Support for character classes with quantifiers

[sebhoss]

I would like to use something like [abc]+ to match values like a, b, c, aa, ab, ac, aabbcc, etc. to match a semantic versioning compatible string. I think such a match could be achieved with [0-9]+.[0-9]+.[0-9]+ (although it does not match the official regex exactly)

[pschichtel]

@bmatcuk would you accept a PR for this?

[hostalp]

Did you try the workaround [0-9]*.[0-9]*.[0-9]*? It isn't optimal as * doesn't act as quantifier here, but it should suffice if there aren't any weird entries such as 1some.2random.3text in the input.

[bmatcuk]

It is possible to achieve more complex filtering using GlobWalk. By providing a simple glob as a sort of first pass to reduce the result set, the function provided to GlobWalk can make a second pass at filtering using whatever methods you'd like, even regular expressions. For example, the doublestar.Glob function itself just wraps GlobWalk when there is a mid-pattern doublestar. This code could be duplicated to provide the second pass filtering you require. Something like:

var matches []string
err := doublestar.GlobWalk(fsys, pattern, func(p string, d fs.DirEntry) error {
	if (matchSomeFilter(p, d)) {
	    	matches = append(matches, p)
	} else if (d.isDir()) {
		return doublestar.SkipDir
	}
    	return nil
})
return matches, err

For your particular use case (matching semantic versioning), you may be able to get away with a combination of character classes and alternatives instead. For example, [0-9]{[0-9]{[0-9],},} will match a 1, 2, or 3 digit number. This could be combined like: [0-9]{[0-9]{[0-9],},}.[0-9]{[0-9]{[0-9],},}.[0-9]{[0-9]{[0-9],},} to essentially mimic the regex [0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}, which should cover the vast majority of semantic versions. If you expect to see version numbers more than 3 digits long, or version numbers with more than 3 parts, you can extend the pattern. It's not as flexible as the regex [0-9]+, but I think it's rare to have a version number longer than 3 or 4 digits, save for maybe the patch version. If you're worried about that, stick a * at the end of your pattern and use GlobWalk to do a second pass filter with an actual regex.