Allow spaces in bootstrap Cargo rustflags by kupiakos · Pull Request #156096 · rust-lang/rust

kupiakos · 2026-05-02T21:13:29Z

This is particularly useful when one's home directory contains a space. Without this change, the assert fails with my home directory when running x test, even when using subst (on Windows) to give the build directory its own drive letter.

This is particularly useful when one's home directory contains a space. Without this change, the assert fails with my home directory, even when using `subst` (on Windows) to give the build dir its own drive letter.

rustbot · 2026-05-02T21:13:33Z

r? @Mark-Simulacrum

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Mark-Simulacrum · 2026-05-09T17:50:59Z

        cargo.rustflags.propagate_rustflag_envs(cargo.build_compiler_stage);
        cargo.rustdocflags.propagate_rustflag_envs(cargo.build_compiler_stage);

        cargo.rustdocflags.propagate_cargo_env("RUSTDOCFLAGS");


Do we need to apply this here as well?

Is there a way we can add a test for this (e.g., maybe on one or more CI runners we can build in a directory with a path containing spaces)?

View changes since the review

@Kobzol

… r=kobzol,mark-simulacrum,bjorn3 bootstrap: fix panic when repo path contains spaces by switching to CARGO_ENCODED_RUSTFLAGS Fixes rust-lang#158052 Closes: rust-lang#156096 ## Problem `./x build` panics with a cryptic assertion error when the repository is checked out under a directory path containing spaces (e.g. `/Users/foo/Open Source/rust`): thread 'main' panicked at src/bootstrap/src/core/builder/cargo.rs:54:9: assertion left == right failed left: 2 right: 1 The root cause: when building tools in `ToolRustcPrivate` or `Codegen` mode, bootstrap calls `llvm-config --libdir` and passes the result as a `-Clink-arg=-L<path>` rustflag. The `Rustflags::arg()` method asserted that arguments contain no spaces, but if the repo path has a space the libdir path inherits it and the assertion fires. The error gives no hint that the path is the problem. A secondary bug: `llvm-config --libdir` output has a trailing newline that was previously stripped accidentally by `RUSTFLAGS` whitespace splitting. Nothing was trimming it explicitly. ## Fix Two changes in `src/bootstrap/src/core/builder/cargo.rs`: 1. **Switch `RUSTFLAGS` → `CARGO_ENCODED_RUSTFLAGS`**: Change `Rustflags` to store args as `Vec<String>` and join with `\x1f` (ASCII unit separator) when setting the env var. Cargo's `CARGO_ENCODED_RUSTFLAGS` (stable since Cargo 1.55) uses `\x1f` as delimiter, which never appears in filesystem paths, so paths with spaces are handled correctly. The space-based assertion in `arg()` is removed. 2. **Trim `llvm-config --libdir` output**: Explicitly `.trim()` the captured stdout so the trailing newline is not included in the linker search path. `RUSTDOCFLAGS` is left as-is (space-joined) since no llvm paths are added to rustdocflags. cc: @Kobzol

