Rollup merge of #155280 - Zalathar:opaque-capture-bug, r=JonathanBrouwer

Tests for precise-capture through RPIT and TAIT

- Tests for https://github.com/rust-lang/rust/issues/155151.

These tests succeed under `-Znext-solver`, but incorrectly fail under the old trait solver.

---

The bug can be triggered via return-position `impl Trait` on stable, but requires some rather contrived code. When using type-alias `impl Trait`, it's easier to imagine the issue being triggered by real code.

tests/ui/impl-trait/rpit/precise-capture-155151.current.stderr

@@ -0,0 +1,12 @@
+error[E0381]: used binding `x` isn't initialized
+  --> $DIR/precise-capture-155151.rs:19:22
+   |
+LL |             let Foo { x } = foo;
+   |                       - binding declared here but left uninitialized
+...
+LL |             let _y = x;
+   |                      ^ `x` used here but it isn't initialized
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0381`.

tests/ui/impl-trait/rpit/precise-capture-155151.rs

@@ -0,0 +1,24 @@
+#![crate_type = "rlib"]
+//@ revisions: current next
+//@ edition: 2021
+//@[current] known-bug: #155151
+//@[current] check-fail
+//@[next] compile-flags: -Znext-solver
+//@[next] check-pass
+
+pub fn wut() -> impl Sized {
+    struct Foo { x: u32 }
+
+    if false {
+        // `foo` has an opaque type, but this function knows that it's `Foo`.
+        let foo = wut();
+        let _closure = move || {
+            let Foo { x } = foo;
+            // `x` should have been captured, but under old-solver the compiler
+            // thinks it's uninitialized here.
+            let _y = x;
+        };
+    }
+
+    Foo { x: 7 }
+}

tests/ui/type-alias-impl-trait/precise-capture-155151.current.stderr

@@ -0,0 +1,12 @@
+error[E0381]: used binding `x` isn't initialized
+  --> $DIR/precise-capture-155151.rs:20:18
+   |
+LL |         let Foo { x } = foo;
+   |                   - binding declared here but left uninitialized
+...
+LL |         let _y = x;
+   |                  ^ `x` used here but it isn't initialized
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0381`.

tests/ui/type-alias-impl-trait/precise-capture-155151.rs

@@ -0,0 +1,22 @@
+#![feature(type_alias_impl_trait)]
+//@ revisions: current next
+//@ edition: 2021
+//@[current] known-bug: #155151
+//@[current] check-fail
+//@[next] compile-flags: -Znext-solver
+//@[next] check-pass
+
+fn main() {
+    struct Foo { x: u32 }
+
+    type T = impl Sized;
+    // `foo` has an opaque type, but this function knows that it's `Foo`.
+    let foo: T = Foo { x: 7 };
+
+    let _closure = move || {
+        let Foo { x } = foo;
+        // `x` should have been captured, but under old-solver the compiler
+        // thinks it's uninitialized here.
+        let _y = x;
+    };
+}