changelogv2: use a dedicated version number

If we want to change the format, we need a new version number. We start with
that.

Differential Revision: https://phab.mercurial-scm.org/D10663

mercurial/revlog.py

@@ -35,6 +35,7 b' from .i18n import _'
 from .pycompat import getattr
 from .revlogutils.constants import (
     ALL_KINDS,
+    CHANGELOGV2,
     COMP_MODE_DEFAULT,
     COMP_MODE_INLINE,
     COMP_MODE_PLAIN,
@@ -460,7 +461,7 b' class revlog(object):'
         opts = self.opener.options
 
         if b'changelogv2' in opts and self.revlog_kind == KIND_CHANGELOG:
-            new_header = REVLOGV2
+            new_header = CHANGELOGV2
         elif b'revlogv2' in opts:
             new_header = REVLOGV2
         elif b'revlogv1' in opts:
@@ -650,6 +651,8 b' class revlog(object):'
             self._parse_index = revlogv0.parse_index_v0
         elif self._format_version == REVLOGV2:
             self._parse_index = parse_index_v2
+        elif self._format_version == CHANGELOGV2:
+            self._parse_index = parse_index_v2
         elif devel_nodemap:
             self._parse_index = parse_index_v1_nodemap
         elif use_rust_index:

mercurial/revlogutils/constants.py

@@ -36,6 +36,8 b' REVLOGV0 = 0'
 REVLOGV1 = 1
 # Dummy value until file format is finalized.
 REVLOGV2 = 0xDEAD
+# Dummy value until file format is finalized.
+CHANGELOGV2 = 0xD34D
 
 ##  global revlog header flags
 # Shared across v1 and v2.
@@ -48,6 +50,7 b' REVLOG_DEFAULT_VERSION = REVLOG_DEFAULT_'
 REVLOGV0_FLAGS = 0
 REVLOGV1_FLAGS = FLAG_INLINE_DATA | FLAG_GENERALDELTA
 REVLOGV2_FLAGS = FLAG_INLINE_DATA
+CHANGELOGV2_FLAGS = 0
 
 ### individual entry
 
@@ -141,6 +144,7 b' SUPPORTED_FLAGS = {'
     REVLOGV0: REVLOGV0_FLAGS,
     REVLOGV1: REVLOGV1_FLAGS,
     REVLOGV2: REVLOGV2_FLAGS,
+    CHANGELOGV2: CHANGELOGV2_FLAGS,
 }
 
 _no = lambda flags: False
@@ -173,6 +177,13 b' FEATURES_BY_VERSION = {'
         b'sidedata': True,
         b'docket': True,
     },
+    CHANGELOGV2: {
+        b'inline': _no,
+        # General delta is useless for changelog since we don't do any delta
+        b'generaldelta': _no,
+        b'sidedata': True,
+        b'docket': True,
+    },
 }
 
 

mercurial/revlogutils/docket.py

@@ -145,7 +145,8 b' class RevlogDocket(object):'
 
 def default_docket(revlog, version_header):
     """given a revlog version a new docket object for the given revlog"""
-    if (version_header & 0xFFFF) != constants.REVLOGV2:
+    rl_version = version_header & 0xFFFF
+    if rl_version not in (constants.REVLOGV2, constants.CHANGELOGV2):
         return None
     comp = util.compengines[revlog._compengine].revlogheader()
     docket = RevlogDocket(