tests: check that enums cannot derive Zeroable

Signed-off-by: Benno Lossin <lossin@kernel.org>

Author: BennoLossin

tests/ui/compile-fail/zeroable/enum.rs

@@ -0,0 +1,16 @@
+extern crate pin_init;
+use pin_init::*;
+
+#[derive(Zeroable)]
+enum Num {
+    A(u32),
+    B(i32),
+}
+
+#[derive(MaybeZeroable)]
+enum Num2 {
+    A(u32),
+    B(i32),
+}
+
+fn main() {}

tests/ui/compile-fail/zeroable/enum.stderr

@@ -0,0 +1,23 @@
+error: no rules expected keyword `enum`
+ --> tests/ui/compile-fail/zeroable/enum.rs:5:1
+  |
+5 | enum Num {
+  | ^^^^ no rules expected this token in macro call
+  |
+note: while trying to match keyword `struct`
+ --> src/macros.rs
+  |
+  |             $vis:vis struct $name:ident
+  |                      ^^^^^^
+
+error: no rules expected keyword `enum`
+  --> tests/ui/compile-fail/zeroable/enum.rs:11:1
+   |
+11 | enum Num2 {
+   | ^^^^ no rules expected this token in macro call
+   |
+note: while trying to match keyword `struct`
+  --> src/macros.rs
+   |
+   |             $vis:vis struct $name:ident
+   |                      ^^^^^^