In Mercurial, can I apply changes from one file to another file in the same branch?

Question

In the good old days of Subversion, I would sometimes derive a new file from an existing one using svn copy. Then if something changed in sections they had in common, I could still use svn merge to update the derived version.

To use the example from hginit.com, say the "guac" recipe already exists, and I want to create a "superguac" that includes instructions on how to serve guacamole to 1000 raving soccer fans. Using the process I just described, I could:

svn cp guac superguac
svn ci -m "Created superguac by copying guac"
(edit superguac)
svn ci -m "Added instructions for serving 1000 raving soccer fans to superguac"
(edit guac)
svn ci -m "Fixed a typo in guac"
svn merge -r3:4 guac superguac

and thus the typo fix would be applied to superguac.

Mercurial provides an hg copy command that marks a file as a copy of the original, but I'm not sure the repository structure supports a similar workflow. Here's the same example, and I carefully only edit a single file in the commit I want to use in the merge:

hg cp guac superguac
hg ci -m "Created superguac by copying guac"
(edit superguac)
hg ci -m "Added instructions for serving 1000 raving soccer fans to superguac"
(edit guac)
hg ci -m "Fixed a typo in guac"

I now want to apply the change in guac to superguac. Is that possible? If so, what's the right command? Is there a different workflow in Mercurial that achieves the same results (limited to a single branch)?

Answer 1

There's no pure-mercurial way to go cross-file with your patches, but if patch is installed on your system you could achieve essentially the same thing by following up your series of mercurial commands with:

hg log -p -r tip -I quac | patch superquac

That's essentially saying: "take the diff (-p) that was applied to file quac (-I quac) in the most recent changeset (-r tip) send it to standard output (hg log), and use that as the input to the patch (| patch) command acting on file superquac (superquac).

Answer 2

You can do this by

hg cp guac superguac
hg ci -m "Created superguac by copying guac" # CS1
(edit superguac)
hg ci -m "Added instructions for serving 1000 raving soccer fans to superguac" # CS2
hg up -r revision-before-copy
(edit guac)
hg ci -m "Fixed a typo in guac" #CS3
hg merge # this will transfer the typo-fix both to guac and superguac
hg ci -m "merged typo-fix from guac" # CS4

After this the repository looks like this

CS1 <--- CS2 <--------- CS4
  \                     /
   \--<-------- CS3 -<-/