builder.rs

// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

use std::any::Any;
use std::cell::{Cell, RefCell};
use std::collections::BTreeSet;
use std::env;
use std::fmt::Debug;
use std::fs;
use std::hash::Hash;
use std::ops::Deref;
use std::path::{Path, PathBuf};
use std::process::Command;
use std::time::{Instant, Duration};
use std::collections::HashMap;

use compile;
use install;
use dist;
use util::{exe, libdir, add_lib_path};
use {Build, Mode};
use cache::{INTERNER, Interned, Cache};
use check;
use test;
use flags::Subcommand;
use doc;
use tool;
use native;

pub use Compiler;

use petgraph::Graph;
use petgraph::graph::NodeIndex;

pub struct Builder<'a> {
    pub build: &'a Build,
    pub top_stage: u32,
    pub kind: Kind,
    cache: Cache,
    stack: RefCell<Vec<Box<Any>>>,
    time_spent_on_dependencies: Cell<Duration>,
    pub paths: Vec<PathBuf>,
    graph_nodes: RefCell<HashMap<String, NodeIndex>>,
    graph: RefCell<Graph<String, bool>>,
    parent: Cell<Option<NodeIndex>>,
}

impl<'a> Deref for Builder<'a> {
    type Target = Build;

    fn deref(&self) -> &Self::Target {
        self.build
    }
}

pub trait Step: 'static + Clone + Debug + PartialEq + Eq + Hash {
    /// `PathBuf` when directories are created or to return a `Compiler` once
    /// it's been assembled.
    type Output: Clone;

    const DEFAULT: bool = false;

    /// Run this rule for all hosts without cross compiling.
    const ONLY_HOSTS: bool = false;

    /// Primary function to execute this rule. Can call `builder.ensure(...)`
    /// with other steps to run those.
    fn run(self, builder: &Builder) -> Self::Output;

    /// When bootstrap is passed a set of paths, this controls whether this rule
    /// will execute. However, it does not get called in a "default" context
    /// when we are not passed any paths; in that case, make_run is called
    /// directly.
    fn should_run(run: ShouldRun) -> ShouldRun;

    /// Build up a "root" rule, either as a default rule or from a path passed
    /// to us.
    ///
    /// When path is `None`, we are executing in a context where no paths were
    /// passed. When `./x.py build` is run, for example, this rule could get
    /// called if it is in the correct list below with a path of `None`.
    fn make_run(_run: RunConfig) {
        // It is reasonable to not have an implementation of make_run for rules
        // who do not want to get called from the root context. This means that
        // they are likely dependencies (e.g., sysroot creation) or similar, and
        // as such calling them from ./x.py isn't logical.
        unimplemented!()
    }
}

pub struct RunConfig<'a> {
    pub builder: &'a Builder<'a>,
    pub host: Interned<String>,
    pub target: Interned<String>,
    pub path: PathBuf,
}

struct StepDescription {
    default: bool,
    only_hosts: bool,
    should_run: fn(ShouldRun) -> ShouldRun,
    make_run: fn(RunConfig),
    name: &'static str,
}

#[derive(Debug, Clone, PartialOrd, Ord, PartialEq, Eq)]
struct PathSet {
    set: BTreeSet<PathBuf>,
}

impl PathSet {
    fn empty() -> PathSet {
        PathSet { set: BTreeSet::new() }
    }

    fn one<P: Into<PathBuf>>(path: P) -> PathSet {
        let mut set = BTreeSet::new();
        set.insert(path.into());
        PathSet { set }
    }

    fn has(&self, needle: &Path) -> bool {
        self.set.iter().any(|p| p.ends_with(needle))
    }

    fn path(&self, builder: &Builder) -> PathBuf {
        self.set.iter().next().unwrap_or(&builder.build.src).to_path_buf()
    }
}

impl StepDescription {
    fn from<S: Step>() -> StepDescription {
        StepDescription {
            default: S::DEFAULT,
            only_hosts: S::ONLY_HOSTS,
            should_run: S::should_run,
            make_run: S::make_run,
            name: unsafe { ::std::intrinsics::type_name::<S>() },
        }
    }

    fn maybe_run(&self, builder: &Builder, pathset: &PathSet) {
        if builder.config.exclude.iter().any(|e| pathset.has(e)) {
            eprintln!("Skipping {:?} because it is excluded", pathset);
            return;
        } else if !builder.config.exclude.is_empty() {
            eprintln!("{:?} not skipped for {:?} -- not in {:?}", pathset,
                self.name, builder.config.exclude);
        }
        let hosts = &builder.hosts;

        // Determine the targets participating in this rule.
        let targets = if self.only_hosts {
            if !builder.config.run_host_only {
                return; // don't run anything
            } else {
                &builder.hosts
            }
        } else {
            &builder.targets
        };

        for host in hosts {
            for target in targets {
                let run = RunConfig {
                    builder,
                    path: pathset.path(builder),
                    host: *host,
                    target: *target,
                };
                (self.make_run)(run);
            }
        }
    }

    fn run(v: &[StepDescription], builder: &Builder, paths: &[PathBuf]) {
        let should_runs = v.iter().map(|desc| {
            (desc.should_run)(ShouldRun::new(builder))
        }).collect::<Vec<_>>();

        // sanity checks on rules
        for (desc, should_run) in v.iter().zip(&should_runs) {
            assert!(!should_run.paths.is_empty(),
                "{:?} should have at least one pathset", desc.name);
        }

        if paths.is_empty() {
            for (desc, should_run) in v.iter().zip(should_runs) {
                if desc.default && should_run.is_really_default {
                    for pathset in &should_run.paths {
                        desc.maybe_run(builder, pathset);
                    }
                }
            }
        } else {
            for path in paths {
                let mut attempted_run = false;
                for (desc, should_run) in v.iter().zip(&should_runs) {
                    if let Some(pathset) = should_run.pathset_for_path(path) {
                        attempted_run = true;
                        desc.maybe_run(builder, pathset);
                    }
                }

                if !attempted_run {
                    panic!("Error: no rules matched {}.", path.display());
                }
            }
        }
    }
}

#[derive(Clone)]
pub struct ShouldRun<'a> {
    pub builder: &'a Builder<'a>,
    // use a BTreeSet to maintain sort order
    paths: BTreeSet<PathSet>,

