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// rustc-cfg emitted by the build script:
//
// "u128"
// Include u128 and i128 constructors for proc_macro2::Literal. Enabled on
// any compiler 1.26+.
//
// "use_proc_macro"
// Link to extern crate proc_macro. Available on any compiler and any target
// except wasm32. Requires "proc-macro" Cargo cfg to be enabled (default is
// enabled). On wasm32 we never link to proc_macro even if "proc-macro" cfg
// is enabled.
//
// "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.
//
// "slow_extend"
// Fallback when `impl Extend for TokenStream` is not available. These impls
// were added one version later than the rest of the proc_macro token API.
// Enabled on rustc 1.29 only.
//
// "nightly"
// Enable the Span::unstable method. This is to support proc_macro_span and
// proc_macro_diagnostic use on the nightly channel without requiring the
// semver exemption opt-in. Enabled when building with nightly.
//
// "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.
use std::env;
use std::process::Command;
use std::str;
fn main() {
println!("cargo:rerun-if-changed=build.rs");
let target = env::var("TARGET").unwrap();
let version = match rustc_version() {
Some(version) => version,
None => return,
};
if version.minor >= 26 {
println!("cargo:rustc-cfg=u128");
}
if !enable_use_proc_macro(&target) {
return;
}
println!("cargo:rustc-cfg=use_proc_macro");
let semver_exempt = cfg!(procmacro2_semver_exempt);
if semver_exempt {
// https://github.com/alexcrichton/proc-macro2/issues/147
println!("cargo:rustc-cfg=procmacro2_semver_exempt");
}
// Rust 1.29 stabilized the necessary APIs in the `proc_macro` crate
if version.nightly || version.minor >= 29 && !semver_exempt {
println!("cargo:rustc-cfg=wrap_proc_macro");
}
if version.minor == 29 {
println!("cargo:rustc-cfg=slow_extend");
}
if version.nightly {
println!("cargo:rustc-cfg=nightly");
}
if semver_exempt && version.nightly {
println!("cargo:rustc-cfg=super_unstable");
}
}
fn enable_use_proc_macro(target: &str) -> bool {
// wasm targets don't have the `proc_macro` crate, disable this feature.
if target.contains("wasm32") {
return false;
}
// Otherwise, only enable it if our feature is actually enabled.
cfg!(feature = "proc-macro")
}
struct RustcVersion {
minor: u32,
nightly: bool,
}
fn rustc_version() -> Option<RustcVersion> {
macro_rules! otry {
($e:expr) => {
match $e {
Some(e) => e,
None => return None,
}
};
}
let rustc = otry!(env::var_os("RUSTC"));
let output = otry!(Command::new(rustc).arg("--version").output().ok());
let version = otry!(str::from_utf8(&output.stdout).ok());
let nightly = version.contains("nightly");
let mut pieces = version.split('.');
if pieces.next() != Some("rustc 1") {
return None;
}
let minor = otry!(pieces.next());
let minor = otry!(minor.parse().ok());
Some(RustcVersion {
minor: minor,
nightly: nightly,
})
}
|
