Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1668 insertions, 0 deletions

diff --git a/src/bootstrap/config.rs b/src/bootstrap/config.rs
new file mode 100644
index 000000000..4325a237c
--- /dev/null
+++ b/src/bootstrap/config.rs
@@ -0,0 +1,1668 @@
+//! Serialized configuration of a build.
+//!
+//! This module implements parsing `config.toml` configuration files to tweak
+//! how the build runs.
+
+use std::cell::{Cell, RefCell};
+use std::cmp;
+use std::collections::{HashMap, HashSet};
+use std::env;
+use std::ffi::OsStr;
+use std::fmt;
+use std::fs;
+use std::path::{Path, PathBuf};
+use std::process::Command;
+use std::str::FromStr;
+
+use crate::builder::{Builder, TaskPath};
+use crate::cache::{Interned, INTERNER};
+use crate::channel::GitInfo;
+pub use crate::flags::Subcommand;
+use crate::flags::{Color, Flags};
+use crate::util::{exe, output, program_out_of_date, t};
+use once_cell::sync::OnceCell;
+use serde::{Deserialize, Deserializer};
+
+macro_rules! check_ci_llvm {
+    ($name:expr) => {
+        assert!(
+            $name.is_none(),
+            "setting {} is incompatible with download-ci-llvm.",
+            stringify!($name)
+        );
+    };
+}
+
+/// Global configuration for the entire build and/or bootstrap.
+///
+/// This structure is derived from a combination of both `config.toml` and
+/// `config.mk`. As of the time of this writing it's unlikely that `config.toml`
+/// is used all that much, so this is primarily filled out by `config.mk` which
+/// is generated from `./configure`.
+///
+/// Note that this structure is not decoded directly into, but rather it is
+/// filled out from the decoded forms of the structs below. For documentation
+/// each field, see the corresponding fields in
+/// `config.toml.example`.
+#[derive(Default)]
+#[cfg_attr(test, derive(Clone))]
+pub struct Config {
+    pub changelog_seen: Option<usize>,
+    pub ccache: Option<String>,
+    /// Call Build::ninja() instead of this.
+    pub ninja_in_file: bool,
+    pub verbose: usize,
+    pub submodules: Option<bool>,
+    pub compiler_docs: bool,
+    pub docs_minification: bool,
+    pub docs: bool,
+    pub locked_deps: bool,
+    pub vendor: bool,
+    pub target_config: HashMap<TargetSelection, Target>,
+    pub full_bootstrap: bool,
+    pub extended: bool,
+    pub tools: Option<HashSet<String>>,
+    pub sanitizers: bool,
+    pub profiler: bool,
+    pub ignore_git: bool,
+    pub exclude: Vec<TaskPath>,
+    pub include_default_paths: bool,
+    pub rustc_error_format: Option<String>,
+    pub json_output: bool,
+    pub test_compare_mode: bool,
+    pub color: Color,
+    pub patch_binaries_for_nix: bool,
+    pub stage0_metadata: Stage0Metadata,
+
+    pub on_fail: Option<String>,
+    pub stage: u32,
+    pub keep_stage: Vec<u32>,
+    pub keep_stage_std: Vec<u32>,
+    pub src: PathBuf,
+    /// defaults to `config.toml`
+    pub config: PathBuf,
+    pub jobs: Option<u32>,
+    pub cmd: Subcommand,
+    pub incremental: bool,
+    pub dry_run: bool,
+    /// `None` if we shouldn't download CI compiler artifacts, or the commit to download if we should.
+    #[cfg(not(test))]
+    download_rustc_commit: Option<String>,
+    #[cfg(test)]
+    pub download_rustc_commit: Option<String>,
+
+    pub deny_warnings: bool,
+    pub backtrace_on_ice: bool,
+
+    // llvm codegen options
+    pub llvm_skip_rebuild: bool,
+    pub llvm_assertions: bool,
+    pub llvm_tests: bool,
+    pub llvm_plugins: bool,
+    pub llvm_optimize: bool,
+    pub llvm_thin_lto: bool,
+    pub llvm_release_debuginfo: bool,
+    pub llvm_version_check: bool,
+    pub llvm_static_stdcpp: bool,
+    /// `None` if `llvm_from_ci` is true and we haven't yet downloaded llvm.
+    #[cfg(not(test))]
+    llvm_link_shared: Cell<Option<bool>>,
+    #[cfg(test)]
+    pub llvm_link_shared: Cell<Option<bool>>,
+    pub llvm_clang_cl: Option<String>,
+    pub llvm_targets: Option<String>,
+    pub llvm_experimental_targets: Option<String>,
+    pub llvm_link_jobs: Option<u32>,
+    pub llvm_version_suffix: Option<String>,
+    pub llvm_use_linker: Option<String>,
+    pub llvm_allow_old_toolchain: bool,
+    pub llvm_polly: bool,
+    pub llvm_clang: bool,
+    pub llvm_from_ci: bool,
+    pub llvm_build_config: HashMap<String, String>,
+
+    pub use_lld: bool,
+    pub lld_enabled: bool,
+    pub llvm_tools_enabled: bool,
+
+    pub llvm_cflags: Option<String>,
+    pub llvm_cxxflags: Option<String>,
+    pub llvm_ldflags: Option<String>,
+    pub llvm_use_libcxx: bool,
+
+    // rust codegen options
+    pub rust_optimize: bool,
+    pub rust_codegen_units: Option<u32>,
+    pub rust_codegen_units_std: Option<u32>,
+    pub rust_debug_assertions: bool,
+    pub rust_debug_assertions_std: bool,
+    pub rust_overflow_checks: bool,
+    pub rust_overflow_checks_std: bool,
+    pub rust_debug_logging: bool,
+    pub rust_debuginfo_level_rustc: u32,
+    pub rust_debuginfo_level_std: u32,
+    pub rust_debuginfo_level_tools: u32,
+    pub rust_debuginfo_level_tests: u32,
+    pub rust_split_debuginfo: SplitDebuginfo,
+    pub rust_rpath: bool,
+    pub rustc_parallel: bool,
+    pub rustc_default_linker: Option<String>,
+    pub rust_optimize_tests: bool,
+    pub rust_dist_src: bool,
+    pub rust_codegen_backends: Vec<Interned<String>>,
+    pub rust_verify_llvm_ir: bool,
+    pub rust_thin_lto_import_instr_limit: Option<u32>,
+    pub rust_remap_debuginfo: bool,
+    pub rust_new_symbol_mangling: Option<bool>,
+    pub rust_profile_use: Option<String>,
+    pub rust_profile_generate: Option<String>,
+    pub llvm_profile_use: Option<String>,
+    pub llvm_profile_generate: bool,
+    pub llvm_libunwind_default: Option<LlvmLibunwind>,
+
+    pub build: TargetSelection,
+    pub hosts: Vec<TargetSelection>,
+    pub targets: Vec<TargetSelection>,
+    pub local_rebuild: bool,
+    pub jemalloc: bool,
+    pub control_flow_guard: bool,
+
+    // dist misc
+    pub dist_sign_folder: Option<PathBuf>,
+    pub dist_upload_addr: Option<String>,
+    pub dist_compression_formats: Option<Vec<String>>,
+
+    // libstd features
+    pub backtrace: bool, // support for RUST_BACKTRACE
+
+    // misc
+    pub low_priority: bool,
+    pub channel: String,
+    pub description: Option<String>,
+    pub verbose_tests: bool,
+    pub save_toolstates: Option<PathBuf>,
+    pub print_step_timings: bool,
+    pub print_step_rusage: bool,
+    pub missing_tools: bool,
+
+    // Fallback musl-root for all targets
+    pub musl_root: Option<PathBuf>,
+    pub prefix: Option<PathBuf>,
+    pub sysconfdir: Option<PathBuf>,
+    pub datadir: Option<PathBuf>,
+    pub docdir: Option<PathBuf>,
+    pub bindir: PathBuf,
+    pub libdir: Option<PathBuf>,
+    pub mandir: Option<PathBuf>,
+    pub codegen_tests: bool,
+    pub nodejs: Option<PathBuf>,
+    pub npm: Option<PathBuf>,
+    pub gdb: Option<PathBuf>,
+    pub python: Option<PathBuf>,
+    pub cargo_native_static: bool,
+    pub configure_args: Vec<String>,
+
+    // These are either the stage0 downloaded binaries or the locally installed ones.
