Bogus error from git log --full-diff

If you have log.follow=true, then git log --full-diff doesn't work any more, giving a bogus error:

$ ./git -c log.follow=true log --full-diff . fatal: --follow requires exactly one pathspec

Andreas.

19.06.2020, 18:59, "Andreas Schwab" <schwab@linux-m68k.org>:

I've reported this issue in February on this very list and didn't get any reaction from developers. Seems like it's not considered to be a bug.

Konstantin Tokarev <annulen@yandex.ru> writes:

Please do not read too much into lack of response. It may be caused by many things, including (certainly non-exhaustive):

 (1) the message may have been un-understandable and/or did not look
     interesting enough to ask for clarifications and more info to
     produce a useful response,

 (2) the message may have been delivered in a hostile tone that
     people chose to ignore even though it raised a valid issue, or

 (3) the message was simply missed because everybody was busy doing
     other things.

By default, everybody should assume the last one. Re-raising the issue after some cooling-off period would be a good strategy.

Thanks.

Andreas Schwab <schwab@linux-m68k.org> writes:

Does "any more" mean it used to work with older version of Git, or it used to work before log.follow is thrown into the configuration file?

I see one and half possible bogosities in here.

 * "--follow" is about following a single path, so even without
   "--full-diff", i.e. "git log --follow .", should not proceed but
   notice it as an error.  The pathspec should name a single path,
   like "helloworld.py" (and no, git does not track directories, so
   "."  is not a single path.  The pathspec "." matches everything
   under that directory).

 * "--full-diff" wants to make a full comparison between two trees
   (in the case of "git log", the child and its parent(s)), but
   "--follow" wants to make a comparison between just two blobs
   (i.e. the path that it is following in the child, and the
   "corresponding" blob in the parent commit(s)), so they are
   inherently incompatible.

Since neither is flagged as an error, the "--follow" logic is upset when "--full-diff" widens the input of the "diff" run internally (the error message comes from the fact that full-diff cleared the pathspec used to generate this diff that the "--follow" logic uses to find the corresponding path it is following---it sees zero when it wants to have one).

I said these are one-and-half, because a reasonable expectation by the end user could be that the configured log.follow is automatically turned off when any incompatible option is given from the command line, i.e.

    git -c log.follow=yes log --full-diff .

should be equivalent to

    git log --full-diff .

and not

    git log --full-diff --follow .

And with that, we should not see the bogus * 1.5 error message.

So, I see 3 potential things that can be improved. Tightened error checking for "--follow" itself, tightened error checking for mutual exclusivity, and turning configured log.follow off automatically.

Thanks.