bootstrap: using a toolchain that includes 'rust-src', `./x check` leaves a dirty working tree, fails to build

[lambdageek]

Summary

When building a recent nightly (after #119899) using a beta toolchain that includes the rust-src component, ./x check leaves a dirty tree (git status shows lots of modified files) and the check build fails.

Command used

git clone https://github.com/rust-lang/rust .
git checkout 5d707b07e42766c080c5012869c9988a18dcbb83

rustup install 1.88.0-beta.4
rustup component add --toolchain 1.88.0-beta.4 rust-src

./configure --set build.cargo=${HOME}/.rustup/toolchains/1.88.0-beta.4-x86_64-unknown-linux-gnu/bin/cargo --set build.rustc=${HOME}/.rustup/toolchains/1.88.0-beta.4-x86_64-unknown-linux-gnu/bin/rustc --set rust.channel=nightly --set profile=dist --set llvm.download-ci-llvm=true --set rust.download-rustc=false

./x check

Expected behaviour

./x check succeeds and git status shows a clean working tree

Actual behaviour

./x check fails. The exact failure differs based on platform and configure options, but this is one example:

Building compiler artifacts (stage0 -> stage1, x86_64-unknown-linux-gnu)
...
  Compiling rustc_proc_macro v0.0.0 (/home/aleksey/hacking/rust-boot/rust/compiler/rustc_proc_macro)
   Compiling ruzstd v0.7.3
   Compiling unicode-script v0.5.7
   Compiling libloading v0.8.7
   Compiling punycode v0.4.1
   Compiling rustc-demangle v0.1.24
   Compiling fallible-iterator v0.3.0
   Compiling regex-syntax v0.6.29
   Compiling rustc_llvm v0.0.0 (/home/aleksey/hacking/rust-boot/rust/compiler/rustc_llvm)
   Compiling lazy_static v1.5.0
error: prefer `FxHashMap` over `HashMap`, it has better performance
  --> compiler/rustc_proc_macro/../../library/proc_macro/src/bridge/fxhash.rs:12:35
   |
12 | ...hMap<K, V> = HashMap<K, V, BuildHasherDefault<FxHasher>>;
   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: a `use rustc_data_structures::fx::FxHashMap` may be necessary
   = note: `-D rustc::default-hash-types` implied by `-D warnings`
   = help: to override `-D warnings` add `#[allow(rustc::default_hash_types)]`

error: could not compile `rustc_proc_macro` (lib) due to 1 previous error
warning: build failed, waiting for other jobs to finish...
Build completed unsuccessfully in 0:01:20