+    pub initial_cargo: PathBuf,
+    pub initial_rustc: PathBuf,
+    #[cfg(not(test))]
+    initial_rustfmt: RefCell<RustfmtState>,
+    #[cfg(test)]
+    pub initial_rustfmt: RefCell<RustfmtState>,
+    pub out: PathBuf,
+}
+
+#[derive(Default, Deserialize)]
+#[cfg_attr(test, derive(Clone))]
+pub struct Stage0Metadata {
+    pub config: Stage0Config,
+    pub checksums_sha256: HashMap<String, String>,
+    pub rustfmt: Option<RustfmtMetadata>,
+}
+#[derive(Default, Deserialize)]
+#[cfg_attr(test, derive(Clone))]
+pub struct Stage0Config {
+    pub dist_server: String,
+    pub artifacts_server: String,
+    pub artifacts_with_llvm_assertions_server: String,
+    pub git_merge_commit_email: String,
+    pub nightly_branch: String,
+}
+#[derive(Default, Deserialize)]
+#[cfg_attr(test, derive(Clone))]
+pub struct RustfmtMetadata {
+    pub date: String,
+    pub version: String,
+}
+
+#[derive(Clone, Debug)]
+pub enum RustfmtState {
+    SystemToolchain(PathBuf),
+    Downloaded(PathBuf),
+    Unavailable,
+    LazyEvaluated,
+}
+
+impl Default for RustfmtState {
+    fn default() -> Self {
+        RustfmtState::LazyEvaluated
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub enum LlvmLibunwind {
+    No,
+    InTree,
+    System,
+}
+
+impl Default for LlvmLibunwind {
+    fn default() -> Self {
+        Self::No
+    }
+}
+
+impl FromStr for LlvmLibunwind {
+    type Err = String;
+
+    fn from_str(value: &str) -> Result<Self, Self::Err> {
+        match value {
+            "no" => Ok(Self::No),
+            "in-tree" => Ok(Self::InTree),
+            "system" => Ok(Self::System),
+            invalid => Err(format!("Invalid value '{}' for rust.llvm-libunwind config.", invalid)),
+        }
+    }
+}
+
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub enum SplitDebuginfo {
+    Packed,
+    Unpacked,
+    Off,
+}
+
+impl Default for SplitDebuginfo {
+    fn default() -> Self {
+        SplitDebuginfo::Off
+    }
+}
+
+impl std::str::FromStr for SplitDebuginfo {
+    type Err = ();
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        match s {
+            "packed" => Ok(SplitDebuginfo::Packed),
+            "unpacked" => Ok(SplitDebuginfo::Unpacked),
+            "off" => Ok(SplitDebuginfo::Off),
+            _ => Err(()),
+        }
+    }
+}
+
+impl SplitDebuginfo {
+    /// Returns the default `-Csplit-debuginfo` value for the current target. See the comment for
+    /// `rust.split-debuginfo` in `config.toml.example`.
+    fn default_for_platform(target: &str) -> Self {
+        if target.contains("apple") {
+            SplitDebuginfo::Unpacked
+        } else if target.contains("windows") {
+            SplitDebuginfo::Packed
+        } else {
+            SplitDebuginfo::Off
+        }
+    }
+}
+
+#[derive(Copy, Clone, Default, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct TargetSelection {
+    pub triple: Interned<String>,
+    file: Option<Interned<String>>,
+}
+
+impl TargetSelection {
+    pub fn from_user(selection: &str) -> Self {
+        let path = Path::new(selection);
+
+        let (triple, file) = if path.exists() {
+            let triple = path
+                .file_stem()
+                .expect("Target specification file has no file stem")
+                .to_str()
+                .expect("Target specification file stem is not UTF-8");
+
+            (triple, Some(selection))
+        } else {
+            (selection, None)
+        };
+
+        let triple = INTERNER.intern_str(triple);
+        let file = file.map(|f| INTERNER.intern_str(f));
+
+        Self { triple, file }
+    }
+
+    pub fn rustc_target_arg(&self) -> &str {
+        self.file.as_ref().unwrap_or(&self.triple)
+    }
+
+    pub fn contains(&self, needle: &str) -> bool {
+        self.triple.contains(needle)
+    }
+
+    pub fn starts_with(&self, needle: &str) -> bool {
+        self.triple.starts_with(needle)
+    }
+
+    pub fn ends_with(&self, needle: &str) -> bool {
+        self.triple.ends_with(needle)
+    }
+}
+
+impl fmt::Display for TargetSelection {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}", self.triple)?;
+        if let Some(file) = self.file {
+            write!(f, "({})", file)?;
+        }
+        Ok(())
+    }
+}
+
+impl fmt::Debug for TargetSelection {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}", self)
+    }
+}
+
+impl PartialEq<&str> for TargetSelection {
+    fn eq(&self, other: &&str) -> bool {
+        self.triple == *other
+    }
+}
+
+/// Per-target configuration stored in the global configuration structure.
+#[derive(Default)]
+#[cfg_attr(test, derive(Clone))]
+pub struct Target {
+    /// Some(path to llvm-config) if using an external LLVM.
+    pub llvm_config: Option<PathBuf>,
+    /// Some(path to FileCheck) if one was specified.
+    pub llvm_filecheck: Option<PathBuf>,
+    pub llvm_libunwind: Option<LlvmLibunwind>,
+    pub cc: Option<PathBuf>,
+    pub cxx: Option<PathBuf>,
+    pub ar: Option<PathBuf>,
+    pub ranlib: Option<PathBuf>,
+    pub default_linker: Option<PathBuf>,
+    pub linker: Option<PathBuf>,
+    pub ndk: Option<PathBuf>,
+    pub sanitizers: Option<bool>,
+    pub profiler: Option<bool>,
+    pub crt_static: Option<bool>,
+    pub musl_root: Option<PathBuf>,
+    pub musl_libdir: Option<PathBuf>,
+    pub wasi_root: Option<PathBuf>,
+    pub qemu_rootfs: Option<PathBuf>,
+    pub no_std: bool,
+}
+
+impl Target {
+    pub fn from_triple(triple: &str) -> Self {
+        let mut target: Self = Default::default();
+        if triple.contains("-none")
+            || triple.contains("nvptx")
+            || triple.contains("switch")
+            || triple.contains("-uefi")
+        {
+            target.no_std = true;
+        }
+        target
+    }
+}
+/// Structure of the `config.toml` file that configuration is read from.
+///
+/// This structure uses `Decodable` to automatically decode a TOML configuration
+/// file into this format, and then this is traversed and written into the above
+/// `Config` structure.
+#[derive(Deserialize, Default)]
+#[serde(deny_unknown_fields, rename_all = "kebab-case")]
+struct TomlConfig {
+    changelog_seen: Option<usize>,
+    build: Option<Build>,
+    install: Option<Install>,
+    llvm: Option<Llvm>,
+    rust: Option<Rust>,
+    target: Option<HashMap<String, TomlTarget>>,
+    dist: Option<Dist>,
+    profile: Option<String>,
+}
+
+trait Merge {
+    fn merge(&mut self, other: Self);
+}
+
+impl Merge for TomlConfig {
+    fn merge(
+        &mut self,
+        TomlConfig { build, install, llvm, rust, dist, target, profile: _, changelog_seen: _ }: Self,
+    ) {
+        fn do_merge<T: Merge>(x: &mut Option<T>, y: Option<T>) {
+            if let Some(new) = y {
+                if let Some(original) = x {
+                    original.merge(new);
+                } else {
+                    *x = Some(new);
+                }
+            }
+        }
+        do_merge(&mut self.build, build);
+        do_merge(&mut self.install, install);
+        do_merge(&mut self.llvm, llvm);
+        do_merge(&mut self.rust, rust);
+        do_merge(&mut self.dist, dist);
+        assert!(target.is_none(), "merging target-specific config is not currently supported");
+    }
+}
+
+// We are using a decl macro instead of a derive proc macro here to reduce the compile time of
+// rustbuild.
+macro_rules! define_config {
+    ($(#[$attr:meta])* struct $name:ident {
+        $($field:ident: Option<$field_ty:ty> = $field_key:literal,)*
+    }) => {
+        $(#[$attr])*
+        struct $name {
+            $($field: Option<$field_ty>,)*
+        }
+
+        impl Merge for $name {
+            fn merge(&mut self, other: Self) {
+                $(
+                    if !self.$field.is_some() {
+                        self.$field = other.$field;
+                    }
+                )*
+            }
+        }
+
+        // The following is a trimmed version of what serde_derive generates. All parts not relevant
+        // for toml deserialization have been removed. This reduces the binary size and improves
+        // compile time of rustbuild.
