Rollup merge of #137637 - compiler-errors:dyn-cast-from-dyn-star, r=oli-obk

Check dyn flavor before registering upcast goal on wide pointer cast in MIR typeck

See the comment on the test :)

Fixes #137579

1 files changed, 19 insertions, 0 deletions

diff --git a/tests/ui/traits/trait-upcasting/dyn-to-dyn-star.rs b/tests/ui/traits/trait-upcasting/dyn-to-dyn-star.rs
new file mode 100644
index 00000000000..5936c93efad
--- /dev/null
+++ b/tests/ui/traits/trait-upcasting/dyn-to-dyn-star.rs
@@ -0,0 +1,19 @@
+// While somewhat nonsensical, this is a cast from a wide pointer to a thin pointer.
+// Thus, we don't need to check an unsize goal here; there isn't any vtable casting
+// happening at all.
+
+// Regression test for <https://github.com/rust-lang/rust/issues/137579>.
+
+//@ check-pass
+
+#![allow(incomplete_features)]
+#![feature(dyn_star)]
+
+trait Foo {}
+trait Bar {}
+
+fn cast(x: *const dyn Foo) {
+    x as *const dyn* Bar;
+}
+
+fn main() {}