lib.rs

//! Implementation of rustbuild, the Rust build system.
//!
//! This module, and its descendants, are the implementation of the Rust build
//! system. Most of this build system is backed by Cargo but the outer layer
//! here serves as the ability to orchestrate calling Cargo, sequencing Cargo
//! builds, building artifacts like LLVM, etc. The goals of rustbuild are:
//!
//! * To be an easily understandable, easily extensible, and maintainable build
//!   system.
//! * Leverage standard tools in the Rust ecosystem to build the compiler, aka
//!   crates.io and Cargo.
//! * A standard interface to build across all platforms, including MSVC
//!
//! ## Further information
//!
//! More documentation can be found in each respective module below, and you can
//! also check out the `src/bootstrap/README.md` file for more information.

use std::cell::{Cell, RefCell};
use std::collections::{HashMap, HashSet};
use std::env;
use std::fmt::Display;
use std::fs::{self, File};
use std::io;
use std::path::{Path, PathBuf};
use std::process::{Command, Output, Stdio};
use std::str;

use build_helper::ci::{gha, CiEnv};
use build_helper::exit;
use build_helper::util::fail;
use filetime::FileTime;
use once_cell::sync::OnceCell;
use termcolor::{ColorChoice, StandardStream, WriteColor};
use utils::channel::GitInfo;

use crate::core::builder;
use crate::core::builder::Kind;
use crate::core::config::flags;
use crate::core::config::{DryRun, Target};
use crate::core::config::{LlvmLibunwind, TargetSelection};
use crate::utils::cache::{Interned, INTERNER};
use crate::utils::exec::{BehaviorOnFailure, BootstrapCommand, OutputMode};
use crate::utils::helpers::{self, dir_is_empty, exe, libdir, mtime, output, symlink_dir};

mod core;
mod utils;

pub use crate::core::builder::PathSet;
pub use crate::core::config::flags::Subcommand;
pub use crate::core::config::Config;

const LLVM_TOOLS: &[&str] = &[
    "llvm-cov",      // used to generate coverage report
    "llvm-nm",       // used to inspect binaries; it shows symbol names, their sizes and visibility
    "llvm-objcopy",  // used to transform ELFs into binary format which flashing tools consume
    "llvm-objdump",  // used to disassemble programs
    "llvm-profdata", // used to inspect and merge files generated by profiles
    "llvm-readobj",  // used to get information from ELFs/objects that the other tools don't provide
    "llvm-size",     // used to prints the size of the linker sections of a program
    "llvm-strip",    // used to discard symbols from binary files to reduce their size
    "llvm-ar",       // used for creating and modifying archive files
    "llvm-as",       // used to convert LLVM assembly to LLVM bitcode
    "llvm-dis",      // used to disassemble LLVM bitcode
    "llc",           // used to compile LLVM bytecode
    "opt",           // used to optimize LLVM bytecode
];

/// LLD file names for all flavors.
const LLD_FILE_NAMES: &[&str] = &["ld.lld", "ld64.lld", "lld-link", "wasm-ld"];

/// Keeps track of major changes made to the bootstrap configuration.
///
/// These values also represent the IDs of the PRs that caused major changes.
/// You can visit `https://github.com/rust-lang/rust/pull/{any-id-from-the-list}` to
/// check for more details regarding each change.
///
/// If you make any major changes (such as adding new values or changing default values), please
/// ensure that the associated PR ID is added to the end of this list.
pub const CONFIG_CHANGE_HISTORY: &[usize] = &[115898, 116998, 117435];

/// Extra --check-cfg to add when building
/// (Mode restriction, config name, config values (if any))
const EXTRA_CHECK_CFGS: &[(Option<Mode>, &str, Option<&[&'static str]>)] = &[
    (None, "bootstrap", None),
    (Some(Mode::Rustc), "parallel_compiler", None),
    (Some(Mode::ToolRustc), "parallel_compiler", None),
    (Some(Mode::Codegen), "parallel_compiler", None),
    (Some(Mode::Std), "stdarch_intel_sde", None),
    (Some(Mode::Std), "no_fp_fmt_parse", None),
    (Some(Mode::Std), "no_global_oom_handling", None),
    (Some(Mode::Std), "no_rc", None),
    (Some(Mode::Std), "no_sync", None),
    (Some(Mode::Std), "freebsd12", None),
    (Some(Mode::Std), "freebsd13", None),
    (Some(Mode::Std), "backtrace_in_libstd", None),
    /* Extra values not defined in the built-in targets yet, but used in std */
    (Some(Mode::Std), "target_env", Some(&["libnx"])),
    // (Some(Mode::Std), "target_os", Some(&[])),
    (Some(Mode::Std), "target_arch", Some(&["asmjs", "spirv", "nvptx", "xtensa"])),
    /* Extra names used by dependencies */
    // FIXME: Used by serde_json, but we should not be triggering on external dependencies.
    (Some(Mode::Rustc), "no_btreemap_remove_entry", None),
    (Some(Mode::ToolRustc), "no_btreemap_remove_entry", None),
    // FIXME: Used by crossbeam-utils, but we should not be triggering on external dependencies.
    (Some(Mode::Rustc), "crossbeam_loom", None),
    (Some(Mode::ToolRustc), "crossbeam_loom", None),
    // FIXME: Used by proc-macro2, but we should not be triggering on external dependencies.
    (Some(Mode::Rustc), "span_locations", None),
    (Some(Mode::ToolRustc), "span_locations", None),
    // FIXME: Used by rustix, but we should not be triggering on external dependencies.
    (Some(Mode::Rustc), "rustix_use_libc", None),
    (Some(Mode::ToolRustc), "rustix_use_libc", None),
    // FIXME: Used by filetime, but we should not be triggering on external dependencies.
    (Some(Mode::Rustc), "emulate_second_only_system", None),
    (Some(Mode::ToolRustc), "emulate_second_only_system", None),
    // Needed to avoid the need to copy windows.lib into the sysroot.
    (Some(Mode::Rustc), "windows_raw_dylib", None),
    (Some(Mode::ToolRustc), "windows_raw_dylib", None),
];

/// A structure representing a Rust compiler.
///
/// Each compiler has a `stage` that it is associated with and a `host` that
/// corresponds to the platform the compiler runs on. This structure is used as
/// a parameter to many methods below.
#[derive(Eq, PartialOrd, Ord, PartialEq, Clone, Copy, Hash, Debug)]
pub struct Compiler {
    stage: u32,
    host: TargetSelection,
}

#[derive(PartialEq, Eq, Copy, Clone, Debug)]
pub enum DocTests {
    /// Run normal tests and doc tests (default).
    Yes,
    /// Do not run any doc tests.
    No,
    /// Only run doc tests.
    Only,
}

pub enum GitRepo {
    Rustc,
    Llvm,
}

/// Global configuration for the build system.
///
/// This structure transitively contains all configuration for the build system.
/// All filesystem-encoded configuration is in `config`, all flags are in
/// `flags`, and then parsed or probed information is listed in the keys below.
///
/// This structure is a parameter of almost all methods in the build system,
/// although most functions are implemented as free functions rather than
/// methods specifically on this structure itself (to make it easier to
/// organize).
#[derive(Clone)]
pub struct Build {
    /// User-specified configuration from `config.toml`.
    config: Config,

    // Version information
    version: String,

    // Properties derived from the above configuration
    src: PathBuf,
    out: PathBuf,
    bootstrap_out: PathBuf,
    cargo_info: GitInfo,
    rust_analyzer_info: GitInfo,
    clippy_info: GitInfo,
    miri_info: GitInfo,
    rustfmt_info: GitInfo,
    in_tree_llvm_info: GitInfo,
    local_rebuild: bool,
    fail_fast: bool,
    doc_tests: DocTests,
    verbosity: usize,

    // Targets for which to build
    build: TargetSelection,
    hosts: Vec<TargetSelection>,
    targets: Vec<TargetSelection>,

    initial_rustc: PathBuf,
    initial_cargo: PathBuf,
    initial_lld: PathBuf,
    initial_libdir: PathBuf,
    initial_sysroot: PathBuf,

