context: rename descendant() to isancestorof()

This makes the direction much clearer, IMO.

Differential Revision: https://phab.mercurial-scm.org/D3936

mercurial/bookmarks.py

@@ -813,7 +813,7 b' def validdest(repo, old, new):'
         return new.node() in obsutil.foreground(repo, [old.node()])
     else:
         # still an independent clause as it is lazier (and therefore faster)
-        return old.descendant(new)
+        return old.isancestorof(new)
 
 def checkformat(repo, mark):
     """return a valid version of a potential bookmark name

mercurial/context.py

@@ -589,8 +589,8 b' class changectx(basectx):'
                             short(n) for n in sorted(cahs) if n != anc))
         return changectx(self._repo, anc)
 
-    def descendant(self, other):
-        """True if other is descendant of this changeset"""
+    def isancestorof(self, other):
+        """True if this changeset is an ancestor of other"""
         return self._repo.changelog.isancestorrev(self._rev, other._rev)
 
     def walk(self, match):

mercurial/copies.py

@@ -416,14 +416,14 b' def _fullcopytracing(repo, c1, c2, base)'
     # common ancestor or not without explicitly checking it, it's better to
     # determine that here.
     #
-    # base.descendant(wc) is False, work around that
+    # base.isancestorof(wc) is False, work around that
     _c1 = c1.p1() if c1.rev() is None else c1
     _c2 = c2.p1() if c2.rev() is None else c2
     # an endpoint is "dirty" if it isn't a descendant of the merge base
     # if we have a dirty endpoint, we need to trigger graft logic, and also
     # keep track of which endpoint is dirty
-    dirtyc1 = not base.descendant(_c1)
-    dirtyc2 = not base.descendant(_c2)
+    dirtyc1 = not base.isancestorof(_c1)
+    dirtyc2 = not base.isancestorof(_c2)
     graft = dirtyc1 or dirtyc2
     tca = base
     if graft: