Merging bookmarks in mercurial

Question

After asking this question yesterday about branching in mercurial, I've decided to try out bookmarks for short-lived branches (features), as shown below.
However now when I am trying to merge my bookmarked heads together into the development revision, I get below error:

hg update dev-1.1
hg merge feature1
abort: nothing to merge

What am I doing wrong?

Graphical representation of my repo:

o  changeset:   5:fa2b19961b46
|  bookmark:    feature1
|  description:  Work on feature 1 finished.
|
| o  changeset:   4:6ea0155d4d89
| |  bookmark:    feature2
| |  description: Work on feature 2 started. 
| |
o |  changeset:   3:44e335b5426c
| |  bookmark:    feature1
|/   description: Work on feature#1 started.
|
@    changeset:    2:407b3b94624f
|    tag:          dev-1.1
|    description:  Development for release 1.1 started. 

Answer 1

Like it says, there is nothing to merge — you should use update instead:

$ hg update feature1

You can only merge divergent parts of history, and here the dev-1.1 changeset is simply an ancestor of the feature1 changeset. Mercurial 2.1 says

$ hg merge feature1
abort: nothing to merge
(use 'hg update' or check 'hg heads')

in this case and we hope this will make the error clearer.

If you had bookmarked the dev-1.1 changeset (instead of tagging it), then a plain

$ hg update

will now (with Mercurial 2.1) result in an update of the dev-1.1 bookmark. So if you start with

$ hg bookmarks
 * dev-1.1                   0:b1163a24728f
   feature1                  3:c84f04513651
   feature2                  2:e60dd08af282

and then update:

$ hg update
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
updating bookmark dev-1.1

then the bookmark is updated:

$ hg bookmarks
 * dev-1.1                   3:c84f04513651
   feature1                  3:c84f04513651
   feature2                  2:e60dd08af282

With earlier versions, you would have to do

$ hg update feature1
$ hg bookmark -f dev-1.1

This still applies if a plain hg update doesn't take you to the right changeset, e.g., if you had wanted to "merge" with feature2 instead.

---

The idea of using merge when history hasn't really diverged comes from Git. In that system, there is a notion of a fast-forward merge, which is what we call an update in Mercurial.

Answer 2

If the changesets have been made public, you can force Mercurial to do a merge if you want to insist on having each feature as a merge in the repository:

$ hg update feature1
$ hg debugsetparents dev-1.1 feature1
$ hg commit -m 'Feature 1 reviewed by me.'
$ hg bookmark -d feature1

If the changesets have not been made public, you can collapse the changesets into one:

$ hg update feature1
$ hg rebase --dest dev-1.1 --collapse
$ hg bookmark -d feature1