637 lines
22 KiB
Rust
637 lines
22 KiB
Rust
//! A Rust library for build scripts to automatically configure code based on
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//! compiler support. Code snippets are dynamically tested to see if the `rustc`
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//! will accept them, rather than hard-coding specific version support.
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//!
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//!
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//! ## Usage
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//!
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//! Add this to your `Cargo.toml`:
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//!
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//! ```toml
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//! [build-dependencies]
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//! autocfg = "1"
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//! ```
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//!
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//! Then use it in your `build.rs` script to detect compiler features. For
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//! example, to test for 128-bit integer support, it might look like:
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//!
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//! ```rust
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//! extern crate autocfg;
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//!
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//! fn main() {
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//! # // Normally, cargo will set `OUT_DIR` for build scripts.
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//! # let exe = std::env::current_exe().unwrap();
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//! # std::env::set_var("OUT_DIR", exe.parent().unwrap());
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//! let ac = autocfg::new();
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//! ac.emit_has_type("i128");
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//!
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//! // (optional) We don't need to rerun for anything external.
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//! autocfg::rerun_path("build.rs");
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//! }
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//! ```
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//!
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//! If the type test succeeds, this will write a `cargo:rustc-cfg=has_i128` line
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//! for Cargo, which translates to Rust arguments `--cfg has_i128`. Then in the
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//! rest of your Rust code, you can add `#[cfg(has_i128)]` conditions on code that
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//! should only be used when the compiler supports it.
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//!
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//! ## Caution
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//!
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//! Many of the probing methods of `AutoCfg` document the particular template they
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//! use, **subject to change**. The inputs are not validated to make sure they are
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//! semantically correct for their expected use, so it's _possible_ to escape and
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//! inject something unintended. However, such abuse is unsupported and will not
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//! be considered when making changes to the templates.
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#![deny(missing_debug_implementations)]
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#![deny(missing_docs)]
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// allow future warnings that can't be fixed while keeping 1.0 compatibility
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#![allow(unknown_lints)]
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#![allow(bare_trait_objects)]
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#![allow(ellipsis_inclusive_range_patterns)]
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/// Local macro to avoid `std::try!`, deprecated in Rust 1.39.
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macro_rules! try {
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($result:expr) => {
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match $result {
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Ok(value) => value,
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Err(error) => return Err(error),
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}
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};
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}
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use std::env;
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use std::ffi::OsString;
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use std::fmt::Arguments;
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use std::fs;
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use std::io::{stderr, Write};
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use std::path::{Path, PathBuf};
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use std::process::Stdio;
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#[allow(deprecated)]
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use std::sync::atomic::ATOMIC_USIZE_INIT;
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use std::sync::atomic::{AtomicUsize, Ordering};
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mod error;
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pub use error::Error;
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mod rustc;
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use rustc::Rustc;
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mod version;
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use version::Version;
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#[cfg(test)]
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mod tests;
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/// Helper to detect compiler features for `cfg` output in build scripts.
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#[derive(Clone, Debug)]
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pub struct AutoCfg {
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out_dir: PathBuf,
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rustc: Rustc,
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rustc_version: Version,
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target: Option<OsString>,
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no_std: bool,
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edition: Option<String>,
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rustflags: Vec<String>,
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uuid: u64,
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}
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/// Writes a config flag for rustc on standard out.
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///
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/// This looks like: `cargo:rustc-cfg=CFG`
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///
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/// Cargo will use this in arguments to rustc, like `--cfg CFG`.
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///
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/// This does not automatically call [`emit_possibility`]
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/// so the compiler my generate an [`unexpected_cfgs` warning][check-cfg-flags].
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/// However, all the builtin emit methods on [`AutoCfg`] call [`emit_possibility`] automatically.
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///
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/// [check-cfg-flags]: https://blog.rust-lang.org/2024/05/06/check-cfg.html
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pub fn emit(cfg: &str) {
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println!("cargo:rustc-cfg={}", cfg);
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}
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/// Writes a line telling Cargo to rerun the build script if `path` changes.
