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`./x check` being killed (by rust-analyzer) may leave `.git/index.lock` file

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
85/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
rust
Domain
build-system

Research direction

The problematic code path is traced in the stacktrace: git subprocesses are spawned from src/bootstrap/src/build_helper/git.rs (run_git_diff_index, changes_since), called via check_path_modifications in src/bootstrap/src/core/config/config.rs and detect_llvm_freshness in src/bootstrap/src/core/build_steps/llvm.rs. Review these locations to add logic that cleans up .git/index.lock if the x.py process is killed while the git subprocess is running. Verify the fix by triggering a check kill during git execution and confirming no lock file remains.

Written by the indexing model from the issue text.

Description

C-bug needs-triage T-bootstrap T-rust-analyzer
Summary

The python x.py check runs git update-index --refresh -q (indirectly in detect_llvm_freshness), which crates .git/index.lock. Normally wen git finishes the index.lock will be deleted.

In rust-analyzer flycheck.rs, it seems that when the previous python x.py check is still running, if check is triggered again, then the previous x process will be killed. If it kills the x process when the git subprocess is running, git will be killed and it will left .git/index.lock file.

When there is a leftover .git/index.lock I cannot do things like commit or push, so I have to manually delete the index.lock.

(I am using Windows, so maybe git runs slower, then it's more likely to trigger than other machines.)

Command used

VSCode rust-analyzer runs python x.py check --json-output --build-dir build-rust-analyzer

Expected behaviour

Not leaving .git/index.lock

Actual behaviour

Leaves .git/index.lock when no git process is running

Bootstrap configuration (bootstrap.toml)
profile = "compiler"  # Includes one of the default files in src/bootstrap/defaults
change-id = 154508
Operating system

Windows 11

HEAD

Closest official commit is 28b6e691688c15cef4c60d9044274e7b84397870

Additional context

In bootstrap, the detect_llvm_freshness indirectly calls git update-index --refresh -q. Stacktrace:

   7: build_helper::git::run_git_diff_index::<build_helper::git::changes_since::{closure#0}, core::result::Result<alloc::vec::Vec<std::path::PathBuf>, alloc::string::String>>
   8: build_helper::git::changes_since
   9: build_helper::git::check_path_modifications
  10: bootstrap::core::config::config::impl$0::check_path_modifications::closure$0
             at .\src\bootstrap\src\core\config\config.rs:1873
  11: std::collections::hash::map::impl$72::or_insert_with::closure$0<alloc::vec::Vec<ref$<str$>,alloc::alloc::Global>,enum2$<build_helper::git::PathFreshness>,alloc::alloc::Global,bootstrap::core::config::config::impl$0::check_path_modifications::closure_env$0>
             at /rustc/cbae9b4cae2b108f6a3d18cfe6075714bb739463/library\std\src\collections\hash\map.rs:2540
  12: std::collections::hash::map::Entry::or_try_insert_with<alloc::vec::Vec<ref$<str$>,alloc::alloc::Global>,enum2$<build_helper::git::PathFreshness>,alloc::alloc::Global,std::collections::hash::map::impl$72::or_insert_with::closure_env$0<alloc::vec::Vec<ref$<s
             at /rustc/cbae9b4cae2b108f6a3d18cfe6075714bb739463/library\std\src\collections\hash\map.rs:2575
  13: std::collections::hash::map::Entry::or_insert_with<alloc::vec::Vec<ref$<str$>,alloc::alloc::Global>,enum2$<build_helper::git::PathFreshness>,alloc::alloc::Global,bootstrap::core::config::config::impl$0::check_path_modifications::closure_env$0>
             at /rustc/cbae9b4cae2b108f6a3d18cfe6075714bb739463/library\std\src\collections\hash\map.rs:2540
  14: bootstrap::core::config::config::Config::check_path_modifications
             at .\src\bootstrap\src\core\config\config.rs:1872
  15: bootstrap::core::build_steps::llvm::detect_llvm_freshness
             at .\src\bootstrap\src\core\build_steps\llvm.rs:327
  16: bootstrap::core::config::config::Config::maybe_download_ci_llvm
             at .\src\bootstrap\src\core\download.rs:281
  17: bootstrap::core::build_steps::llvm::try_download_ci_llvm
             at .\src\bootstrap\src\core\build_steps\llvm.rs:281
  18: bootstrap::core::build_steps::llvm::impl$4::run
             at .\src\bootstrap\src\core\build_steps\llvm.rs:410
  19: bootstrap::core::builder::Builder::ensure<bootstrap::core::build_steps::llvm::LlvmFromCi>
             at .\src\bootstrap\src\core\builder\mod.rs:1643
  20: bootstrap::core::build_steps::llvm::prebuilt_llvm_output
             at .\src\bootstrap\src\core\build_steps\llvm.rs:175
  21: bootstrap::core::build_steps::llvm::get_llvm_build_status
             at .\src\bootstrap\src\core\build_steps\llvm.rs:195
  22: bootstrap::core::build_steps::dist::maybe_install_llvm_target
             at .\src\bootstrap\src\core\build_steps\dist.rs:2610
  23: bootstrap::core::build_steps::compile::impl$15::run
             at .\src\bootstrap\src\core\build_steps\compile.rs:1962
  24: bootstrap::core::builder::Builder::ensure<bootstrap::core::build_steps::compile::Sysroot>
             at .\src\bootstrap\src\core\builder\mod.rs:1643
  25: bootstrap::core::builder::Builder::sysroot
             at .\src\bootstrap\src\core\builder\mod.rs:1339
  26: bootstrap::core::builder::impl$12::run
             at .\src\bootstrap\src\core\builder\mod.rs:730

(line numbers may not match because bootstrap code was changed for debugging. The issue occurs in unchanged bootstrap.)

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