+        impl<'de> Deserialize<'de> for $name {
+            fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+            where
+                D: Deserializer<'de>,
+            {
+                struct Field;
+                impl<'de> serde::de::Visitor<'de> for Field {
+                    type Value = $name;
+                    fn expecting(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+                        f.write_str(concat!("struct ", stringify!($name)))
+                    }
+
+                    #[inline]
+                    fn visit_map<A>(self, mut map: A) -> Result<Self::Value, A::Error>
+                    where
+                        A: serde::de::MapAccess<'de>,
+                    {
+                        $(let mut $field: Option<$field_ty> = None;)*
+                        while let Some(key) =
+                            match serde::de::MapAccess::next_key::<String>(&mut map) {
+                                Ok(val) => val,
+                                Err(err) => {
+                                    return Err(err);
+                                }
+                            }
+                        {
+                            match &*key {
+                                $($field_key => {
+                                    if $field.is_some() {
+                                        return Err(<A::Error as serde::de::Error>::duplicate_field(
+                                            $field_key,
+                                        ));
+                                    }
+                                    $field = match serde::de::MapAccess::next_value::<$field_ty>(
+                                        &mut map,
+                                    ) {
+                                        Ok(val) => Some(val),
+                                        Err(err) => {
+                                            return Err(err);
+                                        }
+                                    };
+                                })*
+                                key => {
+                                    return Err(serde::de::Error::unknown_field(key, FIELDS));
+                                }
+                            }
+                        }
+                        Ok($name { $($field),* })
+                    }
+                }
+                const FIELDS: &'static [&'static str] = &[
+                    $($field_key,)*
+                ];
+                Deserializer::deserialize_struct(
+                    deserializer,
+                    stringify!($name),
+                    FIELDS,
+                    Field,
+                )
+            }
+        }
+    }
+}
+
+define_config! {
+    /// TOML representation of various global build decisions.
+    #[derive(Default)]
+    struct Build {
+        build: Option<String> = "build",
+        host: Option<Vec<String>> = "host",
+        target: Option<Vec<String>> = "target",
+        build_dir: Option<String> = "build-dir",
+        cargo: Option<String> = "cargo",
+        rustc: Option<String> = "rustc",
+        rustfmt: Option<PathBuf> = "rustfmt",
+        docs: Option<bool> = "docs",
+        compiler_docs: Option<bool> = "compiler-docs",
+        docs_minification: Option<bool> = "docs-minification",
+        submodules: Option<bool> = "submodules",
+        gdb: Option<String> = "gdb",
+        nodejs: Option<String> = "nodejs",
+        npm: Option<String> = "npm",
+        python: Option<String> = "python",
+        locked_deps: Option<bool> = "locked-deps",
+        vendor: Option<bool> = "vendor",
+        full_bootstrap: Option<bool> = "full-bootstrap",
+        extended: Option<bool> = "extended",
+        tools: Option<HashSet<String>> = "tools",
+        verbose: Option<usize> = "verbose",
+        sanitizers: Option<bool> = "sanitizers",
+        profiler: Option<bool> = "profiler",
+        cargo_native_static: Option<bool> = "cargo-native-static",
+        low_priority: Option<bool> = "low-priority",
+        configure_args: Option<Vec<String>> = "configure-args",
+        local_rebuild: Option<bool> = "local-rebuild",
+        print_step_timings: Option<bool> = "print-step-timings",
+        print_step_rusage: Option<bool> = "print-step-rusage",
+        check_stage: Option<u32> = "check-stage",
+        doc_stage: Option<u32> = "doc-stage",
+        build_stage: Option<u32> = "build-stage",
+        test_stage: Option<u32> = "test-stage",
+        install_stage: Option<u32> = "install-stage",
+        dist_stage: Option<u32> = "dist-stage",
+        bench_stage: Option<u32> = "bench-stage",
+        patch_binaries_for_nix: Option<bool> = "patch-binaries-for-nix",
+        metrics: Option<bool> = "metrics",
+    }
+}
+
+define_config! {
+    /// TOML representation of various global install decisions.
+    struct Install {
+        prefix: Option<String> = "prefix",
+        sysconfdir: Option<String> = "sysconfdir",
+        docdir: Option<String> = "docdir",
+        bindir: Option<String> = "bindir",
+        libdir: Option<String> = "libdir",
+        mandir: Option<String> = "mandir",
+        datadir: Option<String> = "datadir",
+    }
+}
+
+define_config! {
+    /// TOML representation of how the LLVM build is configured.
+    struct Llvm {
+        skip_rebuild: Option<bool> = "skip-rebuild",
+        optimize: Option<bool> = "optimize",
+        thin_lto: Option<bool> = "thin-lto",
+        release_debuginfo: Option<bool> = "release-debuginfo",
+        assertions: Option<bool> = "assertions",
+        tests: Option<bool> = "tests",
+        plugins: Option<bool> = "plugins",
+        ccache: Option<StringOrBool> = "ccache",
+        version_check: Option<bool> = "version-check",
+        static_libstdcpp: Option<bool> = "static-libstdcpp",
+        ninja: Option<bool> = "ninja",
+        targets: Option<String> = "targets",
+        experimental_targets: Option<String> = "experimental-targets",
+        link_jobs: Option<u32> = "link-jobs",
+        link_shared: Option<bool> = "link-shared",
+        version_suffix: Option<String> = "version-suffix",
+        clang_cl: Option<String> = "clang-cl",
+        cflags: Option<String> = "cflags",
+        cxxflags: Option<String> = "cxxflags",
+        ldflags: Option<String> = "ldflags",
+        use_libcxx: Option<bool> = "use-libcxx",
+        use_linker: Option<String> = "use-linker",
+        allow_old_toolchain: Option<bool> = "allow-old-toolchain",
+        polly: Option<bool> = "polly",
+        clang: Option<bool> = "clang",
+        download_ci_llvm: Option<StringOrBool> = "download-ci-llvm",
+        build_config: Option<HashMap<String, String>> = "build-config",
+    }
+}
+
+define_config! {
+    struct Dist {
+        sign_folder: Option<String> = "sign-folder",
+        gpg_password_file: Option<String> = "gpg-password-file",
+        upload_addr: Option<String> = "upload-addr",
+        src_tarball: Option<bool> = "src-tarball",
+        missing_tools: Option<bool> = "missing-tools",
+        compression_formats: Option<Vec<String>> = "compression-formats",
+    }
+}
+
+#[derive(Deserialize)]
+#[serde(untagged)]
+enum StringOrBool {
+    String(String),
+    Bool(bool),
+}
+
+impl Default for StringOrBool {
+    fn default() -> StringOrBool {
+        StringOrBool::Bool(false)
+    }
+}
+
+define_config! {
+    /// TOML representation of how the Rust build is configured.
+    struct Rust {
+        optimize: Option<bool> = "optimize",
+        debug: Option<bool> = "debug",
+        codegen_units: Option<u32> = "codegen-units",
+        codegen_units_std: Option<u32> = "codegen-units-std",
+        debug_assertions: Option<bool> = "debug-assertions",
+        debug_assertions_std: Option<bool> = "debug-assertions-std",
+        overflow_checks: Option<bool> = "overflow-checks",
+        overflow_checks_std: Option<bool> = "overflow-checks-std",
+        debug_logging: Option<bool> = "debug-logging",
+        debuginfo_level: Option<u32> = "debuginfo-level",
+        debuginfo_level_rustc: Option<u32> = "debuginfo-level-rustc",
+        debuginfo_level_std: Option<u32> = "debuginfo-level-std",
+        debuginfo_level_tools: Option<u32> = "debuginfo-level-tools",
+        debuginfo_level_tests: Option<u32> = "debuginfo-level-tests",
+        split_debuginfo: Option<String> = "split-debuginfo",
+        run_dsymutil: Option<bool> = "run-dsymutil",
+        backtrace: Option<bool> = "backtrace",
+        incremental: Option<bool> = "incremental",
+        parallel_compiler: Option<bool> = "parallel-compiler",
+        default_linker: Option<String> = "default-linker",
+        channel: Option<String> = "channel",
+        description: Option<String> = "description",
+        musl_root: Option<String> = "musl-root",
+        rpath: Option<bool> = "rpath",
+        verbose_tests: Option<bool> = "verbose-tests",
+        optimize_tests: Option<bool> = "optimize-tests",
+        codegen_tests: Option<bool> = "codegen-tests",
+        ignore_git: Option<bool> = "ignore-git",
+        dist_src: Option<bool> = "dist-src",
+        save_toolstates: Option<String> = "save-toolstates",
+        codegen_backends: Option<Vec<String>> = "codegen-backends",
+        lld: Option<bool> = "lld",
+        use_lld: Option<bool> = "use-lld",
+        llvm_tools: Option<bool> = "llvm-tools",
+        deny_warnings: Option<bool> = "deny-warnings",
+        backtrace_on_ice: Option<bool> = "backtrace-on-ice",
+        verify_llvm_ir: Option<bool> = "verify-llvm-ir",
+        thin_lto_import_instr_limit: Option<u32> = "thin-lto-import-instr-limit",
+        remap_debuginfo: Option<bool> = "remap-debuginfo",
+        jemalloc: Option<bool> = "jemalloc",
+        test_compare_mode: Option<bool> = "test-compare-mode",
+        llvm_libunwind: Option<String> = "llvm-libunwind",
+        control_flow_guard: Option<bool> = "control-flow-guard",
+        new_symbol_mangling: Option<bool> = "new-symbol-mangling",
+        profile_generate: Option<String> = "profile-generate",
+        profile_use: Option<String> = "profile-use",
+        // ignored; this is set from an env var set by bootstrap.py
+        download_rustc: Option<StringOrBool> = "download-rustc",
+    }
+}
+
+define_config! {
+    /// TOML representation of how each build target is configured.
