hidden: simplify the computation of consistency blocker

For a couple of years, we now have precomputed set for all mutable phases. We
can use this set restrict our search and quickly detect non-hideable children of
hideable changesets.  This speeds up the hidden computation. See docstring of
the new function for details.

This new version reuses the '_domainancestors' function to keep the computation
of revealed changeset in O(len(visible))

Below are perfvolatilesets timing from two Mozilla repositories with different
contents. hidden cache is disabled while obtaining them.

1) Mozilla repository with:
 * 400667 changesets
 * 35 hidden changesets (first rev-268334)
 * 288 visible drafts
 * 1 unstable changeset

Before:
! visible
! wall 0.001744 comb 0.000000 user 0.000000 sys 0.000000 (best of 1563)

After:
! visible
! wall 0.000742 comb 0.000000 user 0.000000 sys 0.000000 (best of 3755)


The timing above include the computation of obsolete changeset:
! obsolete
! wall 0.000396 comb 0.000000 user 0.000000 sys 0.000000 (best of 6816)

So adjusted time give 1.3ms before versus 0.3ms after. A 4x speedup.

2) Mozilla repository with:
 * 405645 changesets
 * 4312 hidden changesets (first rev-326004)
 * 264 visible drafts
 * 1 unstable changeset

Before:
! visible
! wall 0.025476 comb 0.030000 user 0.030000 sys 0.000000 (best of 111)


After
! visible
! wall 0.007703 comb 0.010000 user 0.010000 sys 0.000000 (best of 358)


The timing above include the computation of obsolete changeset:
! obsolete
! wall 0.006408 comb 0.010000 user 0.010000 sys 0.000000 (best of 404)

So adjusted time give 19ms before versus 1.3ms after. A 17x speedup.

mercurial/repoview.py

@@ -10,7 +10,6 b' from __future__ import absolute_import'
 
 import copy
 import hashlib
-import heapq
 import struct
 
 from .node import nullrev
@@ -63,35 +62,33 b' def _getstatichidden(repo):'
 
     """
     assert not repo.changelog.filteredrevs
-    hidden = set(hideablerevs(repo))
+    hidden = hideablerevs(repo)
     if hidden:
-        getphase = repo._phasecache.phase
-        getparentrevs = repo.changelog.parentrevs
-        # Skip heads which are public (guaranteed to not be hidden)
-        heap = [-r for r in repo.changelog.headrevs() if getphase(repo, r)]
-        heapq.heapify(heap)
-        heappop = heapq.heappop
-        heappush = heapq.heappush
-        seen = set() # no need to init it with heads, they have no children
-        while heap:
-            rev = -heappop(heap)
-            # All children have been processed so at that point, if no children
-            # removed 'rev' from the 'hidden' set, 'rev' is going to be hidden.
-            blocker = rev not in hidden
-            for parent in getparentrevs(rev):
-                if parent == nullrev:
-                    continue
-                if blocker:
-                    # If visible, ensure parent will be visible too
-                    hidden.discard(parent)
-                # - Avoid adding the same revision twice
-                # - Skip nodes which are public (guaranteed to not be hidden)
-                pre = len(seen)
-                seen.add(parent)
-                if pre < len(seen) and getphase(repo, rev):
-                    heappush(heap, -parent)
+        pfunc = repo.changelog.parentrevs
+
+        mutablephases = (phases.draft, phases.secret)
+        mutable = repo._phasecache.getrevset(repo, mutablephases)
+        blockers = _consistencyblocker(pfunc, hidden, mutable)
+
+        if blockers:
+            hidden = hidden - _domainancestors(pfunc, blockers, mutable)
     return hidden
 
+def _consistencyblocker(pfunc, hideable, domain):
+    """return non-hideable changeset blocking hideable one
+
+    For consistency, we cannot actually hide a changeset if one of it children
+    are visible, this function find such children.
+    """
+    others = domain - hideable
+    blockers = set()
+    for r in others:
+        for p in pfunc(r):
+            if p != nullrev and p in hideable:
+                blockers.add(r)
+                break
+    return blockers
+
 def _domainancestors(pfunc, revs, domain):
     """return ancestors of 'revs' within 'domain'