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158 lines
4.8 KiB
Rust
158 lines
4.8 KiB
Rust
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// rustc-cfg emitted by the build script:
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//
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// "u128"
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// Include u128 and i128 constructors for proc_macro2::Literal. Enabled on
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// any compiler 1.26+.
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//
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// "use_proc_macro"
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// Link to extern crate proc_macro. Available on any compiler and any target
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// except wasm32. Requires "proc-macro" Cargo cfg to be enabled (default is
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// enabled). On wasm32 we never link to proc_macro even if "proc-macro" cfg
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// is enabled.
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//
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// "wrap_proc_macro"
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// Wrap types from libproc_macro rather than polyfilling the whole API.
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// Enabled on rustc 1.29+ as long as procmacro2_semver_exempt is not set,
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// because we can't emulate the unstable API without emulating everything
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// else. Also enabled unconditionally on nightly, in which case the
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// procmacro2_semver_exempt surface area is implemented by using the
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// nightly-only proc_macro API.
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//
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// "slow_extend"
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// Fallback when `impl Extend for TokenStream` is not available. These impls
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// were added one version later than the rest of the proc_macro token API.
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// Enabled on rustc 1.29 only.
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//
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// "proc_macro_span"
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// Enable non-dummy behavior of Span::start and Span::end methods which
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// requires an unstable compiler feature. Enabled when building with
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// nightly, unless `-Z allow-feature` in RUSTFLAGS disallows unstable
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// features.
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//
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// "super_unstable"
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// Implement the semver exempt API in terms of the nightly-only proc_macro
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// API. Enabled when using procmacro2_semver_exempt on a nightly compiler.
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//
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// "span_locations"
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// Provide methods Span::start and Span::end which give the line/column
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// location of a token. Enabled by procmacro2_semver_exempt or the
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// "span-locations" Cargo cfg. This is behind a cfg because tracking
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// location inside spans is a performance hit.
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use std::env;
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use std::process::Command;
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use std::str;
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fn main() {
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println!("cargo:rerun-if-changed=build.rs");
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let target = env::var("TARGET").unwrap();
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let version = match rustc_version() {
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Some(version) => version,
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None => return,
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};
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if version.minor >= 26 {
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println!("cargo:rustc-cfg=u128");
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}
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let semver_exempt = cfg!(procmacro2_semver_exempt);
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if semver_exempt {
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// https://github.com/alexcrichton/proc-macro2/issues/147
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println!("cargo:rustc-cfg=procmacro2_semver_exempt");
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}
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if semver_exempt || cfg!(feature = "span-locations") {
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println!("cargo:rustc-cfg=span_locations");
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}
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if !enable_use_proc_macro(&target) {
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return;
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}
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println!("cargo:rustc-cfg=use_proc_macro");
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// Rust 1.29 stabilized the necessary APIs in the `proc_macro` crate
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if version.nightly || version.minor >= 29 && !semver_exempt {
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println!("cargo:rustc-cfg=wrap_proc_macro");
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}
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if version.minor == 29 {
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println!("cargo:rustc-cfg=slow_extend");
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}
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if version.nightly && feature_allowed("proc_macro_span") {
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println!("cargo:rustc-cfg=proc_macro_span");
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}
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if semver_exempt && version.nightly {
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println!("cargo:rustc-cfg=super_unstable");
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}
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}
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fn enable_use_proc_macro(target: &str) -> bool {
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// wasm targets don't have the `proc_macro` crate, disable this feature.
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if target.contains("wasm32") {
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return false;
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}
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// Otherwise, only enable it if our feature is actually enabled.
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cfg!(feature = "proc-macro")
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}
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struct RustcVersion {
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minor: u32,
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nightly: bool,
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}
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fn rustc_version() -> Option<RustcVersion> {
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macro_rules! otry {
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($e:expr) => {
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match $e {
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Some(e) => e,
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None => return None,
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}
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};
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}
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let rustc = otry!(env::var_os("RUSTC"));
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let output = otry!(Command::new(rustc).arg("--version").output().ok());
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let version = otry!(str::from_utf8(&output.stdout).ok());
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let nightly = version.contains("nightly");
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let mut pieces = version.split('.');
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if pieces.next() != Some("rustc 1") {
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return None;
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}
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let minor = otry!(pieces.next());
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let minor = otry!(minor.parse().ok());
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Some(RustcVersion {
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minor: minor,
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nightly: nightly,
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})
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}
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fn feature_allowed(feature: &str) -> bool {
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// Recognized formats:
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//
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// -Z allow-features=feature1,feature2
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//
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// -Zallow-features=feature1,feature2
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if let Some(rustflags) = env::var_os("RUSTFLAGS") {
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for mut flag in rustflags.to_string_lossy().split(' ') {
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if flag.starts_with("-Z") {
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flag = &flag["-Z".len()..];
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}
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if flag.starts_with("allow-features=") {
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flag = &flag["allow-features=".len()..];
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return flag.split(',').any(|allowed| allowed == feature);
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}
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}
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}
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// No allow-features= flag, allowed by default.
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true
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}
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