Mercurial: Any way to "merge and discard changes"?

Question

I have a graphlog that looks something like this:

(snip)   | |   | o    1) Other Dev: Commit   | | \   o | |  2) Me: Commit / | | | | | o |  3) Other Dev: Commits with an error | |/| | | o |/   4) Me: Merge and commit |  /|     |/  | o   |    5) Me: Realize there were bugs in the commit and take earlier version to merge with |   o    6) Other Dev: Fixes error o /      7) Me: committing some changes |/ o        8) Me: Merge fixed tip 

At (8), everything is as it should be with the exception of the dangling extra head at (4). To get rid of it I have to merge (4) -.-> (8) but, since there is nothing in (4) that I need, I can safely discard all of it's changes. I could do this merge manually file-by-file (and usually this isn't that big a deal) but for my own edification - is there a simple one-line way to say "merge (4) with (8) and always take (8)"?

Answer 1

Yes. The internal:local builtin merge tool.

$ hg merge 4 --tool internal:local 

Similarly there's internal:other that picks the other version of files as the merged version.

Here's an example to clarify what's going on, start off with a repo with a single file:

$ echo a >> a $ hg ci -Am. adding a $ echo a >> a $ hg ci -Am. 

Branch it and put a conflict in a:

$ hg up 0 1 files updated, 0 files merged, 0 files removed, 0 files unresolved $ echo b >> a 

Also add another file just in the merged in branch:

$ echo b >> b $ hg ci -Am. adding b created new head 

Go back and merge the anonymous head:

$ hg up 1 1 files updated, 0 files merged, 1 files removed, 0 files unresolved $ hg merge 2 --tool internal:local 1 files updated, 1 files merged, 0 files removed, 0 files unresolved (branch merge, don't forget to commit) 

Naturally at this point without the merge tool we'd get a conflict on a. But using the merge tool, we're telling Mercurial to take the version of the first parent on every file that the merged with cset has also touched.

$ hg st M a M b $ cat a a a $ cat b b