blob: 760648bace1ead165cacdebab8b936be5621d554 [file] [log] [blame]
//! 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 = "0.1"
//! ```
//!
//! 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.
//! println!("cargo:rerun-if-changed=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.
#![deny(missing_debug_implementations)]
#![deny(missing_docs)]
use std::env;
use std::ffi::OsString;
use std::fs;
use std::io::Write;
use std::path::PathBuf;
use std::process::{Command, Stdio};
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>,
}
/// Writes a config flag for rustc on standard out.
pub fn emit(cfg: &str) {
println!("cargo:rustc-cfg={}", cfg);
}
/// 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));
// 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"));
}
Ok(AutoCfg {
out_dir: dir,
rustc: rustc,
rustc_version: rustc_version,
target: env::var_os("TARGET"),
})
}
/// 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> {
use std::sync::atomic::{AtomicUsize, Ordering, ATOMIC_USIZE_INIT};
static ID: AtomicUsize = ATOMIC_USIZE_INIT;
let id = ID.fetch_add(1, Ordering::Relaxed);
let mut command = Command::new(&self.rustc);
command
.arg(format!("--crate-name=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.arg("-").stdin(Stdio::piped());
let mut child = try!(command.spawn().map_err(error::from_io));
try!(
child
.stdin
.take()
.expect("rustc stdin")
.write_all(code.as_ref())
.map_err(error::from_io)
);
let status = try!(child.wait().map_err(error::from_io));
Ok(status.success())
}
/// 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);
}
}
}
fn mangle(s: &str) -> String {
s.chars()
.map(|c| match c {
'A'...'Z' | 'a'...'z' | '0'...'9' => c,
_ => '_',
}).collect()
}