Auto merge of #55808 - estebank:type-arguments, r=petrochenkov

Suggest correct syntax when writing type arg instead of assoc type

- When confusing an associated type with a type argument, suggest the appropriate syntax. Given `Iterator<isize>`, suggest `Iterator<Item = isize>`.
- When encountering multiple missing associated types, emit only one diagnostic.
- Point at associated type def span for context.
- Point at each extra type argument.

Follow up to #48288, fix #20977.

17 files changed, 92 insertions, 30 deletions

diff --git a/src/test/compile-fail/issue-23595-1.rs b/src/test/compile-fail/issue-23595-1.rs
index a3422d859c6..1e615c4c0db 100644
--- a/src/test/compile-fail/issue-23595-1.rs
+++ b/src/test/compile-fail/issue-23595-1.rs
@@ -16,9 +16,7 @@ trait Hierarchy {
     type Value;
     type ChildKey;
     type Children = Index<Self::ChildKey, Output=Hierarchy>;
-    //~^ ERROR: the value of the associated type `ChildKey`
-    //~^^ ERROR: the value of the associated type `Children`
-    //~^^^ ERROR: the value of the associated type `Value`
+    //~^ ERROR: the value of the associated types `Value` (from the trait `Hierarchy`), `ChildKey`
 
     fn data(&self) -> Option<(Self::Value, Self::Children)>;
 }
diff --git a/src/test/ui/associated-type/associated-type-projection-from-multiple-supertraits.stderr b/src/test/ui/associated-type/associated-type-projection-from-multiple-supertraits.stderr
index 7a10b6d021f..b4285c0de29 100644
--- a/src/test/ui/associated-type/associated-type-projection-from-multiple-supertraits.stderr
+++ b/src/test/ui/associated-type/associated-type-projection-from-multiple-supertraits.stderr
@@ -25,8 +25,11 @@ LL | fn dent_object<COLOR>(c: BoxCar<Color=COLOR>) {
 error[E0191]: the value of the associated type `Color` (from the trait `Vehicle`) must be specified
   --> $DIR/associated-type-projection-from-multiple-supertraits.rs:33:26
    |
+LL |     type Color;
+   |     ----------- `Color` defined here
+...
 LL | fn dent_object<COLOR>(c: BoxCar<Color=COLOR>) {
-   |                          ^^^^^^^^^^^^^^^^^^^ missing associated type `Color` value
+   |                          ^^^^^^^^^^^^^^^^^^^ associated type `Color` must be specified
 
 error[E0221]: ambiguous associated type `Color` in bounds of `C`
   --> $DIR/associated-type-projection-from-multiple-supertraits.rs:38:29
diff --git a/src/test/ui/associated-types/associated-types-incomplete-object.rs b/src/test/ui/associated-types/associated-types-incomplete-object.rs
index 9f1df14605b..e575fd695b2 100644
--- a/src/test/ui/associated-types/associated-types-incomplete-object.rs
+++ b/src/test/ui/associated-types/associated-types-incomplete-object.rs
@@ -37,6 +37,5 @@ pub fn main() {
     //~^ ERROR the value of the associated type `A` (from the trait `Foo`) must be specified
 
     let d = &42isize as &Foo;
-    //~^ ERROR the value of the associated type `A` (from the trait `Foo`) must be specified
-    //~| ERROR the value of the associated type `B` (from the trait `Foo`) must be specified
+    //~^ ERROR the value of the associated types `A` (from the trait `Foo`), `B` (from the trait
 }
diff --git a/src/test/ui/associated-types/associated-types-incomplete-object.stderr b/src/test/ui/associated-types/associated-types-incomplete-object.stderr
index 95b1c631250..eb8e6f998a5 100644
--- a/src/test/ui/associated-types/associated-types-incomplete-object.stderr
+++ b/src/test/ui/associated-types/associated-types-incomplete-object.stderr
@@ -1,27 +1,35 @@
 error[E0191]: the value of the associated type `B` (from the trait `Foo`) must be specified
   --> $DIR/associated-types-incomplete-object.rs:33:26
    |
+LL |     type B;
+   |     ------- `B` defined here
+...
 LL |     let b = &42isize as &Foo<A=usize>;
-   |                          ^^^^^^^^^^^^ missing associated type `B` value
+   |                          ^^^^^^^^^^^^ associated type `B` must be specified
 
 error[E0191]: the value of the associated type `A` (from the trait `Foo`) must be specified
   --> $DIR/associated-types-incomplete-object.rs:36:26
    |
+LL |     type A;
+   |     ------- `A` defined here
+...
 LL |     let c = &42isize as &Foo<B=char>;
-   |                          ^^^^^^^^^^^ missing associated type `A` value
+   |                          ^^^^^^^^^^^ associated type `A` must be specified
 