    // Runtime state filled in later on
    // C/C++ compilers and archiver for all targets
    cc: RefCell<HashMap<TargetSelection, cc::Tool>>,
    cxx: RefCell<HashMap<TargetSelection, cc::Tool>>,
    ar: RefCell<HashMap<TargetSelection, PathBuf>>,
    ranlib: RefCell<HashMap<TargetSelection, PathBuf>>,
    // Miscellaneous
    // allow bidirectional lookups: both name -> path and path -> name
    crates: HashMap<Interned<String>, Crate>,
    crate_paths: HashMap<PathBuf, Interned<String>>,
    is_sudo: bool,
    ci_env: CiEnv,
    delayed_failures: RefCell<Vec<String>>,
    prerelease_version: Cell<Option<u32>>,

    #[cfg(feature = "build-metrics")]
    metrics: crate::utils::metrics::BuildMetrics,
}

#[derive(Debug, Clone)]
struct Crate {
    name: Interned<String>,
    deps: HashSet<Interned<String>>,
    path: PathBuf,
    has_lib: bool,
}

impl Crate {
    fn local_path(&self, build: &Build) -> PathBuf {
        self.path.strip_prefix(&build.config.src).unwrap().into()
    }
}

/// When building Rust various objects are handled differently.
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
pub enum DependencyType {
    /// Libraries originating from proc-macros.
    Host,
    /// Typical Rust libraries.
    Target,
    /// Non Rust libraries and objects shipped to ease usage of certain targets.
    TargetSelfContained,
}

/// The various "modes" of invoking Cargo.
///
/// These entries currently correspond to the various output directories of the
/// build system, with each mod generating output in a different directory.
#[derive(Debug, Hash, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
pub enum Mode {
    /// Build the standard library, placing output in the "stageN-std" directory.
    Std,

    /// Build librustc, and compiler libraries, placing output in the "stageN-rustc" directory.
    Rustc,

    /// Build a codegen backend for rustc, placing the output in the "stageN-codegen" directory.
    Codegen,

    /// Build a tool, placing output in the "stage0-bootstrap-tools"
    /// directory. This is for miscellaneous sets of tools that are built
    /// using the bootstrap stage0 compiler in its entirety (target libraries
    /// and all). Typically these tools compile with stable Rust.
    ToolBootstrap,

    /// Build a tool which uses the locally built std, placing output in the
    /// "stageN-tools" directory. Its usage is quite rare, mainly used by
    /// compiletest which needs libtest.
    ToolStd,

    /// Build a tool which uses the locally built rustc and the target std,
    /// placing the output in the "stageN-tools" directory. This is used for
    /// anything that needs a fully functional rustc, such as rustdoc, clippy,
    /// cargo, rls, rustfmt, miri, etc.
    ToolRustc,
}

impl Mode {
    pub fn is_tool(&self) -> bool {
        matches!(self, Mode::ToolBootstrap | Mode::ToolRustc | Mode::ToolStd)
    }

    pub fn must_support_dlopen(&self) -> bool {
        matches!(self, Mode::Std | Mode::Codegen)
    }
}

pub enum CLang {
    C,
    Cxx,
}

macro_rules! forward {
    ( $( $fn:ident( $($param:ident: $ty:ty),* ) $( -> $ret:ty)? ),+ $(,)? ) => {
        impl Build {
            $( fn $fn(&self, $($param: $ty),* ) $( -> $ret)? {
                self.config.$fn( $($param),* )
            } )+
        }
    }
}

forward! {
    verbose(msg: &str),
    is_verbose() -> bool,
    create(path: &Path, s: &str),
    remove(f: &Path),
    tempdir() -> PathBuf,
    llvm_link_shared() -> bool,
    download_rustc() -> bool,
    initial_rustfmt() -> Option<PathBuf>,
}

impl Build {
    /// Creates a new set of build configuration from the `flags` on the command
    /// line and the filesystem `config`.
    ///
    /// By default all build output will be placed in the current directory.
    pub fn new(mut config: Config) -> Build {
        let src = config.src.clone();
        let out = config.out.clone();

        #[cfg(unix)]
        // keep this consistent with the equivalent check in x.py:
        // https://github.com/rust-lang/rust/blob/a8a33cf27166d3eabaffc58ed3799e054af3b0c6/src/bootstrap/bootstrap.py#L796-L797
        let is_sudo = match env::var_os("SUDO_USER") {
            Some(_sudo_user) => {
                // SAFETY: getuid() system call is always successful and no return value is reserved
                // to indicate an error.
                //
                // For more context, see https://man7.org/linux/man-pages/man2/geteuid.2.html
                let uid = unsafe { libc::getuid() };
                uid == 0
            }
            None => false,
        };
        #[cfg(not(unix))]
        let is_sudo = false;

        let omit_git_hash = config.omit_git_hash;
        let rust_info = GitInfo::new(omit_git_hash, &src);
        let cargo_info = GitInfo::new(omit_git_hash, &src.join("src/tools/cargo"));
        let rust_analyzer_info = GitInfo::new(omit_git_hash, &src.join("src/tools/rust-analyzer"));
        let clippy_info = GitInfo::new(omit_git_hash, &src.join("src/tools/clippy"));
        let miri_info = GitInfo::new(omit_git_hash, &src.join("src/tools/miri"));
        let rustfmt_info = GitInfo::new(omit_git_hash, &src.join("src/tools/rustfmt"));

        // we always try to use git for LLVM builds
        let in_tree_llvm_info = GitInfo::new(false, &src.join("src/llvm-project"));

        let initial_target_libdir_str = if config.dry_run() {
            "/dummy/lib/path/to/lib/".to_string()
        } else {
            output(
                Command::new(&config.initial_rustc)
                    .arg("--target")
                    .arg(config.build.rustc_target_arg())
                    .arg("--print")
                    .arg("target-libdir"),
            )
        };
        let initial_target_dir = Path::new(&initial_target_libdir_str).parent().unwrap();
        let initial_lld = initial_target_dir.join("bin").join("rust-lld");

        let initial_sysroot = if config.dry_run() {
            "/dummy".to_string()
        } else {
            output(Command::new(&config.initial_rustc).arg("--print").arg("sysroot"))
        }
        .trim()
        .to_string();

        let initial_libdir = initial_target_dir
            .parent()
            .unwrap()
            .parent()
            .unwrap()
            .strip_prefix(&initial_sysroot)
            .unwrap()
            .to_path_buf();

        let version = std::fs::read_to_string(src.join("src").join("version"))
            .expect("failed to read src/version");
        let version = version.trim();

        let bootstrap_out = std::env::current_exe()
            .expect("could not determine path to running process")
            .parent()
            .unwrap()
            .to_path_buf();
        if !bootstrap_out.join(exe("rustc", config.build)).exists() && !cfg!(test) {
            // this restriction can be lifted whenever https://github.com/rust-lang/rfcs/pull/3028 is implemented
            panic!(
                "`rustc` not found in {}, run `cargo build --bins` before `cargo run`",
                bootstrap_out.display()
            )
        }

        if rust_info.is_from_tarball() && config.description.is_none() {
            config.description = Some("built from a source tarball".to_owned());
        }

        let mut build = Build {
            initial_rustc: config.initial_rustc.clone(),
            initial_cargo: config.initial_cargo.clone(),
            initial_lld,
            initial_libdir,
            initial_sysroot: initial_sysroot.into(),
            local_rebuild: config.local_rebuild,
            fail_fast: config.cmd.fail_fast(),
            doc_tests: config.cmd.doc_tests(),
            verbosity: config.verbose,

            build: config.build,
            hosts: config.hosts.clone(),
            targets: config.targets.clone(),

            config,
            version: version.to_string(),
            src,
            out,
            bootstrap_out,

            cargo_info,
            rust_analyzer_info,
            clippy_info,
            miri_info,
            rustfmt_info,
            in_tree_llvm_info,
            cc: RefCell::new(HashMap::new()),
            cxx: RefCell::new(HashMap::new()),
            ar: RefCell::new(HashMap::new()),
            ranlib: RefCell::new(HashMap::new()),
            crates: HashMap::new(),
            crate_paths: HashMap::new(),
            is_sudo,
            ci_env: CiEnv::current(),
            delayed_failures: RefCell::new(Vec::new()),
            prerelease_version: Cell::new(None),

            #[cfg(feature = "build-metrics")]
            metrics: crate::utils::metrics::BuildMetrics::init(),
        };

