clang-format ignores un-ignored paths in .clang-format-ignore with same prefix

[tdscheper]

Environment

• OS and Version: macOS Sequoia 15.5
• VS Code Version: 1.101.0-insider
• C/C++ Extension Version: 1.3.1

Bug Summary and Steps to Reproduce

Given the following folder structure:

.
├── .clang-format
├── .clang-format-ignore
├── .vscode
│   ├── c_cpp_properties.json
│   └── settings.json
├── foo
│   └── foo.h
└── foo_tests
    └── test_foo.c

And this .clang-format-ignore:

*
!foo/*
!foo_tests/*

Formatting foo/foo.h and foo_tests/test_foo.h via the extension does nothing.

When .clang-format-ignore is instead:

*
!foo/*

Formatting foo/foo.h formats as expected, and foo_tests/test_foo.h does not get formatted, also as expected.

When !foo/* is not there and !foo_tests/* is there, expected behavior occurs also.

With the full .clang-format-ignore and running the clang-format packaged in the extension like this:

~/.vscode-insiders/extensions/ms-vscode.cpptools-1.25.3-darwin-arm64/LLVM/bin/clang-format --style=file -i foo/foo.h

foo/foo.h gets formatted as expected. So, I'd expect this to be an issue with the extension, not clang-format.

Configuration and Logs

-------- Diagnostics - 6/12/2025, 10:25:54 PM
Version: 1.25.3
Current Configuration:
{
    "name": "Mac",
    "includePath": [
        "/Users/tdscheper/dev/repo/sandboxes/C/foo"
    ],
    "defines": [],
    "cStandard": "c17",
    "cppStandard": "c++14",
    "intelliSenseMode": "macos-clang-arm64",
    "compilerPath": "/usr/bin/gcc",
    "compilerPathIsExplicit": true,
    "cStandardIsExplicit": true,
    "cppStandardIsExplicit": true,
    "intelliSenseModeIsExplicit": true,
    "recursiveIncludesReduceIsExplicit": false,
    "recursiveIncludesPriorityIsExplicit": false,
    "recursiveIncludesOrderIsExplicit": false,
    "compilerPathInCppPropertiesJson": "/usr/bin/gcc",
    "mergeConfigurations": false,
    "recursiveIncludes": {},
    "browse": {
        "limitSymbolsToIncludedHeaders": true
    }
}
Modified Settings:
{
    "C_Cpp.default.compilerPath": "/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang"
}
Additional Tracked Settings:
{
    "editorTabSize": 4,
    "editorInsertSpaces": true,
    "editorAutoClosingBrackets": "languageDefined",
    "filesEncoding": "utf8",
    "filesAssociations": {
        ".arxml": "xml",
        ".clang-format": "yaml",
        ".clang-format-ignore": "ignore"
    },
    "filesExclude": {
        "**/.git": true,
        "**/.svn": true,
        "**/.hg": true,
        "**/.DS_Store": true,
        "**/Thumbs.db": true,
        "**/__pycache__": true,
        "**/.ruff_cache": true,
        "**/.mypy_cache": true,
        "**/.pytest_cache": true
    },
    "filesAutoSaveAfterDelay": false,
    "editorInlayHintsEnabled": true,
    "editorParameterHintsEnabled": true,
    "searchExclude": {
        "**/node_modules": true,
        "**/bower_components": true,
        "**/*.code-search": true
    },
    "workbenchSettingsEditor": "ui"
}
cpptools version (native): 1.25.3.0
Current database path: /Users/tdscheper/Library/Caches/vscode-cpptools/e82bc75c15d3363dec518c71b74031cf/.browse.VC.db
Translation Unit Mappings:
[ /Users/tdscheper/dev/repo/sandboxes/C/foo_tests/test_foo.c - source TU]:
    /Users/tdscheper/dev/repo/sandboxes/C/foo/foo.h
Translation Unit Configurations:
[ /Users/tdscheper/dev/repo/sandboxes/C/foo_tests/test_foo.c ]
    Process ID: 6458
    Memory Usage: 32 MB
    Compiler Path: /usr/bin/gcc
    Include paths:
        include: /Users/tdscheper/dev/repo/sandboxes/C/foo
        system include: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/17/include
        system include: /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include
        system include: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include
        system framework search path (default): /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks
    Standard Version: c17
    IntelliSense Mode: macos-clang-arm64
    Other Flags:
        --clang
        --clang_version=170006
Total Memory Usage: 32 MB

------- Workspace parsing diagnostics -------
Number of files discovered (not excluded): 9836
Number of files parsed: 232

Other Extensions

No response

Additional context

No response

[sean-mcmanus]

@tdscheper Did you type something wrong in your bug report -- I don't see what the unexpected behavior is -- you describe everything as expected?

[sean-mcmanus]

@tdscheper Also, if you set C_Cpp.loggingLevel to "Debug" and you run the format command with the params shown in the logging, does the bug repro then? I would guess that it's a clang-format bug with the particular parameters we send it, since we do not specifically do any .clang-format-ignore specific processing.

[tdscheper]

No, I typed correctly. When both foo/ and foo_tests/ are un-ignored in the .clang-format-ignore file, I expect running formatting on those files via the extension to format those files. But, no formatting occurs.

[tdscheper]

@tdscheper Also, if you set C_Cpp.loggingLevel to "Debug" and you run the format command with the params shown in the logging, does the bug repro then? I would guess that it's a clang-format bug with the particular parameters we send it, since we do not specifically do any .clang-format-ignore specific processing.

I will try this when I can, but that sounds correct

[sean-mcmanus]

@tdscheper I do not see the same behavior -- when I run clang-format from the command line with both the command we run and the command line you provide which you say formats, I'm seeing it not format, i.e. from what I'm seeing, it appears to be a clang-format bug (repros with 1.26.1 too, which has a newer clang-format).