revlog: move the details of revlog "v1" index inside revlog.utils.constants

revlog: move the details of revlog "v1" index inside revlog.utils.constants

The revlog module is quite large and this kind of format information would handy
for other module. So let us start to gather this information about the format in
a more appropriate place.

We update various reference to this information to use the new "source of truth"
in the process.

Differential Revision: https://phab.mercurial-scm.org/D10304

--- a/mercurial/pure/parsers.py	Mon Apr 05 12:20:52 2021 +0200
+++ b/mercurial/pure/parsers.py	Mon Apr 05 12:21:01 2021 +0200
@@ -17,6 +17,7 @@
 )
 
 from ..revlogutils import nodemap as nodemaputil
+from ..revlogutils import constants as revlog_constants
 
 stringio = pycompat.bytesio
 
@@ -43,13 +44,13 @@
 
 class BaseIndexObject(object):
     # Format of an index entry according to Python's `struct` language
-    index_format = b">Qiiiiii20s12x"
+    index_format = revlog_constants.INDEX_ENTRY_V1.format
     # Size of a C unsigned long long int, platform independent
     big_int_size = struct.calcsize(b'>Q')
     # Size of a C long int, platform independent
     int_size = struct.calcsize(b'>i')
     # Size of the entire index format
-    index_size = struct.calcsize(index_format)
+    index_size = revlog_constants.INDEX_ENTRY_V1.size
     # An empty index entry, used as a default value to be overridden, or nullrev
     null_item = (0, 0, 0, -1, -1, -1, -1, nullid)
 

--- a/mercurial/revlog.py	Mon Apr 05 12:20:52 2021 +0200
+++ b/mercurial/revlog.py	Mon Apr 05 12:21:01 2021 +0200
@@ -42,6 +42,7 @@
     FLAG_GENERALDELTA,
     FLAG_INLINE_DATA,
     INDEX_ENTRY_V0,
+    INDEX_ENTRY_V1,
     REVLOGV0,
     REVLOGV1,
     REVLOGV1_FLAGS,
@@ -326,18 +327,6 @@
         return INDEX_ENTRY_V0.pack(*e2)
 
 
-# index ng:
-#  6 bytes: offset
-#  2 bytes: flags
-#  4 bytes: compressed length
-#  4 bytes: uncompressed length
-#  4 bytes: base rev
-#  4 bytes: link rev
-#  4 bytes: parent 1 rev
-#  4 bytes: parent 2 rev
-# 32 bytes: nodeid
-indexformatng = struct.Struct(b">Qiiiiii20s12x")
-indexformatng_pack = indexformatng.pack
 versionformat = struct.Struct(b">I")
 versionformat_pack = versionformat.pack
 versionformat_unpack = versionformat.unpack
@@ -349,7 +338,7 @@
 
 class revlogio(object):
     def __init__(self):
-        self.size = indexformatng.size
+        self.size = INDEX_ENTRY_V1.size
 
     def parseindex(self, data, inline):
         # call the C implementation to parse the index data
@@ -357,7 +346,7 @@
         return index, cache
 
     def packentry(self, entry, node, version, rev):
-        p = indexformatng_pack(*entry)
+        p = INDEX_ENTRY_V1.pack(*entry)
         if rev == 0:
             p = versionformat_pack(version) + p[4:]
         return p

--- a/mercurial/revlogutils/constants.py	Mon Apr 05 12:20:52 2021 +0200
+++ b/mercurial/revlogutils/constants.py	Mon Apr 05 12:21:01 2021 +0200
@@ -44,6 +44,19 @@
 # 20 bytes: nodeid
 INDEX_ENTRY_V0 = struct.Struct(b">4l20s20s20s")
 
+## index v1
+#  6 bytes: offset
+#  2 bytes: flags
+#  4 bytes: compressed length
+#  4 bytes: uncompressed length
+#  4 bytes: base rev
+#  4 bytes: link rev
+#  4 bytes: parent 1 rev
+#  4 bytes: parent 2 rev
+# 32 bytes: nodeid
+INDEX_ENTRY_V1 = struct.Struct(b">Qiiiiii20s12x")
+assert INDEX_ENTRY_V1.size == 32 * 2
+
 # revlog index flags
 
 # For historical reasons, revlog's internal flags were exposed via the