git reflog delete / manpage confusion

git reflog delete HEAD{4} indeed deletes HEAD{5} or N+1 ; is there a bug manpage or my interpretation ?

To delete single entries from the reflog, use the subcommand "delete"
and specify the exact entry (e.g. "git
       reflog delete master@{2}").

-Mahesh

On Thu, Jul 01, 2010 at 03:08:04PM +0530, Mahesh Vaidya wrote:

Hmm. I don't think the deletion is wrong, but rather the walker. Try:

  mkdir repo && cd repo && git init
  for i in 1 2 3 4 5; do
    echo $i >file && git add file && git commit -m file
  done
  git reflog -g --oneline >old
  git reflog delete HEAD@{3}
  git reflog -g --oneline >new
  diff -u old new

I get:

  --- old 2010-07-01 05:54:48.000000000 -0400
  +++ new 2010-07-01 05:54:48.000000000 -0400
  @@ -1,5 +1,4 @@
   01bb1c7 HEAD@{0}: commit: file
   c8020a8 HEAD@{1}: commit: file
   d82df6b HEAD@{2}: commit: file
  -364bcc0 HEAD@{3}: commit: file
  -2993260 HEAD@{4}: commit (initial): file
  +364bcc0 HEAD@{3}: commit (initial): file

So we give the proper reflog message (but note that HEAD@{4} has become HEAD@{3}, because we always number compactly). But the sha1 still refers to the deleted entry! We show the initial commit as creating 364bcc0, when it didn't.

What happens is that there is a gap in the reflog (apologies for the long lines):

  $ cat .git/logs/HEAD
  0000000000000000000000000000000000000000 299326064426c58bfec68b44b50a37fe7ec4e15e Jeff King <peff@peff.net> 1277978088 -0400    commit (initial): file
  364bcc0479c8b2d3a8a4be0cd67e46c81afafb03 d82df6b185d19134c7330cb93a7eb7c630b0714a Jeff King <peff@peff.net> 1277978088 -0400    commit: file
  d82df6b185d19134c7330cb93a7eb7c630b0714a c8020a8ead949ab725abc0dfe2345b2aeca6c145 Jeff King <peff@peff.net> 1277978088 -0400    commit: file
  c8020a8ead949ab725abc0dfe2345b2aeca6c145 01bb1c78a68703338810a559cdef270e10192fc3 Jeff King <peff@peff.net> 1277978088 -0400    commit: file

If I do "git show HEAD@{3}" I will properly get 2993260, and a warning:

  warning: Log .git/logs/HEAD has gap after Thu, 1 Jul 2010 05:54:48 -0400.

So I think that delete is behaving properly, but the reflog walker in "git log -g" should be using the second field of HEAD@{3} to determine the commit sha1, not the first field from HEAD@{2}. In the normal case they are the same, but with a gap, they will be different (which should also probably provoke us to print a gap warning as above).

I took a look at how hard this would be to fix. It looks like the wrong sha1 is actually printed by the regular pretty-printer, which then calls show_reflog_message() to show the actual entry. Which means we probably need some special case hackery in show_log() to handle this case.

Shawn, any thoughts?

-Peff

Hi I am confused again as it indeed removed HEAD{4}

 -2993260 HEAD@{4}: commit (initial)

Mahesh Vaidya venit, vidit, dixit 01.07.2010 12:58:

It didn't, that's what Jeff explained and what the content of .git/logs/HEAD showed (which you chose to cut; also, please don't top-post).

It really deleted the line for 364bcc0, but when showing the reflog git mistakenly shows 364bcc0 rather than 2993260 (for the new HEAD{@3}) in this case.

Michael