Mercurial Issue 1877

$ hg init bm
$ cd bm
$ echo 1 > f1
$ hg ci -A -m initial
adding f1
$ hg branch dev
marked working directory as branch dev
$ hg ci -m "new branch dev"
$ hg book -r 0 main
$ hg up main
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg bookmarks
 * main                      0:74b9cee424e1
$ echo 2 > f1
$ hg ci -m "change in main"
$ hg up dev
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg book
   main                      2:ed03f1c5af94
$ hg merge main
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ hg book
   main                      2:ed03f1c5af94
$ hg ci -m "merge main into dev"
$ hg book
 * main                      3:e0ee3d29cab0
$ hg glog
@    changeset:   3:e0ee3d29cab0
|\   branch:      dev
| |  bookmark:    main
| |  tag:         tip
| |  parent:      1:922c079fed68
| |  parent:      2:ed03f1c5af94
| |  ...
| |  summary:     merge main into dev
| |
| o  changeset:   2:ed03f1c5af94
| |  parent:      0:74b9cee424e1
| |  ...
| |  summary:     change in main
| |
o |  changeset:   1:922c079fed68
|/   branch:      dev
|    ...
|    summary:     new branch dev
|
o  changeset:   0:74b9cee424e1
   ...
   summary:     initial
$ hg showconfig | grep book
# no output, i.e. using only defaults for bookmark related options ...