add regression test

tests/ui/abi/issue-94223.rs

@@ -1,8 +0,0 @@
-// check-pass
-#![allow(improper_ctypes_definitions)]
-#![crate_type = "lib"]
-
-// Check that computing the fn abi for `bad`, with a external ABI fn ptr that is not FFI-safe, does
-// not ICE.
-
-pub fn bad(f: extern "C" fn([u8])) {}

tests/ui/abi/unsized-args-in-c-abi-issues-94223-115845.rs

@@ -0,0 +1,30 @@
+// check-pass
+#![allow(improper_ctypes_definitions)]
+#![feature(unsized_tuple_coercion)]
+#![feature(unsized_fn_params)]
+#![crate_type = "lib"]
+
+// Check that computing the fn abi for `bad`, with a external ABI fn ptr that is not FFI-safe, does
+// not ICE.
+
+pub fn bad(f: extern "C" fn([u8])) {}
+
+// While these get accepted, they should also not ICE.
+// (If we ever reject them, remove them from this test to ensure the `bad` above
+// is still tested. Do *not* make this a check/build-fail test.)
+
+pub extern "C" fn declare_bad(_x: str) {}
+
+#[no_mangle]
+pub extern "system" fn declare_more_bad(f: dyn FnOnce()) {
+}
+
+fn make_bad() -> extern "C" fn(([u8],)) {
+    todo!()
+}
+
+pub fn call_bad() {
+    let f = make_bad();
+    let slice: Box<([u8],)> = Box::new(([1; 8],));
+    f(*slice);
+}