fix: incorrect regular expression matching diffcmd

[jingfelix]

current diffcmd_header: ^diff.* (.+) (.+)$
fixed diffcmd_header: ^diff .* (.+) (.+)$

Using the old diffcmd_header may result in lines starting with words like "different" being incorrectly matched as a diff header. Fixing this by adding a blank space.

example: this commit in Linux kernel

[jingfelix]

@cscorley review request

[cscorley]

Nice find, thanks!

Confirmed working with this test

    def test_linux_29e1dfc(self):
        with open(
            "tests/casefiles/linux-29e1dfcd5150097f32f34891c85a50d9ead19df3.patch"
        ) as f:
            text = f.read()

        # testing we get to the diff
        path = "net/bluetooth/6lowpan.c"
        expected = headerobj(
            index_path=None,
            old_path=path,
            old_version="357475cceec61b",
            new_path=path,
            new_version="9a75f9b00b5129",
        )

        results = list(wtp.patch.parse_patch(text))
        self.assertEqual(len(results), 1)
        self.assertEqual(results[0].header, expected)

[cscorley]

I am curious to know why I chose this regex, though, thinking twice about it. There must be some alternative commands out there that would normally be considered. But, unfortunately, no tests indicate this and it's been too long to remember exactly.

[cscorley]

Thinking the better change may be diffcmd_header = re.compile("^diff( .+)? (.+) (.+)$") which just makes the command section optional instead (e.g., diff lao tzu)

Looking at the CVS diffcmd header, we have the same issue: old_cvs_diffcmd_header = re.compile("^diff.* (.+):(.*) (.+):(.*)$") and I'm wondering if the same "fix" applies there

[cscorley]

Went through some old Eclipse patches on Bugzilla and was able to find some interesting cases (e.g. https://bugzillaattachments.eclipsecontent.org/bugs/attachment.cgi?id=1701) but none that show a diffcmd without a space