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

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75f782f
[DO NOT MERGE] bump stage0 to nightly
weihanglo Aug 13, 2026
bc8f4bf
rustc_llvm: bump cc to 1.4.2
weihanglo Aug 14, 2026
6fefad1
bootstrap: remap-debuginfo via cargo trim-paths
weihanglo Aug 7, 2026
8d74918
tests: check `$CARGO_HOME` leaks
weihanglo Aug 13, 2026
019272a
tests: check std rmeta for local path leaks
weihanglo Aug 14, 2026
c5019f0
tests: switch remap prefix expectation to `/cargo/registry`
weihanglo Aug 13, 2026
1ef6077
library: bump cc to 1.4.2
weihanglo Aug 15, 2026
e416b25
bootstrap: move debug-prefix-map C flags to LLVM CMake build
weihanglo Aug 14, 2026
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23 changes: 15 additions & 8 deletions Cargo.lock
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Original file line number Diff line number Diff line change
Expand Up @@ -543,13 +543,14 @@ version = "0.1.0"

[[package]]
name = "cc"
version = "1.2.16"
version = "1.4.2"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "be714c154be609ec7f5dad223a33bf1482fff90472de28f7362806e6d4832b8c"
checksum = "5d262e149917187838d5b42777c8253bcb64500067342904e7d429499a6f277e"
dependencies = [
"find-msvc-tools",
"jobserver",
"libc",
"shlex",
"shlex 2.0.1",
]

[[package]]
Expand Down Expand Up @@ -1437,9 +1438,9 @@ dependencies = [

[[package]]
name = "find-msvc-tools"
version = "0.1.5"
version = "0.1.10"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "3a3076410a55c90011c298b04d0cfa770b00fa04e1e3c97d3f6c9de105a03844"
checksum = "26b73573e6edcd2af0cdf47bd6cb58f0b3839491263c314eaad1ccf24430e1de"

[[package]]
name = "flate2"
Expand Down Expand Up @@ -2222,7 +2223,7 @@ dependencies = [
"jsonpath-rust",
"regex",
"serde_json",
"shlex",
"shlex 1.3.0",
]

[[package]]
Expand Down Expand Up @@ -3995,7 +3996,7 @@ dependencies = [
"rustc_span",
"rustc_target",
"serde_json",
"shlex",
"shlex 1.3.0",
"tracing",
"windows 0.61.3",
]
Expand Down Expand Up @@ -4361,7 +4362,7 @@ version = "0.0.0"
dependencies = [
"cc",
"libc",
"shlex",
"shlex 1.3.0",
]

[[package]]
Expand Down Expand Up @@ -5374,6 +5375,12 @@ version = "1.3.0"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "0fda2ff0d084019ba4d7c6f371c95d8fd75ce3524c3cb8fb653a3023f6323e64"

[[package]]
name = "shlex"
version = "2.0.1"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "f8fadd59c855ef2080decdef8ff161eb6661b86933c9d82e5ba29dc602a55aba"

[[package]]
name = "simd-adler32"
version = "0.3.7"
Expand Down
2 changes: 1 addition & 1 deletion compiler/rustc_llvm/Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -11,7 +11,7 @@ libc = "0.2.73"
[build-dependencies]
# tidy-alphabetical-start
# `cc` updates often break things, so we pin it here.
cc = "=1.2.16"
cc = "=1.4.2"
shlex = "1.3.0"
# tidy-alphabetical-end

Expand Down
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
15 changes: 11 additions & 4 deletions library/Cargo.lock
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Original file line number Diff line number Diff line change
Expand Up @@ -40,10 +40,11 @@ dependencies = [

[[package]]
name = "cc"
version = "1.2.0"
version = "1.4.2"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "1aeb932158bd710538c73702db6945cb68a8fb08c519e6e12706b94263b36db8"
checksum = "5d262e149917187838d5b42777c8253bcb64500067342904e7d429499a6f277e"
dependencies = [
"find-msvc-tools",
"shlex",
]

Expand Down Expand Up @@ -88,6 +89,12 @@ dependencies = [
"windows-sys",
]

