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[experiment] bootstrap: leverage cargo trim-paths #161049

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b399aec
bootstrap: remap-debuginfo via cargo trim-paths
weihanglo Aug 7, 2026
5cf3ce2
tests: check `$CARGO_HOME` leaks
weihanglo Aug 13, 2026
c276905
tests: check std rmeta for local path leaks
weihanglo Aug 14, 2026
cb3818e
tests: switch remap prefix expectation to `/cargo/registry`
weihanglo Aug 13, 2026
7d23b0e
bootstrap: move debug-prefix-map C flags to LLVM CMake build
weihanglo Aug 14, 2026
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9 changes: 0 additions & 9 deletions compiler/rustc_llvm/build.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -290,15 +290,6 @@ fn main() {
cfg.flag(&*flag);
}

// Remap ci-llvm include paths in debug info for reproducible builds.
if let Some(maps) = tracked_env_var_os("RUSTC_DEBUGINFO_MAP")
&& let Some(maps_str) = maps.to_str()
{
for map in maps_str.split('\t') {
cfg.flag_if_supported(&format!("-ffile-prefix-map={map}"));
}
}

for component in &components {
let mut flag = String::from("LLVM_COMPONENT_");
flag.push_str(&component.to_uppercase());
Expand Down
14 changes: 0 additions & 14 deletions src/bootstrap/src/bin/rustc.rs
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Expand Up @@ -163,20 +163,6 @@ fn main() {
}
}

// The remap flags for the compiler and standard library sources.
if let Ok(maps) = env::var("RUSTC_DEBUGINFO_MAP") {
for map in maps.split('\t') {
cmd.arg("--remap-path-prefix").arg(map);
}
}
// The remap flags for Cargo registry sources need to be passed after the remapping for the
// Rust source code directory, to handle cases when $CARGO_HOME is inside the source directory.
if let Ok(maps) = env::var("RUSTC_CARGO_REGISTRY_SRC_TO_REMAP") {
for map in maps.split('\t') {
cmd.arg("--remap-path-prefix").arg(map);
}
}

// Here we pass additional paths that essentially act as a sysroot.
// These are used to load rustc crates (e.g. `extern crate rustc_ast;`)
// for rustc_private tools, so that we do not have to copy them into the
Expand Down
4 changes: 2 additions & 2 deletions src/bootstrap/src/core/build_steps/compile.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -33,7 +33,7 @@ use crate::core::config::toml::target::DefaultLinuxLinkerOverride;
use crate::core::config::{
Allocator, CompilerBuiltins, DebuginfoLevel, LlvmLibunwind, RustcLto, TargetSelection,
};
use crate::core::session::{CLang, DependencyType, FileType, GitRepo, Mode};
use crate::core::session::{CLang, DependencyType, FileType, Mode};
use crate::utils::build_stamp;
use crate::utils::build_stamp::BuildStamp;
use crate::utils::exec::command;
Expand Down Expand Up @@ -1900,7 +1900,7 @@ pub fn compiler_file(
}
let mut cmd = command(compiler);
cmd.args(builder.cc_handled_cflags(target, c));
cmd.args(builder.cc_unhandled_cflags(target, GitRepo::Rustc, c));
cmd.args(builder.cc_unhandled_cflags(target, c));
cmd.arg(format!("-print-file-name={file}"));
let out = cmd.run_capture_stdout(builder).stdout();
PathBuf::from(out.trim())
Expand Down
30 changes: 26 additions & 4 deletions src/bootstrap/src/core/build_steps/llvm.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -21,14 +21,13 @@ use crate::core::builder::{
Builder, CommandLineStep, Kind, RunConfig, ShouldRun, Step, StepMetadata,
};
use crate::core::config::{Config, LlvmCiMode, LlvmPgoGenerationMode, TargetSelection};
use crate::core::session::{CLang, GitRepo};
use crate::core::session::CLang;
use crate::trace;
use crate::utils::build_stamp::{BuildStamp, generate_smart_stamp_hash};
use crate::utils::exec::command;
use crate::utils::helpers::{
self, exe, get_clang_cl_resource_dir, libdir, t, unhashed_basename, up_to_date,
};

/// Path where a file containing the link type (dynamic or static) is stored in the LLVM CI tarball.
pub const LLVM_CI_LINK_TYPE_PATH: &str = "link-type.txt";

Expand Down Expand Up @@ -782,6 +781,27 @@ fn check_llvm_version(builder: &Builder<'_>, llvm_config: &Path) {
panic!("\n\nbad LLVM version: {version}, need >=21\n\n")
}