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///
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/// This looks like: `cargo:rerun-if-changed=PATH`
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///
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/// This requires at least cargo 0.7.0, corresponding to rustc 1.6.0. Earlier
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/// versions of cargo will simply ignore the directive.
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pub fn rerun_path(path: &str) {
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println!("cargo:rerun-if-changed={}", path);
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}
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/// Writes a line telling Cargo to rerun the build script if the environment
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/// variable `var` changes.
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///
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/// This looks like: `cargo:rerun-if-env-changed=VAR`
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///
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/// This requires at least cargo 0.21.0, corresponding to rustc 1.20.0. Earlier
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/// versions of cargo will simply ignore the directive.
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pub fn rerun_env(var: &str) {
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println!("cargo:rerun-if-env-changed={}", var);
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}
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/// Indicates to rustc that a config flag should not generate an [`unexpected_cfgs` warning][check-cfg-flags]
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///
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/// This looks like `cargo:rustc-check-cfg=cfg(VAR)`
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///
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/// As of rust 1.80, the compiler does [automatic checking of cfgs at compile time][check-cfg-flags].
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/// All custom configuration flags must be known to rustc, or they will generate a warning.
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/// This is done automatically when calling the builtin emit methods on [`AutoCfg`],
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/// but not when calling [`autocfg::emit`](crate::emit) directly.
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///
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/// Versions before rust 1.80 will simply ignore this directive.
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///
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/// This function indicates to the compiler that the config flag never has a value.
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/// If this is not desired, see [the blog post][check-cfg].
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///
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/// [check-cfg-flags]: https://blog.rust-lang.org/2024/05/06/check-cfg.html
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pub fn emit_possibility(cfg: &str) {
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println!("cargo:rustc-check-cfg=cfg({})", cfg);
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}
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/// Creates a new `AutoCfg` instance.
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///
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/// # Panics
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///
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/// Panics if `AutoCfg::new()` returns an error.
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pub fn new() -> AutoCfg {
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AutoCfg::new().unwrap()
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}
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impl AutoCfg {
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/// Creates a new `AutoCfg` instance.
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///
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/// # Common errors
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///
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/// - `rustc` can't be executed, from `RUSTC` or in the `PATH`.
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/// - The version output from `rustc` can't be parsed.
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/// - `OUT_DIR` is not set in the environment, or is not a writable directory.
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///
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pub fn new() -> Result<Self, Error> {
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match env::var_os("OUT_DIR") {
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Some(d) => Self::with_dir(d),
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None => Err(error::from_str("no OUT_DIR specified!")),
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}
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}
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/// Creates a new `AutoCfg` instance with the specified output directory.
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///
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/// # Common errors
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///
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/// - `rustc` can't be executed, from `RUSTC` or in the `PATH`.
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/// - The version output from `rustc` can't be parsed.
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/// - `dir` is not a writable directory.
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///
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pub fn with_dir<T: Into<PathBuf>>(dir: T) -> Result<Self, Error> {
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let rustc = Rustc::new();
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let rustc_version = try!(rustc.version());
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let target = env::var_os("TARGET");
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// Sanity check the output directory
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let dir = dir.into();
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let meta = try!(fs::metadata(&dir).map_err(error::from_io));
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if !meta.is_dir() || meta.permissions().readonly() {
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return Err(error::from_str("output path is not a writable directory"));
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}
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let mut ac = AutoCfg {
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rustflags: rustflags(&target, &dir),
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out_dir: dir,
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rustc: rustc,
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rustc_version: rustc_version,
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target: target,
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no_std: false,
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edition: None,
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uuid: new_uuid(),
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};
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// Sanity check with and without `std`.
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if ac.probe_raw("").is_err() {
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if ac.probe_raw("#![no_std]").is_ok() {
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ac.no_std = true;
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} else {
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// Neither worked, so assume nothing...
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let warning = b"warning: autocfg could not probe for `std`\n";
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stderr().write_all(warning).ok();
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}
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}
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Ok(ac)
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}
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/// Returns whether `AutoCfg` is using `#![no_std]` in its probes.
