROR ambiguous associated type
-   |            ^^^^ ambiguous associated type
-   |
-   = note: specify the type using the syntax `<S as Trait>::A`
+   |            ^^^^ help: use fully-qualified syntax: `<S as Trait>::A`
 
 error[E0223]: ambiguous associated type
   --> $DIR/trait-item-privacy.rs:128:12
    |
 LL |     let _: S::B; //~ ERROR ambiguous associated type
-   |            ^^^^ ambiguous associated type
-   |
-   = note: specify the type using the syntax `<S as Trait>::B`
+   |            ^^^^ help: use fully-qualified syntax: `<S as Trait>::B`
 
 error[E0223]: ambiguous associated type
   --> $DIR/trait-item-privacy.rs:129:12
    |
 LL |     let _: S::C; //~ ERROR ambiguous associated type
-   |            ^^^^ ambiguous associated type
-   |
-   = note: specify the type using the syntax `<S as Trait>::C`
+   |            ^^^^ help: use fully-qualified syntax: `<S as Trait>::C`
 
 error: associated type `A` is private
   --> $DIR/trait-item-privacy.rs:131:12

Diff for: src/test/ui/ufcs/ufcs-partially-resolved.stderr

@@ -184,9 +184,7 @@ error[E0223]: ambiguous associated type
   --> $DIR/ufcs-partially-resolved.rs:46:12
    |
 LL |     let _: <u8 as Tr>::Y::NN; //~ ERROR ambiguous associated type
-   |            ^^^^^^^^^^^^^^^^^ ambiguous associated type
-   |
-   = note: specify the type using the syntax `<<u8 as Tr>::Y as Trait>::NN`
+   |            ^^^^^^^^^^^^^^^^^ help: use fully-qualified syntax: `<<u8 as Tr>::Y as Trait>::NN`
 
 error[E0599]: no associated item named `NN` found for type `<u8 as Tr>::Y` in the current scope
   --> $DIR/ufcs-partially-resolved.rs:48:5