    // If this is a default rule, this is an additional constraint placed on
    // its run. Generally something like compiler docs being enabled.
    is_really_default: bool,
}

impl<'a> ShouldRun<'a> {
    fn new(builder: &'a Builder) -> ShouldRun<'a> {
        ShouldRun {
            builder,
            paths: BTreeSet::new(),
            is_really_default: true, // by default no additional conditions
        }
    }

    pub fn default_condition(mut self, cond: bool) -> Self {
        self.is_really_default = cond;
        self
    }

    // Unlike `krate` this will create just one pathset. As such, it probably shouldn't actually
    // ever be used, but as we transition to having all rules properly handle passing krate(...) by
    // actually doing something different for every crate passed.
    pub fn all_krates(mut self, name: &str) -> Self {
        let mut set = BTreeSet::new();
        for krate in self.builder.in_tree_crates(name) {
            set.insert(PathBuf::from(&krate.path));
        }
        self.paths.insert(PathSet { set });
        self
    }

    pub fn krate(mut self, name: &str) -> Self {
        for krate in self.builder.in_tree_crates(name) {
            self.paths.insert(PathSet::one(&krate.path));
        }
        self
    }

    // single, non-aliased path
    pub fn path(self, path: &str) -> Self {
        self.paths(&[path])
    }

    // multiple aliases for the same job
    pub fn paths(mut self, paths: &[&str]) -> Self {
        self.paths.insert(PathSet {
            set: paths.iter().map(PathBuf::from).collect(),
        });
        self
    }

    // allows being more explicit about why should_run in Step returns the value passed to it
    pub fn never(mut self) -> ShouldRun<'a> {
        self.paths.insert(PathSet::empty());
        self
    }

    fn pathset_for_path(&self, path: &Path) -> Option<&PathSet> {
        self.paths.iter().find(|pathset| pathset.has(path))
    }
}

#[derive(Copy, Clone, PartialEq, Eq, Debug)]
pub enum Kind {
    Build,
    Check,
    Test,
    Bench,
    Dist,
    Doc,
    Install,
}

impl<'a> Builder<'a> {
    fn get_step_descriptions(kind: Kind) -> Vec<StepDescription> {
        macro_rules! describe {
            ($($rule:ty),+ $(,)*) => {{
                vec![$(StepDescription::from::<$rule>()),+]
            }};
        }
        match kind {
            Kind::Build => describe!(compile::Std, compile::Test, compile::Rustc,
                compile::StartupObjects, tool::BuildManifest, tool::Rustbook, tool::ErrorIndex,
                tool::UnstableBookGen, tool::Tidy, tool::Linkchecker, tool::CargoTest,
                tool::Compiletest, tool::RemoteTestServer, tool::RemoteTestClient,
                tool::RustInstaller, tool::Cargo, tool::Rls, tool::Rustdoc, tool::Clippy,
                native::Llvm, tool::Rustfmt, tool::Miri, native::Lld),
            Kind::Check => describe!(check::Std, check::Test, check::Rustc, check::CodegenBackend, check::Rustdoc),
            Kind::Test => describe!(test::Tidy, test::Bootstrap, test::Ui, test::RunPass,
                test::CompileFail, test::ParseFail, test::RunFail, test::RunPassValgrind,
                test::MirOpt, test::Codegen, test::CodegenUnits, test::Incremental, test::Debuginfo,
                test::UiFullDeps, test::RunPassFullDeps, test::RunFailFullDeps,
                test::CompileFailFullDeps, test::IncrementalFullDeps, test::Rustdoc, test::Pretty,
                test::RunPassPretty, test::RunFailPretty, test::RunPassValgrindPretty,
                test::RunPassFullDepsPretty, test::RunFailFullDepsPretty,
                test::Crate, test::CrateLibrustc, test::CrateRustdoc, test::Linkcheck,
                test::Cargotest, test::Cargo, test::Rls, test::ErrorIndex, test::Distcheck,
                test::RunMakeFullDeps,
                test::Nomicon, test::Reference, test::RustdocBook, test::RustByExample,
                test::TheBook, test::UnstableBook,
                test::Rustfmt, test::Miri, test::Clippy, test::RustdocJS, test::RustdocTheme,
                // Run run-make last, since these won't pass without make on Windows
                test::RunMake, test::RustdocUi),
            Kind::Bench => describe!(test::Crate, test::CrateLibrustc),
            Kind::Doc => describe!(doc::UnstableBook, doc::UnstableBookGen, doc::TheBook,
                doc::Standalone, doc::Std, doc::Test, doc::WhitelistedRustc, doc::Rustc,
                doc::ErrorIndex, doc::Nomicon, doc::Reference, doc::Rustdoc, doc::RustByExample,
                doc::CargoBook),
            Kind::Dist => describe!(dist::Docs, dist::RustcDocs, dist::Mingw, dist::Rustc,
                dist::DebuggerScripts, dist::Std, dist::Analysis, dist::Src,
                dist::PlainSourceTarball, dist::Cargo, dist::Rls, dist::Rustfmt, dist::Extended,
                dist::HashSign),
            Kind::Install => describe!(install::Docs, install::Std, install::Cargo, install::Rls,
                install::Rustfmt, install::Analysis, install::Src, install::Rustc),
        }
    }

    pub fn get_help(build: &Build, subcommand: &str) -> Option<String> {
        let kind = match subcommand {
            "build" => Kind::Build,
            "doc" => Kind::Doc,
            "test" => Kind::Test,
            "bench" => Kind::Bench,
            "dist" => Kind::Dist,
            "install" => Kind::Install,
            _ => return None,
        };

        let builder = Builder {
            build,
            top_stage: build.config.stage.unwrap_or(2),
            kind,
            cache: Cache::new(),
            stack: RefCell::new(Vec::new()),
            time_spent_on_dependencies: Cell::new(Duration::new(0, 0)),
            paths: vec![],
            graph_nodes: RefCell::new(HashMap::new()),
            graph: RefCell::new(Graph::new()),
            parent: Cell::new(None),
        };

        let builder = &builder;
        let mut should_run = ShouldRun::new(builder);
        for desc in Builder::get_step_descriptions(builder.kind) {
            should_run = (desc.should_run)(should_run);
        }
        let mut help = String::from("Available paths:\n");
        for pathset in should_run.paths {
            for path in pathset.set {
                help.push_str(format!("    ./x.py {} {}\n", subcommand, path.display()).as_str());
            }
        }
        Some(help)
    }