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///
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/// This is automatically detected during construction -- if an empty probe
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/// fails while one with `#![no_std]` succeeds, then the attribute will be
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/// used for all further probes. This is usually only necessary when the
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/// `TARGET` lacks `std` altogether. If neither succeeds, `no_std` is not
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/// set, but that `AutoCfg` will probably only work for version checks.
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///
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/// This attribute changes the implicit [prelude] from `std` to `core`,
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/// which may affect the paths you need to use in other probes. It also
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/// restricts some types that otherwise get additional methods in `std`,
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/// like floating-point trigonometry and slice sorting.
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///
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/// See also [`set_no_std`](#method.set_no_std).
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///
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/// [prelude]: https://doc.rust-lang.org/reference/names/preludes.html#the-no_std-attribute
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pub fn no_std(&self) -> bool {
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self.no_std
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}
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/// Sets whether `AutoCfg` should use `#![no_std]` in its probes.
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///
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/// See also [`no_std`](#method.no_std).
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pub fn set_no_std(&mut self, no_std: bool) {
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self.no_std = no_std;
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}
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/// Returns the `--edition` string that is currently being passed to `rustc`, if any,
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/// as configured by the [`set_edition`][Self::set_edition] method.
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pub fn edition(&self) -> Option<&str> {
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match self.edition {
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Some(ref edition) => Some(&**edition),
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None => None,
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}
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}
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/// Sets the `--edition` string that will be passed to `rustc`,
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/// or `None` to leave the compiler at its default edition.
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///
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/// See also [The Rust Edition Guide](https://doc.rust-lang.org/edition-guide/).
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///
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/// **Warning:** Setting an unsupported edition will likely cause **all** subsequent probes to
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/// fail! As of this writing, the known editions and their minimum Rust versions are:
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///
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/// | Edition | Version |
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/// | ------- | ---------- |
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/// | 2015 | 1.27.0[^1] |
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/// | 2018 | 1.31.0 |
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/// | 2021 | 1.56.0 |
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/// | 2024 | 1.85.0 |
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///
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/// [^1]: Prior to 1.27.0, Rust was effectively 2015 Edition by default, but the concept hadn't
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/// been established yet, so the explicit `--edition` flag wasn't supported either.
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pub fn set_edition(&mut self, edition: Option<String>) {
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self.edition = edition;
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}
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/// Tests whether the current `rustc` reports a version greater than
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/// or equal to "`major`.`minor`".
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pub fn probe_rustc_version(&self, major: usize, minor: usize) -> bool {
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self.rustc_version >= Version::new(major, minor, 0)
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}
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/// Sets a `cfg` value of the form `rustc_major_minor`, like `rustc_1_29`,
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/// if the current `rustc` is at least that version.
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pub fn emit_rustc_version(&self, major: usize, minor: usize) {
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let cfg_flag = format!("rustc_{}_{}", major, minor);
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emit_possibility(&cfg_flag);
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if self.probe_rustc_version(major, minor) {
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emit(&cfg_flag);
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}
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}
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/// Returns a new (hopefully unique) crate name for probes.
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fn new_crate_name(&self) -> String {
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#[allow(deprecated)]
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static ID: AtomicUsize = ATOMIC_USIZE_INIT;
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let id = ID.fetch_add(1, Ordering::Relaxed);
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format!("autocfg_{:016x}_{}", self.uuid, id)
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}
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fn probe_fmt<'a>(&self, source: Arguments<'a>) -> Result<(), Error> {
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let crate_name = self.new_crate_name();
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let mut command = self.rustc.command();
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command
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.arg("--crate-name")
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.arg(&crate_name)
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.arg("--crate-type=lib")
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.arg("--out-dir")
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.arg(&self.out_dir)
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.arg("--emit=llvm-ir");
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if let Some(edition) = self.edition.as_ref() {
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command.arg("--edition").arg(edition);
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}
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if let Some(target) = self.target.as_ref() {
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command.arg("--target").arg(target);
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}
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command.args(&self.rustflags);
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command.arg("-").stdin(Stdio::piped());
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let mut child = try!(command.spawn().map_err(error::from_io));
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let mut stdin = child.stdin.take().expect("rustc stdin");
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try!(stdin.write_fmt(source).map_err(error::from_io));
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drop(stdin);
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match child.wait() {
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Ok(status) if status.success() => {
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// Try to remove the output file so it doesn't look like a build product for
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// systems like bazel -- but this is best-effort, so we can ignore failure.
