Add regression and bug tests

src/test/ui/type-alias-impl-trait/cross_inference.rs

@@ -0,0 +1,10 @@
+// check-pass
+
+#![feature(type_alias_impl_trait)]
+
+fn main() {
+    type T = impl Copy;
+    let foo: T = (1u32, 2u32);
+    let x: (_, _) = foo;
+    println!("{:?}", x);
+}

src/test/ui/type-alias-impl-trait/cross_inference_pattern_bug.rs

@@ -0,0 +1,24 @@
+// known-bug
+// failure-status: 101
+// compile-flags: --edition=2021 --crate-type=lib
+// rustc-env:RUST_BACKTRACE=0
+
+// normalize-stderr-test "thread 'rustc' panicked.*" -> "thread 'rustc' panicked"
+// normalize-stderr-test "note:.*RUST_BACKTRACE=1.*\n" -> ""
+// normalize-stderr-test "\nerror: internal compiler error.*\n\n" -> ""
+// normalize-stderr-test "note:.*unexpectedly panicked.*\n\n" -> ""
+// normalize-stderr-test "note: we would appreciate a bug report.*\n\n" -> ""
+// normalize-stderr-test "note: compiler flags.*\n\n" -> ""
+// normalize-stderr-test "note: rustc.*running on.*\n\n" -> ""
+// normalize-stderr-test "#.*\n" -> ""
+// normalize-stderr-test ".*delayed.*\n" -> ""
+
+// tracked in https://github.com/rust-lang/rust/issues/96572
+
+#![feature(type_alias_impl_trait)]
+
+fn main() {
+    type T = impl Copy;
+    let foo: T = (1u32, 2u32);
+    let (a, b): (u32, u32) = foo;
+}

src/test/ui/type-alias-impl-trait/cross_inference_pattern_bug.stderr

@@ -0,0 +1,32 @@
+error: internal compiler error: no errors encountered even though `delay_span_bug` issued
+
+error: internal compiler error: broken MIR in DefId(0:3 ~ cross_inference_pattern_bug[646d]::main) ((_1.0: u32)): can't project out of PlaceTy { ty: main::T, variant_index: None }
+  --> $DIR/cross_inference_pattern_bug.rs:23:10
+   |
+LL |     let (a, b): (u32, u32) = foo;
+   |          ^
+   |
+
+error: internal compiler error: TyKind::Error constructed but no error reported
+   |
+
+error: internal compiler error: TyKind::Error constructed but no error reported
+   |
+
+error: internal compiler error: broken MIR in DefId(0:3 ~ cross_inference_pattern_bug[646d]::main) ((_1.1: u32)): can't project out of PlaceTy { ty: main::T, variant_index: None }
+  --> $DIR/cross_inference_pattern_bug.rs:23:13
+   |
+LL |     let (a, b): (u32, u32) = foo;
+   |             ^
+   |
+
+error: internal compiler error: TyKind::Error constructed but no error reported
+   |
+
+error: internal compiler error: TyKind::Error constructed but no error reported
+   |
+
+thread 'rustc' panicked
+
+query stack during panic:
+end of query stack

src/test/ui/type-alias-impl-trait/cross_inference_pattern_bug_no_type.rs

@@ -0,0 +1,13 @@
+// known-bug
+// compile-flags: --edition=2021 --crate-type=lib
+// rustc-env:RUST_BACKTRACE=0
+
+// tracked in https://github.com/rust-lang/rust/issues/96572
+
+#![feature(type_alias_impl_trait)]
+
+fn main() {
+    type T = impl Copy;  // error: unconstrained opaque type
+    let foo: T = (1u32, 2u32);
+    let (a, b) = foo; // removing this line makes the code compile
+}

src/test/ui/type-alias-impl-trait/cross_inference_pattern_bug_no_type.stderr

@@ -0,0 +1,10 @@
+error: unconstrained opaque type
+  --> $DIR/cross_inference_pattern_bug_no_type.rs:10:14
+   |
+LL |     type T = impl Copy;  // error: unconstrained opaque type
+   |              ^^^^^^^^^
+   |
+   = note: `T` must be used in combination with a concrete type within the same module
+
+error: aborting due to previous error
+

src/test/ui/type-alias-impl-trait/cross_inference_rpit.rs

@@ -0,0 +1,14 @@
+// check-pass
+
+fn foo(b: bool) -> impl Copy {
+    if b {
+        return (5,6)
+    }
+    let x: (_, _) = foo(true);
+    println!("{:?}", x);
+    (1u32, 2u32)
+}
+
+fn main() {
+    foo(false);
+}