changelog: prefilter in headrevs()

changelog: prefilter in headrevs()

In case where headrevs() is called on some revisions, we perform
the check that aren't filtered in advance, and switch revlog to
use its unchecked form.

This allows to work with alternative implementations that don't have knowledge
of the filtering system, such as the Rust one.

--- a/mercurial/changelog.py	Thu Feb 21 11:23:10 2019 +0100
+++ b/mercurial/changelog.py	Wed Feb 20 11:49:06 2019 +0100
@@ -22,6 +22,7 @@
     error,
     pycompat,
     revlog,
+    util,
 )
 from .utils import (
     dateutil,
@@ -350,6 +351,27 @@
     def reachableroots(self, minroot, heads, roots, includepath=False):
         return self.index.reachableroots2(minroot, heads, roots, includepath)
 
+    def _checknofilteredinrevs(self, revs):
+        """raise the appropriate error if 'revs' contains a filtered revision
+
+        This returns a version of 'revs' to be used thereafter by the caller.
+        In particular, if revs is an iterator, it is converted into a set.
+        """
+        safehasattr = util.safehasattr
+        if safehasattr(revs, '__next__'):
+            # Note that inspect.isgenerator() is not true for iterators,
+            revs = set(revs)
+
+        filteredrevs = self.filteredrevs
+        if safehasattr(revs, 'first'):  # smartset
+            offenders = revs & filteredrevs
+        else:
+            offenders = filteredrevs.intersection(revs)
+
+        for rev in offenders:
+            raise error.FilteredIndexError(rev)
+        return revs
+
     def headrevs(self, revs=None):
         if revs is None and self.filteredrevs:
             try:
@@ -359,6 +381,8 @@
             except AttributeError:
                 return self._headrevs()
 
+        if self.filteredrevs:
+            revs = self._checknofilteredinrevs(revs)
         return super(changelog, self).headrevs(revs)
 
     def strip(self, *args, **kwargs):

--- a/mercurial/revlog.py	Thu Feb 21 11:23:10 2019 +0100
+++ b/mercurial/revlog.py	Wed Feb 20 11:49:06 2019 +0100
@@ -1121,7 +1121,7 @@
                 return self.index.headrevs()
             except AttributeError:
                 return self._headrevs()
-        return dagop.headrevs(revs, self.parentrevs)
+        return dagop.headrevs(revs, self._uncheckedparentrevs)
 
     def computephases(self, roots):
         return self.index.computephasesmapsets(roots)