I use Mercurial, but I believe that any merge tool that knows the version control system under it can do several things that the merge tool that does not know about the version control system, and sees only two “files” in two different folders, could never do.
I use KDIFF3 and recently tried BeyondCompare, and none of them will do this, at least not in a way that I can understand.
What I want to do is best shown in this figure, the annotation column, and perhaps even in the ability to open other windows from these annotation columns so that I can view certain versions of certain files to see the context when trying to merge.
In the image here I show a two-way merger, but the same applies to a three-way merger. To the right or left of the actual file contents displayed, I would like the annotation column in the grooves or on the right to be shown with an annotation of where this change came from. Since Mercurial hex identifiers are relatively unfriendly and useless, and since local repositories - local versions - local repositories, I think a short text description based on commit comments would be most useful. Of course, with Mercurial, 99% of these comments are going to say “Merge,” and nothing more. (Groan.) But let's pretend for a moment that we don’t use the tools and workflows that left us crippled during the merger, and instead we could get a useful commit comment every time:
Now the workflow for complex mergers looks like this for me:
Using my distributed version control tool (mercurial), pull the changes from another repository, which is actually a branch. Merge. The merge window for TortoiseHg usually starts with this. This, in turn, allows me to customize the merge tool (without comparison or Kdiff3).
However, it does not seem that there is any merge tool (which I saw) that can be said: "Hey, you do not just go two paths or three paths with different versions of the file into two completely different folders with the names that I told you but these files are also files that have a complete change history available for you to show your person the actual context, which means that these line changes came with their commit comments, the error number as part of the commit, which will give the person the ability to merge the ability in and et that Heck's really going on.
I would change from Mercurial to Git, for example, even for a real merge experience, which did not force me to do manually what, in my opinion, my tools could do for me automatically. I use Mercurial, TortoiseHG and KDIFF3, and if I could just switch from KDIFF3 to some other tool or do nothing at all to get annotations and merge on one screen, I would like to do that.