+    struct TomlTarget {
+        cc: Option<String> = "cc",
+        cxx: Option<String> = "cxx",
+        ar: Option<String> = "ar",
+        ranlib: Option<String> = "ranlib",
+        default_linker: Option<PathBuf> = "default-linker",
+        linker: Option<String> = "linker",
+        llvm_config: Option<String> = "llvm-config",
+        llvm_filecheck: Option<String> = "llvm-filecheck",
+        llvm_libunwind: Option<String> = "llvm-libunwind",
+        android_ndk: Option<String> = "android-ndk",
+        sanitizers: Option<bool> = "sanitizers",
+        profiler: Option<bool> = "profiler",
+        crt_static: Option<bool> = "crt-static",
+        musl_root: Option<String> = "musl-root",
+        musl_libdir: Option<String> = "musl-libdir",
+        wasi_root: Option<String> = "wasi-root",
+        qemu_rootfs: Option<String> = "qemu-rootfs",
+        no_std: Option<bool> = "no-std",
+    }
+}
+
+impl Config {
+    pub fn default_opts() -> Config {
+        let mut config = Config::default();
+        config.llvm_optimize = true;
+        config.ninja_in_file = true;
+        config.llvm_version_check = true;
+        config.llvm_static_stdcpp = true;
+        config.backtrace = true;
+        config.rust_optimize = true;
+        config.rust_optimize_tests = true;
+        config.submodules = None;
+        config.docs = true;
+        config.docs_minification = true;
+        config.rust_rpath = true;
+        config.channel = "dev".to_string();
+        config.codegen_tests = true;
+        config.rust_dist_src = true;
+        config.rust_codegen_backends = vec![INTERNER.intern_str("llvm")];
+        config.deny_warnings = true;
+        config.bindir = "bin".into();
+
+        // set by build.rs
+        config.build = TargetSelection::from_user(&env!("BUILD_TRIPLE"));
+        let manifest_dir = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
+        // Undo `src/bootstrap`
+        config.src = manifest_dir.parent().unwrap().parent().unwrap().to_owned();
+        config.out = PathBuf::from("build");
+
+        config.initial_cargo = PathBuf::from(env!("CARGO"));
+        config.initial_rustc = PathBuf::from(env!("RUSTC"));
+
+        config
+    }
+
+    pub fn parse(args: &[String]) -> Config {
+        let flags = Flags::parse(&args);
+
+        let mut config = Config::default_opts();
+        config.exclude = flags.exclude.into_iter().map(|path| TaskPath::parse(path)).collect();
+        config.include_default_paths = flags.include_default_paths;
+        config.rustc_error_format = flags.rustc_error_format;
+        config.json_output = flags.json_output;
+        config.on_fail = flags.on_fail;
+        config.jobs = flags.jobs.map(threads_from_config);
+        config.cmd = flags.cmd;
+        config.incremental = flags.incremental;
+        config.dry_run = flags.dry_run;
+        config.keep_stage = flags.keep_stage;
+        config.keep_stage_std = flags.keep_stage_std;
+        config.color = flags.color;
+        if let Some(value) = flags.deny_warnings {
+            config.deny_warnings = value;
+        }
+        config.llvm_profile_use = flags.llvm_profile_use;
+        config.llvm_profile_generate = flags.llvm_profile_generate;
+
+        let stage0_json = t!(std::fs::read(&config.src.join("src").join("stage0.json")));
+        config.stage0_metadata = t!(serde_json::from_slice::<Stage0Metadata>(&stage0_json));
+
+        #[cfg(test)]
+        let get_toml = |_| TomlConfig::default();
+        #[cfg(not(test))]
+        let get_toml = |file: &Path| {
+            let contents =
+                t!(fs::read_to_string(file), format!("config file {} not found", file.display()));
+            // Deserialize to Value and then TomlConfig to prevent the Deserialize impl of
+            // TomlConfig and sub types to be monomorphized 5x by toml.
+            match toml::from_str(&contents)
+                .and_then(|table: toml::Value| TomlConfig::deserialize(table))
+            {
+                Ok(table) => table,
+                Err(err) => {
+                    eprintln!("failed to parse TOML configuration '{}': {}", file.display(), err);
+                    crate::detail_exit(2);
+                }
+            }
+        };
+
+        // Read from `--config`, then `RUST_BOOTSTRAP_CONFIG`, then `./config.toml`, then `config.toml` in the root directory.
+        let toml_path = flags
+            .config
+            .clone()
+            .or_else(|| env::var_os("RUST_BOOTSTRAP_CONFIG").map(PathBuf::from));
+        let using_default_path = toml_path.is_none();
+        let mut toml_path = toml_path.unwrap_or_else(|| PathBuf::from("config.toml"));
+        if using_default_path && !toml_path.exists() {
+            toml_path = config.src.join(toml_path);
+        }
+
+        // Give a hard error if `--config` or `RUST_BOOTSTRAP_CONFIG` are set to a missing path,
+        // but not if `config.toml` hasn't been created.
+        let mut toml = if !using_default_path || toml_path.exists() {
+            get_toml(&toml_path)
+        } else {
+            TomlConfig::default()
+        };
+
+        if let Some(include) = &toml.profile {
+            let mut include_path = config.src.clone();
+            include_path.push("src");
+            include_path.push("bootstrap");
+            include_path.push("defaults");
+            include_path.push(format!("config.{}.toml", include));
+            let included_toml = get_toml(&include_path);
+            toml.merge(included_toml);
+        }
+
+        config.changelog_seen = toml.changelog_seen;
+        config.config = toml_path;
+
+        let build = toml.build.unwrap_or_default();
+
+        set(&mut config.initial_rustc, build.rustc.map(PathBuf::from));
+        set(&mut config.out, flags.build_dir.or_else(|| build.build_dir.map(PathBuf::from)));
+        // NOTE: Bootstrap spawns various commands with different working directories.
+        // To avoid writing to random places on the file system, `config.out` needs to be an absolute path.
+        if !config.out.is_absolute() {
+            // `canonicalize` requires the path to already exist. Use our vendored copy of `absolute` instead.
+            config.out = crate::util::absolute(&config.out);
+        }
+
+        if config.dry_run {
+            let dir = config.out.join("tmp-dry-run");
+            t!(fs::create_dir_all(&dir));
+            config.out = dir;
+        }
+
+        config.hosts = if let Some(arg_host) = flags.host {
+            arg_host
+        } else if let Some(file_host) = build.host {
+            file_host.iter().map(|h| TargetSelection::from_user(h)).collect()
+        } else {
+            vec![config.build]
+        };
+        config.targets = if let Some(arg_target) = flags.target {
+            arg_target
+        } else if let Some(file_target) = build.target {
+            file_target.iter().map(|h| TargetSelection::from_user(h)).collect()
+        } else {
+            // If target is *not* configured, then default to the host
+            // toolchains.
