bundle2: introduce a PushkeyFail error to abort unbundle on pushkey error

The pushkey code is generic and the server side has little context on what the
client is trying to achieve. Generating interesting error messages server side
would be challenging. Instead we introduce a dedicated exception that carries more
data. In particular, it carries the id of the part which failed that will allow
clients to display custom error messages depending on the part intent.

The processing and transfer-over-the-wire of this exception is to be implemented
in coming changesets.

mercurial/bundle2.py

@@ -1330,8 +1330,11 @@ def handlepushkey(op, inpart):
         rpart.addparam('in-reply-to', str(inpart.id), mandatory=False)
         rpart.addparam('return', '%i' % ret, mandatory=False)
     if inpart.mandatory and not ret:
-        raise util.Abort(_('failed to update value for "%s/%s"')
+        kwargs = {}
-                         % (namespace, key))
+        for key in ('namespace', 'key', 'new', 'old', 'ret'):
+            if key in inpart.params:
+                kwargs[key] = inpart.params[key]
+        raise error.PushkeyFailed(partid=str(inpart.id), **kwargs)
 
 @parthandler('reply:pushkey', ('return', 'in-reply-to'))
 def handlepushkeyreply(op, inpart):

mercurial/error.py

@@ -151,6 +151,21 @@ class ReadOnlyPartError(RuntimeError):
     """error raised when code tries to alter a part being generated"""
     pass
 
+class PushkeyFailed(Abort):
+    """error raised when a pushkey part failed to update a value"""
+
+    def __init__(self, partid, namespace=None, key=None, new=None, old=None,
+                 ret=None):
+        self.partid = partid
+        self.namespace = namespace
+        self.key = key
+        self.new = new
+        self.old = old
+        self.ret = ret
+        # no i18n expected to be processed into a better message
+        Abort.__init__(self, 'failed to update value for "%s/%s"'
+                       % (namespace, key))
+
 class CensoredNodeError(RevlogError):
     """error raised when content verification fails on a censored node