[PATCH 15/18] rust: zerocopy-derive: avoid generating non-ASCII identifiers

[Miguel Ojeda <ojeda@kernel.org>]

Linux is built with `-Dnon_ascii_idents`. However, `zerocopy-derive`
uses a non-ASCII character (`ẕ`) internally, which in turn triggers
the lint when attempting to use derives like `FromBytes`:

    error: identifier contains non-ASCII characters
       --> rust/kernel/lib.rs:153:9
        |
    153 |         a: u32,
        |         ^
        |
        = note: requested on the command line with `-D non-ascii-idents`

This was already noticed by another project using
`#![deny(non_ascii_idents)]` [1]. `zerocopy` added an
`#[allow(non_ascii_idents)]` [2], but it does not work since, at the
moment, the `non_ascii_idents` lint is a `crate_level_only` one, and thus
`allow`s only work at the crate root level.

Due to this, an issue about relaxing this restriction was created in
upstream Rust [3]. So far, there have been no replies.

Thus work around it here by using another prefix. The likelihood of a
collision is very small for us, since we control the callers, and this
will hopefully be fixed soon at either the `zerocopy` or the Rust level.

Cc: Joshua Liebow-Feeser <joshlf@google.com>
Cc: Jack Wrenn <jswrenn@amazon.com>
Link: https://github.com/google/zerocopy/issues/2880 [1]
Link: https://github.com/google/zerocopy/pull/2882 [2]
Link: https://github.com/rust-lang/rust/issues/151025 [3]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
 rust/zerocopy-derive/derive/try_from_bytes.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/rust/zerocopy-derive/derive/try_from_bytes.rs b/rust/zerocopy-derive/derive/try_from_bytes.rs
index ce9c926d5b8e..a3e4a75631a5 100644
--- a/rust/zerocopy-derive/derive/try_from_bytes.rs
+++ b/rust/zerocopy-derive/derive/try_from_bytes.rs
@@ -457,7 +457,7 @@ fn derive_has_field_struct_union(ctx: &Ctx, data: &dyn DataExt) -> TokenStream {
     }
 
     let field_tokens = fields.iter().map(|(vis, ident, _)| {
-        let ident = ident!(("ẕ{}", ident), ident.span());
+        let ident = ident!(("__z{}", ident), ident.span());
         quote!(
             #vis enum #ident {}
         )
@@ -487,7 +487,7 @@ fn derive_has_field_struct_union(ctx: &Ctx, data: &dyn DataExt) -> TokenStream {
         })
         .build();
     let has_fields = fields.iter().map(move |(_, ident, ty)| {
-        let field_token = ident!(("ẕ{}", ident), ident.span());
+        let field_token = ident!(("__z{}", ident), ident.span());
         let field: Box<Type> = parse_quote!(#field_token);
         let field_id: Box<Expr> = parse_quote!({ #zerocopy_crate::ident_id!(#ident) });
         let has_field_trait = Trait::HasField {
-- 
2.54.0