Rollup merge of #102338 - compiler-errors:assoc-ty-binding-in-assoc-ty-binding, r=cjgillot

Deny associated type bindings within associated type bindings

Fixes #102335

This was made worse by #100865, which unified the way we generate substs for GATs and non-generic associated types. However, the issue was not _caused_ by #100865, evidenced by the test I added for GATs:

```rust
trait T {
    type A: S<C<(), i32 = ()> = ()>;
    //~^ ERROR associated type bindings are not allowed here
}

trait Q {}

trait S {
    type C<T>: Q;
}

fn main() {}
```

^ which passes on beta (where GATs are stable) and presumably ever since GATs support was added to `create_substs_for_associated_item` in astconv.

8 files changed, 73 insertions, 2 deletions

diff --git a/src/test/ui/associated-consts/issue-102335-const.rs b/src/test/ui/associated-consts/issue-102335-const.rs
new file mode 100644
index 00000000000..f60cb92da7f
--- /dev/null
+++ b/src/test/ui/associated-consts/issue-102335-const.rs
@@ -0,0 +1,12 @@
+#![feature(associated_const_equality)]
+
+trait T {
+    type A: S<C<X = 0i32> = 34>;
+    //~^ ERROR associated type bindings are not allowed here
+}
+
+trait S {
+    const C: i32;
+}
+
+fn main() {}
diff --git a/src/test/ui/associated-consts/issue-102335-const.stderr b/src/test/ui/associated-consts/issue-102335-const.stderr
new file mode 100644
index 00000000000..531d15c5900
--- /dev/null
+++ b/src/test/ui/associated-consts/issue-102335-const.stderr
@@ -0,0 +1,9 @@
+error[E0229]: associated type bindings are not allowed here
+  --> $DIR/issue-102335-const.rs:4:17
+   |
+LL |     type A: S<C<X = 0i32> = 34>;
+   |                 ^^^^^^^^ associated type not allowed here
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0229`.
diff --git a/src/test/ui/associated-type-bounds/issue-102335-ty.rs b/src/test/ui/associated-type-bounds/issue-102335-ty.rs
new file mode 100644
index 00000000000..363df73c1ff
--- /dev/null
+++ b/src/test/ui/associated-type-bounds/issue-102335-ty.rs
@@ -0,0 +1,12 @@
+trait T {
+    type A: S<C<i32 = u32> = ()>;
+    //~^ ERROR associated type bindings are not allowed here
+}
+
+trait Q {}
+
+trait S {
+    type C: Q;
+}
+
+fn main() {}
diff --git a/src/test/ui/associated-type-bounds/issue-102335-ty.stderr b/src/test/ui/associated-type-bounds/issue-102335-ty.stderr
new file mode 100644
index 00000000000..8777b296515
--- /dev/null
+++ b/src/test/ui/associated-type-bounds/issue-102335-ty.stderr
@@ -0,0 +1,9 @@
+error[E0229]: associated type bindings are not allowed here
+  --> $DIR/issue-102335-ty.rs:2:17
+   |
+LL |     type A: S<C<i32 = u32> = ()>;
+   |                 ^^^^^^^^^ associated type not allowed here
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0229`.
diff --git a/src/test/ui/generic-associated-types/issue-102335-gat.rs b/src/test/ui/generic-associated-types/issue-102335-gat.rs
new file mode 100644
index 00000000000..a7255fdcbf5
--- /dev/null
+++ b/src/test/ui/generic-associated-types/issue-102335-gat.rs
@@ -0,0 +1,12 @@
+trait T {
+    type A: S<C<(), i32 = ()> = ()>;
+    //~^ ERROR associated type bindings are not allowed here
+}
+
+trait Q {}
+
+trait S {
+    type C<T>: Q;
+}
+
+fn main() {}
diff --git a/src/test/ui/generic-associated-types/issue-102335-gat.stderr b/src/test/ui/generic-associated-types/issue-102335-gat.stderr
new file mode 100644
index 00000000000..7a7900a1e65
--- /dev/null
+++ b/src/test/ui/generic-associated-types/issue-102335-gat.stderr
@@ -0,0 +1,9 @@
+error[E0229]: associated type bindings are not allowed here
+  --> $DIR/issue-102335-gat.rs:2:21
+   |
+LL |     type A: S<C<(), i32 = ()> = ()>;
+   |                     ^^^^^^^^ associated type not allowed here
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0229`.
diff --git a/src/test/ui/suggestions/issue-85347.rs b/src/test/ui/suggestions/issue-85347.rs
index dd52b315055..02b5fb61894 100644
--- a/src/test/ui/suggestions/issue-85347.rs
+++ b/src/test/ui/suggestions/issue-85347.rs
@@ -2,6 +2,7 @@ use std::ops::Deref;
 trait Foo {
     type Bar<'a>: Deref<Target = <Self>::Bar<Target = Self>>;
     //~^ ERROR this associated type takes 1 lifetime argument but 0 lifetime arguments were supplied
+    //~| ERROR associated type bindings are not allowed here
     //~| HELP add missing
 }
 
diff --git a/src/test/ui/suggestions/issue-85347.stderr b/src/test/ui/suggestions/issue-85347.stderr
index de853de27e4..17c1b7dc4cc 100644
--- a/src/test/ui/suggestions/issue-85347.stderr
+++ b/src/test/ui/suggestions/issue-85347.stderr
@@ -14,6 +14,13 @@ help: add missing lifetime argument
 LL |     type Bar<'a>: Deref<Target = <Self>::Bar<'a, Target = Self>>;
    |                                              +++
 
-error: aborting due to previous error
+error[E0229]: associated type bindings are not allowed here
+  --> $DIR/issue-85347.rs:3:46
+   |
+LL |     type Bar<'a>: Deref<Target = <Self>::Bar<Target = Self>>;
+   |                                              ^^^^^^^^^^^^^ associated type not allowed here
+
+error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0107`.
+Some errors have detailed explanations: E0107, E0229.
+For more information about an error, try `rustc --explain E0107`.