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// The probe itself is already considered successful at this point.
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let mut file = self.out_dir.join(crate_name);
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file.set_extension("ll");
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let _ = fs::remove_file(file);
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Ok(())
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}
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Ok(status) => Err(error::from_exit(status)),
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Err(error) => Err(error::from_io(error)),
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}
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}
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fn probe<'a>(&self, code: Arguments<'a>) -> bool {
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let result = if self.no_std {
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self.probe_fmt(format_args!("#![no_std]\n{}", code))
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} else {
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self.probe_fmt(code)
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};
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result.is_ok()
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}
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/// Tests whether the given code can be compiled as a Rust library.
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///
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/// This will only return `Ok` if the compiler ran and exited successfully,
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/// per `ExitStatus::success()`.
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/// The code is passed to the compiler exactly as-is, notably not even
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/// adding the [`#![no_std]`][Self::no_std] attribute like other probes.
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///
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/// Raw probes are useful for testing functionality that's not yet covered
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/// by the rest of the `AutoCfg` API. For example, the following attribute
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/// **must** be used at the crate level, so it wouldn't work within the code
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/// templates used by other `probe_*` methods.
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///
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/// ```
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/// # extern crate autocfg;
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/// # // Normally, cargo will set `OUT_DIR` for build scripts.
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/// # let exe = std::env::current_exe().unwrap();
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/// # std::env::set_var("OUT_DIR", exe.parent().unwrap());
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/// let ac = autocfg::new();
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/// assert!(ac.probe_raw("#![no_builtins]").is_ok());
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/// ```
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///
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/// Rust nightly features could be tested as well -- ideally including a
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/// code sample to ensure the unstable feature still works as expected.
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/// For example, `slice::group_by` was renamed to `chunk_by` when it was
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/// stabilized, even though the feature name was unchanged, so testing the
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/// `#![feature(..)]` alone wouldn't reveal that. For larger snippets,
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/// [`include_str!`] may be useful to load them from separate files.
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///
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/// ```
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/// # extern crate autocfg;
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/// # // Normally, cargo will set `OUT_DIR` for build scripts.
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/// # let exe = std::env::current_exe().unwrap();
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/// # std::env::set_var("OUT_DIR", exe.parent().unwrap());
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/// let ac = autocfg::new();
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/// let code = r#"
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/// #![feature(slice_group_by)]
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/// pub fn probe(slice: &[i32]) -> impl Iterator<Item = &[i32]> {
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/// slice.group_by(|a, b| a == b)
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/// }
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/// "#;
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/// if ac.probe_raw(code).is_ok() {
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/// autocfg::emit("has_slice_group_by");
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/// }
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/// ```
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pub fn probe_raw(&self, code: &str) -> Result<(), Error> {
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self.probe_fmt(format_args!("{}", code))
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}
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/// Tests whether the given sysroot crate can be used.
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///
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/// The test code is subject to change, but currently looks like:
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///
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/// ```ignore
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/// extern crate CRATE as probe;
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/// ```
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pub fn probe_sysroot_crate(&self, name: &str) -> bool {
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// Note: `as _` wasn't stabilized until Rust 1.33
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self.probe(format_args!("extern crate {} as probe;", name))
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}
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/// Emits a config value `has_CRATE` if `probe_sysroot_crate` returns true.
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pub fn emit_sysroot_crate(&self, name: &str) {
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let cfg_flag = format!("has_{}", mangle(name));
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emit_possibility(&cfg_flag);
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if self.probe_sysroot_crate(name) {
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emit(&cfg_flag);
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}
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}
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/// Tests whether the given path can be used.
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///
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/// The test code is subject to change, but currently looks like:
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///
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/// ```ignore
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/// pub use PATH;
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/// ```
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pub fn probe_path(&self, path: &str) -> bool {
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self.probe(format_args!("pub use {};", path))
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}
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/// Emits a config value `has_PATH` if `probe_path` returns true.
