//! A Rust library for build scripts to automatically configure code based on
//! compiler support. Code snippets are dynamically tested to see if the `rustc`
//! will accept them, rather than hard-coding specific version support.
//!
//!
//! ## Usage
//!
//! Add this to your `Cargo.toml`:
//!
//! ```toml
//! [build-dependencies]
//! autocfg = "1"
//! ```
//!
//! Then use it in your `build.rs` script to detect compiler features. For
//! example, to test for 128-bit integer support, it might look like:
//!
//! ```rust
//! extern crate autocfg;
//!
//! fn main() {
//! # // Normally, cargo will set `OUT_DIR` for build scripts.
//! # std::env::set_var("OUT_DIR", "target");
//! let ac = autocfg::new();
//! ac.emit_has_type("i128");
//!
//! // (optional) We don't need to rerun for anything external.
//! autocfg::rerun_path("build.rs");
//! }
//! ```
//!
//! If the type test succeeds, this will write a `cargo:rustc-cfg=has_i128` line
//! for Cargo, which translates to Rust arguments `--cfg has_i128`. Then in the
//! rest of your Rust code, you can add `#[cfg(has_i128)]` conditions on code that
//! should only be used when the compiler supports it.
//!
//! ## Caution
//!
//! Many of the probing methods of `AutoCfg` document the particular template they
//! use, **subject to change**. The inputs are not validated to make sure they are
//! semantically correct for their expected use, so it's _possible_ to escape and
//! inject something unintended. However, such abuse is unsupported and will not
//! be considered when making changes to the templates.
#![deny(missing_debug_implementations)]
#![deny(missing_docs)]
// allow future warnings that can't be fixed while keeping 1.0 compatibility
#![allow(unknown_lints)]
#![allow(bare_trait_objects)]
#![allow(ellipsis_inclusive_range_patterns)]
/// Local macro to avoid `std::try!`, deprecated in Rust 1.39.
macro_rules! try {
($result:expr) => {
match $result {
Ok(value) => value,
Err(error) => return Err(error),
}
};
}
use std::env;
use std::ffi::OsString;
use std::fs;
use std::io::{stderr, Write};
use std::path::{Path, PathBuf};
use std::process::{Command, Stdio};
#[allow(deprecated)]
use std::sync::atomic::ATOMIC_USIZE_INIT;
use std::sync::atomic::{AtomicUsize, Ordering};
mod error;
pub use error::Error;
mod version;
use version::Version;
#[cfg(test)]
mod tests;
/// Helper to detect compiler features for `cfg` output in build scripts.
#[derive(Clone, Debug)]
pub struct AutoCfg {
out_dir: PathBuf,
rustc: PathBuf,
rustc_version: Version,
target: Option<OsString>,
no_std: bool,
rustflags: Vec<String>,
}
/// Writes a config flag for rustc on standard out.
///
/// This looks like: `cargo:rustc-cfg=CFG`
///
/// Cargo will use this in arguments to rustc, like `--cfg CFG`.
pub fn emit(cfg: &str) {
println!("cargo:rustc-cfg={}", cfg);
}
/// Writes a line telling Cargo to rerun the build script if `path` changes.
///
/// This looks like: `cargo:rerun-if-changed=PATH`
///
/// This requires at least cargo 0.7.0, corresponding to rustc 1.6.0. Earlier
/// versions of cargo will simply ignore the directive.
pub fn rerun_path(path: &str) {
println!("cargo:rerun-if-changed={}", path);
}
/// Writes a line telling Cargo to rerun the build script if the environment
/// variable `var` changes.
///
/// This looks like: `cargo:rerun-if-env-changed=VAR`
///
/// This requires at least cargo 0.21.0, corresponding to rustc 1.20.0. Earlier
/// versions of cargo will simply ignore the directive.
pub fn rerun_env(var: &str) {
println!("cargo:rerun-if-env-changed={}", var);
}
/// Create a new `AutoCfg` instance.
///
/// # Panics
///
/// Panics if `AutoCfg::new()` returns an error.
pub fn new() -> AutoCfg {
AutoCfg::new().unwrap()
}
impl AutoCfg {
/// Create a new `AutoCfg` instance.
///
/// # Common errors
///
/// - `rustc` can't be executed, from `RUSTC` or in the `PATH`.
/// - The version output from `rustc` can't be parsed.
/// - `OUT_DIR` is not set in the environment, or is not a writable directory.
///
pub fn new() -> Result<Self, Error> {
match env::var_os("OUT_DIR") {
Some(d) => Self::with_dir(d),
None => Err(error::from_str("no OUT_DIR specified!")),
}
}
/// Create a new `AutoCfg` instance with the specified output directory.
///
/// # Common errors
///
/// - `rustc` can't be executed, from `RUSTC` or in the `PATH`.
/// - The version output from `rustc` can't be parsed.
/// - `dir` is not a writable directory.