+            config.hosts.clone()
+        };
+
+        config.nodejs = build.nodejs.map(PathBuf::from);
+        config.npm = build.npm.map(PathBuf::from);
+        config.gdb = build.gdb.map(PathBuf::from);
+        config.python = build.python.map(PathBuf::from);
+        config.submodules = build.submodules;
+        set(&mut config.low_priority, build.low_priority);
+        set(&mut config.compiler_docs, build.compiler_docs);
+        set(&mut config.docs_minification, build.docs_minification);
+        set(&mut config.docs, build.docs);
+        set(&mut config.locked_deps, build.locked_deps);
+        set(&mut config.vendor, build.vendor);
+        set(&mut config.full_bootstrap, build.full_bootstrap);
+        set(&mut config.extended, build.extended);
+        config.tools = build.tools;
+        set(&mut config.verbose, build.verbose);
+        set(&mut config.sanitizers, build.sanitizers);
+        set(&mut config.profiler, build.profiler);
+        set(&mut config.cargo_native_static, build.cargo_native_static);
+        set(&mut config.configure_args, build.configure_args);
+        set(&mut config.local_rebuild, build.local_rebuild);
+        set(&mut config.print_step_timings, build.print_step_timings);
+        set(&mut config.print_step_rusage, build.print_step_rusage);
+        set(&mut config.patch_binaries_for_nix, build.patch_binaries_for_nix);
+
+        config.verbose = cmp::max(config.verbose, flags.verbose);
+
+        if let Some(install) = toml.install {
+            config.prefix = install.prefix.map(PathBuf::from);
+            config.sysconfdir = install.sysconfdir.map(PathBuf::from);
+            config.datadir = install.datadir.map(PathBuf::from);
+            config.docdir = install.docdir.map(PathBuf::from);
+            set(&mut config.bindir, install.bindir.map(PathBuf::from));
+            config.libdir = install.libdir.map(PathBuf::from);
+            config.mandir = install.mandir.map(PathBuf::from);
+        }
+
+        // We want the llvm-skip-rebuild flag to take precedence over the
+        // skip-rebuild config.toml option so we store it separately
+        // so that we can infer the right value
+        let mut llvm_skip_rebuild = flags.llvm_skip_rebuild;
+
+        // Store off these values as options because if they're not provided
+        // we'll infer default values for them later
+        let mut llvm_assertions = None;
+        let mut llvm_tests = None;
+        let mut llvm_plugins = None;
+        let mut debug = None;
+        let mut debug_assertions = None;
+        let mut debug_assertions_std = None;
+        let mut overflow_checks = None;
+        let mut overflow_checks_std = None;
+        let mut debug_logging = None;
+        let mut debuginfo_level = None;
+        let mut debuginfo_level_rustc = None;
+        let mut debuginfo_level_std = None;
+        let mut debuginfo_level_tools = None;
+        let mut debuginfo_level_tests = None;
+        let mut optimize = None;
+        let mut ignore_git = None;
+
+        if let Some(llvm) = toml.llvm {
+            match llvm.ccache {
+                Some(StringOrBool::String(ref s)) => config.ccache = Some(s.to_string()),
+                Some(StringOrBool::Bool(true)) => {
+                    config.ccache = Some("ccache".to_string());
+                }
+                Some(StringOrBool::Bool(false)) | None => {}
+            }
+            set(&mut config.ninja_in_file, llvm.ninja);
+            llvm_assertions = llvm.assertions;
+            llvm_tests = llvm.tests;
+            llvm_plugins = llvm.plugins;
+            llvm_skip_rebuild = llvm_skip_rebuild.or(llvm.skip_rebuild);
+            set(&mut config.llvm_optimize, llvm.optimize);
+            set(&mut config.llvm_thin_lto, llvm.thin_lto);
+            set(&mut config.llvm_release_debuginfo, llvm.release_debuginfo);
+            set(&mut config.llvm_version_check, llvm.version_check);
+            set(&mut config.llvm_static_stdcpp, llvm.static_libstdcpp);
+            if let Some(v) = llvm.link_shared {
+                config.llvm_link_shared.set(Some(v));
+            }
+            config.llvm_targets = llvm.targets.clone();
+            config.llvm_experimental_targets = llvm.experimental_targets.clone();
+            config.llvm_link_jobs = llvm.link_jobs;
+            config.llvm_version_suffix = llvm.version_suffix.clone();
+            config.llvm_clang_cl = llvm.clang_cl.clone();
+
+            config.llvm_cflags = llvm.cflags.clone();
+            config.llvm_cxxflags = llvm.cxxflags.clone();
+            config.llvm_ldflags = llvm.ldflags.clone();
+            set(&mut config.llvm_use_libcxx, llvm.use_libcxx);
+            config.llvm_use_linker = llvm.use_linker.clone();
+            config.llvm_allow_old_toolchain = llvm.allow_old_toolchain.unwrap_or(false);
+            config.llvm_polly = llvm.polly.unwrap_or(false);
+            config.llvm_clang = llvm.clang.unwrap_or(false);
+            config.llvm_build_config = llvm.build_config.clone().unwrap_or(Default::default());
+            config.llvm_from_ci = match llvm.download_ci_llvm {
+                Some(StringOrBool::String(s)) => {
+                    assert!(s == "if-available", "unknown option `{}` for download-ci-llvm", s);
+                    // This is currently all tier 1 targets and tier 2 targets with host tools
+                    // (since others may not have CI artifacts)
+                    // https://doc.rust-lang.org/rustc/platform-support.html#tier-1
+                    // FIXME: this is duplicated in bootstrap.py
+                    let supported_platforms = [
+                        // tier 1
+                        "aarch64-unknown-linux-gnu",
+                        "i686-pc-windows-gnu",
+                        "i686-pc-windows-msvc",
+                        "i686-unknown-linux-gnu",
+                        "x86_64-unknown-linux-gnu",
+                        "x86_64-apple-darwin",
+                        "x86_64-pc-windows-gnu",
+                        "x86_64-pc-windows-msvc",
+                        // tier 2 with host tools
+                        "aarch64-apple-darwin",
+                        "aarch64-pc-windows-msvc",
+                        "aarch64-unknown-linux-musl",
+                        "arm-unknown-linux-gnueabi",
+                        "arm-unknown-linux-gnueabihf",
+                        "armv7-unknown-linux-gnueabihf",
+                        "mips-unknown-linux-gnu",
+                        "mips64-unknown-linux-gnuabi64",
+                        "mips64el-unknown-linux-gnuabi64",
+                        "mipsel-unknown-linux-gnu",
+                        "powerpc-unknown-linux-gnu",
+                        "powerpc64-unknown-linux-gnu",
+                        "powerpc64le-unknown-linux-gnu",
+                        "riscv64gc-unknown-linux-gnu",
+                        "s390x-unknown-linux-gnu",
+                        "x86_64-unknown-freebsd",
+                        "x86_64-unknown-illumos",
+                        "x86_64-unknown-linux-musl",
+                        "x86_64-unknown-netbsd",
+                    ];
+                    supported_platforms.contains(&&*config.build.triple)
+                }
+                Some(StringOrBool::Bool(b)) => b,
+                None => false,
+            };
+
+            if config.llvm_from_ci {
+                // None of the LLVM options, except assertions, are supported
+                // when using downloaded LLVM. We could just ignore these but
+                // that's potentially confusing, so force them to not be
+                // explicitly set. The defaults and CI defaults don't
+                // necessarily match but forcing people to match (somewhat
+                // arbitrary) CI configuration locally seems bad/hard.
+                check_ci_llvm!(llvm.optimize);
+                check_ci_llvm!(llvm.thin_lto);
+                check_ci_llvm!(llvm.release_debuginfo);
+                // CI-built LLVM can be either dynamic or static. We won't know until we download it.
+                check_ci_llvm!(llvm.link_shared);
+                check_ci_llvm!(llvm.static_libstdcpp);
+                check_ci_llvm!(llvm.targets);
+                check_ci_llvm!(llvm.experimental_targets);
+                check_ci_llvm!(llvm.link_jobs);
+                check_ci_llvm!(llvm.clang_cl);
+                check_ci_llvm!(llvm.version_suffix);
+                check_ci_llvm!(llvm.cflags);
+                check_ci_llvm!(llvm.cxxflags);
+                check_ci_llvm!(llvm.ldflags);
+                check_ci_llvm!(llvm.use_libcxx);
+                check_ci_llvm!(llvm.use_linker);
+                check_ci_llvm!(llvm.allow_old_toolchain);
+                check_ci_llvm!(llvm.polly);
+                check_ci_llvm!(llvm.clang);
+                check_ci_llvm!(llvm.build_config);
+                check_ci_llvm!(llvm.plugins);
+            }
+
+            // NOTE: can never be hit when downloading from CI, since we call `check_ci_llvm!(thin_lto)` above.
+            if config.llvm_thin_lto && llvm.link_shared.is_none() {
+                // If we're building with ThinLTO on, by default we want to link
+                // to LLVM shared, to avoid re-doing ThinLTO (which happens in
+                // the link step) with each stage.