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///
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/// Any non-identifier characters in the `path` will be replaced with
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/// `_` in the generated config value.
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pub fn emit_has_path(&self, path: &str) {
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self.emit_path_cfg(path, &format!("has_{}", mangle(path)));
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}
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/// Emits the given `cfg` value if `probe_path` returns true.
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pub fn emit_path_cfg(&self, path: &str, cfg: &str) {
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emit_possibility(cfg);
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if self.probe_path(path) {
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emit(cfg);
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}
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}
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/// Tests whether the given trait can be used.
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///
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/// The test code is subject to change, but currently looks like:
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///
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/// ```ignore
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/// pub trait Probe: TRAIT + Sized {}
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/// ```
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pub fn probe_trait(&self, name: &str) -> bool {
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self.probe(format_args!("pub trait Probe: {} + Sized {{}}", name))
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}
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/// Emits a config value `has_TRAIT` if `probe_trait` returns true.
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///
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/// Any non-identifier characters in the trait `name` will be replaced with
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/// `_` in the generated config value.
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pub fn emit_has_trait(&self, name: &str) {
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self.emit_trait_cfg(name, &format!("has_{}", mangle(name)));
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}
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/// Emits the given `cfg` value if `probe_trait` returns true.
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pub fn emit_trait_cfg(&self, name: &str, cfg: &str) {
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emit_possibility(cfg);
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|
if self.probe_trait(name) {
|
|
emit(cfg);
|
|
}
|
|
}
|
|
|
|
/// Tests whether the given type can be used.
|
|
///
|
|
/// The test code is subject to change, but currently looks like:
|
|
///
|
|
/// ```ignore
|
|
/// pub type Probe = TYPE;
|
|
/// ```
|
|
pub fn probe_type(&self, name: &str) -> bool {
|
|
self.probe(format_args!("pub type Probe = {};", name))
|
|
}
|
|
|
|
/// Emits a config value `has_TYPE` if `probe_type` returns true.
|
|
///
|
|
/// Any non-identifier characters in the type `name` will be replaced with
|
|
/// `_` in the generated config value.
|
|
pub fn emit_has_type(&self, name: &str) {
|
|
self.emit_type_cfg(name, &format!("has_{}", mangle(name)));
|
|
}
|
|
|
|
/// Emits the given `cfg` value if `probe_type` returns true.
|
|
pub fn emit_type_cfg(&self, name: &str, cfg: &str) {
|
|
emit_possibility(cfg);
|
|
if self.probe_type(name) {
|
|
emit(cfg);
|
|
}
|
|
}
|
|
|
|
/// Tests whether the given expression can be used.
|
|
///
|
|
/// The test code is subject to change, but currently looks like:
|
|
///
|
|
/// ```ignore
|
|
/// pub fn probe() { let _ = EXPR; }
|
|
/// ```
|
|
pub fn probe_expression(&self, expr: &str) -> bool {
|
|
self.probe(format_args!("pub fn probe() {{ let _ = {}; }}", expr))
|
|
}
|
|
|
|
/// Emits the given `cfg` value if `probe_expression` returns true.
|
|
pub fn emit_expression_cfg(&self, expr: &str, cfg: &str) {
|
|
emit_possibility(cfg);
|
|
if self.probe_expression(expr) {
|
|
emit(cfg);
|
|
}
|
|
}
|
|
|
|
/// Tests whether the given constant expression can be used.
|
|
///
|
|
/// The test code is subject to change, but currently looks like:
|
|
///
|
|
/// ```ignore
|
|
/// pub const PROBE: () = ((), EXPR).0;
|
|
/// ```
|
|
pub fn probe_constant(&self, expr: &str) -> bool {
|
|
self.probe(format_args!("pub const PROBE: () = ((), {}).0;", expr))
|
|
}
|
|
|
|
/// Emits the given `cfg` value if `probe_constant` returns true.