@Kobzol

… r=kobzol,mark-simulacrum,bjorn3 bootstrap: fix panic when repo path contains spaces by switching to CARGO_ENCODED_RUSTFLAGS Fixes rust-lang#158052 Closes: rust-lang#156096 ## Problem `./x build` panics with a cryptic assertion error when the repository is checked out under a directory path containing spaces (e.g. `/Users/foo/Open Source/rust`): thread 'main' panicked at src/bootstrap/src/core/builder/cargo.rs:54:9: assertion left == right failed left: 2 right: 1 The root cause: when building tools in `ToolRustcPrivate` or `Codegen` mode, bootstrap calls `llvm-config --libdir` and passes the result as a `-Clink-arg=-L<path>` rustflag. The `Rustflags::arg()` method asserted that arguments contain no spaces, but if the repo path has a space the libdir path inherits it and the assertion fires. The error gives no hint that the path is the problem. A secondary bug: `llvm-config --libdir` output has a trailing newline that was previously stripped accidentally by `RUSTFLAGS` whitespace splitting. Nothing was trimming it explicitly. ## Fix Two changes in `src/bootstrap/src/core/builder/cargo.rs`: 1. **Switch `RUSTFLAGS` → `CARGO_ENCODED_RUSTFLAGS`**: Change `Rustflags` to store args as `Vec<String>` and join with `\x1f` (ASCII unit separator) when setting the env var. Cargo's `CARGO_ENCODED_RUSTFLAGS` (stable since Cargo 1.55) uses `\x1f` as delimiter, which never appears in filesystem paths, so paths with spaces are handled correctly. The space-based assertion in `arg()` is removed. 2. **Trim `llvm-config --libdir` output**: Explicitly `.trim()` the captured stdout so the trailing newline is not included in the linker search path. `RUSTDOCFLAGS` is left as-is (space-joined) since no llvm paths are added to rustdocflags. cc: @Kobzol

@Kobzol

… r=kobzol,mark-simulacrum,bjorn3 bootstrap: fix panic when repo path contains spaces by switching to CARGO_ENCODED_RUSTFLAGS Fixes rust-lang#158052 Closes: rust-lang#156096 ## Problem `./x build` panics with a cryptic assertion error when the repository is checked out under a directory path containing spaces (e.g. `/Users/foo/Open Source/rust`): thread 'main' panicked at src/bootstrap/src/core/builder/cargo.rs:54:9: assertion left == right failed left: 2 right: 1 The root cause: when building tools in `ToolRustcPrivate` or `Codegen` mode, bootstrap calls `llvm-config --libdir` and passes the result as a `-Clink-arg=-L<path>` rustflag. The `Rustflags::arg()` method asserted that arguments contain no spaces, but if the repo path has a space the libdir path inherits it and the assertion fires. The error gives no hint that the path is the problem. A secondary bug: `llvm-config --libdir` output has a trailing newline that was previously stripped accidentally by `RUSTFLAGS` whitespace splitting. Nothing was trimming it explicitly. ## Fix Two changes in `src/bootstrap/src/core/builder/cargo.rs`: 1. **Switch `RUSTFLAGS` → `CARGO_ENCODED_RUSTFLAGS`**: Change `Rustflags` to store args as `Vec<String>` and join with `\x1f` (ASCII unit separator) when setting the env var. Cargo's `CARGO_ENCODED_RUSTFLAGS` (stable since Cargo 1.55) uses `\x1f` as delimiter, which never appears in filesystem paths, so paths with spaces are handled correctly. The space-based assertion in `arg()` is removed. 2. **Trim `llvm-config --libdir` output**: Explicitly `.trim()` the captured stdout so the trailing newline is not included in the linker search path. `RUSTDOCFLAGS` is left as-is (space-joined) since no llvm paths are added to rustdocflags. cc: @Kobzol

@Kobzol

… r=kobzol,mark-simulacrum,bjorn3 bootstrap: fix panic when repo path contains spaces by switching to CARGO_ENCODED_RUSTFLAGS Fixes rust-lang#158052 Closes: rust-lang#156096 ## Problem `./x build` panics with a cryptic assertion error when the repository is checked out under a directory path containing spaces (e.g. `/Users/foo/Open Source/rust`): thread 'main' panicked at src/bootstrap/src/core/builder/cargo.rs:54:9: assertion left == right failed left: 2 right: 1 The root cause: when building tools in `ToolRustcPrivate` or `Codegen` mode, bootstrap calls `llvm-config --libdir` and passes the result as a `-Clink-arg=-L<path>` rustflag. The `Rustflags::arg()` method asserted that arguments contain no spaces, but if the repo path has a space the libdir path inherits it and the assertion fires. The error gives no hint that the path is the problem. A secondary bug: `llvm-config --libdir` output has a trailing newline that was previously stripped accidentally by `RUSTFLAGS` whitespace splitting. Nothing was trimming it explicitly. ## Fix Two changes in `src/bootstrap/src/core/builder/cargo.rs`: 1. **Switch `RUSTFLAGS` → `CARGO_ENCODED_RUSTFLAGS`**: Change `Rustflags` to store args as `Vec<String>` and join with `\x1f` (ASCII unit separator) when setting the env var. Cargo's `CARGO_ENCODED_RUSTFLAGS` (stable since Cargo 1.55) uses `\x1f` as delimiter, which never appears in filesystem paths, so paths with spaces are handled correctly. The space-based assertion in `arg()` is removed. 2. **Trim `llvm-config --libdir` output**: Explicitly `.trim()` the captured stdout so the trailing newline is not included in the linker search path. `RUSTDOCFLAGS` is left as-is (space-joined) since no llvm paths are added to rustdocflags. cc: @Kobzol

