[PATCH STABLE] revlog: fix resolution of revlog version 0

[Yuya Nishihara]

# HG changeset patch
# User Yuya Nishihara <yuya at tcha.org>
# Date 1548076469 -32400
#      Mon Jan 21 22:14:29 2019 +0900
# Branch stable
# Node ID 498a5d7f8e19d6b430f300ff6687a92270022f81
# Parent  13c23396c7fe1633a2336b29e3a32b9b76274f28
revlog: fix resolution of revlog version 0

This partially backs out cecf3f8bccd3, "revlog: always process opener options."

My understanding is that if there's no "revlog1" nor "revlog2" in .hg/requires,
the repository should stick to the v0 format. The reasoning is briefly
described in 31a5973fcf96, "revlog: get rid of defversion."

Maybe we can drop support for missing opener options, but I didn't do that
in this patch.

diff --git a/mercurial/revlog.py b/mercurial/revlog.py
--- a/mercurial/revlog.py
+++ b/mercurial/revlog.py
@@ -396,6 +396,11 @@ class revlog(object):
             newversionflags = REVLOGV1 | FLAG_INLINE_DATA
             if 'generaldelta' in opts:
                 newversionflags |= FLAG_GENERALDELTA
+        elif getattr(self.opener, 'options', None) is not None:
+            # If options provided but no 'revlog*' found, the repository
+            # would have no 'requires' file in it, which means we have to
+            # stick to the old format.
+            newversionflags = REVLOGV0
         else:
             newversionflags = REVLOG_DEFAULT_VERSION
 
diff --git a/tests/test-clone.t b/tests/test-clone.t
--- a/tests/test-clone.t
+++ b/tests/test-clone.t
@@ -717,6 +717,9 @@ Test clone from the repository in (emula
   $ hg -R src commit -m '#0'
   $ hg -R src log -q
   0:e1bab28bca43
+  $ hg -R src debugrevlog -c | egrep 'format|flags'
+  format : 0
+  flags  : (none)
   $ hg clone -U -q src dst
   $ hg -R dst log -q
   0:e1bab28bca43