changelog-delay: move "delayed" check to a more official API

To avoid reaching inside the inner object in the future, we needs some official
API. We put one of such API early to reduce the size of the final diff.

mercurial/changelog.py

@@ -374,13 +374,17 b' class changelog(revlog.revlog):'
         self._filteredrevs_hashcache = {}
 
     def _write_docket(self, tr):
-        if not self._delayed:
+        if not self.is_delaying:
             super(changelog, self)._write_docket(tr)
 
+    @property
+    def is_delaying(self):
+        return self._delayed
+
     def delayupdate(self, tr):
         """delay visibility of index updates to other readers"""
         assert not self._inner.is_open
-        if self._docket is None and not self._delayed:
+        if self._docket is None and not self.is_delaying:
             if len(self) == 0:
                 self._divert = True
                 if self._realopener.exists(self._indexfile + b'.a'):
@@ -456,7 +460,7 b' class changelog(revlog.revlog):'
         return False
 
     def _enforceinlinesize(self, tr, side_write=True):
-        if not self._delayed:
+        if not self.is_delaying:
             revlog.revlog._enforceinlinesize(self, tr, side_write=side_write)
 
     def read(self, nodeorrev):

mercurial/localrepo.py

@@ -3019,7 +3019,7 b' class localrepository:'
             if (
                 k == b'changelog'
                 and self.currenttransaction()
-                and self.changelog._delayed
+                and self.changelog.is_delaying
             ):
                 # The changelog object may store unwritten revisions. We don't
                 # want to lose them.

mercurial/repoview.py

@@ -416,7 +416,7 b' class repoview:'
         with util.timedcm('repo filter for %s', self.filtername):
             revs = filterrevs(unfi, self.filtername, self._visibilityexceptions)
         cl = self._clcache
-        newkey = (unfilen, unfinode, hash(revs), unfichangelog._delayed)
+        newkey = (unfilen, unfinode, hash(revs), unfichangelog.is_delaying)
         # if cl.index is not unfiindex, unfi.changelog would be
         # recreated, and our clcache refers to garbage object
         if cl is not None and (