@Kobzol

… r=kobzol,mark-simulacrum,bjorn3 bootstrap: fix panic when repo path contains spaces by switching to CARGO_ENCODED_RUSTFLAGS Fixes rust-lang#158052 Closes: rust-lang#156096 ## Problem `./x build` panics with a cryptic assertion error when the repository is checked out under a directory path containing spaces (e.g. `/Users/foo/Open Source/rust`): thread 'main' panicked at src/bootstrap/src/core/builder/cargo.rs:54:9: assertion left == right failed left: 2 right: 1 The root cause: when building tools in `ToolRustcPrivate` or `Codegen` mode, bootstrap calls `llvm-config --libdir` and passes the result as a `-Clink-arg=-L<path>` rustflag. The `Rustflags::arg()` method asserted that arguments contain no spaces, but if the repo path has a space the libdir path inherits it and the assertion fires. The error gives no hint that the path is the problem. A secondary bug: `llvm-config --libdir` output has a trailing newline that was previously stripped accidentally by `RUSTFLAGS` whitespace splitting. Nothing was trimming it explicitly. ## Fix Two changes in `src/bootstrap/src/core/builder/cargo.rs`: 1. **Switch `RUSTFLAGS` → `CARGO_ENCODED_RUSTFLAGS`**: Change `Rustflags` to store args as `Vec<String>` and join with `\x1f` (ASCII unit separator) when setting the env var. Cargo's `CARGO_ENCODED_RUSTFLAGS` (stable since Cargo 1.55) uses `\x1f` as delimiter, which never appears in filesystem paths, so paths with spaces are handled correctly. The space-based assertion in `arg()` is removed. 2. **Trim `llvm-config --libdir` output**: Explicitly `.trim()` the captured stdout so the trailing newline is not included in the linker search path. `RUSTDOCFLAGS` is left as-is (space-joined) since no llvm paths are added to rustdocflags. cc: @Kobzol

@Kobzol

… r=kobzol,mark-simulacrum,bjorn3 bootstrap: fix panic when repo path contains spaces by switching to CARGO_ENCODED_RUSTFLAGS Fixes rust-lang#158052 Closes: rust-lang#156096 ## Problem `./x build` panics with a cryptic assertion error when the repository is checked out under a directory path containing spaces (e.g. `/Users/foo/Open Source/rust`): thread 'main' panicked at src/bootstrap/src/core/builder/cargo.rs:54:9: assertion left == right failed left: 2 right: 1 The root cause: when building tools in `ToolRustcPrivate` or `Codegen` mode, bootstrap calls `llvm-config --libdir` and passes the result as a `-Clink-arg=-L<path>` rustflag. The `Rustflags::arg()` method asserted that arguments contain no spaces, but if the repo path has a space the libdir path inherits it and the assertion fires. The error gives no hint that the path is the problem. A secondary bug: `llvm-config --libdir` output has a trailing newline that was previously stripped accidentally by `RUSTFLAGS` whitespace splitting. Nothing was trimming it explicitly. ## Fix Two changes in `src/bootstrap/src/core/builder/cargo.rs`: 1. **Switch `RUSTFLAGS` → `CARGO_ENCODED_RUSTFLAGS`**: Change `Rustflags` to store args as `Vec<String>` and join with `\x1f` (ASCII unit separator) when setting the env var. Cargo's `CARGO_ENCODED_RUSTFLAGS` (stable since Cargo 1.55) uses `\x1f` as delimiter, which never appears in filesystem paths, so paths with spaces are handled correctly. The space-based assertion in `arg()` is removed. 2. **Trim `llvm-config --libdir` output**: Explicitly `.trim()` the captured stdout so the trailing newline is not included in the linker search path. `RUSTDOCFLAGS` is left as-is (space-joined) since no llvm paths are added to rustdocflags. cc: @Kobzol

