repoview: add _gethiddenblockers method

This is a standalone function that will provide the ability for extensions to
wrap.

mercurial/repoview.py

@@ -19,6 +19,31 b' def hideablerevs(repo):'
     This is a standalone function to help extensions to wrap it."""
     return obsolete.getrevs(repo, 'obsolete')
 
+def _gethiddenblockers(repo):
+    """Get revisions that will block hidden changesets from being filtered
+
+    This is a standalone function to help extensions to wrap it."""
+    assert not repo.changelog.filteredrevs
+    hideable = hideablerevs(repo)
+    blockers = []
+    if hideable:
+        cl = repo.changelog
+        firsthideable = min(hideable)
+        revs = cl.revs(start=firsthideable)
+        tofilter = repo.revs(
+            '(%ld) and children(%ld)', list(revs), list(hideable))
+        blockers = [r for r in tofilter if r not in hideable]
+        for par in repo[None].parents():
+            blockers.append(par.rev())
+        for bm in repo._bookmarks.values():
+            blockers.append(repo[bm].rev())
+        tags = {}
+        tagsmod.readlocaltags(repo.ui, repo, tags, {})
+        if tags:
+            blockers.extend(repo[t[0]].rev() for t in tags.values())
+        blockers.extend(repo[t].rev() for t in tags)
+    return blockers
+
 def computehidden(repo):
     """compute the set of hidden revision to filter