        // If local-rust is the same major.minor as the current version, then force a
        // local-rebuild
        let local_version_verbose =
            output(Command::new(&build.initial_rustc).arg("--version").arg("--verbose"));
        let local_release = local_version_verbose
            .lines()
            .filter_map(|x| x.strip_prefix("release:"))
            .next()
            .unwrap()
            .trim();
        if local_release.split('.').take(2).eq(version.split('.').take(2)) {
            build.verbose(&format!("auto-detected local-rebuild {local_release}"));
            build.local_rebuild = true;
        }

        build.verbose("finding compilers");
        utils::cc_detect::find(&build);
        // When running `setup`, the profile is about to change, so any requirements we have now may
        // be different on the next invocation. Don't check for them until the next time x.py is
        // run. This is ok because `setup` never runs any build commands, so it won't fail if commands are missing.
        //
        // Similarly, for `setup` we don't actually need submodules or cargo metadata.
        if !matches!(build.config.cmd, Subcommand::Setup { .. }) {
            build.verbose("running sanity check");
            crate::core::sanity::check(&mut build);

            // Make sure we update these before gathering metadata so we don't get an error about missing
            // Cargo.toml files.
            let rust_submodules = ["src/tools/cargo", "library/backtrace", "library/stdarch"];
            for s in rust_submodules {
                build.update_submodule(Path::new(s));
            }
            // Now, update all existing submodules.
            build.update_existing_submodules();

            build.verbose("learning about cargo");
            crate::core::metadata::build(&mut build);
        }

        // Make a symbolic link so we can use a consistent directory in the documentation.
        let build_triple = build.out.join(&build.build.triple);
        t!(fs::create_dir_all(&build_triple));
        let host = build.out.join("host");
        if host.is_symlink() {
            // Left over from a previous build; overwrite it.
            // This matters if `build.build` has changed between invocations.
            #[cfg(windows)]
            t!(fs::remove_dir(&host));
            #[cfg(not(windows))]
            t!(fs::remove_file(&host));
        }
        t!(
            symlink_dir(&build.config, &build_triple, &host),
            format!("symlink_dir({} => {}) failed", host.display(), build_triple.display())
        );

        build
    }

    // modified from `check_submodule` and `update_submodule` in bootstrap.py
    /// Given a path to the directory of a submodule, update it.
    ///
    /// `relative_path` should be relative to the root of the git repository, not an absolute path.
    pub(crate) fn update_submodule(&self, relative_path: &Path) {
        if !self.config.submodules(&self.rust_info()) {
            return;
        }

        let absolute_path = self.config.src.join(relative_path);

        // NOTE: The check for the empty directory is here because when running x.py the first time,
        // the submodule won't be checked out. Check it out now so we can build it.
        if !GitInfo::new(false, &absolute_path).is_managed_git_subrepository()
            && !dir_is_empty(&absolute_path)
        {
            return;
        }

        // check_submodule
        let checked_out_hash =
            output(Command::new("git").args(&["rev-parse", "HEAD"]).current_dir(&absolute_path));
        // update_submodules
        let recorded = output(
            Command::new("git")
                .args(&["ls-tree", "HEAD"])
                .arg(relative_path)
                .current_dir(&self.config.src),
        );
        let actual_hash = recorded
            .split_whitespace()
            .nth(2)
            .unwrap_or_else(|| panic!("unexpected output `{}`", recorded));

        // update_submodule
        if actual_hash == checked_out_hash.trim_end() {
            // already checked out
            return;
        }

        println!("Updating submodule {}", relative_path.display());
        self.run(
            Command::new("git")
                .args(&["submodule", "-q", "sync"])
                .arg(relative_path)
                .current_dir(&self.config.src),
        );

        // Try passing `--progress` to start, then run git again without if that fails.
        let update = |progress: bool| {
            // Git is buggy and will try to fetch submodules from the tracking branch for *this* repository,
            // even though that has no relation to the upstream for the submodule.
            let current_branch = {
                let output = self
                    .config
                    .git()
                    .args(["symbolic-ref", "--short", "HEAD"])
                    .stderr(Stdio::inherit())
                    .output();
                let output = t!(output);
                if output.status.success() {
                    Some(String::from_utf8(output.stdout).unwrap().trim().to_owned())
                } else {
                    None
                }
            };

            let mut git = self.config.git();
            if let Some(branch) = current_branch {
                // If there is a tag named after the current branch, git will try to disambiguate by prepending `heads/` to the branch name.
                // This syntax isn't accepted by `branch.{branch}`. Strip it.
                let branch = branch.strip_prefix("heads/").unwrap_or(&branch);
                git.arg("-c").arg(format!("branch.{branch}.remote=origin"));
            }
            git.args(&["submodule", "update", "--init", "--recursive", "--depth=1"]);
            if progress {
                git.arg("--progress");
            }
            git.arg(relative_path);
            git
        };
        // NOTE: doesn't use `try_run` because this shouldn't print an error if it fails.
        if !update(true).status().map_or(false, |status| status.success()) {
            self.run(&mut update(false));
        }

        // Save any local changes, but avoid running `git stash pop` if there are none (since it will exit with an error).
        // diff-index reports the modifications through the exit status
        let has_local_modifications = !self.run_cmd(
            BootstrapCommand::from(
                Command::new("git")
                    .args(&["diff-index", "--quiet", "HEAD"])
                    .current_dir(&absolute_path),
            )
            .allow_failure()
            .output_mode(match self.is_verbose() {
                true => OutputMode::PrintAll,
                false => OutputMode::PrintOutput,
            }),
        );
        if has_local_modifications {
            self.run(Command::new("git").args(&["stash", "push"]).current_dir(&absolute_path));
        }

        self.run(Command::new("git").args(&["reset", "-q", "--hard"]).current_dir(&absolute_path));
        self.run(Command::new("git").args(&["clean", "-qdfx"]).current_dir(&absolute_path));

        if has_local_modifications {
            self.run(Command::new("git").args(&["stash", "pop"]).current_dir(absolute_path));
        }
    }

    /// If any submodule has been initialized already, sync it unconditionally.
    /// This avoids contributors checking in a submodule change by accident.
    pub fn update_existing_submodules(&self) {
        // Avoid running git when there isn't a git checkout.
        if !self.config.submodules(&self.rust_info()) {
            return;
        }
        let output = output(
            self.config
                .git()
                .args(&["config", "--file"])
                .arg(&self.config.src.join(".gitmodules"))
                .args(&["--get-regexp", "path"]),
        );
        for line in output.lines() {
            // Look for `submodule.$name.path = $path`
            // Sample output: `submodule.src/rust-installer.path src/tools/rust-installer`
            let submodule = Path::new(line.splitn(2, ' ').nth(1).unwrap());
            // Don't update the submodule unless it's already been cloned.
            if GitInfo::new(false, submodule).is_managed_git_subrepository() {
                self.update_submodule(submodule);
            }
        }
    }

    /// Executes the entire build, as configured by the flags and configuration.
    pub fn build(&mut self) {
        unsafe {
            crate::utils::job::setup(self);
        }

        // Download rustfmt early so that it can be used in rust-analyzer configs.
        let _ = &builder::Builder::new(&self).initial_rustfmt();

        // hardcoded subcommands
        match &self.config.cmd {
            Subcommand::Format { check } => {
                return core::build_steps::format::format(
                    &builder::Builder::new(&self),
                    *check,
                    &self.config.paths,
                );
            }
            Subcommand::Suggest { run } => {
                return core::build_steps::suggest::suggest(&builder::Builder::new(&self), *run);
            }
            _ => (),
        }

        {
            let builder = builder::Builder::new(&self);
            if let Some(path) = builder.paths.get(0) {
                if path == Path::new("nonexistent/path/to/trigger/cargo/metadata") {
                    return;
                }
            }
        }

        if !self.config.dry_run() {
            {
                self.config.dry_run = DryRun::SelfCheck;
                let builder = builder::Builder::new(&self);
                builder.execute_cli();
            }
            self.config.dry_run = DryRun::Disabled;
            let builder = builder::Builder::new(&self);
            builder.execute_cli();
        } else {
            let builder = builder::Builder::new(&self);
            builder.execute_cli();
        }

