[PATCH 13 of 18 "] verify: document the `checklog` method

[Pierre-Yves David]

# HG changeset patch
# User Pierre-Yves David <pierre-yves.david at octobus.net>
# Date 1551877823 -3600
#      Wed Mar 06 14:10:23 2019 +0100
# Node ID 4390cbb4a01be93907ec49c5dce2599fe5a272df
# Parent  2b4470cd927234cd028051e8ddee77dee82dccec
# EXP-Topic verify
# Available At https://bitbucket.org/octobus/mercurial-devel/
#              hg pull https://bitbucket.org/octobus/mercurial-devel/ -r 4390cbb4a01b
verify: document the `checklog` method

Let us add details about what the function is expected to do.

diff --git a/mercurial/verify.py b/mercurial/verify.py
--- a/mercurial/verify.py
+++ b/mercurial/verify.py
@@ -77,6 +77,13 @@ class verifier(object):
         self._err(linkrev, "%s: %s" % (msg, fmsg), filename)
 
     def checklog(self, obj, name, linkrev):
+        """verify high level property of a revlog
+
+        - revlog is present,
+        - revlog is non-empty,
+        - sizes (index and data) are correct,
+        - revlog's format version is correct.
+        """
         if not len(obj) and (self.havecl or self.havemf):
             self._err(linkrev, _("empty or missing %s") % name)
             return