[PATCH 0/2] Fix a refname trimming problem in `log --bisect`

[Michael Haggerty <mhagger@alum.mit.edu>]

The code for `git log --bisect` was calling
`for_each_ref_in_submodule()` with prefix set to "refs/bisect/bad",
which is the actual name of the reference that it wants. This resulted
in the refname being trimmed completely away and the empty string
being passed to the callback. That became impermissible after

    b9c8e7f2fb prefix_ref_iterator: don't trim too much, 2017-05-22

, so the command was failing.

Fix the problem in two orthogonal ways:

1. Add a new function, `for_each_fullref_in_submodule()`, that doesn't
   trim the refnames that it passes to callbacks, and us that instead.
   I *think* that this is a strict improvement, though I don't know
   the `git log` code well enough to be sure that it won't have bad
   side-effects.

2. Relax the "trimming too many characters" check to allow the full
   length of the refname to be trimmed away (though not more than
   that).

In an ideal world the second patch shouldn't be necessary, because
this calling pattern is questionable and it might be better that we
learn about any other offenders. But if we'd rather be conservative
and not break any other code that might rely on the old behavior,
patch 2 is my suggestion for how to do it.

This patch series can be applied on top of branch
`mh/packed-ref-store-prep`, but it also applies cleanly to master. It
is also available as branch `fix-bisect-trim-check` from my GitHub
fork [1].

Michael

[1] https://github.com/mhagger/git

Michael Haggerty (2):
  for_each_bisect_ref(): don't trim refnames
  prefix_ref_iterator_advance(): relax the check of trim length

 refs.c          | 12 ++++++++++++
 refs.h          |  5 ++++-
 refs/iterator.c |  8 ++++----
 revision.c      |  2 +-
 4 files changed, 21 insertions(+), 6 deletions(-)

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2.11.0