        // Check for postponed failures from `test --no-fail-fast`.
        let failures = self.delayed_failures.borrow();
        if failures.len() > 0 {
            eprintln!("\n{} command(s) did not execute successfully:\n", failures.len());
            for failure in failures.iter() {
                eprintln!("  - {failure}\n");
            }
            exit!(1);
        }

        #[cfg(feature = "build-metrics")]
        self.metrics.persist(self);
    }

    /// Clear out `dir` if `input` is newer.
    ///
    /// After this executes, it will also ensure that `dir` exists.
    fn clear_if_dirty(&self, dir: &Path, input: &Path) -> bool {
        let stamp = dir.join(".stamp");
        let mut cleared = false;
        if mtime(&stamp) < mtime(input) {
            self.verbose(&format!("Dirty - {}", dir.display()));
            let _ = fs::remove_dir_all(dir);
            cleared = true;
        } else if stamp.exists() {
            return cleared;
        }
        t!(fs::create_dir_all(dir));
        t!(File::create(stamp));
        cleared
    }

    fn rust_info(&self) -> &GitInfo {
        &self.config.rust_info
    }

    /// Gets the space-separated set of activated features for the standard
    /// library.
    fn std_features(&self, target: TargetSelection) -> String {
        let mut features = " panic-unwind".to_string();

        match self.config.llvm_libunwind(target) {
            LlvmLibunwind::InTree => features.push_str(" llvm-libunwind"),
            LlvmLibunwind::System => features.push_str(" system-llvm-libunwind"),
            LlvmLibunwind::No => {}
        }
        if self.config.backtrace {
            features.push_str(" backtrace");
        }
        if self.config.profiler_enabled(target) {
            features.push_str(" profiler");
        }
        features
    }

    /// Gets the space-separated set of activated features for the compiler.
    fn rustc_features(&self, kind: Kind) -> String {
        let mut features = vec![];
        if self.config.jemalloc {
            features.push("jemalloc");
        }
        if self.config.llvm_enabled() || kind == Kind::Check {
            features.push("llvm");
        }
        // keep in sync with `bootstrap/compile.rs:rustc_cargo_env`
        if self.config.rustc_parallel {
            features.push("rustc_use_parallel_compiler");
        }

        // If debug logging is on, then we want the default for tracing:
        // https://github.com/tokio-rs/tracing/blob/3dd5c03d907afdf2c39444a29931833335171554/tracing/src/level_filters.rs#L26
        // which is everything (including debug/trace/etc.)
        // if its unset, if debug_assertions is on, then debug_logging will also be on
        // as well as tracing *ignoring* this feature when debug_assertions is on
        if !self.config.rust_debug_logging {
            features.push("max_level_info");
        }

        features.join(" ")
    }

    /// Component directory that Cargo will produce output into (e.g.
    /// release/debug)
    fn cargo_dir(&self) -> &'static str {
        if self.config.rust_optimize.is_release() { "release" } else { "debug" }
    }

    fn tools_dir(&self, compiler: Compiler) -> PathBuf {
        let out = self
            .out
            .join(&*compiler.host.triple)
            .join(format!("stage{}-tools-bin", compiler.stage));
        t!(fs::create_dir_all(&out));
        out
    }

    /// Returns the root directory for all output generated in a particular
    /// stage when running with a particular host compiler.
    ///
    /// The mode indicates what the root directory is for.
    fn stage_out(&self, compiler: Compiler, mode: Mode) -> PathBuf {
        let suffix = match mode {
            Mode::Std => "-std",
            Mode::Rustc => "-rustc",
            Mode::Codegen => "-codegen",
            Mode::ToolBootstrap => "-bootstrap-tools",
            Mode::ToolStd | Mode::ToolRustc => "-tools",
        };
        self.out.join(&*compiler.host.triple).join(format!("stage{}{}", compiler.stage, suffix))
    }

    /// Returns the root output directory for all Cargo output in a given stage,
    /// running a particular compiler, whether or not we're building the
    /// standard library, and targeting the specified architecture.
    fn cargo_out(&self, compiler: Compiler, mode: Mode, target: TargetSelection) -> PathBuf {
        self.stage_out(compiler, mode).join(&*target.triple).join(self.cargo_dir())
    }

    /// Root output directory for LLVM compiled for `target`
    ///
    /// Note that if LLVM is configured externally then the directory returned
    /// will likely be empty.
    fn llvm_out(&self, target: TargetSelection) -> PathBuf {
        self.out.join(&*target.triple).join("llvm")
    }

    fn lld_out(&self, target: TargetSelection) -> PathBuf {
        self.out.join(&*target.triple).join("lld")
    }

    /// Output directory for all documentation for a target
    fn doc_out(&self, target: TargetSelection) -> PathBuf {
        self.out.join(&*target.triple).join("doc")
    }

    /// Output directory for all JSON-formatted documentation for a target
    fn json_doc_out(&self, target: TargetSelection) -> PathBuf {
        self.out.join(&*target.triple).join("json-doc")
    }

    fn test_out(&self, target: TargetSelection) -> PathBuf {
        self.out.join(&*target.triple).join("test")
    }

    /// Output directory for all documentation for a target
    fn compiler_doc_out(&self, target: TargetSelection) -> PathBuf {
        self.out.join(&*target.triple).join("compiler-doc")
    }

    /// Output directory for some generated md crate documentation for a target (temporary)
    fn md_doc_out(&self, target: TargetSelection) -> Interned<PathBuf> {
        INTERNER.intern_path(self.out.join(&*target.triple).join("md-doc"))
    }

    /// Returns `true` if no custom `llvm-config` is set for the specified target.
    ///
    /// If no custom `llvm-config` was specified then Rust's llvm will be used.
    fn is_rust_llvm(&self, target: TargetSelection) -> bool {
        match self.config.target_config.get(&target) {
            Some(Target { llvm_has_rust_patches: Some(patched), .. }) => *patched,
            Some(Target { llvm_config, .. }) => {
                // If the user set llvm-config we assume Rust is not patched,
                // but first check to see if it was configured by llvm-from-ci.
                (self.config.llvm_from_ci && target == self.config.build) || llvm_config.is_none()
            }
            None => true,
        }
    }

    /// Returns the path to `FileCheck` binary for the specified target
    fn llvm_filecheck(&self, target: TargetSelection) -> PathBuf {
        let target_config = self.config.target_config.get(&target);
        if let Some(s) = target_config.and_then(|c| c.llvm_filecheck.as_ref()) {
            s.to_path_buf()
        } else if let Some(s) = target_config.and_then(|c| c.llvm_config.as_ref()) {
            let llvm_bindir = output(Command::new(s).arg("--bindir"));
            let filecheck = Path::new(llvm_bindir.trim()).join(exe("FileCheck", target));
            if filecheck.exists() {
                filecheck
            } else {
                // On Fedora the system LLVM installs FileCheck in the
                // llvm subdirectory of the libdir.
                let llvm_libdir = output(Command::new(s).arg("--libdir"));
                let lib_filecheck =
                    Path::new(llvm_libdir.trim()).join("llvm").join(exe("FileCheck", target));
                if lib_filecheck.exists() {
                    lib_filecheck
                } else {
                    // Return the most normal file name, even though
                    // it doesn't exist, so that any error message
                    // refers to that.
                    filecheck
                }
            }
        } else {
            let base = self.llvm_out(target).join("build");
            let base = if !self.ninja() && target.contains("msvc") {
                if self.config.llvm_optimize {
                    if self.config.llvm_release_debuginfo {
                        base.join("RelWithDebInfo")
                    } else {
                        base.join("Release")
                    }
                } else {
                    base.join("Debug")
                }
            } else {
                base
            };
            base.join("bin").join(exe("FileCheck", target))
        }
    }

    /// Directory for libraries built from C/C++ code and shared between stages.
    fn native_dir(&self, target: TargetSelection) -> PathBuf {
        self.out.join(&*target.triple).join("native")
    }

    /// Root output directory for rust_test_helpers library compiled for
    /// `target`
    fn test_helpers_out(&self, target: TargetSelection) -> PathBuf {
        self.native_dir(target).join("rust-test-helpers")
    }

    /// Adds the `RUST_TEST_THREADS` env var if necessary
    fn add_rust_test_threads(&self, cmd: &mut Command) {
        if env::var_os("RUST_TEST_THREADS").is_none() {
            cmd.env("RUST_TEST_THREADS", self.jobs().to_string());
        }
    }

