verify: do not choke on valid changelog without manifest

Before this change:

  $ hg init
  $ hg branch foo
  $ hg ci -m branchfoo
  $ hg verify
  checking changesets
  checking manifests
   0: empty or missing manifest
  crosschecking files in changesets and manifests
  checking files
  0 files, 1 changesets, 0 total revisions
  1 integrity errors encountered!
  (first damaged changeset appears to be 0)
  [1]

mercurial/verify.py

@@ -120,6 +120,7 b' def _verify(repo):'
     havemf = len(mf) > 0
 
     ui.status(_("checking changesets\n"))
+    hasmanifest = False
     seen = {}
     checklog(cl, "changelog", 0)
     total = len(repo)
@@ -130,16 +131,22 b' def _verify(repo):'
 
         try:
             changes = cl.read(n)
-            mflinkrevs.setdefault(changes[0], []).append(i)
+            if changes[0] != nullid:
+                mflinkrevs.setdefault(changes[0], []).append(i)
+                hasmanifest = True
             for f in changes[3]:
                 filelinkrevs.setdefault(f, []).append(i)
         except Exception, inst:
+            hasmanifest = True
             exc(i, _("unpacking changeset %s") % short(n), inst)
     ui.progress(_('checking'), None)
 
     ui.status(_("checking manifests\n"))
     seen = {}
-    checklog(mf, "manifest", 0)
+    if hasmanifest:
+        # Do not check manifest if there are only changelog entries with
+        # null manifests.
+        checklog(mf, "manifest", 0)
     total = len(mf)
     for i in mf:
         ui.progress(_('checking'), i, total=total, unit=_('manifests'))

tests/test-verify.t

@@ -61,10 +61,22 b' introduce some bugs in repo'
   $ cd ../../..
   $ cd ..
 
-test revlog corruption
+test changelog without a manifest
 
   $ hg init b
   $ cd b
+  $ hg branch foo
+  marked working directory as branch foo
+  (branches are permanent and global, did you want a bookmark?)
+  $ hg ci -m branchfoo
+  $ hg verify
+  checking changesets
+  checking manifests
+  crosschecking files in changesets and manifests
+  checking files
+  0 files, 1 changesets, 0 total revisions
+
+test revlog corruption
 
   $ touch a
   $ hg add a
@@ -79,12 +91,12 b' test revlog corruption'
   checking manifests
   crosschecking files in changesets and manifests
   checking files
-   a@0: broken revlog! (index data/a.i is corrupted)
+   a@1: broken revlog! (index data/a.i is corrupted)
   warning: orphan revlog 'data/a.i'
-  1 files, 1 changesets, 0 total revisions
+  1 files, 2 changesets, 0 total revisions
   1 warnings encountered!
   1 integrity errors encountered!
-  (first damaged changeset appears to be 0)
+  (first damaged changeset appears to be 1)
   [1]
 
   $ cd ..