    pub fn new(build: &Build) -> Builder {
        let (kind, paths) = match build.config.cmd {
            Subcommand::Build { ref paths } => (Kind::Build, &paths[..]),
            Subcommand::Check { ref paths } => (Kind::Check, &paths[..]),
            Subcommand::Doc { ref paths } => (Kind::Doc, &paths[..]),
            Subcommand::Test { ref paths, .. } => (Kind::Test, &paths[..]),
            Subcommand::Bench { ref paths, .. } => (Kind::Bench, &paths[..]),
            Subcommand::Dist { ref paths } => (Kind::Dist, &paths[..]),
            Subcommand::Install { ref paths } => (Kind::Install, &paths[..]),
            Subcommand::Clean { .. } => panic!(),
        };

        let builder = Builder {
            build,
            top_stage: build.config.stage.unwrap_or(2),
            kind,
            cache: Cache::new(),
            stack: RefCell::new(Vec::new()),
            time_spent_on_dependencies: Cell::new(Duration::new(0, 0)),
            paths: paths.to_owned(),
            graph_nodes: RefCell::new(HashMap::new()),
            graph: RefCell::new(Graph::new()),
            parent: Cell::new(None),
        };

        if kind == Kind::Dist {
            assert!(!builder.config.test_miri, "Do not distribute with miri enabled.\n\
                The distributed libraries would include all MIR (increasing binary size).
                The distributed MIR would include validation statements.");
        }

        builder
    }

    pub fn execute_cli(&self) -> Graph<String, bool> {
        self.run_step_descriptions(&Builder::get_step_descriptions(self.kind), &self.paths);
        self.graph.borrow().clone()
    }

    pub fn default_doc(&self, paths: Option<&[PathBuf]>) {
        let paths = paths.unwrap_or(&[]);
        self.run_step_descriptions(&Builder::get_step_descriptions(Kind::Doc), paths);
    }

    fn run_step_descriptions(&self, v: &[StepDescription], paths: &[PathBuf]) {
        StepDescription::run(v, self, paths);
    }

    /// Obtain a compiler at a given stage and for a given host. Explicitly does
    /// not take `Compiler` since all `Compiler` instances are meant to be
    /// obtained through this function, since it ensures that they are valid
    /// (i.e., built and assembled).
    pub fn compiler(&self, stage: u32, host: Interned<String>) -> Compiler {
        self.ensure(compile::Assemble { target_compiler: Compiler { stage, host } })
    }

    pub fn sysroot(&self, compiler: Compiler) -> Interned<PathBuf> {
        self.ensure(compile::Sysroot { compiler })
    }

    /// Returns the libdir where the standard library and other artifacts are
    /// found for a compiler's sysroot.
    pub fn sysroot_libdir(
        &self, compiler: Compiler, target: Interned<String>
    ) -> Interned<PathBuf> {
        #[derive(Debug, Copy, Clone, Hash, PartialEq, Eq)]
        struct Libdir {
            compiler: Compiler,
            target: Interned<String>,
        }
        impl Step for Libdir {
            type Output = Interned<PathBuf>;

            fn should_run(run: ShouldRun) -> ShouldRun {
                run.never()
            }

            fn run(self, builder: &Builder) -> Interned<PathBuf> {
                let compiler = self.compiler;
                let config = &builder.build.config;
                let lib = if compiler.stage >= 1 && config.libdir_relative().is_some() {
                    builder.build.config.libdir_relative().unwrap()
                } else {
                    Path::new("lib")
                };
                let sysroot = builder.sysroot(self.compiler).join(lib)
                    .join("rustlib").join(self.target).join("lib");
                let _ = fs::remove_dir_all(&sysroot);
                t!(fs::create_dir_all(&sysroot));
                INTERNER.intern_path(sysroot)
            }
        }
        self.ensure(Libdir { compiler, target })
    }

    pub fn sysroot_codegen_backends(&self, compiler: Compiler) -> PathBuf {
        self.sysroot_libdir(compiler, compiler.host)
            .with_file_name(self.config.rust_codegen_backends_dir.clone())
    }

    /// Returns the compiler's libdir where it stores the dynamic libraries that
    /// it itself links against.
    ///
    /// For example this returns `<sysroot>/lib` on Unix and `<sysroot>/bin` on
    /// Windows.
    pub fn rustc_libdir(&self, compiler: Compiler) -> PathBuf {
        if compiler.is_snapshot(self) {
            self.rustc_snapshot_libdir()
        } else {
            self.sysroot(compiler).join(libdir(&compiler.host))
        }
    }

    /// Adds the compiler's directory of dynamic libraries to `cmd`'s dynamic
    /// library lookup path.
    pub fn add_rustc_lib_path(&self, compiler: Compiler, cmd: &mut Command) {
        // Windows doesn't need dylib path munging because the dlls for the
        // compiler live next to the compiler and the system will find them
        // automatically.
        if cfg!(windows) {
            return
        }

        add_lib_path(vec![self.rustc_libdir(compiler)], cmd);
    }

    /// Get a path to the compiler specified.
    pub fn rustc(&self, compiler: Compiler) -> PathBuf {
        if compiler.is_snapshot(self) {
            self.initial_rustc.clone()
        } else {
            self.sysroot(compiler).join("bin").join(exe("rustc", &compiler.host))
        }
    }

    pub fn rustdoc(&self, host: Interned<String>) -> PathBuf {
        self.ensure(tool::Rustdoc { host })
    }

    pub fn rustdoc_cmd(&self, host: Interned<String>) -> Command {
        let mut cmd = Command::new(&self.out.join("bootstrap/debug/rustdoc"));
        let compiler = self.compiler(self.top_stage, host);
        cmd.env("RUSTC_STAGE", compiler.stage.to_string())
           .env("RUSTC_SYSROOT", self.sysroot(compiler))
           .env("RUSTDOC_LIBDIR", self.sysroot_libdir(compiler, self.config.build))
           .env("CFG_RELEASE_CHANNEL", &self.config.channel)
           .env("RUSTDOC_REAL", self.rustdoc(host))
           .env("RUSTDOC_CRATE_VERSION", self.rust_version())
           .env("RUSTC_BOOTSTRAP", "1");
        if let Some(linker) = self.linker(host) {
            cmd.env("RUSTC_TARGET_LINKER", linker);
        }
        cmd
    }