+                config.llvm_link_shared.set(Some(true));
+            }
+        }
+
+        if let Some(rust) = toml.rust {
+            debug = rust.debug;
+            debug_assertions = rust.debug_assertions;
+            debug_assertions_std = rust.debug_assertions_std;
+            overflow_checks = rust.overflow_checks;
+            overflow_checks_std = rust.overflow_checks_std;
+            debug_logging = rust.debug_logging;
+            debuginfo_level = rust.debuginfo_level;
+            debuginfo_level_rustc = rust.debuginfo_level_rustc;
+            debuginfo_level_std = rust.debuginfo_level_std;
+            debuginfo_level_tools = rust.debuginfo_level_tools;
+            debuginfo_level_tests = rust.debuginfo_level_tests;
+            config.rust_split_debuginfo = rust
+                .split_debuginfo
+                .as_deref()
+                .map(SplitDebuginfo::from_str)
+                .map(|v| v.expect("invalid value for rust.split_debuginfo"))
+                .unwrap_or(SplitDebuginfo::default_for_platform(&config.build.triple));
+            optimize = rust.optimize;
+            ignore_git = rust.ignore_git;
+            config.rust_new_symbol_mangling = rust.new_symbol_mangling;
+            set(&mut config.rust_optimize_tests, rust.optimize_tests);
+            set(&mut config.codegen_tests, rust.codegen_tests);
+            set(&mut config.rust_rpath, rust.rpath);
+            set(&mut config.jemalloc, rust.jemalloc);
+            set(&mut config.test_compare_mode, rust.test_compare_mode);
+            set(&mut config.backtrace, rust.backtrace);
+            set(&mut config.channel, rust.channel);
+            config.description = rust.description;
+            set(&mut config.rust_dist_src, rust.dist_src);
+            set(&mut config.verbose_tests, rust.verbose_tests);
+            // in the case "false" is set explicitly, do not overwrite the command line args
+            if let Some(true) = rust.incremental {
+                config.incremental = true;
+            }
+            set(&mut config.use_lld, rust.use_lld);
+            set(&mut config.lld_enabled, rust.lld);
+            set(&mut config.llvm_tools_enabled, rust.llvm_tools);
+            config.rustc_parallel = rust.parallel_compiler.unwrap_or(false);
+            config.rustc_default_linker = rust.default_linker;
+            config.musl_root = rust.musl_root.map(PathBuf::from);
+            config.save_toolstates = rust.save_toolstates.map(PathBuf::from);
+            set(&mut config.deny_warnings, flags.deny_warnings.or(rust.deny_warnings));
+            set(&mut config.backtrace_on_ice, rust.backtrace_on_ice);
+            set(&mut config.rust_verify_llvm_ir, rust.verify_llvm_ir);
+            config.rust_thin_lto_import_instr_limit = rust.thin_lto_import_instr_limit;
+            set(&mut config.rust_remap_debuginfo, rust.remap_debuginfo);
+            set(&mut config.control_flow_guard, rust.control_flow_guard);
+            config.llvm_libunwind_default = rust
+                .llvm_libunwind
+                .map(|v| v.parse().expect("failed to parse rust.llvm-libunwind"));
+
+            if let Some(ref backends) = rust.codegen_backends {
+                config.rust_codegen_backends =
+                    backends.iter().map(|s| INTERNER.intern_str(s)).collect();
+            }
+
+            config.rust_codegen_units = rust.codegen_units.map(threads_from_config);
+            config.rust_codegen_units_std = rust.codegen_units_std.map(threads_from_config);
+            config.rust_profile_use = flags.rust_profile_use.or(rust.profile_use);
+            config.rust_profile_generate = flags.rust_profile_generate.or(rust.profile_generate);
+            config.download_rustc_commit = download_ci_rustc_commit(&config, rust.download_rustc);
+        } else {
+            config.rust_profile_use = flags.rust_profile_use;
+            config.rust_profile_generate = flags.rust_profile_generate;
+        }
+
+        if let Some(t) = toml.target {
+            for (triple, cfg) in t {
+                let mut target = Target::from_triple(&triple);
+
+                if let Some(ref s) = cfg.llvm_config {
+                    target.llvm_config = Some(config.src.join(s));
+                }
+                if let Some(ref s) = cfg.llvm_filecheck {
+                    target.llvm_filecheck = Some(config.src.join(s));
+                }
+                target.llvm_libunwind = cfg
+                    .llvm_libunwind
+                    .as_ref()
+                    .map(|v| v.parse().expect("failed to parse rust.llvm-libunwind"));
+                if let Some(ref s) = cfg.android_ndk {
+                    target.ndk = Some(config.src.join(s));
+                }
+                if let Some(s) = cfg.no_std {
+                    target.no_std = s;
+                }
+                target.cc = cfg.cc.map(PathBuf::from);
+                target.cxx = cfg.cxx.map(PathBuf::from);
+                target.ar = cfg.ar.map(PathBuf::from);
+                target.ranlib = cfg.ranlib.map(PathBuf::from);
+                target.linker = cfg.linker.map(PathBuf::from);
+                target.crt_static = cfg.crt_static;
+                target.musl_root = cfg.musl_root.map(PathBuf::from);
+                target.musl_libdir = cfg.musl_libdir.map(PathBuf::from);
+                target.wasi_root = cfg.wasi_root.map(PathBuf::from);
+                target.qemu_rootfs = cfg.qemu_rootfs.map(PathBuf::from);
+                target.sanitizers = cfg.sanitizers;
+                target.profiler = cfg.profiler;
+
+                config.target_config.insert(TargetSelection::from_user(&triple), target);
+            }
+        }
+
+        if config.llvm_from_ci {
+            let triple = &config.build.triple;
+            let mut build_target = config
+                .target_config
+                .entry(config.build)
+                .or_insert_with(|| Target::from_triple(&triple));
+
+            check_ci_llvm!(build_target.llvm_config);
+            check_ci_llvm!(build_target.llvm_filecheck);
+            let ci_llvm_bin = config.out.join(&*config.build.triple).join("ci-llvm/bin");
+            build_target.llvm_config = Some(ci_llvm_bin.join(exe("llvm-config", config.build)));
+            build_target.llvm_filecheck = Some(ci_llvm_bin.join(exe("FileCheck", config.build)));
+        }
+
+        if let Some(t) = toml.dist {
+            config.dist_sign_folder = t.sign_folder.map(PathBuf::from);
+            config.dist_upload_addr = t.upload_addr;
+            config.dist_compression_formats = t.compression_formats;
+            set(&mut config.rust_dist_src, t.src_tarball);
+            set(&mut config.missing_tools, t.missing_tools);
+        }
+
+        if let Some(r) = build.rustfmt {
+            *config.initial_rustfmt.borrow_mut() = if r.exists() {
+                RustfmtState::SystemToolchain(r)
+            } else {
+                RustfmtState::Unavailable
+            };
+        } else {
+            // If using a system toolchain for bootstrapping, see if that has rustfmt available.
+            let host = config.build;
+            let rustfmt_path = config.initial_rustc.with_file_name(exe("rustfmt", host));
+            let bin_root = config.out.join(host.triple).join("stage0");
+            if !rustfmt_path.starts_with(&bin_root) {
+                // Using a system-provided toolchain; we shouldn't download rustfmt.
+                *config.initial_rustfmt.borrow_mut() = RustfmtState::SystemToolchain(rustfmt_path);
+            }
+        }
+
+        // Now that we've reached the end of our configuration, infer the
+        // default values for all options that we haven't otherwise stored yet.
+
+        config.llvm_skip_rebuild = llvm_skip_rebuild.unwrap_or(false);
+        config.llvm_assertions = llvm_assertions.unwrap_or(false);
+        config.llvm_tests = llvm_tests.unwrap_or(false);
+        config.llvm_plugins = llvm_plugins.unwrap_or(false);
+        config.rust_optimize = optimize.unwrap_or(true);
+
+        let default = debug == Some(true);
+        config.rust_debug_assertions = debug_assertions.unwrap_or(default);
+        config.rust_debug_assertions_std =
+            debug_assertions_std.unwrap_or(config.rust_debug_assertions);
+        config.rust_overflow_checks = overflow_checks.unwrap_or(default);
+        config.rust_overflow_checks_std =
+            overflow_checks_std.unwrap_or(config.rust_overflow_checks);
+
+        config.rust_debug_logging = debug_logging.unwrap_or(config.rust_debug_assertions);
+
+        let with_defaults = |debuginfo_level_specific: Option<u32>| {
+            debuginfo_level_specific.or(debuginfo_level).unwrap_or(if debug == Some(true) {
+                1
+            } else {
+                0
+            })
+        };
+        config.rust_debuginfo_level_rustc = with_defaults(debuginfo_level_rustc);
+        config.rust_debuginfo_level_std = with_defaults(debuginfo_level_std);
+        config.rust_debuginfo_level_tools = with_defaults(debuginfo_level_tools);
+        config.rust_debuginfo_level_tests = debuginfo_level_tests.unwrap_or(0);
+
+        let default = config.channel == "dev";
+        config.ignore_git = ignore_git.unwrap_or(default);
+
+        let download_rustc = config.download_rustc_commit.is_some();
+        // See https://github.com/rust-lang/compiler-team/issues/326
+        config.stage = match config.cmd {
+            Subcommand::Check { .. } => flags.stage.or(build.check_stage).unwrap_or(0),
+            // `download-rustc` only has a speed-up for stage2 builds. Default to stage2 unless explicitly overridden.