/// C/C++ debug info remap flags for LLVM build.
///
/// The remap is observable when LLVM is compiled with debug info,
/// for example, with `llvm.release-debuginfo = true`.
fn debuginfo_map_cflags(builder: &Builder<'_>, target: TargetSelection) -> Vec<String> {
if !builder.config.rust_remap_debuginfo {
return Vec::new();
}

let mut flags = Vec::new();
let map = format!("{}=/rustc/llvm", builder.src.display());
let cc = builder.cc_tool(target);
if cc.is_like_clang() || cc.is_like_gnu() {
flags.push(format!("-fdebug-prefix-map={map}"));
} else if cc.is_like_clang_cl() {
flags.push("-Xclang".into());
flags.push(format!("-fdebug-prefix-map={map}"));
}
flags
}

fn configure_cmake(
builder: &Builder<'_>,
target: TargetSelection,
Expand Down Expand Up @@ -946,7 +966,8 @@ fn configure_cmake(
for flag in builder
.cc_handled_cflags(target, CLang::C)
.into_iter()
.chain(builder.cc_unhandled_cflags(target, GitRepo::Llvm, CLang::C))
.chain(builder.cc_unhandled_cflags(target, CLang::C))
.chain(debuginfo_map_cflags(builder, target))
.filter(|flag| !suppressed_compiler_flag_prefixes.iter().any(|p| flag.starts_with(p)))
{
cflags.push(" ");
Expand All @@ -967,7 +988,8 @@ fn configure_cmake(
for flag in builder
.cc_handled_cflags(target, CLang::Cxx)
.into_iter()
.chain(builder.cc_unhandled_cflags(target, GitRepo::Llvm, CLang::Cxx))
.chain(builder.cc_unhandled_cflags(target, CLang::Cxx))
.chain(debuginfo_map_cflags(builder, target))
.filter(|flag| {
!suppressed_compiler_flag_prefixes
.iter()
Expand Down
7 changes: 3 additions & 4 deletions src/bootstrap/src/core/build_steps/test.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -38,7 +38,7 @@ use crate::core::builder::{
use crate::core::compiler::Compiler;
use crate::core::config::TargetSelection;
use crate::core::config::flags::{Subcommand, get_completion, top_level_help};
use crate::core::session::{CLang, GitRepo, Mode};
use crate::core::session::{CLang, Mode};
use crate::core::{android, debuggers};
use crate::utils::build_stamp::{self, BuildStamp};
use crate::utils::exec::{BootstrapCommand, command};
Expand All @@ -48,7 +48,6 @@ use crate::utils::helpers::{
target_supports_cranelift_backend, up_to_date,
};
use crate::utils::render_tests::{add_flags_and_try_run_tests, try_run_tests};

mod compiletest;
pub mod failed_tests;

Expand Down Expand Up @@ -2829,9 +2828,9 @@ Please disable assertions with `rust.debug-assertions = false`.
// requires that a C++ compiler was configured which isn't always the case.
if !builder.config.dry_run() && mode == CompiletestMode::RunMake {
let mut cflags = builder.cc_handled_cflags(target, CLang::C);
cflags.extend(builder.cc_unhandled_cflags(target, GitRepo::Rustc, CLang::C));
cflags.extend(builder.cc_unhandled_cflags(target, CLang::C));
let mut cxxflags = builder.cc_handled_cflags(target, CLang::Cxx);
cxxflags.extend(builder.cc_unhandled_cflags(target, GitRepo::Rustc, CLang::Cxx));
cxxflags.extend(builder.cc_unhandled_cflags(target, CLang::Cxx));
cmd.arg("--cc")
.arg(builder.cc(target))
.arg("--cxx")
Expand Down
87 changes: 15 additions & 72 deletions src/bootstrap/src/core/builder/cargo.rs
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Expand Up @@ -14,11 +14,10 @@ use crate::core::config::toml::pgo::PgoConfig;
use crate::core::config::{
CompressDebuginfo, Config, DryRun, RustcLto, SplitDebuginfo, TargetSelection,
};
use crate::core::session::{CLang, GitRepo, Mode, RemapScheme};
use crate::core::session::{CLang, Mode, RemapScheme};
use crate::utils::build_stamp;
use crate::utils::exec::{BootstrapCommand, command};
use crate::utils::helpers::{self, LldThreads, check_cfg_arg, envify, linker_flags, t};

/// Extra `--check-cfg` to add when building the compiler or tools
/// (Mode restriction, config name, config values (if any))
#[expect(clippy::type_complexity)] // It's fine for hard-coded list and type is explained above.
Expand Down Expand Up @@ -471,8 +470,7 @@ impl Cargo {