    /// Returns the libdir of the snapshot compiler.
    fn rustc_snapshot_libdir(&self) -> PathBuf {
        self.rustc_snapshot_sysroot().join(libdir(self.config.build))
    }

    /// Returns the sysroot of the snapshot compiler.
    fn rustc_snapshot_sysroot(&self) -> &Path {
        static SYSROOT_CACHE: OnceCell<PathBuf> = once_cell::sync::OnceCell::new();
        SYSROOT_CACHE.get_or_init(|| {
            let mut rustc = Command::new(&self.initial_rustc);
            rustc.args(&["--print", "sysroot"]);
            output(&mut rustc).trim().into()
        })
    }

    /// Runs a command, printing out nice contextual information if it fails.
    fn run(&self, cmd: &mut Command) {
        self.run_cmd(BootstrapCommand::from(cmd).fail_fast().output_mode(
            match self.is_verbose() {
                true => OutputMode::PrintAll,
                false => OutputMode::PrintOutput,
            },
        ));
    }

    /// Runs a command, printing out contextual info if it fails, and delaying errors until the build finishes.
    pub(crate) fn run_delaying_failure(&self, cmd: &mut Command) -> bool {
        self.run_cmd(BootstrapCommand::from(cmd).delay_failure().output_mode(
            match self.is_verbose() {
                true => OutputMode::PrintAll,
                false => OutputMode::PrintOutput,
            },
        ))
    }

    /// Runs a command, printing out nice contextual information if it fails.
    fn run_quiet(&self, cmd: &mut Command) {
        self.run_cmd(
            BootstrapCommand::from(cmd).fail_fast().output_mode(OutputMode::SuppressOnSuccess),
        );
    }

    /// Runs a command, printing out nice contextual information if it fails.
    /// Exits if the command failed to execute at all, otherwise returns its
    /// `status.success()`.
    fn run_quiet_delaying_failure(&self, cmd: &mut Command) -> bool {
        self.run_cmd(
            BootstrapCommand::from(cmd).delay_failure().output_mode(OutputMode::SuppressOnSuccess),
        )
    }

    /// A centralized function for running commands that do not return output.
    pub(crate) fn run_cmd<'a, C: Into<BootstrapCommand<'a>>>(&self, cmd: C) -> bool {
        if self.config.dry_run() {
            return true;
        }

        let command = cmd.into();
        self.verbose(&format!("running: {command:?}"));

        let (output, print_error) = match command.output_mode {
            mode @ (OutputMode::PrintAll | OutputMode::PrintOutput) => (
                command.command.status().map(|status| Output {
                    status,
                    stdout: Vec::new(),
                    stderr: Vec::new(),
                }),
                matches!(mode, OutputMode::PrintAll),
            ),
            OutputMode::SuppressOnSuccess => (command.command.output(), true),
        };

        let output = match output {
            Ok(output) => output,
            Err(e) => fail(&format!("failed to execute command: {:?}\nerror: {}", command, e)),
        };
        let result = if !output.status.success() {
            if print_error {
                println!(
                    "\n\ncommand did not execute successfully: {:?}\n\
                    expected success, got: {}\n\n\
                    stdout ----\n{}\n\
                    stderr ----\n{}\n\n",
                    command.command,
                    output.status,
                    String::from_utf8_lossy(&output.stdout),
                    String::from_utf8_lossy(&output.stderr)
                );
            }
            Err(())
        } else {
            Ok(())
        };

        match result {
            Ok(_) => true,
            Err(_) => {
                match command.failure_behavior {
                    BehaviorOnFailure::DelayFail => {
                        if self.fail_fast {
                            exit!(1);
                        }

                        let mut failures = self.delayed_failures.borrow_mut();
                        failures.push(format!("{command:?}"));
                    }
                    BehaviorOnFailure::Exit => {
                        exit!(1);
                    }
                    BehaviorOnFailure::Ignore => {}
                }
                false
            }
        }
    }

    pub fn is_verbose_than(&self, level: usize) -> bool {
        self.verbosity > level
    }

    /// Prints a message if this build is configured in more verbose mode than `level`.
    fn verbose_than(&self, level: usize, msg: &str) {
        if self.is_verbose_than(level) {
            println!("{msg}");
        }
    }

    fn info(&self, msg: &str) {
        match self.config.dry_run {
            DryRun::SelfCheck => (),
            DryRun::Disabled | DryRun::UserSelected => {
                println!("{msg}");
            }
        }
    }

    #[must_use = "Groups should not be dropped until the Step finishes running"]
    #[track_caller]
    fn msg_check(
        &self,
        what: impl Display,
        target: impl Into<Option<TargetSelection>>,
    ) -> Option<gha::Group> {
        self.msg(Kind::Check, self.config.stage, what, self.config.build, target)
    }

    #[must_use = "Groups should not be dropped until the Step finishes running"]
    #[track_caller]
    fn msg_doc(
        &self,
        compiler: Compiler,
        what: impl Display,
        target: impl Into<Option<TargetSelection>> + Copy,
    ) -> Option<gha::Group> {
        self.msg(Kind::Doc, compiler.stage, what, compiler.host, target.into())
    }

    #[must_use = "Groups should not be dropped until the Step finishes running"]
    #[track_caller]
    fn msg_build(
        &self,
        compiler: Compiler,
        what: impl Display,
        target: impl Into<Option<TargetSelection>>,
    ) -> Option<gha::Group> {
        self.msg(Kind::Build, compiler.stage, what, compiler.host, target)
    }

    /// Return a `Group` guard for a [`Step`] that is built for each `--stage`.
    ///
    /// [`Step`]: crate::core::builder::Step
    #[must_use = "Groups should not be dropped until the Step finishes running"]
    #[track_caller]
    fn msg(
        &self,
        action: impl Into<Kind>,
        stage: u32,
        what: impl Display,
        host: impl Into<Option<TargetSelection>>,
        target: impl Into<Option<TargetSelection>>,
    ) -> Option<gha::Group> {
        let action = action.into().description();
        let msg = |fmt| format!("{action} stage{stage} {what}{fmt}");
        let msg = if let Some(target) = target.into() {
            let host = host.into().unwrap();
            if host == target {
                msg(format_args!(" ({target})"))
            } else {
                msg(format_args!(" ({host} -> {target})"))
            }
        } else {
            msg(format_args!(""))
        };
        self.group(&msg)
    }

    /// Return a `Group` guard for a [`Step`] that is only built once and isn't affected by `--stage`.
    ///
    /// [`Step`]: crate::core::builder::Step
    #[must_use = "Groups should not be dropped until the Step finishes running"]
    #[track_caller]
    fn msg_unstaged(
        &self,
        action: impl Into<Kind>,
        what: impl Display,
        target: TargetSelection,
    ) -> Option<gha::Group> {
        let action = action.into().description();
        let msg = format!("{action} {what} for {target}");
        self.group(&msg)
    }

    #[must_use = "Groups should not be dropped until the Step finishes running"]
    #[track_caller]
    fn msg_sysroot_tool(
        &self,
        action: impl Into<Kind>,
        stage: u32,
        what: impl Display,
        host: TargetSelection,
        target: TargetSelection,
    ) -> Option<gha::Group> {
        let action = action.into().description();
        let msg = |fmt| format!("{action} {what} {fmt}");
        let msg = if host == target {
            msg(format_args!("(stage{stage} -> stage{}, {target})", stage + 1))
        } else {
            msg(format_args!("(stage{stage}:{host} -> stage{}:{target})", stage + 1))
        };
        self.group(&msg)
    }

    #[track_caller]
    fn group(&self, msg: &str) -> Option<gha::Group> {
        match self.config.dry_run {
            DryRun::SelfCheck => None,
            DryRun::Disabled | DryRun::UserSelected => Some(gha::group(&msg)),
        }
    }