[[package]]
name = "find-msvc-tools"
version = "0.1.11"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "d45db016d36b838f563236e9193d0ee6ce38f3f68b6c94e914b4929c96bbb890"

[[package]]
name = "foldhash"
version = "0.2.0"
Expand Down Expand Up @@ -314,9 +321,9 @@ dependencies = [

[[package]]
name = "shlex"
version = "1.3.0"
version = "2.0.1"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "0fda2ff0d084019ba4d7c6f371c95d8fd75ce3524c3cb8fb653a3023f6323e64"
checksum = "f8fadd59c855ef2080decdef8ff161eb6661b86933c9d82e5ba29dc602a55aba"

[[package]]
name = "std"
Expand Down
2 changes: 1 addition & 1 deletion library/profiler_builtins/Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -12,4 +12,4 @@ doc = false

[build-dependencies]
# Pinned so `cargo update` bumps don't cause breakage
cc = "=1.2.0"
cc = "=1.4.2"
14 changes: 0 additions & 14 deletions src/bootstrap/src/bin/rustc.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -165,20 +165,6 @@ 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
5 changes: 2 additions & 3 deletions src/bootstrap/src/core/build_steps/compile.rs
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Expand Up @@ -37,8 +37,7 @@ use crate::utils::helpers::{
self, exe, get_clang_cl_resource_dir, is_debug_info, is_dylib, symlink_dir, t, up_to_date,
};
use crate::{
CLang, CodegenBackendKind, Compiler, DependencyType, FileType, GitRepo, LLVM_TOOLS, Mode,
debug, trace,
CLang, CodegenBackendKind, Compiler, DependencyType, FileType, LLVM_TOOLS, Mode, debug, trace,
};

/// Build a standard library for the given `target` using the given `build_compiler`.
Expand Down Expand Up @@ -1898,7 +1897,7 @@ 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
29 changes: 26 additions & 3 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 @@ -26,7 +26,7 @@ use crate::utils::exec::command;
use crate::utils::helpers::{
self, exe, get_clang_cl_resource_dir, libdir, t, unhashed_basename, up_to_date,
};
use crate::{CLang, GitRepo, trace};
use crate::{CLang, trace};

/// Result of building or downloading LLVM artifacts.
#[derive(Clone)]
Expand Down Expand Up @@ -663,6 +663,27 @@ 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 @@ -827,7 +848,8 @@ 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 @@ -848,7 +870,8 @@ 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
6 changes: 3 additions & 3 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 @@ -45,7 +45,7 @@ use crate::utils::helpers::{
up_to_date,
};
use crate::utils::render_tests::{add_flags_and_try_run_tests, try_run_tests};
use crate::{CLang, CodegenBackendKind, GitRepo, Mode, TestTarget, envify};
use crate::{CLang, CodegenBackendKind, Mode, TestTarget, envify};

mod compiletest;
pub mod failed_tests;
Expand Down Expand Up @@ -2781,9 +2781,9 @@ 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
88 changes: 15 additions & 73 deletions src/bootstrap/src/core/builder/cargo.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -11,9 +11,7 @@ use crate::core::config::{CompressDebuginfo, Config, DryRun, SplitDebuginfo, Tar
use crate::utils::build_stamp;
use crate::utils::exec::{BootstrapCommand, command};
use crate::utils::helpers::{self, LldThreads, check_cfg_arg, linker_flags, t};
use crate::{
CLang, Compiler, EXTRA_CHECK_CFGS, GitRepo, Mode, RemapScheme, prepare_behaviour_dump_dir,
};
use crate::{CLang, Compiler, EXTRA_CHECK_CFGS, Mode, RemapScheme, prepare_behaviour_dump_dir};

/// Represents flag values in `String` form with a `\x1f` delimiter to pass to the compiler later.
///
Expand Down Expand Up @@ -431,8 +429,7 @@ 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 Ok(var) = std::env::var(&env) {
cflags.push(' ');
cflags.push_str(&var);
Expand All @@ -452,8 +449,7 @@ 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 Ok(var) = std::env::var(&env) {
cxxflags.push(' ');
cxxflags.push_str(&var);
Expand Down Expand Up @@ -1107,90 +1103,36 @@ 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
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