Add .gitignore file in .cache/clangd/index

[mrexodia]

This solves a common issue where users have to manually add the .cache/clangd/index/ folder to their .gitignore. I got this idea from ruff, which creates .ruff_cache/.gitignore and it would greatly improve the user experience for everyone without requiring per-computer configurations and without any significant cost.

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[llvmbot]

@llvm/pr-subscribers-clang-tools-extra

@llvm/pr-subscribers-clangd

Author: Duncan Ogilvie (mrexodia)

Changes

This solves a common issue where users have to manually add the .cache/clangd/index/ folder to their .gitignore. I got this idea from ruff, which creates .ruff_cache/.gitignore and it would greatly improve the user experience for everyone without requiring per-computer configurations and without any significant cost.

---

Full diff: https://github.com/llvm/llvm-project/pull/170003.diff

1 Files Affected:

• (modified) clang-tools-extra/clangd/index/BackgroundIndexStorage.cpp (+14)

diff --git a/clang-tools-extra/clangd/index/BackgroundIndexStorage.cpp b/clang-tools-extra/clangd/index/BackgroundIndexStorage.cpp
index d887b09482a95..1dff0b55f82cd 100644
--- a/clang-tools-extra/clangd/index/BackgroundIndexStorage.cpp
+++ b/clang-tools-extra/clangd/index/BackgroundIndexStorage.cpp
@@ -45,6 +45,20 @@ class DiskBackedIndexStorage : public BackgroundIndexStorage {
     if (EC != OK) {
       elog("Failed to create directory {0} for index storage: {1}",
            DiskShardRoot, EC.message());
+    } else {
+      // Create a .gitignore file in the directory to ignore all files.
+      llvm::SmallString<128> GitignorePath(DiskShardRoot);
+      llvm::sys::path::append(GitignorePath, ".gitignore");
+      if (!llvm::sys::fs::exists(GitignorePath)) {
+        llvm::raw_fd_ostream GitignoreFile(GitignorePath, EC,
+                                          llvm::sys::fs::OF_None);
+        if (EC == OK) {
+          GitignoreFile << "*\n";
+        } else {
+          elog("Failed to create .gitignore in {0}: {1}", DiskShardRoot,
+              EC.message());
+        }
+      }
     }
   }
 

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[mrexodia]

• Apparently there was a previous patch for this that never got merged: https://reviews.llvm.org/D130863
• Discussion thread that went nowhere: https://discourse.llvm.org/t/clangd-feature-request-automatically-generate-gitignore-in-the-cache-directory/87390
• Cargo is discussing adopting a similar approach: instead of writing a .gitignore with /target -- output a .gitignore with * *inside* target/ rust-lang/cargo#11548 (comment)
• virtualenv does this https://virtualenv.pypa.io/en/latest/changelog.html#bugfixes-20-0-24
• Meson does this too
• Loads of projects add this to their .gitignore already: https://github.com/search?type=code&q=.cache%2Fclangd

[badumbatish]

hi @kadircet , i'm not in the clangd team but would this be a helpful addition to the clangd functionality? (I've tagged you in the reviewer section just in case)

[vbvictor]

Thank you for raising this once again.

Would be good to add release notes here:

llvm-project/clang-tools-extra/docs/ReleaseNotes.rst

Lines 89 to 90 in 333ee93

	Improvements to clangd
	----------------------

[Copilot]

Pull request overview

This PR automatically creates a .gitignore file in the clangd index directory (.cache/clangd/index/) to prevent index files from being tracked by Git. This improves user experience by eliminating the need for manual .gitignore configuration.

Key Changes:

• Adds automatic .gitignore creation during index directory initialization
• Updates release notes to document this new behavior

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
clang-tools-extra/clangd/index/BackgroundIndexStorage.cpp	Implements .gitignore creation logic in the DiskBackedIndexStorage constructor, creating a wildcard ignore file when the index directory is first initialized
clang-tools-extra/docs/ReleaseNotes.rst	Documents the new automatic .gitignore file creation feature in the Miscellaneous section

---

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[github-actions]

🐧 Linux x64 Test Results

• 3050 tests passed
• 7 tests skipped

✅ The build succeeded and all tests passed.

[github-actions]

🪟 Windows x64 Test Results

• 2988 tests passed
• 30 tests skipped

✅ The build succeeded and all tests passed.

[mrexodia]

Thanks a lot for the help everyone! I added a test and made sure everything works locally.

[sweiglbosker]

I think this can be merged if it looks good to you @kadircet

[kadircet]

thanks a lot!

[github-actions]

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