Re: Bug in git log -S

From: Jeff King <peff@peff.net>
Date: May 15, 2024, 06:34 UTC
Message-ID: <20240515063400.GD110841@coredump.intra.peff.net>
In-Reply-To: <6d7ac19b-fede-4534-aee2-5c0cb20f955e@kdbg.org>

On Mon, May 13, 2024 at 11:01:25PM +0200, Johannes Sixt wrote:

Show 10 quoted lines

> Am 13.05.24 um 20:58 schrieb Sam Clymer:
> > There does seem to be a bug on my end. I am searching for
> > “net8.0-windows” and it’s not finding an instance where it’s added.
> > It is not a line of code that is moved around it is purely added so I
> > think there is indeed something wrong with git log -S.
> 
> You would have to show more evidence for a bug before anything can
> happen. Start with showing the commands typed and their output, ideally
> you point at a commit history that shows the problem, etc. Otherwise, we
> can only say: "it works here".

I agree that we do not have much to go on here, but here are some possible lines of enquiry:

  - if we have a specific commit that we expect "-S" to find, what does
    that commit look like? Is it a merge commit? If so, then maybe "-m"
    or "-c" would help? By default I don't think "log -S" will diff
    merges at all. "-m" will diff against both parents (so it is more
    likely to find introductions/deletions, but may show diffs against
    both parents). "-c" should I think mostly show just places where the
    content was introduced by the merge itself, though I haven't thought
    very hard on whether there are weird corner cases.

  - if there's a non-merge commit that we expect to find it in, then
    maybe checking:

      git cat-file blob $commit:$file | grep -Fc net8.0-windows
      git cat-file blob $commit^:$file | grep -Fc net8.0-windows

    would verify that the counts before/after that commit have changed?
    Note that "-F" is important, because -S is by default a string
    match, not a regex. And if the suspected file is binary, then the
    results may depend on your version of grep (GNU grep will correctly
    report the count for items in a binary file).

-Peff