-error[E0191]: the value of the associated type `A` (from the trait `Foo`) must be specified
-  --> $DIR/associated-types-incomplete-object.rs:39:26
-   |
-LL |     let d = &42isize as &Foo;
-   |                          ^^^ missing associated type `A` value
-
-error[E0191]: the value of the associated type `B` (from the trait `Foo`) must be specified
+error[E0191]: the value of the associated types `A` (from the trait `Foo`), `B` (from the trait `Foo`) must be specified
   --> $DIR/associated-types-incomplete-object.rs:39:26
    |
+LL |     type A;
+   |     ------- `A` defined here
+LL |     type B;
+   |     ------- `B` defined here
+...
 LL |     let d = &42isize as &Foo;
-   |                          ^^^ missing associated type `B` value
+   |                          ^^^
+   |                          |
+   |                          associated type `A` must be specified
+   |                          associated type `B` must be specified
 
-error: aborting due to 4 previous errors
+error: aborting due to 3 previous errors
 
 For more information about this error, try `rustc --explain E0191`.
diff --git a/src/test/ui/error-codes/E0107.rs b/src/test/ui/error-codes/E0107.rs
index 815c7fefd2a..87ac9e37853 100644
--- a/src/test/ui/error-codes/E0107.rs
+++ b/src/test/ui/error-codes/E0107.rs
@@ -26,7 +26,8 @@ struct Baz<'a, 'b, 'c> {
     //~| unexpected lifetime argument
     foo2: Foo<'a, 'b, 'c>,
     //~^ ERROR E0107
-    //~| 2 unexpected lifetime arguments
+    //~| unexpected lifetime argument
+    //~| unexpected lifetime argument
 }
 
 fn main() {}
diff --git a/src/test/ui/error-codes/E0107.stderr b/src/test/ui/error-codes/E0107.stderr
index 497fa91bd4f..a07c92cf26a 100644
--- a/src/test/ui/error-codes/E0107.stderr
+++ b/src/test/ui/error-codes/E0107.stderr
@@ -11,10 +11,12 @@ LL |     bar: Bar<'a>,
    |              ^^ unexpected lifetime argument
 
 error[E0107]: wrong number of lifetime arguments: expected 1, found 3
-  --> $DIR/E0107.rs:27:11
+  --> $DIR/E0107.rs:27:19
    |
 LL |     foo2: Foo<'a, 'b, 'c>,
-   |           ^^^^^^^^^^^^^^^ 2 unexpected lifetime arguments
+   |                   ^^  ^^ unexpected lifetime argument
+   |                   |
+   |                   unexpected lifetime argument
 
