feat(runway): use singular Change on MergeStep instead of repeated

api/runway/messagequeue/merge_test.go

@@ -33,12 +33,12 @@ func TestMergeRequestRoundTrip(t *testing.T) {
 		Steps: []*MergeStep{
 			{
 				StepId:   "queue-a/1",
-				Changes:  []*changepb.Change{{Uris: []string{"github://github.example.com/uber/repo/pull/1/0123456789abcdef0123456789abcdef01234567"}}},
+				Change:   &changepb.Change{Uris: []string{"github://github.example.com/uber/repo/pull/1/0123456789abcdef0123456789abcdef01234567"}},
 				Strategy: strategypb.Strategy_REBASE,
 			},
 			{
 				StepId:   "queue-a/2",
-				Changes:  []*changepb.Change{{Uris: []string{"github://github.example.com/uber/repo/pull/2/89abcdef0123456789abcdef0123456789abcdef"}}},
+				Change:   &changepb.Change{Uris: []string{"github://github.example.com/uber/repo/pull/2/89abcdef0123456789abcdef0123456789abcdef"}},
 				Strategy: strategypb.Strategy_MERGE,
 			},
 		},

api/runway/messagequeue/proto/merge.proto

@@ -25,19 +25,21 @@ option java_multiple_files = true;
 option java_outer_classname = "MergeProto";
 option java_package = "com.uber.submitqueue.runway.messagequeue";
 
-// MergeStep is one step of an ordered merge: a single set of change(s) applied
-// with a strategy. Runway applies the steps of a request in order on top of the
-// merge target; the ordering encodes the base-layering (earlier steps are the
-// in-flight base, the last step is the candidate).
+// MergeStep is one step of an ordered merge: a single change applied with a
+// strategy. Runway applies the steps of a request in order on top of the merge
+// target; the ordering encodes the base-layering (earlier steps are the
+// in-flight base, the last step is the candidate). A change may contain
+// multiple URIs (e.g. stacked PRs that land together).
 message MergeStep {
     // step_id is an opaque, caller-assigned identifier for this step. Runway
     // treats it as an attribution token only -- it echoes it back per-step in
     // StepResult so a multi-step result is attributable -- and never interprets
     // its contents.
     string step_id = 1;
-    // changes are the code change(s) to apply for this step.
-    repeated uber.base.change.Change changes = 2;
-    // strategy is how this step's changes are integrated into the merge target.
+    // change is the code change to apply for this step. A change may carry
+    // multiple URIs when the step represents stacked or grouped changes.
+    uber.base.change.Change change = 2;
+    // strategy is how this step's change is integrated into the merge target.
     uber.base.mergestrategy.Strategy strategy = 3;
 }
 

runway/extension/merger/noop/noop_test.go

@@ -33,12 +33,12 @@ func testRequest() *runwaymq.MergeRequest {
 		Steps: []*runwaymq.MergeStep{
 			{
 				StepId:   "queue-a/1",
-				Changes:  []*changepb.Change{{Uris: []string{"github://github.example.com/uber/repo/pull/1/abcdef0123456789abcdef0123456789abcdef01"}}},
+				Change:   &changepb.Change{Uris: []string{"github://github.example.com/uber/repo/pull/1/abcdef0123456789abcdef0123456789abcdef01"}},
 				Strategy: strategypb.Strategy_REBASE,
 			},
 			{
 				StepId:   "queue-a/2",
-				Changes:  []*changepb.Change{{Uris: []string{"github://github.example.com/uber/repo/pull/2/89abcdef0123456789abcdef0123456789abcdef"}}},
+				Change:   &changepb.Change{Uris: []string{"github://github.example.com/uber/repo/pull/2/89abcdef0123456789abcdef0123456789abcdef"}},
 				Strategy: strategypb.Strategy_MERGE,
 			},
 		},

submitqueue/orchestrator/controller/merge/merge.go

@@ -165,7 +165,7 @@ func (c *Controller) buildMergeRequest(ctx context.Context, batch entity.Batch)
 		}
 		steps = append(steps, &runwaymq.MergeStep{
 			StepId:   request.ID,
-			Changes:  []*changepb.Change{{Uris: request.Change.URIs}},
+			Change:   &changepb.Change{Uris: request.Change.URIs},
 			Strategy: toProtoStrategy(request.LandStrategy),
 		})
 	}

submitqueue/orchestrator/controller/merge/merge_test.go

@@ -146,12 +146,12 @@ func TestProcess_PublishesFullPayloadToRunway(t *testing.T) {
 	require.Len(t, got.Steps, 2)
 	// One step per member request, in Contains order, attributed by request id.
 	assert.Equal(t, req1.ID, got.Steps[0].StepId)
-	require.Len(t, got.Steps[0].Changes, 1)
-	assert.Equal(t, req1.Change.URIs, got.Steps[0].Changes[0].Uris)
+	require.NotNil(t, got.Steps[0].Change)
+	assert.Equal(t, req1.Change.URIs, got.Steps[0].Change.Uris)
 	assert.Equal(t, strategypb.Strategy_SQUASH_REBASE, got.Steps[0].Strategy)
 	assert.Equal(t, req2.ID, got.Steps[1].StepId)
-	require.Len(t, got.Steps[1].Changes, 1)
-	assert.Equal(t, req2.Change.URIs, got.Steps[1].Changes[0].Uris)
+	require.NotNil(t, got.Steps[1].Change)
+	assert.Equal(t, req2.Change.URIs, got.Steps[1].Change.Uris)
 	assert.Equal(t, strategypb.Strategy_REBASE, got.Steps[1].Strategy)
 }
 

submitqueue/orchestrator/controller/validate/validate.go

@@ -200,7 +200,7 @@ func (c *Controller) Process(ctx context.Context, delivery consumer.Delivery) er
 		Steps: []*runwaymq.MergeStep{
 			{
 				StepId:   request.ID,
-				Changes:  []*changepb.Change{{Uris: request.Change.URIs}},
+				Change:   &changepb.Change{Uris: request.Change.URIs},
 				Strategy: toProtoStrategy(request.LandStrategy),
 			},
 		},

submitqueue/orchestrator/controller/validate/validate_test.go

@@ -220,8 +220,8 @@ func TestController_Process_PublishesCheckToRunway(t *testing.T) {
 	assert.Equal(t, request.Queue, got.QueueName)
 	require.Len(t, got.Steps, 1)
 	assert.Equal(t, request.ID, got.Steps[0].StepId)
-	require.Len(t, got.Steps[0].Changes, 1)
-	assert.Equal(t, request.Change.URIs, got.Steps[0].Changes[0].Uris)
+	require.NotNil(t, got.Steps[0].Change)
+	assert.Equal(t, request.Change.URIs, got.Steps[0].Change.Uris)
 	assert.Equal(t, strategypb.Strategy_REBASE, got.Steps[0].Strategy)
 }