Oddities in gitignore matching

[John Thorvald Wodder II <jwodder@gmail.com>]

Git developers & fans,

I'm developing a Python library for performing gitignore-style path matching (because all the pre-existing ones I've found so far leave something to be desired), and, in my experiments to nail down Git's exact behavior, I've encountered three odd things that may be bugs or may be deficiencies in the documentation; let me know which.

First: I've found that the pattern "foo**/bar" causes the path "foo/glarch/bar" (as well as "foobie/glarch/bar") to be ignored.  However, the gitignore(5) documentation states that "**/" only has special meaning when it's "leading"; in other circumstances, the double star should be treated the same as a single star (and "foo*/bar" does not match "foo/glarch/bar").  Is this behavior of non-leading "**/" deliberate or a bug?

Interestingly, checking the pattern with the wildmatch test-tool (`t/helper/test-tool wildmatch wildmatch foo/glarch/bar 'foo**/bar'`) shows that the pattern should not match the path.

Second: The pattern "[[:space:]]" does not match 0x0B (\v, vertical tab) or 0x0C (\f, form feed) despite the fact that the C isspace() function accepts these characters, and I cannot figure out the cause for this discrepancy.  (The pattern does match the other characters that isspace() accepts, though — tab, line feed, carriage return, and space character.)  The wildmatch test-tool agrees with this behavior, though.

Third: While the documentation for `git-check-ignore` only states that it works on files, I've found that it also works with directory paths, as well as treating any nonexistent path ending in a slash as a directory.  For example, in a fresh repository containing only a .gitignore file with the pattern "foo/", `git-check-ignore` will accept the path "foo/" but not "foo", and if `mkdir foo` is run, it will accept both.

However, I've found a case in which `git-check-ignore` deviates from the actual .gitignore behavior regarding ignoring directories.  If .gitignore contains only the pattern "foo/*", then (regardless of whether a directory named "foo" exists or not), `git-check-ignore` will accept "foo/" but not "foo" — and yet, if you do `mkdir foo; touch foo/bar` and run `git status --ignored=matching --porcelain`, it shows "!! foo/bar", rather than "!! foo/" (which you get with the .gitignore pattern "foo/"), indicating that "foo/*" matches the contents of "foo" but not "foo" itself, in apparent disagreement with `git-check-ignore`.  Is this a flaw in `git-check-ignore`, or should it just not be trusted in the first place when it comes to directories?

These observations were made using Git version 2.36.1, installed via Homebrew on macOS 11.6.6, with test-tool compiled from commit 39c15e4855 of the Git source.

Thank you for your time reading & responding,

-- John Wodder