    /// Prepares an invocation of `cargo` to be run.
    ///
    /// This will create a `Command` that represents a pending execution of
    /// Cargo. This cargo will be configured to use `compiler` as the actual
    /// rustc compiler, its output will be scoped by `mode`'s output directory,
    /// it will pass the `--target` flag for the specified `target`, and will be
    /// executing the Cargo command `cmd`.
    pub fn cargo(&self,
             compiler: Compiler,
             mode: Mode,
             target: Interned<String>,
             cmd: &str) -> Command {
        let mut cargo = Command::new(&self.initial_cargo);
        let out_dir = self.stage_out(compiler, mode);
        cargo.env("CARGO_TARGET_DIR", out_dir)
             .arg(cmd)
             .arg("--target")
             .arg(target);

        // Set a flag for `check` so that certain build scripts can do less work
        // (e.g. not building/requiring LLVM).
        if cmd == "check" {
            cargo.env("RUST_CHECK", "1");
        }

        // If we were invoked from `make` then that's already got a jobserver
        // set up for us so no need to tell Cargo about jobs all over again.
        if env::var_os("MAKEFLAGS").is_none() && env::var_os("MFLAGS").is_none() {
             cargo.arg("-j").arg(self.jobs().to_string());
        }

        // FIXME: Temporary fix for https://github.com/rust-lang/cargo/issues/3005
        // Force cargo to output binaries with disambiguating hashes in the name
        cargo.env("__CARGO_DEFAULT_LIB_METADATA", &self.config.channel);

        let stage;
        if compiler.stage == 0 && self.local_rebuild {
            // Assume the local-rebuild rustc already has stage1 features.
            stage = 1;
        } else {
            stage = compiler.stage;
        }

        let mut extra_args = env::var(&format!("RUSTFLAGS_STAGE_{}", stage)).unwrap_or_default();
        if stage != 0 {
            let s = env::var("RUSTFLAGS_STAGE_NOT_0").unwrap_or_default();
            if !extra_args.is_empty() {
                extra_args.push_str(" ");
            }
            extra_args.push_str(&s);
        }

        if !extra_args.is_empty() {
            cargo.env("RUSTFLAGS",
                format!("{} {}", env::var("RUSTFLAGS").unwrap_or_default(), extra_args));
        }

        // Customize the compiler we're running. Specify the compiler to cargo
        // as our shim and then pass it some various options used to configure
        // how the actual compiler itself is called.
        //
        // These variables are primarily all read by
        // src/bootstrap/bin/{rustc.rs,rustdoc.rs}
        cargo.env("RUSTBUILD_NATIVE_DIR", self.native_dir(target))
             .env("RUSTC", self.out.join("bootstrap/debug/rustc"))
             .env("RUSTC_REAL", self.rustc(compiler))
             .env("RUSTC_STAGE", stage.to_string())
             .env("RUSTC_DEBUG_ASSERTIONS",
                  self.config.rust_debug_assertions.to_string())
             .env("RUSTC_SYSROOT", self.sysroot(compiler))
             .env("RUSTC_LIBDIR", self.rustc_libdir(compiler))
             .env("RUSTC_RPATH", self.config.rust_rpath.to_string())
             .env("RUSTDOC", self.out.join("bootstrap/debug/rustdoc"))
             .env("RUSTDOC_REAL", if cmd == "doc" || cmd == "test" {
                 self.rustdoc(compiler.host)
             } else {
                 PathBuf::from("/path/to/nowhere/rustdoc/not/required")
             })
             .env("TEST_MIRI", self.config.test_miri.to_string())
             .env("RUSTC_ERROR_METADATA_DST", self.extended_error_dir());

        if let Some(host_linker) = self.linker(compiler.host) {
            cargo.env("RUSTC_HOST_LINKER", host_linker);
        }
        if let Some(target_linker) = self.linker(target) {
            cargo.env("RUSTC_TARGET_LINKER", target_linker);
        }
        if let Some(ref error_format) = self.config.rustc_error_format {
            cargo.env("RUSTC_ERROR_FORMAT", error_format);
        }
        if cmd != "build" && cmd != "check" {
            cargo.env("RUSTDOC_LIBDIR", self.rustc_libdir(self.compiler(2, self.config.build)));
        }

        if mode == Mode::Tool {
            // Tools like cargo and rls don't get debuginfo by default right now, but this can be
            // enabled in the config.  Adding debuginfo makes them several times larger.
            if self.config.rust_debuginfo_tools {
                cargo.env("RUSTC_DEBUGINFO", self.config.rust_debuginfo.to_string());
                cargo.env("RUSTC_DEBUGINFO_LINES", self.config.rust_debuginfo_lines.to_string());
            }
        } else {
            cargo.env("RUSTC_DEBUGINFO", self.config.rust_debuginfo.to_string());
            cargo.env("RUSTC_DEBUGINFO_LINES", self.config.rust_debuginfo_lines.to_string());
            cargo.env("RUSTC_FORCE_UNSTABLE", "1");

            // Currently the compiler depends on crates from crates.io, and
            // then other crates can depend on the compiler (e.g. proc-macro
            // crates). Let's say, for example that rustc itself depends on the
            // bitflags crate. If an external crate then depends on the
            // bitflags crate as well, we need to make sure they don't
            // conflict, even if they pick the same version of bitflags. We'll
            // want to make sure that e.g. a plugin and rustc each get their
            // own copy of bitflags.

            // Cargo ensures that this works in general through the -C metadata
            // flag. This flag will frob the symbols in the binary to make sure
            // they're different, even though the source code is the exact
            // same. To solve this problem for the compiler we extend Cargo's
            // already-passed -C metadata flag with our own. Our rustc.rs
            // wrapper around the actual rustc will detect -C metadata being
            // passed and frob it with this extra string we're passing in.
            cargo.env("RUSTC_METADATA_SUFFIX", "rustc");
        }

        if let Some(x) = self.crt_static(target) {
            cargo.env("RUSTC_CRT_STATIC", x.to_string());
        }

        // Enable usage of unstable features
        cargo.env("RUSTC_BOOTSTRAP", "1");
        self.add_rust_test_threads(&mut cargo);

