Ignore zero-sized types in wasm future-compat warning

This commit fixes a false positive of the warning triggered for #138762
and the fix is to codify that zero-sized types are "safe" in both the
old and new ABIs.

1 files changed, 6 insertions, 0 deletions

diff --git a/tests/ui/lint/wasm_c_abi_transition.rs b/tests/ui/lint/wasm_c_abi_transition.rs
index 1fe81679e65..6a933a0de03 100644
--- a/tests/ui/lint/wasm_c_abi_transition.rs
+++ b/tests/ui/lint/wasm_c_abi_transition.rs
@@ -39,3 +39,9 @@ pub fn call_other_fun(x: MyType) {
     unsafe { other_fun(x) } //~ERROR: wasm ABI transition
     //~^WARN: previously accepted
 }
+
+// Zero-sized types are safe in both ABIs
+#[repr(C)]
+pub struct MyZstType;
+#[allow(improper_ctypes_definitions)]
+pub extern "C" fn zst_safe(_x: (), _y: MyZstType) {}