Unrolled build for #158454

Rollup merge of #158454 - Albab-Hasan:fix-restrict-bound-double-angle, r=folkertdev

regression test for `Trait<A><B>` in "consider further restricting this bound" suggestion

when a bound already has generic args (e.g. `impl Pair<Left = A>`) the "consider further restricting this bound" suggestion would generate invalid syntax by appending a new `<Right = B>` producing `Pair<Left = A><Right = B>`.

the fix detects when the insertion point immediately follows a `>` and merges into the existing arg list instead producing the valid `Pair<Left = A, Right = B>`.

fixes #142803

Author: rust-timer

tests/ui/suggestions/restrict-bound-already-has-generic-args.rs

@@ -0,0 +1,27 @@
+// Regression test for https://github.com/rust-lang/rust/issues/142803.
+
+trait Pair {
+    type Left;
+    type Right;
+
+    fn split(self) -> (Self::Left, Self::Right);
+}
+
+impl<A, B> Pair for (A, B) {
+    type Left = A;
+    type Right = B;
+
+    fn split(self) -> (Self::Left, Self::Right) {
+        self
+    }
+}
+
+fn frob<A, B>(pair: impl Pair<Left = A>) -> impl Pair<Left = A, Right = B> {
+    //~^ ERROR type mismatch
+    //~| HELP consider further restricting this bound
+    //~| SUGGESTION , Right = B
+    let (left, right) = pair.split();
+    (left, right)
+}
+
+fn main() {}

tests/ui/suggestions/restrict-bound-already-has-generic-args.stderr

@@ -0,0 +1,24 @@
+error[E0271]: type mismatch resolving `<(A, <impl Pair<Left = A> as Pair>::Right) as Pair>::Right == B`
+  --> $DIR/restrict-bound-already-has-generic-args.rs:19:45
+   |
+LL | fn frob<A, B>(pair: impl Pair<Left = A>) -> impl Pair<Left = A, Right = B> {
+   |            - expected this type parameter   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type mismatch resolving `<(A, <impl Pair<Left = A> as Pair>::Right) as Pair>::Right == B`
+...
+LL |     (left, right)
+   |     ------------- return type was inferred to be `(A, <impl Pair<Left = A> as Pair>::Right)` here
+   |
+note: expected this to be `B`
+  --> $DIR/restrict-bound-already-has-generic-args.rs:12:18
+   |
+LL |     type Right = B;
+   |                  ^
+   = note: expected type parameter `B`
+             found associated type `<impl Pair<Left = A> as Pair>::Right`
+help: consider further restricting this bound
+   |
+LL | fn frob<A, B>(pair: impl Pair<Left = A, Right = B>) -> impl Pair<Left = A, Right = B> {
+   |                                       +++++++++++
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0271`.