|
|
pub fn emit_constant_cfg(&self, expr: &str, cfg: &str) {
|
|
emit_possibility(cfg);
|
|
if self.probe_constant(expr) {
|
|
emit(cfg);
|
|
}
|
|
}
|
|
}
|
|
|
|
fn mangle(s: &str) -> String {
|
|
s.chars()
|
|
.map(|c| match c {
|
|
'A'...'Z' | 'a'...'z' | '0'...'9' => c,
|
|
_ => '_',
|
|
})
|
|
.collect()
|
|
}
|
|
|
|
fn dir_contains_target(
|
|
target: &Option<OsString>,
|
|
dir: &Path,
|
|
cargo_target_dir: Option<OsString>,
|
|
) -> bool {
|
|
target
|
|
.as_ref()
|
|
.and_then(|target| {
|
|
dir.to_str().and_then(|dir| {
|
|
let mut cargo_target_dir = cargo_target_dir
|
|
.map(PathBuf::from)
|
|
.unwrap_or_else(|| PathBuf::from("target"));
|
|
cargo_target_dir.push(target);
|
|
|
|
cargo_target_dir
|
|
.to_str()
|
|
.map(|cargo_target_dir| dir.contains(cargo_target_dir))
|
|
})
|
|
})
|
|
.unwrap_or(false)
|
|
}
|
|
|
|
fn rustflags(target: &Option<OsString>, dir: &Path) -> Vec<String> {
|
|
// Starting with rust-lang/cargo#9601, shipped in Rust 1.55, Cargo always sets
|
|
// CARGO_ENCODED_RUSTFLAGS for any host/target build script invocation. This
|
|
// includes any source of flags, whether from the environment, toml config, or
|
|
// whatever may come in the future. The value is either an empty string, or a
|
|
// list of arguments separated by the ASCII unit separator (US), 0x1f.
|
|
if let Ok(a) = env::var("CARGO_ENCODED_RUSTFLAGS") {
|
|
return if a.is_empty() {
|
|
Vec::new()
|
|
} else {
|
|
a.split('\x1f').map(str::to_string).collect()
|
|
};
|
|
}
|
|
|
|
// Otherwise, we have to take a more heuristic approach, and we don't
|
|
// support values from toml config at all.
|
|
//
|
|
// Cargo only applies RUSTFLAGS for building TARGET artifact in
|
|
// cross-compilation environment. Sadly, we don't have a way to detect
|
|
// when we're building HOST artifact in a cross-compilation environment,
|
|
// so for now we only apply RUSTFLAGS when cross-compiling an artifact.
|
|
//
|
|
// See https://github.com/cuviper/autocfg/pull/10#issuecomment-527575030.
|
|
if *target != env::var_os("HOST")
|
|
|| dir_contains_target(target, dir, env::var_os("CARGO_TARGET_DIR"))
|
|
{
|
|
if let Ok(rustflags) = env::var("RUSTFLAGS") {
|
|
// This is meant to match how cargo handles the RUSTFLAGS environment variable.
|
|
// See https://github.com/rust-lang/cargo/blob/69aea5b6f69add7c51cca939a79644080c0b0ba0/src/cargo/core/compiler/build_context/target_info.rs#L434-L441
|
|
return rustflags
|
|
.split(' ')
|
|
.map(str::trim)
|
|
.filter(|s| !s.is_empty())
|
|
.map(str::to_string)
|
|
.collect();
|
|
}
|
|
}
|
|
|
|
Vec::new()
|
|
}
|
|
|
|
/// Generates a numeric ID to use in probe crate names.
|
|
///
|
|
/// This attempts to be random, within the constraints of Rust 1.0 and no dependencies.
|
|
fn new_uuid() -> u64 {
|
|
const FNV_OFFSET_BASIS: u64 = 0xcbf2_9ce4_8422_2325;
|
|
const FNV_PRIME: u64 = 0x100_0000_01b3;
|
|
|
|
// This set should have an actual random hasher.
|
|
let set: std::collections::HashSet<u64> = (0..256).collect();
|
|
|
|
// Feed the `HashSet`-shuffled order into FNV-1a.
|
|
let mut hash: u64 = FNV_OFFSET_BASIS;
|
|
for x in set {
|
|
hash = (hash ^ x).wrapping_mul(FNV_PRIME);
|
|
}
|
|
hash
|
|
}
|