dtolnay/cxx

#[cxx::bridge] doesn't apply #[cfg(not(feature))]

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#1,299 创建于 2024年1月3日

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help wanted

描述

It looks like #[cfg(not(feature))] is ignored by #[cxx::bridge], so the marked field would always exist:

mod ffi {
    #[repr(u32)]
    enum Variant {
        #[cfg(not(feature = "v2"))]
        A,
        B,
    }
}

See this demo repo for a reproducible example.

#[cfg(not(feature))] is useful when a newer version of a C++ library dropped something, while we would like to support both new and old versions with Cargo feature flags.

贡献者指南

技术栈
rust
领域
backend
议题类型
bug
难度面向新贡献者的预计实现难度，1 表示很小改动，5 表示专家级工作。
3
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1-3 hours
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fresh
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clear
前置要求
Rust macro knowledgeUnderstanding of #[cfg]
新手友好度1-100 的估计分数，表示该议题对首次贡献者的友好程度。
50
研究方向
The issue demonstrates that #[cfg(not(feature))] is ignored by #[cxx::bridge]. The likely fix is in the macro expansion code, possibly in the `bridge` module or the enum processing logic. Investigate how the macro handles enum variants and ensure that cfg attributes are properly evaluated. The demo repo at https://github.com/hombit/cxx not feature can be used for testing.
#[cxx::bridge] doesn't apply #[cfg(not(feature))] · dtolnay/cxx#1299 | Good First Issue