// Extend `CXXFLAGS_$TARGET` with our extra flags.
let env = format!("CFLAGS_{triple_underscored}");
let mut cflags =
builder.cc_unhandled_cflags(target, GitRepo::Rustc, CLang::C).join(" ");
let mut cflags = builder.cc_unhandled_cflags(target, CLang::C).join(" ");
if let Some(lto_cflag) = lto_cflag {
cflags.push(' ');
cflags.push_str(lto_cflag);
Expand All @@ -496,8 +494,7 @@ impl Cargo {

// Extend `CXXFLAGS_$TARGET` with our extra flags.
let env = format!("CXXFLAGS_{triple_underscored}");
let mut cxxflags =
builder.cc_unhandled_cflags(target, GitRepo::Rustc, CLang::Cxx).join(" ");
let mut cxxflags = builder.cc_unhandled_cflags(target, CLang::Cxx).join(" ");
if let Some(lto_cflag) = lto_cflag {
cxxflags.push(' ');
cxxflags.push_str(lto_cflag);
Expand Down Expand Up @@ -1161,90 +1158,36 @@ impl Builder<'_> {
//
// Keep this scheme in sync with `rustc_metadata::rmeta::decoder`'s
// `try_to_translate_virtual_to_real`.
//
// `RUSTC_DEBUGINFO_MAP` is used to pass through to the underlying rustc
// `--remap-path-prefix`.
let trim_paths = |cargo: &mut BootstrapCommand, ws_remap: &str| {
cargo.arg("-Ztrim-paths");
cargo.arg("--config").arg("profile.release.trim-paths='all'");
cargo.arg("--config").arg("profile.dev.trim-paths='all'");
cargo.env("__CARGO_RUSTC_BOOTSTRAP_WS_REMAP", ws_remap);
};

match mode {
Mode::Rustc | Mode::Codegen => {
if let Some(ref map_to) =
self.build.debuginfo_map_to(GitRepo::Rustc, RemapScheme::NonCompiler)
{
if let Some(ref map_to) = self.build.debuginfo_map_to(RemapScheme::NonCompiler) {
// Tell the compiler which prefix was used for remapping the standard library
cargo.env("CFG_VIRTUAL_RUST_SOURCE_BASE_DIR", map_to);
}

if let Some(ref map_to) =
self.build.debuginfo_map_to(GitRepo::Rustc, RemapScheme::Compiler)
{
if let Some(ref map_to) = self.build.debuginfo_map_to(RemapScheme::Compiler) {
// Tell the compiler which prefix was used for remapping the compiler it-self
cargo.env("CFG_VIRTUAL_RUSTC_DEV_SOURCE_BASE_DIR", map_to);

// When building compiler sources, we want to apply the compiler remap scheme.
let map = [
// Cargo use relative paths for workspace members, so let's remap those.
format!("compiler/={map_to}/compiler"),
// rustc creates absolute paths (in part bc of the `rust-src` unremap
// and for working directory) so let's remap the build directory as well.
format!("{}={map_to}", self.build.src.display()),
// remap OUT_DIR so they don't leak into artifacts.
format!("{}={map_to}/out", self.build.out.display()),
// on windows, rustc may use forward slashes internally
#[cfg(windows)]
format!(
"{}={map_to}\\out",
self.build.out.display().to_string().replace('/', "\\")
),
]
.join("\t");
cargo.env("RUSTC_DEBUGINFO_MAP", map);
trim_paths(&mut cargo, map_to);
}
}
Mode::Std
| Mode::ToolBootstrap
| Mode::ToolRustcPrivate
| Mode::ToolStd
| Mode::ToolTarget => {
if let Some(ref map_to) =
self.build.debuginfo_map_to(GitRepo::Rustc, RemapScheme::NonCompiler)
{
// When building the standard library sources, we want to apply the std remap scheme.
let map = [
// Cargo use relative paths for workspace members, so let's remap those.
format!("library/={map_to}/library"),

@Urgau Urgau Aug 15, 2026 •
edited by rustbot
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Seems like this remapping isn't done anymore.

$ rustc +62cf67c121864e5bfc57b32497dc24e22b7a91a0 diag.rs
error[E0277]: the trait bound `{integer}: AsRef<Path>` is not satisfied
 --> diag.rs:2:37
  |
2 |     let a = std::fs::read_to_string(12).unwrap();
  |             ----------------------- ^^ the trait `AsRef<Path>` is not implemented for `{integer}`
  |             |
  |             required by a bound introduced by this call
  |
note: required by a bound in `std::fs::read_to_string`
 --> library/std/src/fs.rs:383:0

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0277`.

View changes since the review

@weihanglo weihanglo Aug 15, 2026

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Ah, we forgot library=<map_to>/library remap, which its relative form not covered by Cargo's <absolute-workspace-root>=<map_to>

@Urgau Urgau Aug 15, 2026

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Yeah, the same is probably also not done for compiler.

