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|
// rustc-cfg emitted by the build script:
//
// "wrap_proc_macro"
// Wrap types from libproc_macro rather than polyfilling the whole API.
// Enabled on rustc 1.29+ as long as procmacro2_semver_exempt is not set,
// because we can't emulate the unstable API without emulating everything
// else. Also enabled unconditionally on nightly, in which case the
// procmacro2_semver_exempt surface area is implemented by using the
// nightly-only proc_macro API.
//
// "hygiene"
// Enable Span::mixed_site() and non-dummy behavior of Span::resolved_at
// and Span::located_at. Enabled on Rust 1.45+.
//
// "proc_macro_span"
// Enable non-dummy behavior of Span::start and Span::end methods which
// requires an unstable compiler feature. Enabled when building with
// nightly, unless `-Z allow-feature` in RUSTFLAGS disallows unstable
// features.
//
// "super_unstable"
// Implement the semver exempt API in terms of the nightly-only proc_macro
// API. Enabled when using procmacro2_semver_exempt on a nightly compiler.
//
// "span_locations"
// Provide methods Span::start and Span::end which give the line/column
// location of a token. Enabled by procmacro2_semver_exempt or the
// "span-locations" Cargo cfg. This is behind a cfg because tracking
// location inside spans is a performance hit.
//
// "is_available"
// Use proc_macro::is_available() to detect if the proc macro API is
// available or needs to be polyfilled instead of trying to use the proc
// macro API and catching a panic if it isn't available. Enabled on Rust
// 1.57+.
use std::env;
use std::process::Command;
use std::str;
use std::u32;
fn main() {
println!("cargo:rerun-if-changed=build.rs");
let version = rustc_version().unwrap_or(RustcVersion {
minor: u32::MAX,
nightly: false,
});
let docs_rs = env::var_os("DOCS_RS").is_some();
let semver_exempt = cfg!(procmacro2_semver_exempt) || docs_rs;
if semver_exempt {
// https://github.com/dtolnay/proc-macro2/issues/147
println!("cargo:rustc-cfg=procmacro2_semver_exempt");
}
if semver_exempt || cfg!(feature = "span-locations") {
println!("cargo:rustc-cfg=span_locations");
}
if version.minor < 57 {
println!("cargo:rustc-cfg=no_is_available");
}
if version.minor < 66 {
println!("cargo:rustc-cfg=no_source_text");
}
if !cfg!(feature = "proc-macro") {
return;
}
if version.nightly || !semver_exempt {
println!("cargo:rustc-cfg=wrap_proc_macro");
}
if version.nightly && feature_allowed("proc_macro_span") {
println!("cargo:rustc-cfg=proc_macro_span");
}
if semver_exempt && version.nightly {
println!("cargo:rustc-cfg=super_unstable");
}
}
struct RustcVersion {
minor: u32,
nightly: bool,
}
fn rustc_version() -> Option<RustcVersion> {
let rustc = env::var_os("RUSTC")?;
let output = Command::new(rustc).arg("--version").output().ok()?;
let version = str::from_utf8(&output.stdout).ok()?;
let nightly = version.contains("nightly") || version.contains("dev");
let mut pieces = version.split('.');
if pieces.next() != Some("rustc 1") {
return None;
}
let minor = pieces.next()?.parse().ok()?;
Some(RustcVersion { minor, nightly })
}
fn feature_allowed(feature: &str) -> bool {
// Recognized formats:
//
// -Z allow-features=feature1,feature2
//
// -Zallow-features=feature1,feature2
let flags_var;
let flags_var_string;
let flags = if let Some(encoded_rustflags) = env::var_os("CARGO_ENCODED_RUSTFLAGS") {
flags_var = encoded_rustflags;
flags_var_string = flags_var.to_string_lossy();
flags_var_string.split('\x1f')
} else {
return true;
};
for mut flag in flags {
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);
}
}
// No allow-features= flag, allowed by default.
true
}
|