And git status shows many modified files

$ git status
On branch aleksey-wip1
Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git restore <file>..." to discard changes in working directory)
  (commit or discard the untracked or modified content in submodules)
	modified:   library/Cargo.lock
	modified:   library/alloc/Cargo.toml
	modified:   library/alloc/src/collections/btree/map.rs
	modified:   library/alloc/src/collections/btree/map/tests.rs
	modified:   library/alloc/src/collections/btree/set.rs
	modified:   library/alloc/src/collections/btree/set/tests.rs
	modified:   library/alloc/src/collections/linked_list.rs
	modified:   library/alloc/src/collections/vec_deque/mod.rs
	modified:   library/alloc/src/raw_vec/mod.rs
	modified:   library/alloc/src/slice.rs
	modified:   library/alloc/src/str.rs
	modified:   library/alloc/src/string.rs
	modified:   library/alloc/src/vec/mod.rs
	modified:   library/alloctests/benches/btree/map.rs
	modified:   library/alloctests/benches/btree/set.rs
	modified:   library/alloctests/tests/autotraits.rs
	modified:   library/alloctests/tests/fmt.rs
	modified:   library/core/Cargo.toml
	modified:   library/core/src/alloc/layout.rs
	modified:   library/core/src/array/mod.rs
	modified:   library/core/src/ascii/ascii_char.rs
	modified:   library/core/src/cell/lazy.rs
	modified:   library/core/src/char/convert.rs
	modified:   library/core/src/char/methods.rs
	modified:   library/core/src/clone.rs
	modified:   library/core/src/convert/mod.rs
	modified:   library/core/src/ffi/c_str.rs
	modified:   library/core/src/ffi/mod.rs
	modified:   library/core/src/ffi/primitives.rs
	modified:   library/core/src/ffi/va_list.rs
	modified:   library/core/src/fmt/float.rs
	modified:   library/core/src/fmt/mod.rs
	modified:   library/core/src/fmt/num.rs
	modified:   library/core/src/fmt/rt.rs
	modified:   library/core/src/future/async_drop.rs
	modified:   library/core/src/future/mod.rs
	modified:   library/core/src/hint.rs
	modified:   library/core/src/intrinsics/mod.rs
	modified:   library/core/src/intrinsics/simd.rs
	modified:   library/core/src/iter/traits/collect.rs
	modified:   library/core/src/iter/traits/iterator.rs
	modified:   library/core/src/lib.rs
	modified:   library/core/src/macros/mod.rs
	modified:   library/core/src/marker.rs
	modified:   library/core/src/marker/variance.rs
	modified:   library/core/src/mem/maybe_uninit.rs
	modified:   library/core/src/mem/mod.rs
	modified:   library/core/src/net/ip_addr.rs
	modified:   library/core/src/num/dec2flt/float.rs
	modified:   library/core/src/num/dec2flt/mod.rs
	modified:   library/core/src/num/f128.rs
	modified:   library/core/src/num/f16.rs
	modified:   library/core/src/num/f32.rs
	modified:   library/core/src/num/f64.rs
	modified:   library/core/src/num/flt2dec/decoder.rs
	modified:   library/core/src/num/int_macros.rs
	modified:   library/core/src/num/mod.rs
	modified:   library/core/src/num/nonzero.rs
	modified:   library/core/src/num/uint_macros.rs
	modified:   library/core/src/ops/arith.rs
	modified:   library/core/src/ops/function.rs
	modified:   library/core/src/ops/index.rs
	modified:   library/core/src/ops/index_range.rs
	modified:   library/core/src/ops/try_trait.rs
	modified:   library/core/src/option.rs
	modified:   library/core/src/panicking.rs
	modified:   library/core/src/pin.rs
	modified:   library/core/src/pin/unsafe_pinned.rs
	modified:   library/core/src/prelude/v1.rs
	modified:   library/core/src/primitive_docs.rs
	modified:   library/core/src/ptr/alignment.rs
	modified:   library/core/src/ptr/const_ptr.rs
	modified:   library/core/src/ptr/mod.rs
	modified:   library/core/src/ptr/mut_ptr.rs
	modified:   library/core/src/ptr/non_null.rs
	modified:   library/core/src/result.rs
	modified:   library/core/src/slice/index.rs
	modified:   library/core/src/slice/mod.rs
	modified:   library/core/src/slice/raw.rs
	modified:   library/core/src/slice/sort/select.rs
	modified:   library/core/src/slice/sort/stable/mod.rs
	modified:   library/core/src/slice/sort/unstable/mod.rs
	modified:   library/core/src/slice/sort/unstable/quicksort.rs
	modified:   library/core/src/str/converts.rs
	modified:   library/core/src/str/mod.rs
	modified:   library/core/src/str/traits.rs