@Kobzol

Rollup merge of #158073 - Rohan-Singla:fix/#158052, r=kobzol,mark-simulacrum,bjorn3 bootstrap: fix panic when repo path contains spaces by switching to CARGO_ENCODED_RUSTFLAGS Fixes #158052 Closes: #156096 ## Problem `./x build` panics with a cryptic assertion error when the repository is checked out under a directory path containing spaces (e.g. `/Users/foo/Open Source/rust`): thread 'main' panicked at src/bootstrap/src/core/builder/cargo.rs:54:9: assertion left == right failed left: 2 right: 1 The root cause: when building tools in `ToolRustcPrivate` or `Codegen` mode, bootstrap calls `llvm-config --libdir` and passes the result as a `-Clink-arg=-L<path>` rustflag. The `Rustflags::arg()` method asserted that arguments contain no spaces, but if the repo path has a space the libdir path inherits it and the assertion fires. The error gives no hint that the path is the problem. A secondary bug: `llvm-config --libdir` output has a trailing newline that was previously stripped accidentally by `RUSTFLAGS` whitespace splitting. Nothing was trimming it explicitly. ## Fix Two changes in `src/bootstrap/src/core/builder/cargo.rs`: 1. **Switch `RUSTFLAGS` → `CARGO_ENCODED_RUSTFLAGS`**: Change `Rustflags` to store args as `Vec<String>` and join with `\x1f` (ASCII unit separator) when setting the env var. Cargo's `CARGO_ENCODED_RUSTFLAGS` (stable since Cargo 1.55) uses `\x1f` as delimiter, which never appears in filesystem paths, so paths with spaces are handled correctly. The space-based assertion in `arg()` is removed. 2. **Trim `llvm-config --libdir` output**: Explicitly `.trim()` the captured stdout so the trailing newline is not included in the linker search path. `RUSTDOCFLAGS` is left as-is (space-joined) since no llvm paths are added to rustdocflags. cc: @Kobzol

Allow spaces in bootstrap Cargo rustflags

13335af

This is particularly useful when one's home directory contains a space. Without this change, the assert fails with my home directory, even when using `subst` (on Windows) to give the build dir its own drive letter.

rustbot assigned Mark-Simulacrum May 2, 2026

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-bootstrap Relevant to the bootstrap subteam: Rust's build system (x.py and src/bootstrap) labels May 2, 2026

Mark-Simulacrum reviewed May 9, 2026

View reviewed changes

Mark-Simulacrum added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jun 1, 2026

Mark-Simulacrum mentioned this pull request Jun 18, 2026

bootstrap: fix panic when repo path contains spaces by switching to CARGO_ENCODED_RUSTFLAGS #158073

Merged

rust-bors Bot closed this in b674511 Jun 30, 2026

rustbot removed the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Jun 30, 2026

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Allow spaces in bootstrap Cargo rustflags#156096

Allow spaces in bootstrap Cargo rustflags#156096
kupiakos wants to merge 1 commit into
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kupiakos:spaces-in-bootstrap-rustflag

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