    /// Returns the number of parallel jobs that have been configured for this
    /// build.
    fn jobs(&self) -> u32 {
        self.config.jobs.unwrap_or_else(|| {
            std::thread::available_parallelism().map_or(1, std::num::NonZeroUsize::get) as u32
        })
    }

    fn debuginfo_map_to(&self, which: GitRepo) -> Option<String> {
        if !self.config.rust_remap_debuginfo {
            return None;
        }

        match which {
            GitRepo::Rustc => {
                let sha = self.rust_sha().unwrap_or(&self.version);
                Some(format!("/rustc/{sha}"))
            }
            GitRepo::Llvm => Some(String::from("/rustc/llvm")),
        }
    }

    /// Returns the path to the C compiler for the target specified.
    fn cc(&self, target: TargetSelection) -> PathBuf {
        if self.config.dry_run() {
            return PathBuf::new();
        }
        self.cc.borrow()[&target].path().into()
    }

    /// Returns a list of flags to pass to the C compiler for the target
    /// specified.
    fn cflags(&self, target: TargetSelection, which: GitRepo, c: CLang) -> Vec<String> {
        if self.config.dry_run() {
            return Vec::new();
        }
        let base = match c {
            CLang::C => self.cc.borrow()[&target].clone(),
            CLang::Cxx => self.cxx.borrow()[&target].clone(),
        };

        // Filter out -O and /O (the optimization flags) that we picked up from
        // cc-rs because the build scripts will determine that for themselves.
        let mut base = base
            .args()
            .iter()
            .map(|s| s.to_string_lossy().into_owned())
            .filter(|s| !s.starts_with("-O") && !s.starts_with("/O"))
            .collect::<Vec<String>>();

        // If we're compiling on macOS then we add a few unconditional flags
        // indicating that we want libc++ (more filled out than libstdc++) and
        // we want to compile for 10.7. This way we can ensure that
        // LLVM/etc are all properly compiled.
        if target.contains("apple-darwin") {
            base.push("-stdlib=libc++".into());
        }

        // Work around an apparently bad MinGW / GCC optimization,
        // See: https://lists.llvm.org/pipermail/cfe-dev/2016-December/051980.html
        // See: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78936
        if &*target.triple == "i686-pc-windows-gnu" {
            base.push("-fno-omit-frame-pointer".into());
        }

        if let Some(map_to) = self.debuginfo_map_to(which) {
            let map = format!("{}={}", self.src.display(), map_to);
            let cc = self.cc(target);
            if cc.ends_with("clang") || cc.ends_with("gcc") {
                base.push(format!("-fdebug-prefix-map={map}"));
            } else if cc.ends_with("clang-cl.exe") {
                base.push("-Xclang".into());
                base.push(format!("-fdebug-prefix-map={map}"));
            }
        }
        base
    }

    /// Returns the path to the `ar` archive utility for the target specified.
    fn ar(&self, target: TargetSelection) -> Option<PathBuf> {
        if self.config.dry_run() {
            return None;
        }
        self.ar.borrow().get(&target).cloned()
    }

    /// Returns the path to the `ranlib` utility for the target specified.
    fn ranlib(&self, target: TargetSelection) -> Option<PathBuf> {
        if self.config.dry_run() {
            return None;
        }
        self.ranlib.borrow().get(&target).cloned()
    }

    /// Returns the path to the C++ compiler for the target specified.
    fn cxx(&self, target: TargetSelection) -> Result<PathBuf, String> {
        if self.config.dry_run() {
            return Ok(PathBuf::new());
        }
        match self.cxx.borrow().get(&target) {
            Some(p) => Ok(p.path().into()),
            None => Err(format!("target `{target}` is not configured as a host, only as a target")),
        }
    }

    /// Returns the path to the linker for the given target if it needs to be overridden.
    fn linker(&self, target: TargetSelection) -> Option<PathBuf> {
        if self.config.dry_run() {
            return Some(PathBuf::new());
        }
        if let Some(linker) = self.config.target_config.get(&target).and_then(|c| c.linker.clone())
        {
            Some(linker)
        } else if target.contains("vxworks") {
            // need to use CXX compiler as linker to resolve the exception functions
            // that are only existed in CXX libraries
            Some(self.cxx.borrow()[&target].path().into())
        } else if target != self.config.build
            && helpers::use_host_linker(target)
            && !target.contains("msvc")
        {
            Some(self.cc(target))
        } else if self.config.use_lld && !self.is_fuse_ld_lld(target) && self.build == target {
            Some(self.initial_lld.clone())
        } else {
            None
        }
    }

    // LLD is used through `-fuse-ld=lld` rather than directly.
    // Only MSVC targets use LLD directly at the moment.
    fn is_fuse_ld_lld(&self, target: TargetSelection) -> bool {
        self.config.use_lld && !target.contains("msvc")
    }

    fn lld_flags(&self, target: TargetSelection) -> impl Iterator<Item = String> {
        let mut options = [None, None];

        if self.config.use_lld {
            if self.is_fuse_ld_lld(target) {
                options[0] = Some("-Clink-arg=-fuse-ld=lld".to_string());
            }

            let no_threads = helpers::lld_flag_no_threads(target.contains("windows"));
            options[1] = Some(format!("-Clink-arg=-Wl,{no_threads}"));
        }

        IntoIterator::into_iter(options).flatten()
    }

    /// Returns if this target should statically link the C runtime, if specified
    fn crt_static(&self, target: TargetSelection) -> Option<bool> {
        if target.contains("pc-windows-msvc") {
            Some(true)
        } else {
            self.config.target_config.get(&target).and_then(|t| t.crt_static)
        }
    }

    /// Returns the "musl root" for this `target`, if defined
    fn musl_root(&self, target: TargetSelection) -> Option<&Path> {
        self.config
            .target_config
            .get(&target)
            .and_then(|t| t.musl_root.as_ref())
            .or_else(|| self.config.musl_root.as_ref())
            .map(|p| &**p)
    }

    /// Returns the "musl libdir" for this `target`.
    fn musl_libdir(&self, target: TargetSelection) -> Option<PathBuf> {
        let t = self.config.target_config.get(&target)?;
        if let libdir @ Some(_) = &t.musl_libdir {
            return libdir.clone();
        }
        self.musl_root(target).map(|root| root.join("lib"))
    }

    /// Returns the sysroot for the wasi target, if defined
    fn wasi_root(&self, target: TargetSelection) -> Option<&Path> {
        self.config.target_config.get(&target).and_then(|t| t.wasi_root.as_ref()).map(|p| &**p)
    }

    /// Returns `true` if this is a no-std `target`, if defined
    fn no_std(&self, target: TargetSelection) -> Option<bool> {
        self.config.target_config.get(&target).map(|t| t.no_std)
    }

    /// Returns `true` if the target will be tested using the `remote-test-client`
    /// and `remote-test-server` binaries.
    fn remote_tested(&self, target: TargetSelection) -> bool {
        self.qemu_rootfs(target).is_some()
            || target.contains("android")
            || env::var_os("TEST_DEVICE_ADDR").is_some()
    }

    /// Returns the root of the "rootfs" image that this target will be using,
    /// if one was configured.
    ///
    /// If `Some` is returned then that means that tests for this target are
    /// emulated with QEMU and binaries will need to be shipped to the emulator.
    fn qemu_rootfs(&self, target: TargetSelection) -> Option<&Path> {
        self.config.target_config.get(&target).and_then(|t| t.qemu_rootfs.as_ref()).map(|p| &**p)
    }

    /// Path to the python interpreter to use
    fn python(&self) -> &Path {
        if self.config.build.ends_with("apple-darwin") {
            // Force /usr/bin/python3 on macOS for LLDB tests because we're loading the
            // LLDB plugin's compiled module which only works with the system python
            // (namely not Homebrew-installed python)
            Path::new("/usr/bin/python3")
        } else {
            self.config
                .python
                .as_ref()
                .expect("python is required for running LLDB or rustdoc tests")
        }
    }

    /// Temporary directory that extended error information is emitted to.
    fn extended_error_dir(&self) -> PathBuf {
        self.out.join("tmp/extended-error-metadata")
    }