 error: aborting due to 3 previous errors
 
diff --git a/src/test/ui/error-codes/E0191.stderr b/src/test/ui/error-codes/E0191.stderr
index 08b0a845814..f07529e7e9e 100644
--- a/src/test/ui/error-codes/E0191.stderr
+++ b/src/test/ui/error-codes/E0191.stderr
@@ -1,8 +1,11 @@
 error[E0191]: the value of the associated type `Bar` (from the trait `Trait`) must be specified
   --> $DIR/E0191.rs:15:12
    |
+LL |     type Bar;
+   |     --------- `Bar` defined here
+...
 LL | type Foo = Trait; //~ ERROR E0191
-   |            ^^^^^ missing associated type `Bar` value
+   |            ^^^^^ associated type `Bar` must be specified
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/error-codes/E0220.stderr b/src/test/ui/error-codes/E0220.stderr
index c8a587f2b53..d26e61fba8c 100644
--- a/src/test/ui/error-codes/E0220.stderr
+++ b/src/test/ui/error-codes/E0220.stderr
@@ -7,8 +7,11 @@ LL | type Foo = Trait<F=i32>; //~ ERROR E0220
 error[E0191]: the value of the associated type `Bar` (from the trait `Trait`) must be specified
   --> $DIR/E0220.rs:15:12
    |
+LL |     type Bar;
+   |     --------- `Bar` defined here
+...
 LL | type Foo = Trait<F=i32>; //~ ERROR E0220
-   |            ^^^^^^^^^^^^ missing associated type `Bar` value
+   |            ^^^^^^^^^^^^ associated type `Bar` must be specified
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/issues/issue-19482.stderr b/src/test/ui/issues/issue-19482.stderr
index 5e2d427ab72..d125438b851 100644
--- a/src/test/ui/issues/issue-19482.stderr
+++ b/src/test/ui/issues/issue-19482.stderr
@@ -1,8 +1,11 @@
 error[E0191]: the value of the associated type `A` (from the trait `Foo`) must be specified
   --> $DIR/issue-19482.rs:20:12
    |
+LL |     type A;
+   |     ------- `A` defined here
+...
 LL | fn bar(x: &Foo) {}
-   |            ^^^ missing associated type `A` value
+   |            ^^^ associated type `A` must be specified
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/issues/issue-21950.stderr b/src/test/ui/issues/issue-21950.stderr
index a2f74a29aab..33c89dd4994 100644
--- a/src/test/ui/issues/issue-21950.stderr
+++ b/src/test/ui/issues/issue-21950.stderr
@@ -10,7 +10,7 @@ error[E0191]: the value of the associated type `Output` (from the trait `std::op
   --> $DIR/issue-21950.rs:17:14
    |
 LL |             &Add;
-   |              ^^^ missing associated type `Output` value
+   |              ^^^ associated type `Output` must be specified
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/issues/issue-22434.stderr b/src/test/ui/issues/issue-22434.stderr
index 914da801ad4..3ba77346a1f 100644
--- a/src/test/ui/issues/issue-22434.stderr
+++ b/src/test/ui/issues/issue-22434.stderr
@@ -1,8 +1,11 @@
 error[E0191]: the value of the associated type `A` (from the trait `Foo`) must be specified
   --> $DIR/issue-22434.rs:15:19
    |
+LL |     type A;
+   |     ------- `A` defined here
+...
 LL | type I<'a> = &'a (Foo + 'a);
-   |                   ^^^^^^^^ missing associated type `A` value
+   |                   ^^^^^^^^ associated type `A` must be specified
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/issues/issue-22560.stderr b/src/test/ui/issues/issue-22560.stderr
index b5524036fae..715f84011f6 100644
--- a/src/test/ui/issues/issue-22560.stderr
+++ b/src/test/ui/issues/issue-22560.stderr
@@ -28,7 +28,7 @@ LL |   type Test = Add +
 LL | |             //~^ ERROR E0393
 LL | |             //~| ERROR E0191
 LL | |             Sub;
-   | |_______________^ missing associated type `Output` value
+   | |_______________^ associated type `Output` must be specified
 
 error: aborting due to 4 previous errors
 
diff --git a/src/test/ui/issues/issue-23024.stderr b/src/test/ui/issues/issue-23024.stderr
index 129d0945303..adee12a36d3 100644
--- a/src/test/ui/issues/issue-23024.stderr
+++ b/src/test/ui/issues/issue-23024.stderr
@@ -16,7 +16,7 @@ error[E0191]: the value of the associated type `Output` (from the trait `std::op
   --> $DIR/issue-23024.rs:19:35
    |
 LL |     println!("{:?}",(vfnfer[0] as Fn)(3));
-   |                                   ^^ missing associated type `Output` value
+   |                                   ^^ associated type `Output` must be specified
 
 error: aborting due to 3 previous errors
 
diff --git a/src/test/ui/issues/issue-28344.stderr b/src/test/ui/issues/issue-28344.stderr
index 7ef2e906422..734c761d0b7 100644
--- a/src/test/ui/issues/issue-28344.stderr
+++ b/src/test/ui/issues/issue-28344.stderr
@@ -2,7 +2,7 @@ error[E0191]: the value of the associated type `Output` (from the trait `std::op
   --> $DIR/issue-28344.rs:14:17
    |
 LL |     let x: u8 = BitXor::bitor(0 as u8, 0 as u8);
-   |                 ^^^^^^^^^^^^^ missing associated type `Output` value
+   |                 ^^^^^^^^^^^^^ associated type `Output` must be specified
 
