[clang-format] .clang-format-ignore does not match `/` with `*` wildcard

[ameerj]

When using a .clang-format-ignore file, a * wildcard is expected to match a directory separator.
For example, a line containing *g_* should match any file in the current directory and all subdirectories that match the pattern *g_*

Currently, the * does not match the path separator. So a *g_* in the .clang-format-ignore file will only match this pattern for the current working directory. There does not seem to be a way to match the pattern for the current dir and subdirs.

Looking into the source code, it seems that this behavior is from the matchFilePath function, which is based on the POSIX fnmatch() function

llvm-project/clang/lib/Format/MatchFilePath.cpp

Lines 10 to 11 in d4d38bc

	/// This file implements the functionality of matching a file path name to
	/// a pattern, similar to the POSIX fnmatch() function.

All of the following tests added to MatchFilePathTest.cpp fail:

  EXPECT_TRUE(match("some/nested/dir/file.cpp", "*nested*"));
  EXPECT_TRUE(match("some/nested/dir/file.cpp", "*/nested/*"));
  EXPECT_TRUE(match("some/nested/dir/g_file.cpp", "*g_*"));
  EXPECT_TRUE(match("some/nested/dir/g_file.cpp", "*/g_*"));

The fnmatch() function matches these cases:
https://godbolt.org/z/6qxYW41Yv

@owenca is this expected behavior?

P.S. I am seeing this behavior on Windows/MSVC, not sure if this affects all environments or is Windows specific.

[owenca]

This is expected behavior and works as documented.

Looking into the source code, it seems that this behavior is from the matchFilePath function, which is based on the POSIX fnmatch() function

llvm-project/clang/lib/Format/MatchFilePath.cpp

Lines 10 to 11 in d4d38bc

	/// This file implements the functionality of matching a file path name to
	/// a pattern, similar to the POSIX fnmatch() function.

See the comments after that:

llvm-project/clang/lib/Format/MatchFilePath.cpp

Lines 22 to 23 in d4d38bc

	// Check whether `FilePath` matches `Pattern` based on POSIX 2.13.1, 2.13.2, and
	// Rule 1 of 2.13.3.

The fnmatch() function matches these cases: https://godbolt.org/z/6qxYW41Yv

Not if FNM_PATHNAME is set: https://godbolt.org/z/Gc8z3KceE

[ameerj]

Would you be open to supporting the double asterisk ** to match directory separators?

As used in gitignore

[owenca]

Would you be open to supporting the double asterisk ** to match directory separators?

As used in gitignore

See #110560 (comment).

[owenca]

Related to #114969.