+            Subcommand::Doc { .. } => {
+                flags.stage.or(build.doc_stage).unwrap_or(if download_rustc { 2 } else { 0 })
+            }
+            Subcommand::Build { .. } => {
+                flags.stage.or(build.build_stage).unwrap_or(if download_rustc { 2 } else { 1 })
+            }
+            Subcommand::Test { .. } => {
+                flags.stage.or(build.test_stage).unwrap_or(if download_rustc { 2 } else { 1 })
+            }
+            Subcommand::Bench { .. } => flags.stage.or(build.bench_stage).unwrap_or(2),
+            Subcommand::Dist { .. } => flags.stage.or(build.dist_stage).unwrap_or(2),
+            Subcommand::Install { .. } => flags.stage.or(build.install_stage).unwrap_or(2),
+            // These are all bootstrap tools, which don't depend on the compiler.
+            // The stage we pass shouldn't matter, but use 0 just in case.
+            Subcommand::Clean { .. }
+            | Subcommand::Clippy { .. }
+            | Subcommand::Fix { .. }
+            | Subcommand::Run { .. }
+            | Subcommand::Setup { .. }
+            | Subcommand::Format { .. } => flags.stage.unwrap_or(0),
+        };
+
+        // CI should always run stage 2 builds, unless it specifically states otherwise
+        #[cfg(not(test))]
+        if flags.stage.is_none() && crate::CiEnv::current() != crate::CiEnv::None {
+            match config.cmd {
+                Subcommand::Test { .. }
+                | Subcommand::Doc { .. }
+                | Subcommand::Build { .. }
+                | Subcommand::Bench { .. }
+                | Subcommand::Dist { .. }
+                | Subcommand::Install { .. } => {
+                    assert_eq!(
+                        config.stage, 2,
+                        "x.py should be run with `--stage 2` on CI, but was run with `--stage {}`",
+                        config.stage,
+                    );
+                }
+                Subcommand::Clean { .. }
+                | Subcommand::Check { .. }
+                | Subcommand::Clippy { .. }
+                | Subcommand::Fix { .. }
+                | Subcommand::Run { .. }
+                | Subcommand::Setup { .. }
+                | Subcommand::Format { .. } => {}
+            }
+        }
+
+        config
+    }
+
+    /// A git invocation which runs inside the source directory.
+    ///
+    /// Use this rather than `Command::new("git")` in order to support out-of-tree builds.
+    pub(crate) fn git(&self) -> Command {
+        let mut git = Command::new("git");
+        git.current_dir(&self.src);
+        git
+    }
+
+    pub(crate) fn artifact_channel(&self, commit: &str) -> String {
+        let mut channel = self.git();
+        channel.arg("show").arg(format!("{}:src/ci/channel", commit));
+        let channel = output(&mut channel);
+        channel.trim().to_owned()
+    }
+
+    /// Try to find the relative path of `bindir`, otherwise return it in full.
+    pub fn bindir_relative(&self) -> &Path {
+        let bindir = &self.bindir;
+        if bindir.is_absolute() {
+            // Try to make it relative to the prefix.
+            if let Some(prefix) = &self.prefix {
+                if let Ok(stripped) = bindir.strip_prefix(prefix) {
+                    return stripped;
+                }
+            }
+        }
+        bindir
+    }
+
+    /// Try to find the relative path of `libdir`.
+    pub fn libdir_relative(&self) -> Option<&Path> {
+        let libdir = self.libdir.as_ref()?;
+        if libdir.is_relative() {
+            Some(libdir)
+        } else {
+            // Try to make it relative to the prefix.
+            libdir.strip_prefix(self.prefix.as_ref()?).ok()
+        }
+    }
+
+    /// The absolute path to the downloaded LLVM artifacts.
+    pub(crate) fn ci_llvm_root(&self) -> PathBuf {
+        assert!(self.llvm_from_ci);
+        self.out.join(&*self.build.triple).join("ci-llvm")
+    }
+
+    /// Determine whether llvm should be linked dynamically.
+    ///
+    /// If `false`, llvm should be linked statically.
+    /// This is computed on demand since LLVM might have to first be downloaded from CI.
+    pub(crate) fn llvm_link_shared(builder: &Builder<'_>) -> bool {
+        let mut opt = builder.config.llvm_link_shared.get();
+        if opt.is_none() && builder.config.dry_run {
+            // just assume static for now - dynamic linking isn't supported on all platforms
+            return false;
+        }
+
+        let llvm_link_shared = *opt.get_or_insert_with(|| {
+            if builder.config.llvm_from_ci {
+                crate::native::maybe_download_ci_llvm(builder);
+                let ci_llvm = builder.config.ci_llvm_root();
+                let link_type = t!(
+                    std::fs::read_to_string(ci_llvm.join("link-type.txt")),
+                    format!("CI llvm missing: {}", ci_llvm.display())
+                );
+                link_type == "dynamic"
+            } else {
+                // unclear how thought-through this default is, but it maintains compatibility with
+                // previous behavior
+                false
+            }
+        });
+        builder.config.llvm_link_shared.set(opt);
+        llvm_link_shared
+    }
+
+    /// Return whether we will use a downloaded, pre-compiled version of rustc, or just build from source.
+    pub(crate) fn download_rustc(builder: &Builder<'_>) -> bool {
+        static DOWNLOAD_RUSTC: OnceCell<bool> = OnceCell::new();
+        if builder.config.dry_run && DOWNLOAD_RUSTC.get().is_none() {
+            // avoid trying to actually download the commit
+            return false;
+        }
+
+        *DOWNLOAD_RUSTC.get_or_init(|| match &builder.config.download_rustc_commit {
+            None => false,
+            Some(commit) => {
+                download_ci_rustc(builder, commit);
+                true
+            }
+        })
+    }
+
+    pub(crate) fn initial_rustfmt(builder: &Builder<'_>) -> Option<PathBuf> {
+        match &mut *builder.config.initial_rustfmt.borrow_mut() {
+            RustfmtState::SystemToolchain(p) | RustfmtState::Downloaded(p) => Some(p.clone()),
+            RustfmtState::Unavailable => None,
+            r @ RustfmtState::LazyEvaluated => {
+                if builder.config.dry_run {
+                    return Some(PathBuf::new());
+                }
+                let path = maybe_download_rustfmt(builder);
+                *r = if let Some(p) = &path {
+                    RustfmtState::Downloaded(p.clone())
+                } else {
+                    RustfmtState::Unavailable
+                };
+                path
+            }
+        }
+    }
+
+    pub fn verbose(&self) -> bool {
+        self.verbose > 0
+    }
+
+    pub fn sanitizers_enabled(&self, target: TargetSelection) -> bool {
+        self.target_config.get(&target).map(|t| t.sanitizers).flatten().unwrap_or(self.sanitizers)
+    }
+
+    pub fn any_sanitizers_enabled(&self) -> bool {
+        self.target_config.values().any(|t| t.sanitizers == Some(true)) || self.sanitizers
+    }
+
+    pub fn profiler_enabled(&self, target: TargetSelection) -> bool {
+        self.target_config.get(&target).map(|t| t.profiler).flatten().unwrap_or(self.profiler)
+    }
+
+    pub fn any_profiler_enabled(&self) -> bool {
+        self.target_config.values().any(|t| t.profiler == Some(true)) || self.profiler
+    }
+
+    pub fn llvm_enabled(&self) -> bool {
+        self.rust_codegen_backends.contains(&INTERNER.intern_str("llvm"))
+    }
+
+    pub fn llvm_libunwind(&self, target: TargetSelection) -> LlvmLibunwind {
+        self.target_config
+            .get(&target)
+            .and_then(|t| t.llvm_libunwind)
+            .or(self.llvm_libunwind_default)
+            .unwrap_or(LlvmLibunwind::No)
+    }
+
+    pub fn submodules(&self, rust_info: &GitInfo) -> bool {
+        self.submodules.unwrap_or(rust_info.is_git())
+    }
+}
+
+fn set<T>(field: &mut T, val: Option<T>) {
+    if let Some(v) = val {
+        *field = v;
+    }
+}
+
+fn threads_from_config(v: u32) -> u32 {
+    match v {
+        0 => num_cpus::get() as u32,
+        n => n,
+    }
+}
+
+/// Returns the commit to download, or `None` if we shouldn't download CI artifacts.