	modified:   library/core/src/sync/atomic.rs
	modified:   library/core/src/time.rs
	modified:   library/core/src/ub_checks.rs
	modified:   library/coretests/Cargo.toml
	modified:   library/coretests/tests/array.rs
	modified:   library/coretests/tests/ffi/cstr.rs
	modified:   library/coretests/tests/lib.rs
	modified:   library/coretests/tests/macros.rs
	modified:   library/coretests/tests/num/dec2flt/decimal.rs
	modified:   library/coretests/tests/num/dec2flt/float.rs
	modified:   library/coretests/tests/num/dec2flt/lemire.rs
	modified:   library/coretests/tests/num/dec2flt/mod.rs
	modified:   library/coretests/tests/num/dec2flt/parse.rs
	modified:   library/coretests/tests/num/flt2dec/mod.rs
	modified:   library/coretests/tests/num/flt2dec/random.rs
	modified:   library/coretests/tests/num/flt2dec/strategy/dragon.rs
	modified:   library/coretests/tests/num/flt2dec/strategy/grisu.rs
	modified:   library/coretests/tests/num/mod.rs
	modified:   library/coretests/tests/pin_macro.rs
	modified:   library/coretests/tests/time.rs
	modified:   library/panic_abort/Cargo.toml
	modified:   library/panic_abort/src/lib.rs
	modified:   library/panic_unwind/src/hermit.rs
	modified:   library/proc_macro/Cargo.toml
	modified:   library/proc_macro/src/bridge/arena.rs
	modified:   library/proc_macro/src/lib.rs
	modified:   library/std/Cargo.toml
	modified:   library/std/src/collections/hash/map.rs
	modified:   library/std/src/collections/hash/set.rs
	modified:   library/std/src/ffi/mod.rs
	modified:   library/std/src/ffi/os_str.rs
	modified:   library/std/src/fs.rs
	modified:   library/std/src/fs/tests.rs
	modified:   library/std/src/io/error.rs
	modified:   library/std/src/io/mod.rs
	modified:   library/std/src/io/pipe.rs
	modified:   library/std/src/io/tests.rs
	modified:   library/std/src/lib.rs
	modified:   library/std/src/os/net/linux_ext/addr.rs
	modified:   library/std/src/os/net/linux_ext/socket.rs
	modified:   library/std/src/os/net/linux_ext/tcp.rs
	modified:   library/std/src/os/unix/net/stream.rs
	modified:   library/std/src/os/unix/process.rs
	modified:   library/std/src/os/wasi/fs.rs
	modified:   library/std/src/os/windows/process.rs
	modified:   library/std/src/panic.rs
	modified:   library/std/src/panicking.rs
	modified:   library/std/src/path.rs
	modified:   library/std/src/prelude/v1.rs
	modified:   library/std/src/process.rs
	modified:   library/std/src/rt.rs
	modified:   library/std/src/sync/lazy_lock.rs
	modified:   library/std/src/sync/mpmc/list.rs
	modified:   library/std/src/sync/once_lock.rs
	modified:   library/std/src/sync/poison/mutex.rs
	modified:   library/std/src/sync/poison/rwlock.rs
	modified:   library/std/src/sync/reentrant_lock.rs
	modified:   library/std/src/sys/cmath.rs
	modified:   library/std/src/sys/fs/unix.rs
	modified:   library/std/src/sys/fs/windows.rs
	modified:   library/std/src/sys/net/connection/uefi/mod.rs
	modified:   library/std/src/sys/os_str/wtf8.rs
	modified:   library/std/src/sys/pal/hermit/mod.rs
	modified:   library/std/src/sys/pal/sgx/mod.rs
	modified:   library/std/src/sys/pal/uefi/helpers.rs
	modified:   library/std/src/sys/pal/uefi/mod.rs
	modified:   library/std/src/sys/pal/unix/stack_overflow.rs
	modified:   library/std/src/sys/pal/unix/thread.rs
	modified:   library/std/src/sys/pal/windows/mod.rs
	modified:   library/std/src/sys/pal/xous/mod.rs
	modified:   library/std/src/sys/pal/xous/os.rs
	modified:   library/std/src/sys/process/unix/common.rs
	modified:   library/std/src/sys/process/unix/unix.rs
	modified:   library/std/src/sys/process/unix/vxworks.rs
	modified:   library/std/src/sys/process/windows.rs
	modified:   library/std/src/sys/sync/mutex/futex.rs
	modified:   library/std/src/sys/sync/mutex/pthread.rs
	modified:   library/std/src/sys/thread_local/guard/key.rs
	modified:   library/std/src/sys/thread_local/native/lazy.rs
	modified:   library/std/src/thread/mod.rs
	modified:   library/std/tests/floats/f128.rs
	modified:   library/std/tests/floats/f16.rs
	modified:   library/std/tests/floats/f32.rs
	modified:   library/std/tests/floats/f64.rs
	modified:   library/std/tests/floats/lib.rs
	modified:   library/std/tests/path.rs
	modified:   library/stdarch (modified content)

