test marcro ordering

Signed-off-by: Ahmed Abdelraoof <ahmed.abdelraoof@huawei.com>

Author: Ahmed Abdelraoof

safe-discriminant-derive/src/lib.rs

@@ -148,3 +148,10 @@ pub fn remove_repr(_: TokenStream, item: TokenStream) -> TokenStream {
 pub fn repr(_: TokenStream, item: TokenStream) -> TokenStream {
     item
 }
+
+#[cfg(feature = "test-utils")]
+/// exactly as the name suggests!
+#[proc_macro_attribute]
+pub fn do_nothing(_: TokenStream, item: TokenStream) -> TokenStream {
+    item
+}

safe-discriminant/tests/fail/do_nothing_last.rs

@@ -0,0 +1,12 @@
+use safe_discriminant::Discriminant;
+use safe_discriminant_derive::do_nothing;
+
+#[repr(u8)]
+#[derive(Discriminant)]
+#[do_nothing]
+pub enum Foo {
+    A = 0,
+    B = 1,
+}
+
+fn main() {}

safe-discriminant/tests/fail/do_nothing_last.stderr

@@ -0,0 +1,5 @@
+error: Discriminant is not compatiable with any top level `#[attr]` except `#[repr(_)]`.
+ --> tests/fail/do_nothing_last.rs:7:10
+  |
+7 | pub enum Foo {
+  |          ^^^

safe-discriminant/tests/pass/do_nothing_first.rs

@@ -0,0 +1,15 @@
+use safe_discriminant::Discriminant;
+use safe_discriminant_derive::do_nothing;
+
+#[do_nothing]
+#[repr(u8)]
+#[derive(Discriminant)]
+pub enum Foo {
+    A = 0,
+    B = 1,
+}
+
+fn main() {
+    assert_eq!(Foo::A.discriminant(), 0);
+    assert_eq!(Foo::B.discriminant(), 1);
+}