    /// Tests whether the `compiler` compiling for `target` should be forced to
    /// use a stage1 compiler instead.
    ///
    /// Currently, by default, the build system does not perform a "full
    /// bootstrap" by default where we compile the compiler three times.
    /// Instead, we compile the compiler two times. The final stage (stage2)
    /// just copies the libraries from the previous stage, which is what this
    /// method detects.
    ///
    /// Here we return `true` if:
    ///
    /// * The build isn't performing a full bootstrap
    /// * The `compiler` is in the final stage, 2
    /// * We're not cross-compiling, so the artifacts are already available in
    ///   stage1
    ///
    /// When all of these conditions are met the build will lift artifacts from
    /// the previous stage forward.
    fn force_use_stage1(&self, stage: u32, target: TargetSelection) -> bool {
        !self.config.full_bootstrap
            && !self.config.download_rustc()
            && stage >= 2
            && (self.hosts.iter().any(|h| *h == target) || target == self.build)
    }

    /// Checks whether the `compiler` compiling for `target` should be forced to
    /// use a stage2 compiler instead.
    ///
    /// When we download the pre-compiled version of rustc and compiler stage is >= 2,
    /// it should be forced to use a stage2 compiler.
    fn force_use_stage2(&self, stage: u32) -> bool {
        self.config.download_rustc() && stage >= 2
    }

    /// Given `num` in the form "a.b.c" return a "release string" which
    /// describes the release version number.
    ///
    /// For example on nightly this returns "a.b.c-nightly", on beta it returns
    /// "a.b.c-beta.1" and on stable it just returns "a.b.c".
    fn release(&self, num: &str) -> String {
        match &self.config.channel[..] {
            "stable" => num.to_string(),
            "beta" => {
                if !self.config.omit_git_hash {
                    format!("{}-beta.{}", num, self.beta_prerelease_version())
                } else {
                    format!("{num}-beta")
                }
            }
            "nightly" => format!("{num}-nightly"),
            _ => format!("{num}-dev"),
        }
    }

    fn beta_prerelease_version(&self) -> u32 {
        fn extract_beta_rev_from_file<P: AsRef<Path>>(version_file: P) -> Option<String> {
            let version = fs::read_to_string(version_file).ok()?;

            helpers::extract_beta_rev(&version)
        }

        if let Some(s) = self.prerelease_version.get() {
            return s;
        }

        // First check if there is a version file available.
        // If available, we read the beta revision from that file.
        // This only happens when building from a source tarball when Git should not be used.
        let count = extract_beta_rev_from_file(self.src.join("version")).unwrap_or_else(|| {
            // Figure out how many merge commits happened since we branched off master.
            // That's our beta number!
            // (Note that we use a `..` range, not the `...` symmetric difference.)
            output(self.config.git().arg("rev-list").arg("--count").arg("--merges").arg(format!(
                "refs/remotes/origin/{}..HEAD",
                self.config.stage0_metadata.config.nightly_branch
            )))
        });
        let n = count.trim().parse().unwrap();
        self.prerelease_version.set(Some(n));
        n
    }

    /// Returns the value of `release` above for Rust itself.
    fn rust_release(&self) -> String {
        self.release(&self.version)
    }

    /// Returns the "package version" for a component given the `num` release
    /// number.
    ///
    /// The package version is typically what shows up in the names of tarballs.
    /// For channels like beta/nightly it's just the channel name, otherwise
    /// it's the `num` provided.
    fn package_vers(&self, num: &str) -> String {
        match &self.config.channel[..] {
            "stable" => num.to_string(),
            "beta" => "beta".to_string(),
            "nightly" => "nightly".to_string(),
            _ => format!("{num}-dev"),
        }
    }

    /// Returns the value of `package_vers` above for Rust itself.
    fn rust_package_vers(&self) -> String {
        self.package_vers(&self.version)
    }

    /// Returns the `version` string associated with this compiler for Rust
    /// itself.
    ///
    /// Note that this is a descriptive string which includes the commit date,
    /// sha, version, etc.
    fn rust_version(&self) -> String {
        let mut version = self.rust_info().version(self, &self.version);
        if let Some(ref s) = self.config.description {
            version.push_str(" (");
            version.push_str(s);
            version.push(')');
        }
        version
    }

    /// Returns the full commit hash.
    fn rust_sha(&self) -> Option<&str> {
        self.rust_info().sha()
    }

    /// Returns the `a.b.c` version that the given package is at.
    fn release_num(&self, package: &str) -> String {
        let toml_file_name = self.src.join(&format!("src/tools/{package}/Cargo.toml"));
        let toml = t!(fs::read_to_string(&toml_file_name));
        for line in toml.lines() {
            if let Some(stripped) =
                line.strip_prefix("version = \"").and_then(|s| s.strip_suffix("\""))
            {
                return stripped.to_owned();
            }
        }

        panic!("failed to find version in {package}'s Cargo.toml")
    }

    /// Returns `true` if unstable features should be enabled for the compiler
    /// we're building.
    fn unstable_features(&self) -> bool {
        match &self.config.channel[..] {
            "stable" | "beta" => false,
            "nightly" | _ => true,
        }
    }

    /// Returns a Vec of all the dependencies of the given root crate,
    /// including transitive dependencies and the root itself. Only includes
    /// "local" crates (those in the local source tree, not from a registry).
    fn in_tree_crates(&self, root: &str, target: Option<TargetSelection>) -> Vec<&Crate> {
        let mut ret = Vec::new();
        let mut list = vec![INTERNER.intern_str(root)];
        let mut visited = HashSet::new();
        while let Some(krate) = list.pop() {
            let krate = self
                .crates
                .get(&krate)
                .unwrap_or_else(|| panic!("metadata missing for {krate}: {:?}", self.crates));
            ret.push(krate);
            for dep in &krate.deps {
                if !self.crates.contains_key(dep) {
                    // Ignore non-workspace members.
                    continue;
                }
                // Don't include optional deps if their features are not
                // enabled. Ideally this would be computed from `cargo
                // metadata --features …`, but that is somewhat slow. In
                // the future, we may want to consider just filtering all
                // build and dev dependencies in metadata::build.
                if visited.insert(dep)
                    && (dep != "profiler_builtins"
                        || target
                            .map(|t| self.config.profiler_enabled(t))
                            .unwrap_or_else(|| self.config.any_profiler_enabled()))
                    && (dep != "rustc_codegen_llvm" || self.config.llvm_enabled())
                {
                    list.push(*dep);
                }
            }
        }
        ret.sort_unstable_by_key(|krate| krate.name); // reproducible order needed for tests
        ret
    }

    fn read_stamp_file(&self, stamp: &Path) -> Vec<(PathBuf, DependencyType)> {
        if self.config.dry_run() {
            return Vec::new();
        }

        if !stamp.exists() {
            eprintln!(
                "Error: Unable to find the stamp file {}, did you try to keep a nonexistent build stage?",
                stamp.display()
            );
            crate::exit!(1);
        }

        let mut paths = Vec::new();
        let contents = t!(fs::read(stamp), &stamp);
        // This is the method we use for extracting paths from the stamp file passed to us. See
        // run_cargo for more information (in compile.rs).
        for part in contents.split(|b| *b == 0) {
            if part.is_empty() {
                continue;
            }
            let dependency_type = match part[0] as char {
                'h' => DependencyType::Host,
                's' => DependencyType::TargetSelfContained,
                't' => DependencyType::Target,
                _ => unreachable!(),
            };
            let path = PathBuf::from(t!(str::from_utf8(&part[1..])));
            paths.push((path, dependency_type));
        }
        paths
    }

    /// Copies a file from `src` to `dst`
    pub fn copy(&self, src: &Path, dst: &Path) {
        self.copy_internal(src, dst, false);
    }

    fn copy_internal(&self, src: &Path, dst: &Path, dereference_symlinks: bool) {
        if self.config.dry_run() {
            return;
        }
        self.verbose_than(1, &format!("Copy {src:?} to {dst:?}"));
        if src == dst {
            return;
        }
        let _ = fs::remove_file(&dst);
        let metadata = t!(src.symlink_metadata());
        let mut src = src.to_path_buf();
        if metadata.file_type().is_symlink() {
            if dereference_symlinks {
                src = t!(fs::canonicalize(src));
            } else {
                let link = t!(fs::read_link(src));
                t!(self.symlink_file(link, dst));
                return;
            }
        }
        if let Ok(()) = fs::hard_link(&src, dst) {
            // Attempt to "easy copy" by creating a hard link
            // (symlinks don't work on windows), but if that fails
            // just fall back to a slow `copy` operation.
        } else {
            if let Err(e) = fs::copy(&src, dst) {
                panic!("failed to copy `{}` to `{}`: {}", src.display(), dst.display(), e)
            }
            t!(fs::set_permissions(dst, metadata.permissions()));
            let atime = FileTime::from_last_access_time(&metadata);
            let mtime = FileTime::from_last_modification_time(&metadata);
            t!(filetime::set_file_times(dst, atime, mtime));
        }
    }

