[PATCH v3] rust: macros: vtable: fix `HAS_*` redefinition (`gen_const_name`)

[Qingsong Chen]

If we define the same function name twice in a trait (using `#[cfg]`),
the `vtable` macro will redefine its `gen_const_name`, e.g. this will
define `HAS_BAR` twice:

    #[vtable]
    pub trait Foo {
        #[cfg(CONFIG_X)]
        fn bar();

        #[cfg(not(CONFIG_X))]
        fn bar(x: usize);
    }

Fixes: b44becc5ee80 ("rust: macros: add `#[vtable]` proc macro")
Signed-off-by: Qingsong Chen <changxian.cqs@xxxxxxxxxxxx>
---
v1 -> v2:
- Use `BTreeSet` and existing `consts` as suggested by Alice and Gary.
- Reword commit messages as suggested by Miguel.
v2 -> v3:
- No need to replace `HashSet` with `BTreeSet`, since `consts` is never
  iterated on.

 rust/macros/vtable.rs | 1 +
 1 file changed, 1 insertion(+)

diff --git a/rust/macros/vtable.rs b/rust/macros/vtable.rs
index 34d5e7fb5768..ee06044fcd4f 100644
--- a/rust/macros/vtable.rs
+++ b/rust/macros/vtable.rs
@@ -74,6 +74,7 @@ pub(crate) fn vtable(_attr: TokenStream, ts: TokenStream) -> TokenStream {
                 const {gen_const_name}: bool = false;",
             )
             .unwrap();
+            consts.insert(gen_const_name);
         }
     } else {
         const_items = "const USE_VTABLE_ATTR: () = ();".to_owned();
-- 
2.40.1