Re: [PATCH 1/1] rust: macros: fix redefine const_name in `vtable`

["Qingsong Chen" <changxian.cqs@antgroup.com>]

On 8/3/23 4:02 AM, Gary Guo wrote:
> On Wed,  2 Aug 2023 19:50:20 +0000
> Alice Ryhl <aliceryhl@google.com> wrote:
> 
>> Qingsong Chen <changxian.cqs@antgroup.com> writes:
>>>      let mut body_it = body.stream().into_iter();
>>> -    let mut functions = Vec::new();
>>> +    let mut functions = HashSet::new();
>>
>> Please use a `BTreeSet` instead of a `HashSet`. A `HashSet` has
>> non-deterministic iteration order, so this will make the macro output
>> different things each time you run it.
>>
>> Alice
>>
> 
> Good point.
> 
> Another way is to just use the existing `consts` HashSet to avoid
> duplication. Something like
> 
> 	consts.insert(gen_const_name);
> 
> after emitting the const item would probably be sufficient.

According to the suggestions of Alice and Gary, we could do the fix
like this:

--- a/rust/macros/vtable.rs
+++ b/rust/macros/vtable.rs
@@ -1,7 +1,7 @@
  // SPDX-License-Identifier: GPL-2.0

  use proc_macro::{Delimiter, Group, TokenStream, TokenTree};
-use std::collections::HashSet;
+use std::collections::BTreeSet;
  use std::fmt::Write;

  pub(crate) fn vtable(_attr: TokenStream, ts: TokenStream) -> TokenStream {
@@ -28,7 +28,7 @@ pub(crate) fn vtable(_attr: TokenStream, ts: 
TokenStream) -> TokenStream {

      let mut body_it = body.stream().into_iter();
      let mut functions = Vec::new();
-    let mut consts = HashSet::new();
+    let mut consts = BTreeSet::new();
      while let Some(token) = body_it.next() {
          match token {
              TokenTree::Ident(ident) if ident.to_string() == "fn" => {
@@ -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();