third_party/rust_crates/vendor/autocfg/src/lib.rs - fuchsia - Git at Google

 //! 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::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: Option<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));

         // 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"));
         }

         // 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.
         let rustflags = if env::var_os("TARGET") != env::var_os("HOST") {
             env::var("RUSTFLAGS").ok().map(|rustflags| {
                 // This is meant to match how cargo handles the RUSTFLAG environment
                 // variable.
                 // See https://github.com/rust-lang/cargo/blob/69aea5b6f69add7c51cca939a79644080c0b0ba0/src/cargo/core/compiler/build_context/target_info.rs#L434-L441
                 rustflags
                     .split(' ')
                     .map(str::trim)
                     .filter(|s| !s.is_empty())
                     .map(str::to_string)
                     .collect::<Vec<String>>()
             })
         } else {
             None
         };

         let mut ac = AutoCfg {
             out_dir: dir,
             rustc: rustc,
             rustc_version: rustc_version,
             target: env::var_os("TARGET"),
             no_std: false,
             rustflags: rustflags,
         };

         // 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(ref rustflags) = &self.rustflags {
             command.args(rustflags);
         }

         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));
         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 Rust 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()
 }
	//! 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::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: Option<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));

	// 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"));
	}

	// 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.
	let rustflags = if env::var_os("TARGET") != env::var_os("HOST") {
	env::var("RUSTFLAGS").ok().map(\|rustflags\| {
	// This is meant to match how cargo handles the RUSTFLAG environment
	// variable.
	// See https://github.com/rust-lang/cargo/blob/69aea5b6f69add7c51cca939a79644080c0b0ba0/src/cargo/core/compiler/build_context/target_info.rs#L434-L441
	rustflags
	.split(' ')
	.map(str::trim)
	.filter(\|s\| !s.is_empty())
	.map(str::to_string)
	.collect::<Vec<String>>()
	})
	} else {
	None
	};

	let mut ac = AutoCfg {
	out_dir: dir,
	rustc: rustc,
	rustc_version: rustc_version,
	target: env::var_os("TARGET"),
	no_std: false,
	rustflags: rustflags,
	};

	// 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(ref rustflags) = &self.rustflags {
	command.args(rustflags);
	}

	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));
	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 Rust 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()
	}