Untracked files:
  (use "git add <file>..." to include in what will be committed)
	bootstrap.toml.aleksey
	library/std/src/f128.rs
	library/std/src/f16.rs
	library/std/src/f32.rs
	library/std/src/f64.rs
	library/std/src/num.rs

no changes added to commit (use "git add" and/or "git commit -a")

Bootstrap configuration (bootstrap.toml)

# Use different pre-set defaults than the global defaults.
#
# See `src/bootstrap/defaults` for more information.
# Note that this has no default value (x.py uses the defaults in `bootstrap.example.toml`).
profile = 'dist'

[llvm]

# Currently, we only support this when building LLVM for the build triple.
#
# Note that many of the LLVM options are not currently supported for
# downloading. Currently only the "assertions" option can be toggled.
download-ci-llvm = true

[gcc]
# Download GCC from CI instead of building it locally.
# Note that this will attempt to download GCC even if there are local
# modifications to the `src/gcc` submodule.
# Currently, this is only supported for the `x86_64-unknown-linux-gnu` target.
#download-ci-gcc = false

[build]

# Instead of downloading the src/stage0 version of Cargo specified, use
# this Cargo binary instead to build all Rust code
# If you set this, you likely want to set `rustc` as well.
cargo = '/home/aleksey/.rustup/toolchains/1.88.0-beta.4-x86_64-unknown-linux-gnu/bin/cargo'

# Instead of downloading the src/stage0 version of the compiler
# specified, use this rustc binary instead as the stage0 snapshot compiler.
# If you set this, you likely want to set `cargo` as well.
rustc = '/home/aleksey/.rustup/toolchains/1.88.0-beta.4-x86_64-unknown-linux-gnu/bin/rustc'

# Arguments passed to the `./configure` script, used during distcheck. You
# probably won't fill this in but rather it's filled in by the `./configure`
# script. Useful for debugging.
configure-args = ['--set', 'build.cargo=/home/aleksey/.rustup/toolchains/1.88.0-beta.4-x86_64-unknown-linux-gnu/bin/cargo', '--set', 'build.rustc=/home/aleksey/.rustup/toolchains/1.88.0-beta.4-x86_64-unknown-linux-gnu/bin/rustc', '--set', 'rust.channel=nightly', '--set', 'profile=dist', '--set', 'llvm.download-ci-llvm=true', '--set', 'rust.download-rustc=false']

[install]

[rust]

# Whether to download the stage 1 and 2 compilers from CI. This is useful if you
# are working on tools, doc-comments, or library (you will be able to build the
# standard library without needing to build the compiler).
#
# Set this to "if-unchanged" if you are working on `src/tools`, `tests` or
# `library` (on CI, `library` changes triggers in-tree compiler build) to speed
# up the build process if you don't need to build a compiler from the latest
# commit from `master`.
#
# Set this to `true` to always download or `false` to always use the in-tree
# compiler.
download-rustc = false

# The "channel" for the Rust build to produce. The stable/beta channels only
# allow using stable features, whereas the nightly and dev channels allow using
# nightly features.
#
# You can set the channel to "auto-detect" to load the channel name from `src/ci/channel`.
#
# If using tarball sources, default value is "auto-detect", otherwise, it's "dev".
channel = 'nightly'

[target.x86_64-unknown-linux-gnu]

[dist]

Operating system

Observed on: Debian trixie (amd64), also macOS 15.5 (arm64)

HEAD

5d707b0

Additional context

At work we try to build nightlies using our in-house custom beta toolchain which includes a number of components (including 'rust-src') by default.

Build Log

log.txt

[lambdageek]

Added some tracing and I see this:

          DEBUG bootstrap::core::build_steps::compile building compiler libraries to link to, build_compiler=Compiler { stage: 0, host: x86_64-unknown-linux-gnu, forced_compiler: false }, target_compiler.host=x86_64-unknown-linux-gnu
           bootstrap::core::build_steps::compile::Rustc::run previous_compiler=Compiler { stage: 0, host: x86_64-unknown-linux-gnu, forced_compiler: false }, target=x86_64-unknown-linux-gnu
             bootstrap::core::build_steps::compile::Std::run target=x86_64-unknown-linux-gnu, compiler=Compiler { stage: 0, host: x86_64-unknown-linux-gnu, forced_compiler: false }, force_recompile=false
               bootstrap::core::build_steps::compile::StdLink::run compiler=Compiler { stage: 0, host: x86_64-unknown-linux-gnu, forced_compiler: false }, target_compiler=Compiler { stage: 0, host: x86_64-unknown-linux-gnu, forced_compiler: false }, target=x86_64-unknown-linux-gnu
                 bootstrap::core::build_steps::compile::Sysroot::run compiler=Compiler { stage: 0, host: x86_64-unknown-linux-gnu, forced_compiler: false }
                  TRACE bootstrap::core::build_steps::compile stage=0, sysroot="/home/aleksey/hacking/rust-boot/rust/build/x86_64-unknown-linux-gnu/stage0-sysroot"
                   bootstrap::core::build_steps::dist::maybe_install_llvm_target llvm_link_shared=false, target=x86_64-unknown-linux-gnu, sysroot="/home/aleksey/hacking/rust-boot/rust/build/x86_64-unknown-linux-gnu/stage0-sysroot"
                  DEBUG bootstrap::core::build_steps::compile Creating Symlink  src: /home/aleksey/hacking/rust-boot/rust, sysroot_src: /home/aleksey/hacking/rust-boot/rust/build/x86_64-unknown-linux-gnu/stage0-sysroot/lib/rustlib/src/rust
                DEBUG bootstrap::core::build_steps::compile StdLink::run stage0 case, cp_link_r src: /home/aleksey/.rustup/toolchains/1.88.0-beta.4-x86_64-unknown-linux-gnu/lib, dest: /home/aleksey/hacking/rust-boot/rust/build/x86_64-unknown-linux-gnu/stage0-sysroot/lib

