destupdate: have a generic and extensible way to run each step

We want extension to be able to easily override or add new way to select the
default update destination. We use the same list + dict approach as in other
parts of the code.

mercurial/destutil.py

@@ -1,179 +1,186 b''
 # destutil.py - Mercurial utility function for command destination
 #
 #  Copyright Matt Mackall <[e-mail]> and other
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 from .i18n import _
 from . import (
     bookmarks,
     error,
     obsolete,
 )
 
 def _destupdatevalidate(repo, rev, clean, check):
     """validate that the destination comply to various rules
 
     This exists as its own function to help wrapping from extensions."""
     wc = repo[None]
     p1 = wc.p1()
     if not clean:
         # Check that the update is linear.
         #
         # Mercurial do not allow update-merge for non linear pattern
         # (that would be technically possible but was considered too confusing
         # for user a long time ago)
         #
         # See mercurial.merge.update for details
         if p1.rev() not in repo.changelog.ancestors([rev], inclusive=True):
             dirty = wc.dirty(missing=True)
             foreground = obsolete.foreground(repo, [p1.node()])
             if not repo[rev].node() in foreground:
                 if dirty:
                     msg = _("uncommitted changes")
                     hint = _("commit and merge, or update --clean to"
                              " discard changes")
                     raise error.UpdateAbort(msg, hint=hint)
                 elif not check:  # destination is not a descendant.
                     msg = _("not a linear update")
                     hint = _("merge or update --check to force update")
                     raise error.UpdateAbort(msg, hint=hint)
 
 def _destupdateobs(repo, clean, check):
     """decide of an update destination from obsolescence markers"""
     node = None
     wc = repo[None]
     p1 = wc.p1()
     movemark = None
 
     if p1.obsolete() and not p1.children():
         # allow updating to successors
         successors = obsolete.successorssets(repo, p1.node())
 
         # behavior of certain cases is as follows,
         #
         # divergent changesets: update to highest rev, similar to what
         #     is currently done when there are more than one head
         #     (i.e. 'tip')
         #
         # replaced changesets: same as divergent except we know there
         # is no conflict
         #
         # pruned changeset: no update is done; though, we could
         #     consider updating to the first non-obsolete parent,
         #     similar to what is current done for 'hg prune'
 
         if successors:
             # flatten the list here handles both divergent (len > 1)
             # and the usual case (len = 1)
             successors = [n for sub in successors for n in sub]
 
             # get the max revision for the given successors set,
             # i.e. the 'tip' of a set
             node = repo.revs('max(%ln)', successors).first()
             if bookmarks.isactivewdirparent(repo):
                 movemark = repo['.'].node()
     return node, movemark, None
 
 def _destupdatebook(repo, clean, check):
     """decide on an update destination from active bookmark"""
     # we also move the active bookmark, if any
     activemark = None
     node, movemark = bookmarks.calculateupdate(repo.ui, repo, None)
     if node is not None:
         activemark = node
     return node, movemark, activemark
 
 def _destupdatebranch(repo, clean, check):
     """decide on an update destination from current branch"""
     wc = repo[None]
     movemark = node = None
     try:
         node = repo.branchtip(wc.branch())
         if bookmarks.isactivewdirparent(repo):
             movemark = repo['.'].node()
     except error.RepoLookupError:
         if wc.branch() == 'default': # no default branch!
             node = repo.lookup('tip') # update to tip
         else:
             raise error.Abort(_("branch %s not found") % wc.branch())
     return node, movemark, None
 
+# order in which each step should be evalutated
+# steps are run until one finds a destination
+destupdatesteps = ['evolution', 'bookmark', 'branch']
+# mapping to ease extension overriding steps.
+destupdatestepmap = {'evolution': _destupdateobs,
+                     'bookmark': _destupdatebook,
+                     'branch': _destupdatebranch,
+                     }
+
 def destupdate(repo, clean=False, check=False):
     """destination for bare update operation
 
     return (rev, movemark, activemark)
 
     - rev: the revision to update to,
     - movemark: node to move the active bookmark from
                 (cf bookmark.calculate update),
     - activemark: a bookmark to activate at the end of the update.
     """
-    node = None
-    movemark = activemark = None
+    node = movemark = activemark = None
 
-    node, movemark, activemark = _destupdateobs(repo, clean, check)
-    if node is None:
-        node, movemark, activemark = _destupdatebook(repo, clean, check)
-    if node is None:
-        node, movemark, activemark = _destupdatebranch(repo, clean, check)
+    for step in destupdatesteps:
+        node, movemark, activemark = destupdatestepmap[step](repo, clean, check)
+        if node is not None:
+            break
     rev = repo[node].rev()
 
     _destupdatevalidate(repo, rev, clean, check)
 
     return rev, movemark, activemark
 
 def destmerge(repo):
     if repo._activebookmark:
         bmheads = repo.bookmarkheads(repo._activebookmark)
         curhead = repo[repo._activebookmark].node()
         if len(bmheads) == 2:
             if curhead == bmheads[0]:
                 node = bmheads[1]
             else:
                 node = bmheads[0]
         elif len(bmheads) > 2:
             raise error.Abort(_("multiple matching bookmarks to merge - "
                 "please merge with an explicit rev or bookmark"),
                 hint=_("run 'hg heads' to see all heads"))
         elif len(bmheads) <= 1:
             raise error.Abort(_("no matching bookmark to merge - "
                 "please merge with an explicit rev or bookmark"),
                 hint=_("run 'hg heads' to see all heads"))
     else:
         branch = repo[None].branch()
         bheads = repo.branchheads(branch)
         nbhs = [bh for bh in bheads if not repo[bh].bookmarks()]
 
         if len(nbhs) > 2:
             raise error.Abort(_("branch '%s' has %d heads - "
                                "please merge with an explicit rev")
                              % (branch, len(bheads)),
                              hint=_("run 'hg heads .' to see heads"))
 
         parent = repo.dirstate.p1()
         if len(nbhs) <= 1:
             if len(bheads) > 1:
                 raise error.Abort(_("heads are bookmarked - "
                                    "please merge with an explicit rev"),
                                  hint=_("run 'hg heads' to see all heads"))
             if len(repo.heads()) > 1:
                 raise error.Abort(_("branch '%s' has one head - "
                                    "please merge with an explicit rev")
                                  % branch,
                                  hint=_("run 'hg heads' to see all heads"))
             msg, hint = _('nothing to merge'), None
             if parent != repo.lookup(branch):
                 hint = _("use 'hg update' instead")
             raise error.Abort(msg, hint=hint)
 
         if parent not in bheads:
             raise error.Abort(_('working directory not at a head revision'),
                              hint=_("use 'hg update' or merge with an "
                                     "explicit revision"))
         if parent == nbhs[0]:
             node = nbhs[-1]
         else:
             node = nbhs[0]
     return repo[node].rev()