        // Almost all of the crates that we compile as part of the bootstrap may
        // have a build script, including the standard library. To compile a
        // build script, however, it itself needs a standard library! This
        // introduces a bit of a pickle when we're compiling the standard
        // library itself.
        //
        // To work around this we actually end up using the snapshot compiler
        // (stage0) for compiling build scripts of the standard library itself.
        // The stage0 compiler is guaranteed to have a libstd available for use.
        //
        // For other crates, however, we know that we've already got a standard
        // library up and running, so we can use the normal compiler to compile
        // build scripts in that situation.
        //
        // If LLVM support is disabled we need to use the snapshot compiler to compile
        // build scripts, as the new compiler doesn't support executables.
        if mode == Mode::Libstd || !self.config.llvm_enabled {
            cargo.env("RUSTC_SNAPSHOT", &self.initial_rustc)
                 .env("RUSTC_SNAPSHOT_LIBDIR", self.rustc_snapshot_libdir());
        } else {
            cargo.env("RUSTC_SNAPSHOT", self.rustc(compiler))
                 .env("RUSTC_SNAPSHOT_LIBDIR", self.rustc_libdir(compiler));
        }

        // Ignore incremental modes except for stage0, since we're
        // not guaranteeing correctness across builds if the compiler
        // is changing under your feet.`
        if self.config.incremental && compiler.stage == 0 {
            cargo.env("CARGO_INCREMENTAL", "1");
        }

        if let Some(ref on_fail) = self.config.on_fail {
            cargo.env("RUSTC_ON_FAIL", on_fail);
        }

        if self.config.print_step_timings {
            cargo.env("RUSTC_PRINT_STEP_TIMINGS", "1");
        }

        cargo.env("RUSTC_VERBOSE", format!("{}", self.verbosity));

        // in std, we want to avoid denying warnings for stage 0 as that makes cfg's painful.
        if self.config.deny_warnings && !(mode == Mode::Libstd && stage == 0) {
            cargo.env("RUSTC_DENY_WARNINGS", "1");
        }

        // Throughout the build Cargo can execute a number of build scripts
        // compiling C/C++ code and we need to pass compilers, archivers, flags, etc
        // obtained previously to those build scripts.
        // Build scripts use either the `cc` crate or `configure/make` so we pass
        // the options through environment variables that are fetched and understood by both.
        //
        // FIXME: the guard against msvc shouldn't need to be here
        if !target.contains("msvc") {
            let ccache = self.config.ccache.as_ref();
            let ccacheify = |s: &Path| {
                let ccache = match ccache {
                    Some(ref s) => s,
                    None => return s.display().to_string(),
                };
                // FIXME: the cc-rs crate only recognizes the literal strings
                // `ccache` and `sccache` when doing caching compilations, so we
                // mirror that here. It should probably be fixed upstream to
                // accept a new env var or otherwise work with custom ccache
                // vars.
                match &ccache[..] {
                    "ccache" | "sccache" => format!("{} {}", ccache, s.display()),
                    _ => s.display().to_string(),
                }
            };
            let cc = ccacheify(&self.cc(target));
            cargo.env(format!("CC_{}", target), &cc)
                 .env("CC", &cc);

            let cflags = self.cflags(target).join(" ");
            cargo.env(format!("CFLAGS_{}", target), cflags.clone())
                 .env("CFLAGS", cflags.clone());

            if let Some(ar) = self.ar(target) {
                let ranlib = format!("{} s", ar.display());
                cargo.env(format!("AR_{}", target), ar)
                     .env("AR", ar)
                     .env(format!("RANLIB_{}", target), ranlib.clone())
                     .env("RANLIB", ranlib);
            }

            if let Ok(cxx) = self.cxx(target) {
                let cxx = ccacheify(&cxx);
                cargo.env(format!("CXX_{}", target), &cxx)
                     .env("CXX", &cxx)
                     .env(format!("CXXFLAGS_{}", target), cflags.clone())
                     .env("CXXFLAGS", cflags);
            }
        }

        if cmd == "build" && mode == Mode::Libstd
            && self.config.extended && compiler.is_final_stage(self)
        {
            cargo.env("RUSTC_SAVE_ANALYSIS", "api".to_string());
        }

        // For `cargo doc` invocations, make rustdoc print the Rust version into the docs
        cargo.env("RUSTDOC_CRATE_VERSION", self.rust_version());

        // Environment variables *required* throughout the build
        //
        // FIXME: should update code to not require this env var
        cargo.env("CFG_COMPILER_HOST_TRIPLE", target);

        // Set this for all builds to make sure doc builds also get it.
        cargo.env("CFG_RELEASE_CHANNEL", &self.config.channel);

        // This one's a bit tricky. As of the time of this writing the compiler
        // links to the `winapi` crate on crates.io. This crate provides raw
        // bindings to Windows system functions, sort of like libc does for
        // Unix. This crate also, however, provides "import libraries" for the
        // MinGW targets. There's an import library per dll in the windows
        // distribution which is what's linked to. These custom import libraries
        // are used because the winapi crate can reference Windows functions not
        // present in the MinGW import libraries.
        //
        // For example MinGW may ship libdbghelp.a, but it may not have
        // references to all the functions in the dbghelp dll. Instead the
        // custom import library for dbghelp in the winapi crates has all this
        // information.
        //
        // Unfortunately for us though the import libraries are linked by
        // default via `-ldylib=winapi_foo`. That is, they're linked with the
        // `dylib` type with a `winapi_` prefix (so the winapi ones don't
        // conflict with the system MinGW ones). This consequently means that
        // the binaries we ship of things like rustc_trans (aka the rustc_trans
        // DLL) when linked against *again*, for example with procedural macros
        // or plugins, will trigger the propagation logic of `-ldylib`, passing
        // `-lwinapi_foo` to the linker again. This isn't actually available in
        // our distribution, however, so the link fails.
        //
        // To solve this problem we tell winapi to not use its bundled import
        // libraries. This means that it will link to the system MinGW import
        // libraries by default, and the `-ldylib=foo` directives will still get
        // passed to the final linker, but they'll look like `-lfoo` which can
        // be resolved because MinGW has the import library. The downside is we
        // don't get newer functions from Windows, but we don't use any of them
        // anyway.
        if mode != Mode::Tool {
            cargo.env("WINAPI_NO_BUNDLED_LIBRARIES", "1");
        }

        for _ in 1..self.verbosity {
            cargo.arg("-v");
        }

        // This must be kept before the thinlto check, as we set codegen units
        // to 1 forcibly there.
        if let Some(n) = self.config.rust_codegen_units {
            cargo.env("RUSTC_CODEGEN_UNITS", n.to_string());
        }

