Merge pull request #12437 from achilleasa/2.9-set-unit-error-state-wh…

…en-relation-created-hooks-fail

#12437

This is a forward port of #12431.

## QA steps


```sh
# apply this patch
diff --git a/acceptancetests/repository/charms/ubuntu/metadata.yaml b/acceptancetests/repository/charms/ubuntu/metadata.yaml
index 1846048417..e5b7b19648 100644
--- a/acceptancetests/repository/charms/ubuntu/metadata.yaml
+++ b/acceptancetests/repository/charms/ubuntu/metadata.yaml
@@ -12,4 +12,6 @@ series:
 - bionic
 - eoan
 - focal
-
+peers:
+ peer:
+ interface: http


# Then create this file with the specified contents
$ cat acceptancetests/repository/charms/ubuntu/hooks/peer-relation-created
#!/bin/bash
set -e
# This should fail when executed by a non-leader unit!
relation-set -r $JUJU_RELATION_ID --app foo=bar

# Finally, run the following command and check that the non-leader unit reaches an error state
$ juju deploy -n2 ./acceptancetests/repository/charms/ubuntu

$ juju status
Model Controller Cloud/Region Version SLA Timestamp
default test lxd-with-cache/default 2.8.7.1 unsupported 18:33:58Z

App Version Status Scale Charm Store Rev OS Notes
ubuntu error 2 ubuntu local 1 ubuntu

Unit Workload Agent Machine Public address Ports Message
ubuntu/0* unknown idle 0 10.59.233.117
ubuntu/1 error idle 1 10.59.233.252 hook failed: "peer-relation-created" <---- look for this

Machine State DNS Inst id Series AZ Message
0 started 10.59.233.117 juju-be2af9-0 bionic Running
1 started 10.59.233.252 juju-be2af9-1 bionic Running
```

## Bug reference
https://bugs.launchpad.net/juju/+bug/1906706

worker/uniter/relation/resolver.go

@@ -325,6 +325,11 @@ func (r *createdRelationsResolver) NextOp(
 		return nil, resolver.ErrNoOperation
 	}
 
+	// We should only evaluate the resolver logic if there is no other pending operation
+	if localState.Kind != operation.Continue {
+		return nil, resolver.ErrNoOperation
+	}
+
 	if err := r.stateTracker.SynchronizeScopes(remoteState); err != nil {
 		return nil, errors.Trace(err)
 	}

worker/uniter/relation/resolver_test.go

@@ -1295,6 +1295,29 @@ func (s *relationCreatedResolverSuite) TestCreatedRelationResolverFordRelationNo
 	})
 }
 
+// This is a regression test for LP1906706
+func (s *relationCreatedResolverSuite) TestCreatedRelationsResolverWithPendingHook(c *gc.C) {
+	ctrl := gomock.NewController(c)
+	defer ctrl.Finish()
+
+	r := mocks.NewMockRelationStateTracker(ctrl)
+
+	localState := resolver.LocalState{
+		State: operation.State{
+			Installed: true,
+			Kind:      operation.RunHook,
+			Step:      operation.Pending,
+		},
+	}
+	remoteState := remotestate.Snapshot{
+		Life: life.Alive,
+	}
+
+	createdRelationsResolver := relation.NewCreatedRelationResolver(r)
+	_, err := createdRelationsResolver.NextOp(localState, remoteState, &mockOperations{})
+	c.Assert(errors.Cause(err), gc.Equals, resolver.ErrNoOperation, gc.Commentf("expected to get ErrNoOperation when a RunHook operation is pending"))
+}
+
 type mockRelationResolverSuite struct {
 	mockRelStTracker *mocks.MockRelationStateTracker
 	mockSupDestroyer *mocks.MockSubordinateDestroyer