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// Copyright © 2018–2026 Trevor Spiteri
// Copying and distribution of this file, with or without
// modification, are permitted in any medium without royalty provided
// the copyright notice and this notice are preserved. This file is
// offered as-is, without any warranty.
#![allow(dead_code)]
#![allow(unused_variables)]
#![cfg_attr(feature = "fail-on-warnings", deny(warnings))]
use std::env;
use std::ffi::OsString;
use std::fs;
use std::fs::File;
use std::io::{Result as IoResult, Write};
use std::path::{Path, PathBuf};
use std::process::Command;
struct Environment {
out_dir: PathBuf,
rustc: OsString,
}
fn main() {
let env = Environment {
out_dir: PathBuf::from(cargo_env("OUT_DIR")),
rustc: cargo_env("RUSTC"),
};
}
#[derive(Clone, Copy, PartialEq)]
struct Optional(bool);
impl Environment {
// 1. If optional feature is availble (both with and without flag), output:
// cargo::rustc-cfg=<name>
// 2. If feature is available with flag (both optional and not), output:
// cargo::rustc-cfg=nightly_<name>
// 3. If non-optional feature is not available, panic.
fn check_feature(
&self,
name: &str,
optional: Optional,
contents: &str,
nightly_features: Option<&str>,
) {
let try_dir = self.out_dir.join(format!("try_{name}"));
let filename = format!("try_{name}.rs");
create_dir_or_panic(&try_dir);
println!("$ cd {try_dir:?}");
#[derive(PartialEq)]
enum Iteration {
Stable,
Unstable,
}
let mut found = false;
for i in &[Iteration::Stable, Iteration::Unstable] {
let s;
let file_contents = match *i {
Iteration::Stable => contents,
Iteration::Unstable => match nightly_features {
Some(features) => {
s = format!("#![feature({features})]\n{contents}");
&s
}
None => continue,
},
};
create_file_or_panic(&try_dir.join(&filename), file_contents);
let mut cmd = Command::new(&self.rustc);
cmd.current_dir(&try_dir)
.args([&filename, "--emit=dep-info,metadata"]);
println!("$ {cmd:?}");
let status = cmd
.status()
.unwrap_or_else(|_| panic!("Unable to execute: {cmd:?}"));
println!("cargo::rustc-cfg=cfg({name})");
println!("cargo::rustc-cfg=cfg(nightly_{name})");
if status.success() {
if optional.0 {
println!("cargo::rustc-cfg={name}");
}
if *i == Iteration::Unstable {
println!("cargo::rustc-cfg=nightly_{name}");
}
found = true;
break;
}
}
remove_dir_or_panic(&try_dir);
assert!(
found || optional.0,
"essential feature not supported by compiler: {name}"
);
}
}
fn cargo_env(name: &str) -> OsString {
env::var_os(name)
.unwrap_or_else(|| panic!("environment variable not found: {name}, please use cargo"))
}
fn remove_dir(dir: &Path) -> IoResult<()> {
if !dir.exists() {
return Ok(());
}
assert!(dir.is_dir(), "Not a directory: {dir:?}");
println!("$ rm -r {dir:?}");
fs::remove_dir_all(dir)
}
fn remove_dir_or_panic(dir: &Path) {
remove_dir(dir).unwrap_or_else(|_| panic!("Unable to remove directory: {dir:?}"));
}
fn create_dir(dir: &Path) -> IoResult<()> {
println!("$ mkdir -p {dir:?}");
fs::create_dir_all(dir)
}
fn create_dir_or_panic(dir: &Path) {
create_dir(dir).unwrap_or_else(|_| panic!("Unable to create directory: {dir:?}"));
}
fn create_file_or_panic(filename: &Path, contents: &str) {
println!("$ printf '%s' {:?}... > {:?}", &contents[0..20], filename);
let mut file =
File::create(filename).unwrap_or_else(|_| panic!("Unable to create file: {filename:?}"));
file.write_all(contents.as_bytes())
.unwrap_or_else(|_| panic!("Unable to write to file: {filename:?}"));
}
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