        if self.config.rust_optimize {
            // FIXME: cargo bench does not accept `--release`
            if cmd != "bench" {
                cargo.arg("--release");
            }
        }

        if self.config.locked_deps {
            cargo.arg("--locked");
        }
        if self.config.vendor || self.is_sudo {
            cargo.arg("--frozen");
        }

        self.ci_env.force_coloring_in_ci(&mut cargo);

        cargo
    }

    /// Ensure that a given step is built, returning its output. This will
    /// cache the step, so it is safe (and good!) to call this as often as
    /// needed to ensure that all dependencies are built.
    pub fn ensure<S: Step>(&'a self, step: S) -> S::Output {
        {
            let mut stack = self.stack.borrow_mut();
            for stack_step in stack.iter() {
                // should skip
                if stack_step.downcast_ref::<S>().map_or(true, |stack_step| *stack_step != step) {
                    continue;
                }
                let mut out = String::new();
                out += &format!("\n\nCycle in build detected when adding {:?}\n", step);
                for el in stack.iter().rev() {
                    out += &format!("\t{:?}\n", el);
                }
                panic!(out);
            }
            if let Some(out) = self.cache.get(&step) {
                self.verbose(&format!("{}c {:?}", "  ".repeat(stack.len()), step));

                {
                    let mut graph = self.graph.borrow_mut();
                    let parent = self.parent.get();
                    let us = *self.graph_nodes.borrow_mut()
                        .entry(format!("{:?}", step))
                        .or_insert_with(|| graph.add_node(format!("{:?}", step)));
                    if let Some(parent) = parent {
                        graph.add_edge(parent, us, false);
                    }
                }

                return out;
            }
            self.verbose(&format!("{}> {:?}", "  ".repeat(stack.len()), step));
            stack.push(Box::new(step.clone()));
        }

        let prev_parent = self.parent.get();

        {
            let mut graph = self.graph.borrow_mut();
            let parent = self.parent.get();
            let us = *self.graph_nodes.borrow_mut()
                .entry(format!("{:?}", step))
                .or_insert_with(|| graph.add_node(format!("{:?}", step)));
            self.parent.set(Some(us));
            if let Some(parent) = parent {
                graph.add_edge(parent, us, true);
            }
        }

        let (out, dur) = {
            let start = Instant::now();
            let zero = Duration::new(0, 0);
            let parent = self.time_spent_on_dependencies.replace(zero);
            let out = step.clone().run(self);
            let dur = start.elapsed();
            let deps = self.time_spent_on_dependencies.replace(parent + dur);
            (out, dur - deps)
        };

        self.parent.set(prev_parent);

        if self.config.print_step_timings && dur > Duration::from_millis(100) {
            println!("[TIMING] {:?} -- {}.{:03}",
                     step,
                     dur.as_secs(),
                     dur.subsec_nanos() / 1_000_000);
        }

        {
            let mut stack = self.stack.borrow_mut();
            let cur_step = stack.pop().expect("step stack empty");
            assert_eq!(cur_step.downcast_ref(), Some(&step));
        }
        self.verbose(&format!("{}< {:?}", "  ".repeat(self.stack.borrow().len()), step));
        self.cache.put(step, out.clone());
        out
    }
}

#[cfg(test)]
mod __test {
    use config::Config;
    use std::thread;
    use super::*;

    fn configure(host: &[&str], target: &[&str]) -> Config {
        let mut config = Config::default_opts();
        // don't save toolstates
        config.save_toolstates = None;
        config.run_host_only = true;
        config.dry_run = true;
        // try to avoid spurious failures in dist where we create/delete each others file
        let dir = config.out.join("tmp-rustbuild-tests")
            .join(&thread::current().name().unwrap_or("unknown").replace(":", "-"));
        t!(fs::create_dir_all(&dir));
        config.out = dir;
        config.build = INTERNER.intern_str("A");
        config.hosts = vec![config.build].clone().into_iter()
            .chain(host.iter().map(|s| INTERNER.intern_str(s))).collect::<Vec<_>>();
        config.targets = config.hosts.clone().into_iter()
            .chain(target.iter().map(|s| INTERNER.intern_str(s))).collect::<Vec<_>>();
        config
    }

    fn first<A, B>(v: Vec<(A, B)>) -> Vec<A> {
        v.into_iter().map(|(a, _)| a).collect::<Vec<_>>()
    }

    #[test]
    fn dist_baseline() {
        let build = Build::new(configure(&[], &[]));
        let mut builder = Builder::new(&build);
        builder.run_step_descriptions(&Builder::get_step_descriptions(Kind::Dist), &[]);

        let a = INTERNER.intern_str("A");

        assert_eq!(first(builder.cache.all::<dist::Docs>()), &[
            dist::Docs { stage: 2, host: a },
        ]);
        assert_eq!(first(builder.cache.all::<dist::Mingw>()), &[
            dist::Mingw { host: a },
        ]);
        assert_eq!(first(builder.cache.all::<dist::Rustc>()), &[
            dist::Rustc { compiler: Compiler { host: a, stage: 2 } },
        ]);
        assert_eq!(first(builder.cache.all::<dist::Std>()), &[
            dist::Std {
                compiler: Compiler { host: a, stage: 2 },
                target: a,
            },
        ]);
        assert_eq!(first(builder.cache.all::<dist::Src>()), &[dist::Src]);
    }

    #[test]
    fn dist_with_targets() {
        let build = Build::new(configure(&[], &["B"]));
        let mut builder = Builder::new(&build);
        builder.run_step_descriptions(&Builder::get_step_descriptions(Kind::Dist), &[]);

        let a = INTERNER.intern_str("A");
        let b = INTERNER.intern_str("B");

        assert_eq!(first(builder.cache.all::<dist::Docs>()), &[
            dist::Docs { stage: 2, host: a },
            dist::Docs { stage: 2, host: b },
        ]);
        assert_eq!(first(builder.cache.all::<dist::Mingw>()), &[
            dist::Mingw { host: a },
            dist::Mingw { host: b },
        ]);
        assert_eq!(first(builder.cache.all::<dist::Rustc>()), &[
            dist::Rustc { compiler: Compiler { host: a, stage: 2 } },
        ]);
        assert_eq!(first(builder.cache.all::<dist::Std>()), &[
            dist::Std {
                compiler: Compiler { host: a, stage: 2 },
                target: a,
            },
            dist::Std {
                compiler: Compiler { host: a, stage: 2 },
                target: b,
            },
        ]);
        assert_eq!(first(builder.cache.all::<dist::Src>()), &[dist::Src]);
    }

