strip: introduce a soft strip option

This is the first user-accessible way to use the archived phase introduced in
4.8. This implements a feature discussed during the Stockholm sprint, using
the archived phase for hiding changesets.

The archived phase behaves exactly as stripping: changesets are no longer
visible, but pulling/unbundling them will make then reappear. The only notable
difference is that unlike hard stripping, soft stripping does not affect
obsmarkers.

The next changeset will make use of the archived phase for history rewriting
command. However, having a way to manually trigger the feature first seems a
necessary step before exposing users to this phase; there is a way to
un-archived changesets (unbundling), so there must be a way to archive them
again.

Adding a flag to strip is a good way to provide access to the feature without
taking a too big risk on the final UI we want. The flag is experimental so it
won't be exposed by default.

Using the archived phase is faster and less traumatic for the repository than
actually stripping changesets.

tests/test-phase-archived.t

@@ -0,0 +1,77 b''
+=========================================================
+Test features and behaviors related to the archived phase
+=========================================================
+
+  $ cat << EOF >> $HGRCPATH
+  > [format]
+  > internal-phase=yes
+  > [extensions]
+  > strip=
+  > [experimental]
+  > EOF
+
+  $ hg init repo
+  $ cd repo
+  $ echo  root > a
+  $ hg add a
+  $ hg ci -m 'root'
+
+Test that bundle can unarchive a changeset
+------------------------------------------
+
+  $ echo foo >> a
+  $ hg st
+  M a
+  $ hg ci -m 'unbundletesting'
+  $ hg log -G
+  @  changeset:   1:883aadbbf309
+  |  tag:         tip
+  |  user:        test
+  |  date:        Thu Jan 01 00:00:00 1970 +0000
+  |  summary:     unbundletesting
+  |
+  o  changeset:   0:c1863a3840c6
+     user:        test
+     date:        Thu Jan 01 00:00:00 1970 +0000
+     summary:     root
+  
+  $ hg strip --soft --rev '.'
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  saved backup bundle to $TESTTMP/repo/.hg/strip-backup/883aadbbf309-efc55adc-backup.hg
+  $ hg log -G
+  @  changeset:   0:c1863a3840c6
+     tag:         tip
+     user:        test
+     date:        Thu Jan 01 00:00:00 1970 +0000
+     summary:     root
+  
+  $ hg log -G --hidden
+  o  changeset:   1:883aadbbf309
+  |  tag:         tip
+  |  user:        test
+  |  date:        Thu Jan 01 00:00:00 1970 +0000
+  |  summary:     unbundletesting
+  |
+  @  changeset:   0:c1863a3840c6
+     user:        test
+     date:        Thu Jan 01 00:00:00 1970 +0000
+     summary:     root
+  
+  $ hg unbundle .hg/strip-backup/883aadbbf309-efc55adc-backup.hg
+  adding changesets
+  adding manifests
+  adding file changes
+  added 0 changesets with 0 changes to 1 files
+  (run 'hg update' to get a working copy)
+  $ hg log -G
+  o  changeset:   1:883aadbbf309
+  |  tag:         tip
+  |  user:        test
+  |  date:        Thu Jan 01 00:00:00 1970 +0000
+  |  summary:     unbundletesting
+  |
+  @  changeset:   0:c1863a3840c6
+     user:        test
+     date:        Thu Jan 01 00:00:00 1970 +0000
+     summary:     root
+  

hgext/strip.py

@@ -76,7 +76,8 b' def _findupdatetarget(repo, nodes):'
 
     return unode
 
-def strip(ui, repo, revs, update=True, backup=True, force=None, bookmarks=None):
+def strip(ui, repo, revs, update=True, backup=True, force=None, bookmarks=None,
+          soft=False):
     with repo.wlock(), repo.lock():
 
         if update:
@@ -85,7 +86,10 b' def strip(ui, repo, revs, update=True, b'
             hg.clean(repo, urev)
             repo.dirstate.write(repo.currenttransaction())
 
-        repair.strip(ui, repo, revs, backup)
+        if soft:
+            repair.softstrip(ui, repo, revs, backup)
+        else:
+            repair.strip(ui, repo, revs, backup)
 
         repomarks = repo._bookmarks
         if bookmarks:
@@ -110,7 +114,10 b' def strip(ui, repo, revs, update=True, b'
           ('k', 'keep', None, _("do not modify working directory during "
                                 "strip")),
           ('B', 'bookmark', [], _("remove revs only reachable from given"
-                                  " bookmark"), _('BOOKMARK'))],
+                                  " bookmark"), _('BOOKMARK')),
+          ('', 'soft', None,
+          _("simply drop changesets from visible history (EXPERIMENTAL)")),
+         ],
           _('hg strip [-k] [-f] [-B bookmark] [-r] REV...'),
           helpcategory=command.CATEGORY_MAINTENANCE)
 def stripcmd(ui, repo, *revs, **opts):
@@ -235,6 +242,7 b' def stripcmd(ui, repo, *revs, **opts):'
 
 
         strip(ui, repo, revs, backup=backup, update=update,
-              force=opts.get('force'), bookmarks=bookmarks)
+              force=opts.get('force'), bookmarks=bookmarks,
+              soft=opts['soft'])
 
     return 0

mercurial/repair.py

@@ -252,6 +252,24 b' def strip(ui, repo, nodelist, backup=Tru'
     # extensions can use it
     return backupfile
 
+def softstrip(ui, repo, nodelist, backup=True, topic='backup'):
+    """perform a "soft" strip using the archived phase"""
+    tostrip = [c.node() for c in repo.set('sort(%ln::)', nodelist)]
+    if not tostrip:
+        return None
+
+    newbmtarget, updatebm = _bookmarkmovements(repo, tostrip)
+    if backup:
+        node = tostrip[0]
+        backupfile = _createstripbackup(repo, tostrip, node, topic)
+
+    with repo.transaction('strip') as tr:
+        phases.retractboundary(repo, tr, phases.archived, tostrip)
+        bmchanges = [(m, repo[newbmtarget].node()) for m in updatebm]
+        repo._bookmarks.applychanges(repo, tr, bmchanges)
+    return backupfile
+
+
 def _bookmarkmovements(repo, tostrip):
     # compute necessary bookmark movement
     bm = repo._bookmarks