exchange: advertise if a clone bundle was attempted

The client now sends a "cbattempted" boolean flag to the "getbundle"
wire protocol command to tell the server whether a clone bundle was
attempted.

The presence of this flag will enable the server to conditionally emit a
bundle2 "output" part advertising the availability of clone bundles to
compatible clients that don't have it enabled.

mercurial/exchange.py

@@ -1179,6 +1179,16 b' def _pullbundle2(pullop):'
             # make sure to always includes bookmark data when migrating
             # `hg incoming --bundle` to using this function.
             kwargs['listkeys'].append('bookmarks')
+
+    # If this is a full pull / clone and the server supports the clone bundles
+    # feature, tell the server whether we attempted a clone bundle. The
+    # presence of this flag indicates the client supports clone bundles. This
+    # will enable the server to treat clients that support clone bundles
+    # differently from those that don't.
+    if (pullop.remote.capable('clonebundles')
+        and pullop.heads is None and list(pullop.common) == [nullid]):
+        kwargs['cbattempted'] = pullop.clonebundleattempted
+
     if streaming:
         pullop.repo.ui.status(_('streaming all changes\n'))
     elif not pullop.fetch:

mercurial/wireproto.py

@@ -160,7 +160,8 b" gboptsmap = {'heads': 'nodes',"
              'obsmarkers': 'boolean',
              'bundlecaps': 'scsv',
              'listkeys': 'csv',
-             'cg': 'boolean'}
+             'cg': 'boolean',
+             'cbattempted': 'boolean'}
 
 # client side