Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 37 insertions, 0 deletions

diff --git a/src/test/ui/never_type/diverging-fallback-unconstrained-return.rs b/src/test/ui/never_type/diverging-fallback-unconstrained-return.rs
new file mode 100644
index 000000000..7ea97126f
--- /dev/null
+++ b/src/test/ui/never_type/diverging-fallback-unconstrained-return.rs
@@ -0,0 +1,37 @@
+// Variant of diverging-falllback-control-flow that tests
+// the specific case of a free function with an unconstrained
+// return type. This captures the pattern we saw in the wild
+// in the objc crate, where changing the fallback from `!` to `()`
+// resulted in unsoundness.
+//
+// check-pass
+
+// revisions: nofallback fallback
+
+#![cfg_attr(fallback, feature(never_type, never_type_fallback))]
+
+
+fn make_unit() {}
+
+trait UnitReturn {}
+impl UnitReturn for i32 {}
+impl UnitReturn for () {}
+
+fn unconstrained_return<T: UnitReturn>() -> T {
+    unsafe {
+        let make_unit_fn: fn() = make_unit;
+        let ffi: fn() -> T = std::mem::transmute(make_unit_fn);
+        ffi()
+    }
+}
+
+fn main() {
+    // In Ye Olde Days, the `T` parameter of `unconstrained_return`
+    // winds up "entangled" with the `!` type that results from
+    // `panic!`, and hence falls back to `()`. This is kind of unfortunate
+    // and unexpected. When we introduced the `!` type, the original
+    // idea was to change that fallback to `!`, but that would have resulted
+    // in this code no longer compiling (or worse, in some cases it injected
+    // unsound results).
+    let _ = if true { unconstrained_return() } else { panic!() };
+}