Mercurial: Merging one file between branches in one repo

When I have two branches in Hg repo, how to merge only one file with another branch, without having all other files from changeset merged?

Is it possible to merge only certain files, instead of whole changeset?

Solution 1:

WARNING: such a "dummy merge", as is recommended by @Martin_Geisler, can really mess you up, if later you want to do a true merge of the two branches. The dummy merge will be recorded, and say that you merge into the branch you did the dummy merge to -- you will not see the changes. Or if you merge into the other branch, the changes on that other branch will be undone.

If all you want is to copy an entire file from one branch to another, you can simply do:

   hg update -r to-branch
   hg revert -r from-branch file
   hg ci -m 'copied single file from from-branch to to-branch

If you want to select different parts of that file, then "hg record" is useful.

I just did this on my home directory .hgignore.

If both branches have made changes to a file that you want to keep, a dirty trick would be to create a merge of the two branches using hg merge, possibly/probably on still another branch, check that in, and then copy a single file between the merge and the to-branch:

   hg update -r to-branch
   branch merge-branch
   hg merge -r from-branch
   hg ci -m 'temp merge to be discarded"
   hg update -r to-branch
   hg revert -r merge-branch single-file
   hg ci -m 'merged single-file from from-branch to to-branch"
   hg strip merge-branch

It is worth mentioning: the way to "copy a single file between branches" (or revisions, or from revision to merge, or....) is "hg revert". I.e.

   hg update -r Where-you-want-to-copy-to
   hg revert -r Where-you-want-to-copy-from file-you-want-to-copy
   ...
   hg ci

For some reason I, and some of my coworkers, find this VERY confusing. "revert"=="copy" ... makes sense for some usage patterns, but not all.

Solution 2:

Nope. Mercurial works on a changeset basis.

But you can do a "dummy merge" where you ignore the incoming changes from one of the branches. Before you commit you could then revert selected files to whatever state you want:

% HGMERGE=internal:local hg merge     # keep my files
% hg revert --rev other-branch a.txt  # update a.txt to other branch
% hg commit -m 'Dummy merge to pick a.txt from other-branch.'

Maybe that will help you a bit.

Solution 3:

I would just use an external tool like vimdiff to diff the two files that I want to merge and then merge them. The advantage of this is that you can do selective editing on parts of the file. E.g:

hg update -r branch-merging-to
hg extdiff -p vimdiff -r branch-merging-from file-I-am-merging

To do this you need to enable the external tools in your .hgrc, which just means adding these lines:

[extensions]
hgext.extdiff =