Rollup merge of #104508 - compiler-errors:dyn-return, r=oli-obk

Check `dyn*` return type correctly

In `check_fn`, if the declared return type is `dyn Trait`, then we check the return type separately to produce better diagnostics, because this is never valid -- however, when `dyn*` was introduced, this check was never adjusted to only account for *unsized* `dyn Trait` and not *sized* `dyn* Trait`.

Fixes #104501

2 files changed, 21 insertions, 0 deletions

diff --git a/src/test/ui/dyn-star/return.rs b/src/test/ui/dyn-star/return.rs
new file mode 100644
index 00000000000..fa3d8d7d506
--- /dev/null
+++ b/src/test/ui/dyn-star/return.rs
@@ -0,0 +1,10 @@
+// check-pass
+
+#![feature(dyn_star)]
+//~^ WARN the feature `dyn_star` is incomplete and may not be safe to use and/or cause compiler crashes
+
+fn _foo() -> dyn* Unpin {
+    4usize
+}
+
+fn main() {}
diff --git a/src/test/ui/dyn-star/return.stderr b/src/test/ui/dyn-star/return.stderr
new file mode 100644
index 00000000000..e000351a68f
--- /dev/null
+++ b/src/test/ui/dyn-star/return.stderr
@@ -0,0 +1,11 @@
+warning: the feature `dyn_star` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/return.rs:3:12
+   |
+LL | #![feature(dyn_star)]
+   |            ^^^^^^^^
+   |
+   = note: see issue #91611 <https://github.com/rust-lang/rust/issues/91611> for more information
+   = note: `#[warn(incomplete_features)]` on by default
+
+warning: 1 warning emitted
+