///
pub fn with_dir<T: Into<PathBuf>>(dir: T) -> Result<Self, Error> {
let rustc = env::var_os("RUSTC").unwrap_or_else(|| "rustc".into());
let rustc: PathBuf = rustc.into();
let rustc_version = try!(Version::from_rustc(&rustc));
let target = env::var_os("TARGET");
// Sanity check the output directory
let dir = dir.into();
let meta = try!(fs::metadata(&dir).map_err(error::from_io));
if !meta.is_dir() || meta.permissions().readonly() {
return Err(error::from_str("output path is not a writable directory"));
}
let mut ac = AutoCfg {
rustflags: rustflags(&target, &dir),
out_dir: dir,
rustc: rustc,
rustc_version: rustc_version,
target: target,
no_std: false,
};
// Sanity check with and without `std`.
if !ac.probe("").unwrap_or(false) {
ac.no_std = true;
if !ac.probe("").unwrap_or(false) {
// Neither worked, so assume nothing...
ac.no_std = false;
let warning = b"warning: autocfg could not probe for `std`\n";
stderr().write_all(warning).ok();
}
}
Ok(ac)
}
/// Test whether the current `rustc` reports a version greater than
/// or equal to "`major`.`minor`".
pub fn probe_rustc_version(&self, major: usize, minor: usize) -> bool {
self.rustc_version >= Version::new(major, minor, 0)
}
/// Sets a `cfg` value of the form `rustc_major_minor`, like `rustc_1_29`,
/// if the current `rustc` is at least that version.
pub fn emit_rustc_version(&self, major: usize, minor: usize) {
if self.probe_rustc_version(major, minor) {
emit(&format!("rustc_{}_{}", major, minor));
}
}
fn probe<T: AsRef<[u8]>>(&self, code: T) -> Result<bool, Error> {
#[allow(deprecated)]
static ID: AtomicUsize = ATOMIC_USIZE_INIT;
let id = ID.fetch_add(1, Ordering::Relaxed);
let mut command = Command::new(&self.rustc);
command
.arg("--crate-name")
.arg(format!("probe{}", id))
.arg("--crate-type=lib")
.arg("--out-dir")
.arg(&self.out_dir)
.arg("--emit=llvm-ir");
if let Some(target) = self.target.as_ref() {
command.arg("--target").arg(target);
}
command.args(&self.rustflags);
// Mozilla-local change: throw away stderr output.
//
// Mozilla's build system runs cargo with `-v -v` to help diagnose rustc
// selection problems. Without the change below, that causes error
// messages from autocfg compiler invocations (which simply indicate
// that the feature autocfg was checking for isn't available, and are
// not actual build errors) to show up in the build output stream, where
// they confuse other parts of Mozilla's build system that try to
// highlight and track errors.
//
// See:
https://github.com/cuviper/autocfg/issues/30
command.arg("-").stdin(Stdio::piped()).stderr(Stdio::null());
let mut child = try!(command.spawn().map_err(error::from_io));
let mut stdin = child.stdin.take().expect("rustc stdin");
if self.no_std {
try!(stdin.write_all(b"#![no_std]\n").map_err(error::from_io));
}
try!(stdin.write_all(code.as_ref()).map_err(error::from_io));
drop(stdin);
let status = try!(child.wait().map_err(error::from_io));
Ok(status.success())
}
/// Tests whether the given sysroot crate can be used.
///
/// The test code is subject to change, but currently looks like:
///
/// ```ignore
/// extern crate CRATE as probe;
/// ```
pub fn probe_sysroot_crate(&self, name: &str) -> bool {
self.probe(format!("extern crate {} as probe;", name)) // `as _` wasn't stabilized until Rus
t 1.33
.unwrap_or(false)
}
/// Emits a config value `has_CRATE` if `probe_sysroot_crate` returns true.
pub fn emit_sysroot_crate(&self, name: &str) {
if self.probe_sysroot_crate(name) {
emit(&format!("has_{}", mangle(name)));
}
}
/// Tests whether the given path can be used.
///
/// The test code is subject to change, but currently looks like:
///
/// ```ignore
/// pub use PATH;
/// ```
pub fn probe_path(&self, path: &str) -> bool {
self.probe(format!("pub use {};", path)).unwrap_or(false)
}
/// Emits a config value `has_PATH` if `probe_path` returns true.
///
/// Any non-identifier characters in the `path` will be replaced with
/// `_` in the generated config value.
pub fn emit_has_path(&self, path: &str) {
if self.probe_path(path) {
emit(&format!("has_{}", mangle(path)));
}
}
/// Emits the given `cfg` value if `probe_path` returns true.
pub fn emit_path_cfg(&self, path: &str, cfg: &str) {
if self.probe_path(path) {
emit(cfg);
}
}
/// Tests whether the given trait can be used.
///
/// The test code is subject to change, but currently looks like:
///
/// ```ignore
/// pub trait Probe: TRAIT + Sized {}
/// ```
pub fn probe_trait(&self, name: &str) -> bool {
self.probe(format!("pub trait Probe: {} + Sized {{}}", name))
.unwrap_or(false)
}
/// Emits a config value `has_TRAIT` if `probe_trait` returns true.
///
/// Any non-identifier characters in the trait `name` will be replaced with
/// `_` in the generated config value.
pub fn emit_has_trait(&self, name: &str) {
if self.probe_trait(name) {
emit(&format!("has_{}", mangle(name)));
}
}
/// Emits the given `cfg` value if `probe_trait` returns true.
pub fn emit_trait_cfg(&self, name: &str, cfg: &str) {
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!("pub type Probe = {};", name))
.unwrap_or(false)
}
/// 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) {
if self.probe_type(name) {
emit(&format!("has_{}", mangle(name)));
}
}
/// Emits the given `cfg` value if `probe_type` returns true.
pub fn emit_type_cfg(&self, name: &str, cfg: &str) {
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!("pub fn probe() {{ let _ = {}; }}", expr))
.unwrap_or(false)
}
/// Emits the given `cfg` value if `probe_expression` returns true.
pub fn emit_expression_cfg(&self, expr: &str, cfg: &str) {
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!("pub const PROBE: () = ((), {}).0;", expr))
.unwrap_or(false)
}
/// Emits the given `cfg` value if `probe_constant` returns true.
pub fn emit_constant_cfg(&self, expr: &str, cfg: &str) {
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()
}
