On 09/04/2013 21:00, Kevin Bracey wrote:

So, how to automatically find a merge that ignored a known change?

I think I've found the problem. It only doesn't work _if you specify the file_.

Specifically, if I was missing an addition, my first attempt to find it would be

  git log -p -m -S<addition> <file>

If the addition was lost in a merge, that doesn't even show the addition, which is surprising, but intentional. The addition isn't part of the HEAD version of <file>, so no point going down that path of the merge. Fine. However, I expected this to work:

  git log --full-history -p -m -S<addition> <file>

But it doesn't. It finds the addition, but _not_ the loss in the merge commit.

But this does work:

  git log -p -m -S<addition>

That really feels like a bug to me. By specifying a file, I've made it miss the change, and I can see no way to get the change without making it a full-tree operation.

Looking at try_to_simplify_commit() it appears the merge that removed the addition is excluded because it's TREESAME to its _other_ parent. But with --full-history, we should only be eliminating a merge if its TREESAME to all parents, surely? Otherwise we have this case that we show a commit but not its reversion.

And the code doing this looks broken, or at least illogical - the parent loop sets "tree_same" for a same parent in --full-history, rather than immediately setting the TREESAME flag, so maybe previous authors were thinking about this. But setting tree_same guarantees that TREESAME is always set on exit anyway, so it's pointless (unless I'm missing something).

It does appear this is documented behaviour in the manual: "full-history without parent rewriting" .. "P and M were excluded because they are TREESAME to _a_ parent." I would say that they should have been excluded due to being TREESAME to _all_ parents. I really don't want a merge where one version of my file was chosen over another excluded from its so-called "full history".

Now, obviously in a sane environment, most merges won't be that interesting, as they'll just be propagating wanted patches from the real commits already in the log. But I'd like some way to find merges that drop code in a specified file, and surely "--full-history" is it?


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