"Creating Symlink" is a debug! right here:

rust/src/bootstrap/src/core/build_steps/compile.rs

Line 1884 in 792fc2b

if let Err(e) = symlink_dir(&builder.config, &builder.src, &sysroot_lib_rustlib_src_rust) {

and "StdLink::run stage0 case" is a debug! over here:

rust/src/bootstrap/src/core/build_steps/compile.rs

Line 799 in 792fc2b

builder.cp_link_r(&builder.initial_sysroot.join("lib"), &sysroot.join("lib"));

So we first symlink the git repo root into stage0-sysroot/lib/rustlib/src/rust
and then we copy everything from .rustup/toolchains/1.88.0-beta.4-x86_64-unknown-linux-gnu/lib (including its rustlib/src/rust/ contents) into the sysroot and end up writing over the repo sources

My guess is we probably don't want to create that symlink if compiler.stage == 0 now, does that make sense?
Update yeah, this fixes it for me:

patch

diff --git a/src/bootstrap/src/core/build_steps/compile.rs b/src/bootstrap/src/core/build_steps/compile.rs
index 40247288e75..3729af3a2e5 100644
--- a/src/bootstrap/src/core/build_steps/compile.rs
+++ b/src/bootstrap/src/core/build_steps/compile.rs
@@ -1870,26 +1870,28 @@ fn run(self, builder: &Builder<'_>) -> PathBuf {
         // so that any tools relying on `rust-src` also work for local builds,
         // and also for translating the virtual `/rustc/$hash` back to the real
         // directory (for running tests with `rust.remap-debuginfo = true`).
-        let sysroot_lib_rustlib_src = sysroot.join("lib/rustlib/src");
-        t!(fs::create_dir_all(&sysroot_lib_rustlib_src));
-        let sysroot_lib_rustlib_src_rust = sysroot_lib_rustlib_src.join("rust");
-        if let Err(e) = symlink_dir(&builder.config, &builder.src, &sysroot_lib_rustlib_src_rust) {
-            eprintln!(
-                "ERROR: creating symbolic link `{}` to `{}` failed with {}",
-                sysroot_lib_rustlib_src_rust.display(),
-                builder.src.display(),
-                e,
-            );
-            if builder.config.rust_remap_debuginfo {
+        if compiler.stage != 0 {
+            let sysroot_lib_rustlib_src = sysroot.join("lib/rustlib/src");
+            t!(fs::create_dir_all(&sysroot_lib_rustlib_src));
+            let sysroot_lib_rustlib_src_rust = sysroot_lib_rustlib_src.join("rust");
+            if let Err(e) = symlink_dir(&builder.config, &builder.src, &sysroot_lib_rustlib_src_rust) {
                 eprintln!(
-                    "ERROR: some `tests/ui` tests will fail when lacking `{}`",
+                    "ERROR: creating symbolic link `{}` to `{}` failed with {}",
                     sysroot_lib_rustlib_src_rust.display(),
+                    builder.src.display(),
+                    e,
                 );
+                if builder.config.rust_remap_debuginfo {
+                    eprintln!(
+                        "ERROR: some `tests/ui` tests will fail when lacking `{}`",
+                        sysroot_lib_rustlib_src_rust.display(),
+                    );
+                }
+                build_helper::exit!(1);
             }
-            build_helper::exit!(1);
         }

[onur-ozkan]

That seems to make sense. Would you mind sending a PR?

[lambdageek]

@onur-ozkan #142000