clang-tidy header filter fails with regex

[gnzlbg]

Bugzilla Link	25216
Version	unspecified
OS	Linux

Extended Description

I'm passing

-header-filter="^((?!ThisNeverMatches).)*$"

so that clang-tidy matches all files whose path does not contain ThisNeverMatches in them.

That is:

home/files/foo.hpp (matches)
home/files/ThisNeverMatches.hpp (doesn't match)
home/files/ThisNeverMatches/foo.hpp (doesn't match)
home/files/ThisNeverMatches-1.2/foo.hpp (doesn't match)
home/files/ThisNeverMatches-1.2.hpp (doesn't match)

Clang-tidy doesn't display any errors for the regex, and it doesn't show any warnings for any files...

So that's the bug.

Here are some other related things that could be improved:

• it is not clear which kind of regex clang-tidy expects (there are a lot of different varieties, with and without lookahead). This should be documented.
• it is not clear if the regex is applied to the absolute file path, some relative file path, or only to the file name. This should be documented.
• writing a regex that doesn't match something is much harder than writing a regex for matching something. It would be better if there also was a -header-remove=regex that allows writing a patter to remove some headers.

[llvmbot]

I struggled with a similar issue today.

Because LLVM regexes use POSIX ERE, negative lookahead isn't supported. Source: http://stackoverflow.com/questions/15377469/posix-regular-expressions-excluding-a-word-in-an-expression http://llvm.org/docs/doxygen/html/Regex_8h_source.html

Negative lookahead would be great when you want to ignore all headers under a particular directory.

I would add these possible improvements to what the OP suggested:

• Document which regex standard is used in the header-filter flag.
• Implement more powerful regexes.

[llvmbot]

Will glob expressions (used for -checks= option) be enough for your use cases of -header-filter?

[gnzlbg]

Hey Alexander, thanks for chiming in. I gave an example of some files and directories in the original report and added which ones I want to match / not match.

Could you maybe show how you would achieve the same with glob expressions?

[llvmbot]

That would be something similar to -hypothetical-glob-based-header-filter=home/files/*,-ThisNeverMatches (which can be read as "include paths starting with 'home/files/' except for paths containing 'ThisNeverMatches').

[gnzlbg]

Yes this would be enough for my use cases.