bundle2: fix bundle2 pulling all revs on empty pulls

When bundle2 was enabled, if hg pull had no commits to pull, it would print
'no changes found' and then download the entire repository from the server. This
was caused by heads and common being set to None, which gets treated as
heads=cl.heads() and common=[nullid], which means download the entire repo.

Pulling bundles without a changegroup is a valid use case (like if we're just
updating bookmarks), so this modifes the bundle code to allow not adding
changegroups.

mercurial/exchange.py

@@ -573,12 +573,13 b' def _pullbundle2(pullop):'
     kwargs['bundlecaps'].add('bundle2=' + urllib.quote(capsblob))
     # pulling changegroup
     pullop.todosteps.remove('changegroup')
+
+    kwargs['common'] = pullop.common
+    kwargs['heads'] = pullop.heads or pullop.rheads
     if not pullop.fetch:
         pullop.repo.ui.status(_("no changes found\n"))
         pullop.cgresult = 0
     else:
-        kwargs['common'] = pullop.common
-        kwargs['heads'] = pullop.heads or pullop.rheads
         if pullop.heads is None and list(pullop.common) == [nullid]:
             pullop.repo.ui.status(_("requesting all changes\n"))
     _pullbundle2extraprepare(pullop, kwargs)
@@ -589,8 +590,10 b' def _pullbundle2(pullop):'
         op = bundle2.processbundle(pullop.repo, bundle, pullop.gettransaction)
     except bundle2.UnknownPartError, exc:
         raise util.Abort('missing support for %s' % exc)
-    assert len(op.records['changegroup']) == 1
-    pullop.cgresult = op.records['changegroup'][0]['return']
+
+    if pullop.fetch:
+        assert len(op.records['changegroup']) == 1
+        pullop.cgresult = op.records['changegroup'][0]['return']
 
 def _pullbundle2extraprepare(pullop, kwargs):
     """hook function so that extensions can extend the getbundle call"""
@@ -684,7 +687,7 b' def getbundle(repo, source, heads=None, '
     The implementation is at a very early stage and will get massive rework
     when the API of bundle is refined.
     """
-    # build bundle here.
+    # build changegroup bundle here.
     cg = changegroup.getbundle(repo, source, heads=heads,
                                common=common, bundlecaps=bundlecaps)
     if bundlecaps is None or 'HG2X' not in bundlecaps:
@@ -697,8 +700,9 b' def getbundle(repo, source, heads=None, '
             blob = urllib.unquote(bcaps[len('bundle2='):])
             b2caps.update(bundle2.decodecaps(blob))
     bundler = bundle2.bundle20(repo.ui, b2caps)
-    part = bundle2.bundlepart('b2x:changegroup', data=cg.getchunks())
-    bundler.addpart(part)
+    if cg:
+        part = bundle2.bundlepart('b2x:changegroup', data=cg.getchunks())
+        bundler.addpart(part)
     _getbundleextrapart(bundler, repo, source, heads=heads, common=common,
                         bundlecaps=bundlecaps, **kwargs)
     return util.chunkbuffer(bundler.getchunks())

tests/test-bundle2.t

@@ -791,6 +791,12 b' pull'
   added 1 changesets with 1 changes to 1 files (+1 heads)
   (run 'hg heads' to see heads, 'hg merge' to merge)
 
+pull empty
+
+  $ hg -R other pull -r 24b6387c8c8c
+  pulling from $TESTTMP/main (glob)
+  no changes found
+
 push
 
   $ hg -R main push other --rev eea13746799a