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

[Qingsong Chen]

On 8/3/23 4:02 AM, Gary Guo wrote:
> On Wed,  2 Aug 2023 19:50:20 +0000
> Alice Ryhl <aliceryhl@xxxxxxxxxx> wrote:
>
> > Qingsong Chen <changxian.cqs@xxxxxxxxxxxx> 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();