Re: Bizarre missing changes (git bug?)

On Jul 21, 2008, at 2:37 PM, Linus Torvalds wrote:

On Mon, 21 Jul 2008, Tim Harper wrote:

quoted

Anyone run into this before?  Any idea what might have caused it?   
We're a bit
concerned about this because if we don't know how to avoid this, we  
no longer
can feel certain that when something is committed, it will make it  
out in our
release.

Read up on '--full-history'.

By default, git simplifies the history for logs that have path
simplification: only walking down the side of a merge that all the  
data
came from (ie the unchanged side). So it only leaves merges around if
there was changes from _all_ parents.

So without --full-history, if any parent matches the state, it just
removes the merge and picks that parent that contained all the state.
Obviously, any changes to that file can be sufficiently explained by
walking just that limited history, because they must have changed in
_that_ history too!

That default behaviour leads to a *much* simpler history, and is  
usually
what you want - it avoids unnecessary duplication when something was
changed trivially the same way in both branches - 'git log' will  
just pick
the first branch.

Agreed - this was an insightful decision.

So, if you had two (or more) commits that both fixed the same bug in
different branches, and thus both branches actually ended up with  
the same
contents, it does mean that "git log <filename>" will only show  
_one_ of
the fixes.

In this case, it apparently showed another version than the one you  
were
looking for.

				Linus

Git has made me feel stupid on various occasions.  This is no  
exception as the problem turned out being in the chair, not in git.

After running through git bisect, and ran the command Alex Riesen  
suggested, it made it pretty crystal clear where things went wrong.   
It turned out to be a bad merge that was from a conflict related to  
white-space issues, and the wrong resolution was chosen (a resolution  
that also consequently turned out to be no change).

Another false impression I had is a merge conflict resolution would  
always be displayed in a merge commit.  However, after running over  
the merges again, if you pick the right or left, discarding the one or  
the other, nothing is shown in "git log -p" for the merge commit.  Is  
there a way to see what was chosen for a conflict resolution?  Seeing  
that in the merge commit would have made things a little more clear.

Thank you for articulating git branch's behavior - all is clear as mud  
now :)

Tim