[Bug 5540] New: Stripping a working directory parent may switch named branches

[mercurial-bugs at mercurial-scm.org]

https://bz.mercurial-scm.org/show_bug.cgi?id=5540

            Bug ID: 5540
           Summary: Stripping a working directory parent may switch named
                    branches
           Product: Mercurial
           Version: default branch
          Hardware: PC
                OS: Windows
            Status: UNCONFIRMED
          Severity: feature
          Priority: wish
         Component: strip
          Assignee: bugzilla at mercurial-scm.org
          Reporter: matt_harbison at yahoo.com
                CC: mercurial-devel at mercurial-scm.org

It's a bit surprising, given how hard `hg update` tries to stay on the current
named branch without an explicit destination.  There's no indication of the
switch in the command output (though there is an "X files
updated/merged/removed" message).  It requires a merge as part of the strip
range to trigger.  Here's an example based on the tests for 4.2-rc:

diff --git a/tests/test-strip.t b/tests/test-strip.t
--- a/tests/test-strip.t
+++ b/tests/test-strip.t
@@ -935,4 +935,97 @@
   abort: boom
   [255]

+  $ hg log -G
+  @  changeset:   1:eca11cf91c71
+  |  tag:         tip
+  |  user:        test
+  |  date:        Thu Jan 01 00:00:00 1970 +0000
+  |  summary:     commitB
+  |
+  o  changeset:   0:105141ef12d0
+     user:        test
+     date:        Thu Jan 01 00:00:00 1970 +0000
+     summary:     commitA
+
+  $ hg branch new-branch
+  marked working directory as branch new-branch
+  (branches are permanent and global, did you want a bookmark?)
+  $ hg ci -m "start new branch"
+  $ echo 'foo' > foo.txt
+  $ hg ci -Aqm foo
+  $ hg up default
+  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
+  $ echo 'bar' > bar.txt
+  $ hg ci -Aqm bar
+  $ hg up new-branch
+  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
+  $ hg merge default
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  (branch merge, don't forget to commit)
+  $ hg ci -m merge
+  $ hg log -G
+  @    changeset:   5:4cf5e92caec2
+  |/   branch:      new-branch (glob)
+  | |  tag:         tip
+  | |  parent:      3:f62c6c09b707
+  | |  parent:      4:35358f982181
+  | |  user:        test
+  | |  date:        Thu Jan 01 00:00:00 1970 +0000
+  | |  summary:     merge
+  | |
+  | o  changeset:   4:35358f982181
+  | |  parent:      1:eca11cf91c71
+  | |  user:        test
+  | |  date:        Thu Jan 01 00:00:00 1970 +0000
+  | |  summary:     bar
+  | |
+  o |  changeset:   3:f62c6c09b707
+  | |  branch:      new-branch
+  | |  user:        test
+  | |  date:        Thu Jan 01 00:00:00 1970 +0000
+  | |  summary:     foo
+  | |
+  o |  changeset:   2:b1d33a8cadd9
+  |/   branch:      new-branch
+  |    user:        test
+  |    date:        Thu Jan 01 00:00:00 1970 +0000
+  |    summary:     start new branch
+  |
+  o  changeset:   1:eca11cf91c71
+  |  user:        test
+  |  date:        Thu Jan 01 00:00:00 1970 +0000
+  |  summary:     commitB
+  |
+  o  changeset:   0:105141ef12d0
+     user:        test
+     date:        Thu Jan 01 00:00:00 1970 +0000
+     summary:     commitA
+
+  $ hg strip -r 35358f982181
+  0 files updated, 0 files merged, 2 files removed, 0 files unresolved
+  saved backup bundle to
$TESTTMP\issue4736\.hg\strip-backup/35358f982181-a6f020aa-backup.hg (glob)
+  $ hg log -G
+  o  changeset:   3:f62c6c09b707
+  |  branch:      new-branch
+  |  tag:         tip
+  |  user:        test
+  |  date:        Thu Jan 01 00:00:00 1970 +0000
+  |  summary:     foo
+  |
+  o  changeset:   2:b1d33a8cadd9
+  |  branch:      new-branch
+  |  user:        test
+  |  date:        Thu Jan 01 00:00:00 1970 +0000
+  |  summary:     start new branch
+  |
+  @  changeset:   1:eca11cf91c71
+  |  user:        test
+  |  date:        Thu Jan 01 00:00:00 1970 +0000
+  |  summary:     commitB
+  |
+  o  changeset:   0:105141ef12d0
+     user:        test
+     date:        Thu Jan 01 00:00:00 1970 +0000
+     summary:     commitA
+


It is documented in the help, but it's not hard to read it such that --rev '.'
is part of the strip (especially if a range revset is given to the command),
and *its* most recent ancestor used.  If '.' was stripped explicitly in this
example instead, it does stay on the same branch.  (But isn't 35358f982181 "the
most recent available ancestor", per the help text?  The current behavior in
this case seems better in that it is more deterministic, in addition to staying
on the same branch.)

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