@weihanglo weihanglo Aug 15, 2026

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Posted rust-lang/cargo#17366

// rustc creates absolute paths (in part bc of the `rust-src` unremap
// and for working directory) so let's remap the build directory as well.
format!("{}={map_to}", self.build.src.display()),
// remap OUT_DIR so they don't leak into artifacts.
format!("{}={map_to}/out", self.build.out.display()),
// on windows, rustc may use forward slashes internally
#[cfg(windows)]
format!(
"{}={map_to}\\out",
self.build.out.display().to_string().replace('/', "\\")
),
]
.join("\t");
cargo.env("RUSTC_DEBUGINFO_MAP", map);
}
}
}

if self.config.rust_remap_debuginfo {
let mut env_var = OsString::new();
if let Some(vendor) = self.build.vendored_crates_path() {
env_var.push(vendor);
env_var.push("=/rust/deps");
} else {
let registry_src = t!(home::cargo_home()).join("registry").join("src");
for entry in t!(std::fs::read_dir(registry_src)) {
if !env_var.is_empty() {
env_var.push("\t");
}
env_var.push(t!(entry).path());
env_var.push("=/rust/deps");
if let Some(ref map_to) = self.build.debuginfo_map_to(RemapScheme::NonCompiler) {
trim_paths(&mut cargo, map_to);
}
}
cargo.env("RUSTC_CARGO_REGISTRY_SRC_TO_REMAP", env_var);
}

// Enable usage of unstable features
Expand Down
67 changes: 19 additions & 48 deletions src/bootstrap/src/core/session.rs
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Expand Up @@ -29,11 +29,6 @@ use crate::utils::helpers::{
};
use crate::{debug, trace};

pub(crate) enum GitRepo {
Rustc,
Llvm,
}

/// Global configuration for the build system.
///
/// This structure transitively contains all configuration for the build system.
Expand Down Expand Up @@ -995,38 +990,29 @@ impl Build {
})
}

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

match which {
GitRepo::Rustc => {
let sha = self.rust_sha().unwrap_or(&self.version);

match remap_scheme {
RemapScheme::Compiler => {
// For compiler sources, remap via `/rustc-dev/{sha}` to allow
// distinguishing between compiler sources vs library sources, since
// `rustc-dev` dist component places them under
// `$sysroot/lib/rustlib/rustc-src/rust` as opposed to `rust-src`'s
// `$sysroot/lib/rustlib/src/rust`.
//
// Keep this scheme in sync with `rustc_metadata::rmeta::decoder`'s
// `try_to_translate_virtual_to_real`.
Some(format!("/rustc-dev/{sha}"))
}
RemapScheme::NonCompiler => {
// For non-compiler sources, use `/rustc/{sha}` remapping scheme.
Some(format!("/rustc/{sha}"))
}
}
let sha = self.rust_sha().unwrap_or(&self.version);

match remap_scheme {
RemapScheme::Compiler => {
// For compiler sources, remap via `/rustc-dev/{sha}` to allow
// distinguishing between compiler sources vs library sources, since
// `rustc-dev` dist component places them under
// `$sysroot/lib/rustlib/rustc-src/rust` as opposed to `rust-src`'s
// `$sysroot/lib/rustlib/src/rust`.
//
// Keep this scheme in sync with `rustc_metadata::rmeta::decoder`'s
// `try_to_translate_virtual_to_real`.
Some(format!("/rustc-dev/{sha}"))
}
RemapScheme::NonCompiler => {
// For non-compiler sources, use `/rustc/{sha}` remapping scheme.
Some(format!("/rustc/{sha}"))
}
GitRepo::Llvm => Some(String::from("/rustc/llvm")),
}
}

Expand Down Expand Up @@ -1069,12 +1055,7 @@ impl Build {
}

/// Returns extra C flags that `cc-rs` doesn't handle.
pub(crate) fn cc_unhandled_cflags(
&self,
target: TargetSelection,
which: GitRepo,
c: CLang,
) -> Vec<String> {
pub(crate) fn cc_unhandled_cflags(&self, target: TargetSelection, c: CLang) -> Vec<String> {
let mut base = Vec::new();

// If we're compiling C++ on macOS then we add a flag indicating that
Expand All @@ -1091,16 +1072,6 @@ impl Build {
base.push("-fno-omit-frame-pointer".into());
}

if let Some(map_to) = self.debuginfo_map_to(which, RemapScheme::NonCompiler) {
let map = format!("{}={}", self.src.display(), map_to);
let cc = self.cc_tool(target);
if cc.is_like_clang() || cc.is_like_gnu() {
base.push(format!("-fdebug-prefix-map={map}"));
} else if cc.is_like_clang_cl() {
base.push("-Xclang".into());
base.push(format!("-fdebug-prefix-map={map}"));
}
}
base
}

Expand Down
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