    #[test]
    fn dist_with_hosts() {
        let build = Build::new(configure(&["B"], &[]));
        let mut builder = Builder::new(&build);
        builder.run_step_descriptions(&Builder::get_step_descriptions(Kind::Dist), &[]);

        let a = INTERNER.intern_str("A");
        let b = INTERNER.intern_str("B");

        assert_eq!(first(builder.cache.all::<dist::Docs>()), &[
            dist::Docs { stage: 2, host: a },
            dist::Docs { stage: 2, host: b },
        ]);
        assert_eq!(first(builder.cache.all::<dist::Mingw>()), &[
            dist::Mingw { host: a },
            dist::Mingw { host: b },
        ]);
        assert_eq!(first(builder.cache.all::<dist::Rustc>()), &[
            dist::Rustc { compiler: Compiler { host: a, stage: 2 } },
            dist::Rustc { compiler: Compiler { host: b, stage: 2 } },
        ]);
        assert_eq!(first(builder.cache.all::<dist::Std>()), &[
            dist::Std {
                compiler: Compiler { host: a, stage: 2 },
                target: a,
            },
            dist::Std {
                compiler: Compiler { host: a, stage: 2 },
                target: b,
            },
        ]);
        assert_eq!(first(builder.cache.all::<dist::Src>()), &[dist::Src]);
    }

    #[test]
    fn dist_with_targets_and_hosts() {
        let build = Build::new(configure(&["B"], &["C"]));
        let mut builder = Builder::new(&build);
        builder.run_step_descriptions(&Builder::get_step_descriptions(Kind::Dist), &[]);

        let a = INTERNER.intern_str("A");
        let b = INTERNER.intern_str("B");
        let c = INTERNER.intern_str("C");

        assert_eq!(first(builder.cache.all::<dist::Docs>()), &[
            dist::Docs { stage: 2, host: a },
            dist::Docs { stage: 2, host: b },
            dist::Docs { stage: 2, host: c },
        ]);
        assert_eq!(first(builder.cache.all::<dist::Mingw>()), &[
            dist::Mingw { host: a },
            dist::Mingw { host: b },
            dist::Mingw { host: c },
        ]);
        assert_eq!(first(builder.cache.all::<dist::Rustc>()), &[
            dist::Rustc { compiler: Compiler { host: a, stage: 2 } },
            dist::Rustc { compiler: Compiler { host: b, stage: 2 } },
        ]);
        assert_eq!(first(builder.cache.all::<dist::Std>()), &[
            dist::Std {
                compiler: Compiler { host: a, stage: 2 },
                target: a,
            },
            dist::Std {
                compiler: Compiler { host: a, stage: 2 },
                target: b,
            },
            dist::Std {
                compiler: Compiler { host: a, stage: 2 },
                target: c,
            },
        ]);
        assert_eq!(first(builder.cache.all::<dist::Src>()), &[dist::Src]);
    }

    #[test]
    fn dist_with_target_flag() {
        let mut config = configure(&["B"], &["C"]);
        config.run_host_only = false; // as-if --target=C was passed
        let build = Build::new(config);
        let mut builder = Builder::new(&build);
        builder.run_step_descriptions(&Builder::get_step_descriptions(Kind::Dist), &[]);

        let a = INTERNER.intern_str("A");
        let b = INTERNER.intern_str("B");
        let c = INTERNER.intern_str("C");

        assert_eq!(first(builder.cache.all::<dist::Docs>()), &[
            dist::Docs { stage: 2, host: a },
            dist::Docs { stage: 2, host: b },
            dist::Docs { stage: 2, host: c },
        ]);
        assert_eq!(first(builder.cache.all::<dist::Mingw>()), &[
            dist::Mingw { host: a },
            dist::Mingw { host: b },
            dist::Mingw { host: c },
        ]);
        assert_eq!(first(builder.cache.all::<dist::Rustc>()), &[]);
        assert_eq!(first(builder.cache.all::<dist::Std>()), &[
            dist::Std {
                compiler: Compiler { host: a, stage: 2 },
                target: a,
            },
            dist::Std {
                compiler: Compiler { host: a, stage: 2 },
                target: b,
            },
            dist::Std {
                compiler: Compiler { host: a, stage: 2 },
                target: c,
            },
        ]);
        assert_eq!(first(builder.cache.all::<dist::Src>()), &[]);
    }

    #[test]
    fn dist_with_same_targets_and_hosts() {
        let build = Build::new(configure(&["B"], &["B"]));
        let mut builder = Builder::new(&build);
        builder.run_step_descriptions(&Builder::get_step_descriptions(Kind::Dist), &[]);

        let a = INTERNER.intern_str("A");
        let b = INTERNER.intern_str("B");

        assert_eq!(first(builder.cache.all::<dist::Docs>()), &[
            dist::Docs { stage: 2, host: a },
            dist::Docs { stage: 2, host: b },
        ]);
        assert_eq!(first(builder.cache.all::<dist::Mingw>()), &[
            dist::Mingw { host: a },
            dist::Mingw { host: b },
        ]);
        assert_eq!(first(builder.cache.all::<dist::Rustc>()), &[
            dist::Rustc { compiler: Compiler { host: a, stage: 2 } },
            dist::Rustc { compiler: Compiler { host: b, stage: 2 } },
        ]);
        assert_eq!(first(builder.cache.all::<dist::Std>()), &[
            dist::Std {
                compiler: Compiler { host: a, stage: 2 },
                target: a,
            },
            dist::Std {
                compiler: Compiler { host: a, stage: 2 },
                target: b,
            },
        ]);
        assert_eq!(first(builder.cache.all::<dist::Src>()), &[dist::Src]);
        assert_eq!(first(builder.cache.all::<compile::Std>()), &[
            compile::Std {
                compiler: Compiler { host: a, stage: 0 },
                target: a,
            },
            compile::Std {
                compiler: Compiler { host: a, stage: 1 },
                target: a,
            },
            compile::Std {
                compiler: Compiler { host: a, stage: 2 },
                target: a,
            },
            compile::Std {
                compiler: Compiler { host: a, stage: 1 },
                target: b,
            },
            compile::Std {
                compiler: Compiler { host: a, stage: 2 },
                target: b,
            },
        ]);
        assert_eq!(first(builder.cache.all::<compile::Test>()), &[
            compile::Test {
                compiler: Compiler { host: a, stage: 0 },
                target: a,
            },
            compile::Test {
                compiler: Compiler { host: a, stage: 1 },
                target: a,
            },
            compile::Test {
                compiler: Compiler { host: a, stage: 2 },
                target: a,
            },
            compile::Test {
                compiler: Compiler { host: a, stage: 1 },
                target: b,
            },
            compile::Test {
                compiler: Compiler { host: a, stage: 2 },
                target: b,
            },
        ]);
        assert_eq!(first(builder.cache.all::<compile::Assemble>()), &[
            compile::Assemble {
                target_compiler: Compiler { host: a, stage: 0 },
            },
            compile::Assemble {
                target_compiler: Compiler { host: a, stage: 1 },
            },
            compile::Assemble {
                target_compiler: Compiler { host: a, stage: 2 },
            },
            compile::Assemble {
                target_compiler: Compiler { host: b, stage: 2 },
            },
        ]);
    }