    /// Copies the `src` directory recursively to `dst`. Both are assumed to exist
    /// when this function is called.
    pub fn cp_r(&self, src: &Path, dst: &Path) {
        if self.config.dry_run() {
            return;
        }
        for f in self.read_dir(src) {
            let path = f.path();
            let name = path.file_name().unwrap();
            let dst = dst.join(name);
            if t!(f.file_type()).is_dir() {
                t!(fs::create_dir_all(&dst));
                self.cp_r(&path, &dst);
            } else {
                let _ = fs::remove_file(&dst);
                self.copy(&path, &dst);
            }
        }
    }

    /// Copies the `src` directory recursively to `dst`. Both are assumed to exist
    /// when this function is called. Unwanted files or directories can be skipped
    /// by returning `false` from the filter function.
    pub fn cp_filtered(&self, src: &Path, dst: &Path, filter: &dyn Fn(&Path) -> bool) {
        // Immediately recurse with an empty relative path
        self.recurse_(src, dst, Path::new(""), filter)
    }

    // Inner function does the actual work
    fn recurse_(&self, src: &Path, dst: &Path, relative: &Path, filter: &dyn Fn(&Path) -> bool) {
        for f in self.read_dir(src) {
            let path = f.path();
            let name = path.file_name().unwrap();
            let dst = dst.join(name);
            let relative = relative.join(name);
            // Only copy file or directory if the filter function returns true
            if filter(&relative) {
                if t!(f.file_type()).is_dir() {
                    let _ = fs::remove_dir_all(&dst);
                    self.create_dir(&dst);
                    self.recurse_(&path, &dst, &relative, filter);
                } else {
                    let _ = fs::remove_file(&dst);
                    self.copy(&path, &dst);
                }
            }
        }
    }

    fn copy_to_folder(&self, src: &Path, dest_folder: &Path) {
        let file_name = src.file_name().unwrap();
        let dest = dest_folder.join(file_name);
        self.copy(src, &dest);
    }

    fn install(&self, src: &Path, dstdir: &Path, perms: u32) {
        if self.config.dry_run() {
            return;
        }
        let dst = dstdir.join(src.file_name().unwrap());
        self.verbose_than(1, &format!("Install {src:?} to {dst:?}"));
        t!(fs::create_dir_all(dstdir));
        if !src.exists() {
            panic!("Error: File \"{}\" not found!", src.display());
        }
        self.copy_internal(src, &dst, true);
        chmod(&dst, perms);
    }

    fn read(&self, path: &Path) -> String {
        if self.config.dry_run() {
            return String::new();
        }
        t!(fs::read_to_string(path))
    }

    fn create_dir(&self, dir: &Path) {
        if self.config.dry_run() {
            return;
        }
        t!(fs::create_dir_all(dir))
    }

    fn remove_dir(&self, dir: &Path) {
        if self.config.dry_run() {
            return;
        }
        t!(fs::remove_dir_all(dir))
    }

    fn read_dir(&self, dir: &Path) -> impl Iterator<Item = fs::DirEntry> {
        let iter = match fs::read_dir(dir) {
            Ok(v) => v,
            Err(_) if self.config.dry_run() => return vec![].into_iter(),
            Err(err) => panic!("could not read dir {dir:?}: {err:?}"),
        };
        iter.map(|e| t!(e)).collect::<Vec<_>>().into_iter()
    }

    fn symlink_file<P: AsRef<Path>, Q: AsRef<Path>>(&self, src: P, link: Q) -> io::Result<()> {
        #[cfg(unix)]
        use std::os::unix::fs::symlink as symlink_file;
        #[cfg(windows)]
        use std::os::windows::fs::symlink_file;
        if !self.config.dry_run() { symlink_file(src.as_ref(), link.as_ref()) } else { Ok(()) }
    }

    /// Returns if config.ninja is enabled, and checks for ninja existence,
    /// exiting with a nicer error message if not.
    fn ninja(&self) -> bool {
        let mut cmd_finder = crate::core::sanity::Finder::new();

        if self.config.ninja_in_file {
            // Some Linux distros rename `ninja` to `ninja-build`.
            // CMake can work with either binary name.
            if cmd_finder.maybe_have("ninja-build").is_none()
                && cmd_finder.maybe_have("ninja").is_none()
            {
                eprintln!(
                    "
Couldn't find required command: ninja (or ninja-build)

You should install ninja as described at
<https://github.com/ninja-build/ninja/wiki/Pre-built-Ninja-packages>,
or set `ninja = false` in the `[llvm]` section of `config.toml`.
Alternatively, set `download-ci-llvm = true` in that `[llvm]` section
to download LLVM rather than building it.
"
                );
                exit!(1);
            }
        }

        // If ninja isn't enabled but we're building for MSVC then we try
        // doubly hard to enable it. It was realized in #43767 that the msbuild
        // CMake generator for MSVC doesn't respect configuration options like
        // disabling LLVM assertions, which can often be quite important!
        //
        // In these cases we automatically enable Ninja if we find it in the
        // environment.
        if !self.config.ninja_in_file
            && self.config.build.contains("msvc")
            && cmd_finder.maybe_have("ninja").is_some()
        {
            return true;
        }

        self.config.ninja_in_file
    }

    pub fn colored_stdout<R, F: FnOnce(&mut dyn WriteColor) -> R>(&self, f: F) -> R {
        self.colored_stream_inner(StandardStream::stdout, self.config.stdout_is_tty, f)
    }

    pub fn colored_stderr<R, F: FnOnce(&mut dyn WriteColor) -> R>(&self, f: F) -> R {
        self.colored_stream_inner(StandardStream::stderr, self.config.stderr_is_tty, f)
    }

    fn colored_stream_inner<R, F, C>(&self, constructor: C, is_tty: bool, f: F) -> R
    where
        C: Fn(ColorChoice) -> StandardStream,
        F: FnOnce(&mut dyn WriteColor) -> R,
    {
        let choice = match self.config.color {
            flags::Color::Always => ColorChoice::Always,
            flags::Color::Never => ColorChoice::Never,
            flags::Color::Auto if !is_tty => ColorChoice::Never,
            flags::Color::Auto => ColorChoice::Auto,
        };
        let mut stream = constructor(choice);
        let result = f(&mut stream);
        stream.reset().unwrap();
        result
    }
}

#[cfg(unix)]
fn chmod(path: &Path, perms: u32) {
    use std::os::unix::fs::*;
    t!(fs::set_permissions(path, fs::Permissions::from_mode(perms)));
}
#[cfg(windows)]
fn chmod(_path: &Path, _perms: u32) {}

impl Compiler {
    pub fn with_stage(mut self, stage: u32) -> Compiler {
        self.stage = stage;
        self
    }

    /// Returns `true` if this is a snapshot compiler for `build`'s configuration
    pub fn is_snapshot(&self, build: &Build) -> bool {
        self.stage == 0 && self.host == build.build
    }

    /// Returns if this compiler should be treated as a final stage one in the
    /// current build session.
    /// This takes into account whether we're performing a full bootstrap or
    /// not; don't directly compare the stage with `2`!
    pub fn is_final_stage(&self, build: &Build) -> bool {
        let final_stage = if build.config.full_bootstrap { 2 } else { 1 };
        self.stage >= final_stage
    }
}

fn envify(s: &str) -> String {
    s.chars()
        .map(|c| match c {
            '-' => '_',
            c => c,
        })
        .flat_map(|c| c.to_uppercase())
        .collect()
}

pub fn find_recent_config_change_ids(current_id: usize) -> Vec<usize> {
    let index = CONFIG_CHANGE_HISTORY
        .iter()
        .position(|&id| id == current_id)
        .expect(&format!("Value `{}` was not found in `CONFIG_CHANGE_HISTORY`.", current_id));

    CONFIG_CHANGE_HISTORY
        .iter()
        .skip(index + 1) // Skip the current_id and IDs before it
        .cloned()
        .collect()
}