add test for unions and repr(transparent) with ZST fields

tests/ui/cmse-nonsecure/cmse-nonsecure-call/return-via-stack.rs

@@ -39,3 +39,22 @@ pub fn test(
     f6(); //~ ERROR [E0798]
     f7(); //~ ERROR [E0798]
 }
+
+#[repr(C)]
+pub union ReprCUnionU64 {
+    _unused: u64,
+}
+
+#[repr(Rust)]
+pub union ReprRustUnionU64 {
+    _unused: u64,
+}
+
+#[no_mangle]
+pub fn test_union(
+    f1: extern "C-cmse-nonsecure-call" fn() -> ReprRustUnionU64, //~ WARNING [improper_ctypes_definitions]
+    f2: extern "C-cmse-nonsecure-call" fn() -> ReprCUnionU64,
+) {
+    f1(); //~ ERROR [E0798]
+    f2(); //~ ERROR [E0798]
+}

tests/ui/cmse-nonsecure/cmse-nonsecure-call/return-via-stack.stderr

@@ -15,6 +15,20 @@ LL |     f7: extern "C-cmse-nonsecure-call" fn() -> i128,
    |
    = note: 128-bit integers don't currently have a known stable ABI
 
+warning: `extern` fn uses type `ReprRustUnionU64`, which is not FFI-safe
+  --> $DIR/return-via-stack.rs:55:9
+   |
+LL |     f1: extern "C-cmse-nonsecure-call" fn() -> ReprRustUnionU64,
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
+   |
+   = help: consider adding a `#[repr(C)]` or `#[repr(transparent)]` attribute to this union
+   = note: this union has unspecified layout
+note: the type is defined here
+  --> $DIR/return-via-stack.rs:49:1
+   |
+LL | pub union ReprRustUnionU64 {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^
+
 error[E0798]: return value of `C-cmse-nonsecure-call` function too large to pass via registers
   --> $DIR/return-via-stack.rs:34:5
    |
@@ -92,6 +106,28 @@ LL |     f7();
    |
    = note: functions with the `C-cmse-nonsecure-call` ABI must pass their result via the available return registers
 
-error: aborting due to 7 previous errors; 2 warnings emitted
+error[E0798]: return value of `C-cmse-nonsecure-call` function too large to pass via registers
+  --> $DIR/return-via-stack.rs:58:5
+   |
+LL |     f1: extern "C-cmse-nonsecure-call" fn() -> ReprRustUnionU64,
+   |     -- this function uses the `C-cmse-nonsecure-call` ABI
+...
+LL |     f1();
+   |     ^^^^ but its return value doesn't fit in the available registers
+   |
+   = note: functions with the `C-cmse-nonsecure-call` ABI must pass their result via the available return registers
+
+error[E0798]: return value of `C-cmse-nonsecure-call` function too large to pass via registers
+  --> $DIR/return-via-stack.rs:59:5
+   |
+LL |     f2: extern "C-cmse-nonsecure-call" fn() -> ReprCUnionU64,
+   |     -- this function uses the `C-cmse-nonsecure-call` ABI
+...
+LL |     f2();
+   |     ^^^^ but its return value doesn't fit in the available registers
+   |
+   = note: functions with the `C-cmse-nonsecure-call` ABI must pass their result via the available return registers
+
+error: aborting due to 9 previous errors; 3 warnings emitted
 
 For more information about this error, try `rustc --explain E0798`.

tests/ui/cmse-nonsecure/cmse-nonsecure-call/via-registers.rs

@@ -10,7 +10,12 @@ pub trait Copy {}
 impl Copy for u32 {}
 
 #[repr(transparent)]
-pub struct ReprTransparentStructU64(u64);
+pub struct ReprTransparentStructU64 {
+    _marker1: (),
+    _marker2: (),
+    field: u64,
+    _marker3: (),
+}
 
 #[repr(transparent)]
 pub enum ReprTransparentEnumU64 {
@@ -36,7 +41,10 @@ pub fn params(
     f3(1, 2);
     f4(1);
     f5(1.0, 2.0, 3.0);
-    f6(ReprTransparentStructU64(1), U32Compound(2, 3));
+    f6(
+        ReprTransparentStructU64 { _marker1: (), _marker2: (), field: 1, _marker3: () },
+        U32Compound(2, 3),
+    );
     f7([0xDEADBEEF; 4]);
 }