rust-analyzer/crates/project_model/src/rustc_cfg.rs

//! Runs `rustc --print cfg` to get built-in cfg flags.

use std::process::Command;

use paths::AbsPath;

use crate::{cfg_flag::CfgFlag, utf8_stdout};

pub(crate) fn get(cargo_toml: Option<&AbsPath>, target: Option<&str>) -> Vec<CfgFlag> {
    let _p = profile::span("rustc_cfg::get");
    let mut res = Vec::with_capacity(6 * 2 + 1);

    // Some nightly-only cfgs, which are required for stdlib
    res.push(CfgFlag::Atom("target_thread_local".into()));
    for &ty in ["8", "16", "32", "64", "cas", "ptr"].iter() {
        for &key in ["target_has_atomic", "target_has_atomic_load_store"].iter() {
            res.push(CfgFlag::KeyValue { key: key.to_string(), value: ty.into() });
        }
    }

    let rustc_cfgs = {
        cargo_toml
            .and_then(|cargo_toml| {
                let mut cargo_config = Command::new(toolchain::cargo());
                cargo_config.current_dir(cargo_toml.parent().unwrap()).args(&[
                    "+nightly",
                    "-Z",
                    "unstable-options",
                    "rustc",
                    "--print",
                    "cfg",
                ]);
                if let Some(target) = target {
                    cargo_config.args(&["--target", target]);
                }
                utf8_stdout(cargo_config).ok()
            })
            .map_or_else(
                || {
                    // using unstable cargo features failed, fall back to using plain rustc
                    let mut cmd = Command::new(toolchain::rustc());
                    cmd.args(&["--print", "cfg", "-O"]);
                    if let Some(target) = target {
                        cmd.args(&["--target", target]);
                    }
                    utf8_stdout(cmd)
                },
                Ok,
            )
    };

    match rustc_cfgs {
        Ok(rustc_cfgs) => res.extend(rustc_cfgs.lines().map(|it| it.parse().unwrap())),
        Err(e) => log::error!("failed to get rustc cfgs: {:#}", e),
    }

    res
}