 error[E0599]: no function or associated item named `bitor` found for type `dyn std::ops::BitXor<_>` in the current scope
   --> $DIR/issue-28344.rs:14:17
@@ -16,7 +16,7 @@ error[E0191]: the value of the associated type `Output` (from the trait `std::op
   --> $DIR/issue-28344.rs:18:13
    |
 LL |     let g = BitXor::bitor;
-   |             ^^^^^^^^^^^^^ missing associated type `Output` value
+   |             ^^^^^^^^^^^^^ associated type `Output` must be specified
 
 error[E0599]: no function or associated item named `bitor` found for type `dyn std::ops::BitXor<_>` in the current scope
   --> $DIR/issue-28344.rs:18:13
diff --git a/src/test/ui/suggestions/use-type-argument-instead-of-assoc-type.rs b/src/test/ui/suggestions/use-type-argument-instead-of-assoc-type.rs
new file mode 100644
index 00000000000..58e7718ba5b
--- /dev/null
+++ b/src/test/ui/suggestions/use-type-argument-instead-of-assoc-type.rs
@@ -0,0 +1,8 @@
+pub trait T<X, Y> {
+    type A;
+    type B;
+    type C;
+}
+ pub struct Foo { i: Box<T<usize, usize, usize, usize, B=usize>> }
+
+ fn main() {}
diff --git a/src/test/ui/suggestions/use-type-argument-instead-of-assoc-type.stderr b/src/test/ui/suggestions/use-type-argument-instead-of-assoc-type.stderr
new file mode 100644
index 00000000000..b62b5d3b04c
--- /dev/null
+++ b/src/test/ui/suggestions/use-type-argument-instead-of-assoc-type.stderr
@@ -0,0 +1,31 @@
+error[E0107]: wrong number of type arguments: expected 2, found 4
+  --> $DIR/use-type-argument-instead-of-assoc-type.rs:6:42
+   |
+LL |  pub struct Foo { i: Box<T<usize, usize, usize, usize, B=usize>> }
+   |                                          ^^^^^  ^^^^^ unexpected type argument
+   |                                          |
+   |                                          unexpected type argument
+
+error[E0191]: the value of the associated types `A` (from the trait `T`), `C` (from the trait `T`) must be specified
+  --> $DIR/use-type-argument-instead-of-assoc-type.rs:6:26
+   |
+LL |     type A;
+   |     ------- `A` defined here
+LL |     type B;
+LL |     type C;
+   |     ------- `C` defined here
+LL | }
+LL |  pub struct Foo { i: Box<T<usize, usize, usize, usize, B=usize>> }
+   |                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                          |
+   |                          associated type `A` must be specified
+   |                          associated type `C` must be specified
+help: if you meant to specify the associated types, write
+   |
+LL |  pub struct Foo { i: Box<T<usize, usize, A = usize, C = usize, B=usize>> }
+   |                                          ^^^^^^^^^  ^^^^^^^^^
+
+error: aborting due to 2 previous errors
+
+Some errors occurred: E0107, E0191.
+For more information about an error, try `rustc --explain E0107`.
diff --git a/src/test/ui/traits/trait-alias-object.stderr b/src/test/ui/traits/trait-alias-object.stderr
index 6b7b322a53d..fdb9427cba7 100644
--- a/src/test/ui/traits/trait-alias-object.stderr
+++ b/src/test/ui/traits/trait-alias-object.stderr
@@ -10,7 +10,7 @@ error[E0191]: the value of the associated type `Item` (from the trait `std::iter
   --> $DIR/trait-alias-object.rs:18:13
    |
 LL |     let _: &dyn IteratorAlias = &vec![123].into_iter();
-   |             ^^^^^^^^^^^^^^^^^ missing associated type `Item` value
+   |             ^^^^^^^^^^^^^^^^^ associated type `Item` must be specified
 
 error: aborting due to 2 previous errors