Make distributer.fire work as it did

synapse/util/distributor.py

@@ -15,6 +15,12 @@
 
 from twisted.internet import defer
 
+from synapse.util.logcontext import (
+    PreserveLoggingContext, preserve_context_over_deferred,
+)
+
+from synapse.util import unwrapFirstError
+
 import logging
 
 
@@ -99,6 +105,7 @@ class Signal(object):
         Returns a Deferred that will complete when all the observers have
         completed."""
 
+        def do(observer):
             def eb(failure):
                 logger.warning(
                     "%s signal observer %s failed: %r",
@@ -108,14 +115,17 @@ class Signal(object):
                         failure.value,
                         failure.getTracebackObject()))
                 if not self.suppress_failures:
-                failure.raiseException()
+                    return failure
+            return defer.maybeDeferred(observer, *args, **kwargs).addErrback(eb)
 
+        with PreserveLoggingContext():
             deferreds = [
-            defer.maybeDeferred(observer, *args, **kwargs)
+                do(observer)
                 for observer in self.observers
             ]
 
             d = defer.gatherResults(deferreds, consumeErrors=True)
-        d.addErrback(eb)
 
-        return d
+        d.addErrback(unwrapFirstError)
+
+        return preserve_context_over_deferred(d)