Re: rev-list and "ambiguous" IDs

[Jeff King <peff@peff.net>]

On Fri, Nov 15, 2019 at 01:12:47AM +0100, Thomas Braun wrote:

> > That would probably help in a lot of cases, but the argument
> > against it is that when it goes wrong, it may be quite confusing (so
> > we're better off with the current message, which punts back to the
> > user).
> 
> Just out of curiosity: Is there a use case for inspecting non-commit
> objects with git log?

Not that I can think of. You can't even say "--objects" there.

And indeed, "git log" already prefers commits for disambiguation, since
d5f6b1d756 (revision.c: the "log" family, except for "show", takes
committish, 2012-07-02).

But...

> If I do (in the git repo)
> 
> $ git log 1231
> 
> I get
> 
> error: short SHA1 1231 is ambiguous
> hint: The candidates are:
> hint:   123139fc89 tree
> hint:   12316a1673 tree
> hint:   123144fe8a blob
> fatal: ambiguous argument '1231': unknown revision or path not in the
> working tree.
> Use '--' to separate paths from revisions, like this:
> 'git <command> [<revision>...] -- [<file>...]'
> 
> with
> $ git --version
> git version 2.24.0.windows.2
> 
> and all of these candidates are no commits.

...remember that the disambiguation code is just about preferring one
object to the other. If the rule in effect doesn't have a preference,
it's still ambiguous. On my system, "1231" actually _does_ have a
commit:

  $ git show 1231
  error: short SHA1 1231 is ambiguous
  hint: The candidates are:
  hint:   12319e3bf2 commit 2017-03-25 - Merge 'git-gui-add-2nd-line' into HEAD
  hint:   123139fc89 tree
  hint:   12315b58b8 tree
  hint:   12316a1673 tree
  hint:   12317ab2d9 tree
  hint:   123193f802 tree
  hint:   123144fe8a blob
  fatal: ambiguous argument '1231': unknown revision or path not in the working tree.
  Use '--' to separate paths from revisions, like this:
  'git <command> [<revision>...] -- [<file>...]'

That's ambiguous because git-show can handle trees and blobs, too. But
if I feed that sha1 to git-log:

  $ git log --oneline -1 1231
  12319e3bf2 Merge 'git-gui-add-2nd-line' into HEAD

it's perfectly fine, because git-log knows to disambiguate the commit.
But if I choose another prefix that has no commits at all, it's
ambiguous under either, because the "committish" rule has no way to
decide:

  $ git show abcd2
  error: short SHA1 abcd2 is ambiguous
  hint: The candidates are:
  hint:   abcd22f55e tree
  hint:   abcd238df0 tree
  hint:   abcd2b1cc8 blob
  
  $ git log abcd2
  error: short SHA1 abcd2 is ambiguous
  hint: The candidates are:
  hint:   abcd22f55e tree
  hint:   abcd238df0 tree
  hint:   abcd2b1cc8 blob

-Peff