phases: provide a test and accessor for non-public phase roots

phases: provide a test and accessor for non-public phase roots

This decouples users from the implementation details of the phasecache.
Also document a historic artifact about the stored phaseroots.

Differential Revision: https://phab.mercurial-scm.org/D8694

--- a/mercurial/phases.py	Wed Jun 24 17:53:44 2020 +0200
+++ b/mercurial/phases.py	Tue Jul 07 21:45:10 2020 +0200
@@ -323,6 +323,28 @@
             self.filterunknown(repo)
             self.opener = repo.svfs
 
+    def hasnonpublicphases(self, repo):
+        """detect if there are revisions with non-public phase"""
+        repo = repo.unfiltered()
+        cl = repo.changelog
+        if len(cl) >= self._loadedrevslen:
+            self.invalidate()
+            self.loadphaserevs(repo)
+        return any(self.phaseroots[1:])
+
+    def nonpublicphaseroots(self, repo):
+        """returns the roots of all non-public phases
+
+        The roots are not minimized, so if the secret revisions are
+        descendants of draft revisions, their roots will still be present.
+        """
+        repo = repo.unfiltered()
+        cl = repo.changelog
+        if len(cl) >= self._loadedrevslen:
+            self.invalidate()
+            self.loadphaserevs(repo)
+        return set().union(*[roots for roots in self.phaseroots[1:] if roots])
+
     def getrevset(self, repo, phases, subset=None):
         """return a smartset for the given phases"""
         self.loadphaserevs(repo)  # ensure phase's sets are loaded

--- a/mercurial/repoview.py	Wed Jun 24 17:53:44 2020 +0200
+++ b/mercurial/repoview.py	Tue Jul 07 21:45:10 2020 +0200
@@ -129,7 +129,7 @@
 def computemutable(repo, visibilityexceptions=None):
     assert not repo.changelog.filteredrevs
     # fast check to avoid revset call on huge repo
-    if any(repo._phasecache.phaseroots[1:]):
+    if repo._phasecache.hasnonpublicphases(repo):
         getphase = repo._phasecache.phase
         maymutable = filterrevs(repo, b'base')
         return frozenset(r for r in maymutable if getphase(repo, r))
@@ -154,9 +154,9 @@
     assert not repo.changelog.filteredrevs
     cl = repo.changelog
     firstmutable = len(cl)
-    for roots in repo._phasecache.phaseroots[1:]:
-        if roots:
-            firstmutable = min(firstmutable, min(cl.rev(r) for r in roots))
+    roots = repo._phasecache.nonpublicphaseroots(repo)
+    if roots:
+        firstmutable = min(firstmutable, min(cl.rev(r) for r in roots))
     # protect from nullrev root
     firstmutable = max(0, firstmutable)
     return frozenset(pycompat.xrange(firstmutable, len(cl)))