merge.mergestate: factor out code to validate v1/v2 records

We're going to need this in another place in upcoming patches.

mercurial/merge.py

@@ -117,15 +117,9 b' class mergestate(object):'
         returns list of record [(TYPE, data), ...]"""
         v1records = self._readrecordsv1()
         v2records = self._readrecordsv2()
-        oldv2 = set() # old format version of v2 record
-        for rec in v2records:
-            if rec[0] == 'L':
-                oldv2.add(rec)
-            elif rec[0] == 'F':
-                # drop the onode data (not contained in v1)
-                oldv2.add(('F', _droponode(rec[1])))
-        for rec in v1records:
-            if rec not in oldv2:
+        if self._v1v2match(v1records, v2records):
+            return v2records
+        else:
                 # v1 file is newer than v2 file, use it
                 # we have to infer the "other" changeset of the merge
                 # we cannot do better than that with v1 of the format
@@ -140,8 +134,20 b' class mergestate(object):'
                         bits.insert(-2, '')
                         v1records[idx] = (r[0], '\0'.join(bits))
                 return v1records
+
+    def _v1v2match(self, v1records, v2records):
+        oldv2 = set() # old format version of v2 record
+        for rec in v2records:
+            if rec[0] == 'L':
+                oldv2.add(rec)
+            elif rec[0] == 'F':
+                # drop the onode data (not contained in v1)
+                oldv2.add(('F', _droponode(rec[1])))
+        for rec in v1records:
+            if rec not in oldv2:
+                return False
         else:
-            return v2records
+            return True
 
     def _readrecordsv1(self):
         """read on disk merge state for version 1 file