+fn download_ci_rustc_commit(
+    config: &Config,
+    download_rustc: Option<StringOrBool>,
+) -> Option<String> {
+    // If `download-rustc` is not set, default to rebuilding.
+    let if_unchanged = match download_rustc {
+        None | Some(StringOrBool::Bool(false)) => return None,
+        Some(StringOrBool::Bool(true)) => false,
+        Some(StringOrBool::String(s)) if s == "if-unchanged" => true,
+        Some(StringOrBool::String(other)) => {
+            panic!("unrecognized option for download-rustc: {}", other)
+        }
+    };
+
+    // Handle running from a directory other than the top level
+    let top_level = output(config.git().args(&["rev-parse", "--show-toplevel"]));
+    let top_level = top_level.trim_end();
+    let compiler = format!("{top_level}/compiler/");
+    let library = format!("{top_level}/library/");
+
+    // Look for a version to compare to based on the current commit.
+    // Only commits merged by bors will have CI artifacts.
+    let merge_base = output(
+        config
+            .git()
+            .arg("rev-list")
+            .arg(format!("--author={}", config.stage0_metadata.config.git_merge_commit_email))
+            .args(&["-n1", "--first-parent", "HEAD"]),
+    );
+    let commit = merge_base.trim_end();
+    if commit.is_empty() {
+        println!("error: could not find commit hash for downloading rustc");
+        println!("help: maybe your repository history is too shallow?");
+        println!("help: consider disabling `download-rustc`");
+        println!("help: or fetch enough history to include one upstream commit");
+        crate::detail_exit(1);
+    }
+
+    // Warn if there were changes to the compiler or standard library since the ancestor commit.
+    let has_changes = !t!(config
+        .git()
+        .args(&["diff-index", "--quiet", &commit, "--", &compiler, &library])
+        .status())
+    .success();
+    if has_changes {
+        if if_unchanged {
+            if config.verbose > 0 {
+                println!(
+                    "warning: saw changes to compiler/ or library/ since {commit}; \
+                          ignoring `download-rustc`"
+                );
+            }
+            return None;
+        }
+        println!(
+            "warning: `download-rustc` is enabled, but there are changes to \
+                  compiler/ or library/"
+        );
+    }
+
+    Some(commit.to_string())
+}
+
+fn maybe_download_rustfmt(builder: &Builder<'_>) -> Option<PathBuf> {
+    let RustfmtMetadata { date, version } = builder.config.stage0_metadata.rustfmt.as_ref()?;
+    let channel = format!("{version}-{date}");
+
+    let host = builder.config.build;
+    let rustfmt_path = builder.config.initial_rustc.with_file_name(exe("rustfmt", host));
+    let bin_root = builder.config.out.join(host.triple).join("stage0");
+    let rustfmt_stamp = bin_root.join(".rustfmt-stamp");
+    if rustfmt_path.exists() && !program_out_of_date(&rustfmt_stamp, &channel) {
+        return Some(rustfmt_path);
+    }
+
+    let filename = format!("rustfmt-{version}-{build}.tar.xz", build = host.triple);
+    download_component(builder, DownloadSource::Dist, filename, "rustfmt-preview", &date, "stage0");
+
+    builder.fix_bin_or_dylib(&bin_root.join("bin").join("rustfmt"));
+    builder.fix_bin_or_dylib(&bin_root.join("bin").join("cargo-fmt"));
+
+    builder.create(&rustfmt_stamp, &channel);
+    Some(rustfmt_path)
+}
+
+fn download_ci_rustc(builder: &Builder<'_>, commit: &str) {
+    builder.verbose(&format!("using downloaded stage2 artifacts from CI (commit {commit})"));
+    let channel = builder.config.artifact_channel(commit);
+    let host = builder.config.build.triple;
+    let bin_root = builder.out.join(host).join("ci-rustc");
+    let rustc_stamp = bin_root.join(".rustc-stamp");
+
+    if !bin_root.join("bin").join("rustc").exists() || program_out_of_date(&rustc_stamp, commit) {
+        if bin_root.exists() {
+            t!(fs::remove_dir_all(&bin_root));
+        }
+        let filename = format!("rust-std-{channel}-{host}.tar.xz");
+        let pattern = format!("rust-std-{host}");
+        download_ci_component(builder, filename, &pattern, commit);
+        let filename = format!("rustc-{channel}-{host}.tar.xz");
+        download_ci_component(builder, filename, "rustc", commit);
+        // download-rustc doesn't need its own cargo, it can just use beta's.
+        let filename = format!("rustc-dev-{channel}-{host}.tar.xz");
+        download_ci_component(builder, filename, "rustc-dev", commit);
+
+        builder.fix_bin_or_dylib(&bin_root.join("bin").join("rustc"));
+        builder.fix_bin_or_dylib(&bin_root.join("bin").join("rustdoc"));
+        let lib_dir = bin_root.join("lib");
+        for lib in t!(fs::read_dir(&lib_dir), lib_dir.display().to_string()) {
+            let lib = t!(lib);
+            if lib.path().extension() == Some(OsStr::new("so")) {
+                builder.fix_bin_or_dylib(&lib.path());
+            }
+        }
+        t!(fs::write(rustc_stamp, commit));
+    }
+}
+
+pub(crate) enum DownloadSource {
+    CI,
+    Dist,
+}
+
+/// Download a single component of a CI-built toolchain (not necessarily a published nightly).
+// NOTE: intentionally takes an owned string to avoid downloading multiple times by accident
+fn download_ci_component(builder: &Builder<'_>, filename: String, prefix: &str, commit: &str) {
+    download_component(builder, DownloadSource::CI, filename, prefix, commit, "ci-rustc")
+}
+
+fn download_component(
+    builder: &Builder<'_>,
+    mode: DownloadSource,
+    filename: String,
+    prefix: &str,
+    key: &str,
+    destination: &str,
+) {
+    let cache_dst = builder.out.join("cache");
+    let cache_dir = cache_dst.join(key);
+    if !cache_dir.exists() {
+        t!(fs::create_dir_all(&cache_dir));
+    }
+
+    let bin_root = builder.out.join(builder.config.build.triple).join(destination);
+    let tarball = cache_dir.join(&filename);
+    let (base_url, url, should_verify) = match mode {
+        DownloadSource::CI => (
+            builder.config.stage0_metadata.config.artifacts_server.clone(),
+            format!("{key}/{filename}"),
+            false,
+        ),
+        DownloadSource::Dist => {
+            let dist_server = env::var("RUSTUP_DIST_SERVER")
+                .unwrap_or(builder.config.stage0_metadata.config.dist_server.to_string());
+            // NOTE: make `dist` part of the URL because that's how it's stored in src/stage0.json
+            (dist_server, format!("dist/{key}/{filename}"), true)
+        }
+    };
+
+    // For the beta compiler, put special effort into ensuring the checksums are valid.
+    // FIXME: maybe we should do this for download-rustc as well? but it would be a pain to update
+    // this on each and every nightly ...
+    let checksum = if should_verify {
+        let error = format!(
+            "src/stage0.json doesn't contain a checksum for {url}. \
+            Pre-built artifacts might not be available for this \
+            target at this time, see https://doc.rust-lang.org/nightly\
+            /rustc/platform-support.html for more information."
+        );
+        let sha256 = builder.config.stage0_metadata.checksums_sha256.get(&url).expect(&error);
+        if tarball.exists() {
+            if builder.verify(&tarball, sha256) {
+                builder.unpack(&tarball, &bin_root, prefix);
+                return;
+            } else {
+                builder.verbose(&format!(
+                    "ignoring cached file {} due to failed verification",
+                    tarball.display()
+                ));
+                builder.remove(&tarball);
+            }
+        }
+        Some(sha256)
+    } else if tarball.exists() {
+        builder.unpack(&tarball, &bin_root, prefix);
+        return;
+    } else {
+        None
+    };
+
+    builder.download_component(&format!("{base_url}/{url}"), &tarball, "");
+    if let Some(sha256) = checksum {
+        if !builder.verify(&tarball, sha256) {
+            panic!("failed to verify {}", tarball.display());
+        }
+    }
+
+    builder.unpack(&tarball, &bin_root, prefix);
+}