    #[test]
    fn build_default() {
        let build = Build::new(configure(&["B"], &["C"]));
        let mut builder = Builder::new(&build);
        builder.run_step_descriptions(&Builder::get_step_descriptions(Kind::Build), &[]);

        let a = INTERNER.intern_str("A");
        let b = INTERNER.intern_str("B");
        let c = INTERNER.intern_str("C");

        assert!(!builder.cache.all::<compile::Std>().is_empty());
        assert!(!builder.cache.all::<compile::Assemble>().is_empty());
        assert_eq!(first(builder.cache.all::<compile::Rustc>()), &[
            compile::Rustc {
                compiler: Compiler { host: a, stage: 0 },
                target: a,
            },
            compile::Rustc {
                compiler: Compiler { host: a, stage: 1 },
                target: a,
            },
            compile::Rustc {
                compiler: Compiler { host: a, stage: 2 },
                target: a,
            },
            compile::Rustc {
                compiler: Compiler { host: b, stage: 2 },
                target: a,
            },
            compile::Rustc {
                compiler: Compiler { host: a, stage: 0 },
                target: b,
            },
            compile::Rustc {
                compiler: Compiler { host: a, stage: 1 },
                target: b,
            },
            compile::Rustc {
                compiler: Compiler { host: a, stage: 2 },
                target: b,
            },
            compile::Rustc {
                compiler: Compiler { host: b, stage: 2 },
                target: b,
            },
        ]);

        assert_eq!(first(builder.cache.all::<compile::Test>()), &[
            compile::Test {
                compiler: Compiler { host: a, stage: 0 },
                target: a,
            },
            compile::Test {
                compiler: Compiler { host: a, stage: 1 },
                target: a,
            },
            compile::Test {
                compiler: Compiler { host: a, stage: 2 },
                target: a,
            },
            compile::Test {
                compiler: Compiler { host: b, stage: 2 },
                target: a,
            },
            compile::Test {
                compiler: Compiler { host: a, stage: 0 },
                target: b,
            },
            compile::Test {
                compiler: Compiler { host: a, stage: 1 },
                target: b,
            },
            compile::Test {
                compiler: Compiler { host: a, stage: 2 },
                target: b,
            },
            compile::Test {
                compiler: Compiler { host: b, stage: 2 },
                target: b,
            },
            compile::Test {
                compiler: Compiler { host: a, stage: 2 },
                target: c,
            },
            compile::Test {
                compiler: Compiler { host: b, stage: 2 },
                target: c,
            },
        ]);
    }

    #[test]
    fn build_with_target_flag() {
        let mut config = configure(&["B"], &["C"]);
        config.run_host_only = false;
        let build = Build::new(config);
        let mut builder = Builder::new(&build);
        builder.run_step_descriptions(&Builder::get_step_descriptions(Kind::Build), &[]);

        let a = INTERNER.intern_str("A");
        let b = INTERNER.intern_str("B");
        let c = INTERNER.intern_str("C");

        assert!(!builder.cache.all::<compile::Std>().is_empty());
        assert_eq!(first(builder.cache.all::<compile::Assemble>()), &[
            compile::Assemble {
                target_compiler: Compiler { host: a, stage: 0 },
            },
            compile::Assemble {
                target_compiler: Compiler { host: a, stage: 1 },
            },
            compile::Assemble {
                target_compiler: Compiler { host: b, stage: 1 },
            },
            compile::Assemble {
                target_compiler: Compiler { host: a, stage: 2 },
            },
            compile::Assemble {
                target_compiler: Compiler { host: b, stage: 2 },
            },
        ]);
        assert_eq!(first(builder.cache.all::<compile::Rustc>()), &[
            compile::Rustc {
                compiler: Compiler { host: a, stage: 0 },
                target: a,
            },
            compile::Rustc {
                compiler: Compiler { host: a, stage: 1 },
                target: a,
            },
            compile::Rustc {
                compiler: Compiler { host: a, stage: 0 },
                target: b,
            },
            compile::Rustc {
                compiler: Compiler { host: a, stage: 1 },
                target: b,
            },
        ]);

        assert_eq!(first(builder.cache.all::<compile::Test>()), &[
            compile::Test {
                compiler: Compiler { host: a, stage: 0 },
                target: a,
            },
            compile::Test {
                compiler: Compiler { host: a, stage: 1 },
                target: a,
            },
            compile::Test {
                compiler: Compiler { host: a, stage: 2 },
                target: a,
            },
            compile::Test {
                compiler: Compiler { host: b, stage: 2 },
                target: a,
            },
            compile::Test {
                compiler: Compiler { host: a, stage: 0 },
                target: b,
            },
            compile::Test {
                compiler: Compiler { host: a, stage: 1 },
                target: b,
            },
            compile::Test {
                compiler: Compiler { host: a, stage: 2 },
                target: b,
            },
            compile::Test {
                compiler: Compiler { host: b, stage: 2 },
                target: b,
            },
            compile::Test {
                compiler: Compiler { host: a, stage: 2 },
                target: c,
            },
            compile::Test {
                compiler: Compiler { host: b, stage: 2 },
                target: c,
            },
        ]);
    }
}