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54: Detect if the proc_macro_def_site feature is not disallowed by -Zallow-features r=taiki-e a=taiki-e Apart from what I mentioned in #53 (comment), there are cases where you want to completely avoid using the nightly function in the first place. Refs: dtolnay/proc-macro2#175 Co-authored-by: Taiki Endo <te316e89@gmail.com>
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.DS_Store | ||
.idea/ | ||
.vscode/ | ||
target/ | ||
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// Based on https://stackoverflow.com/a/49250753/1290530 | ||
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use std::env; | ||
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use rustc_version::{version_meta, Channel}; | ||
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fn main() { | ||
// Set cfg flags depending on release channel | ||
match version_meta().unwrap().channel { | ||
// Enable our feature on nightly, or when using a | ||
// locally build rustc | ||
Channel::Nightly | Channel::Dev => { | ||
println!("cargo:rustc-cfg=feature=\"RUSTC_IS_NIGHTLY\""); | ||
// locally build rustc, unless `-Zallow-features` | ||
// in RUSTFLAGS disallows unstable features. | ||
Channel::Nightly | Channel::Dev if feature_allowed("proc_macro_def_site") => { | ||
println!("cargo:rustc-cfg=proc_macro_def_site"); | ||
} | ||
_ => {} | ||
} | ||
} | ||
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// Based on https://github.com/alexcrichton/proc-macro2/pull/176 | ||
fn feature_allowed(feature: &str) -> bool { | ||
if let Some(rustflags) = env::var_os("RUSTFLAGS") { | ||
for mut flag in rustflags.to_string_lossy().split(' ') { | ||
if flag.starts_with("-Z") { | ||
flag = &flag["-Z".len()..]; | ||
} | ||
if flag.starts_with("allow-features=") { | ||
flag = &flag["allow-features=".len()..]; | ||
return flag.split(',').any(|allowed| allowed == feature); | ||
} | ||
} | ||
} | ||
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// No allow-features= flag, allowed by default. | ||
true | ||
} |
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