core, xds: Populate explicit attempt delay annotations in initial pickers (Proposal A121)

Author: AgraVator

core/src/main/java/io/grpc/internal/PickFirstLeafLoadBalancer.java

@@ -447,8 +447,9 @@ private void updateHealthCheckedState(SubchannelData subchannelData) {
       updateBalancingState(TRANSIENT_FAILURE, new FixedResultPicker(PickResult.withError(
           subchannelData.healthStateInfo.getStatus())));
     } else if (concludedState != TRANSIENT_FAILURE) {
-      updateBalancingState(subchannelData.getHealthState(),
-          new FixedResultPicker(PickResult.withNoResult()));
+      updateBalancingState(subchannelData.getHealthState(), new FixedResultPicker(
+          PickResult.withNoResult("connecting",
+              "health check state: " + subchannelData.getHealthState())));
     }
   }
 

core/src/test/java/io/grpc/internal/PickFirstLeafLoadBalancerTest.java

@@ -1439,6 +1439,9 @@ public void updateAddresses_disjoint_ready_twice() {
     inOrder.verify(mockSubchannel3).requestConnection();
     stateListener3.onSubchannelState(ConnectivityStateInfo.forNonError(CONNECTING));
     inOrder.verify(mockHelper).updateBalancingState(eq(CONNECTING), pickerCaptor.capture());
+    PickResult connectingPick = pickerCaptor.getValue().pickSubchannel(mockArgs);
+    assertEquals("connecting", connectingPick.getDelayType());
+    assertEquals("pick_first: attempting to connect", connectingPick.getDelayReason());
 
     if (enableHappyEyeballs) {
       forwardTimeByConnectionDelay();

xds/src/main/java/io/grpc/xds/PriorityLoadBalancer.java

@@ -225,7 +225,8 @@ private final class ChildLbState {
     // deactivated.
     @Nullable ScheduledHandle deletionTimer;
     ConnectivityState connectivityState = CONNECTING;
-    SubchannelPicker picker = new FixedResultPicker(PickResult.withNoResult());
+    SubchannelPicker picker = new FixedResultPicker(
+        PickResult.withNoResult("connecting", "priority child state uninitialized"));
 
     ChildLbState(final String priority, boolean ignoreReresolution) {
       this.priority = priority;

xds/src/test/java/io/grpc/xds/PriorityLoadBalancerTest.java

@@ -1095,6 +1095,28 @@ public PickResult pickSubchannel(PickSubchannelArgs args) {
         "waiting on priority group p0 (waiting on priority group p1 (child_reason))");
   }
 
+  @Test
+  public void initialChildPicker_returnsAnnotatedDelayAttributes() throws Exception {
+    PriorityChildConfig priorityChildConfig0 =
+        new PriorityChildConfig(newChildConfig(fooLbProvider, new Object()), true);
+    PriorityLbConfig priorityLbConfig =
+        new PriorityLbConfig(ImmutableMap.of("p0", priorityChildConfig0), ImmutableList.of("p0"));
+    priorityLb.acceptResolvedAddresses(
+        ResolvedAddresses.newBuilder()
+            .setAddresses(ImmutableList.<EquivalentAddressGroup>of())
+            .setLoadBalancingPolicyConfig(priorityLbConfig)
+            .build());
+
+    verify(helper, atLeastOnce())
+        .updateBalancingState(eq(CONNECTING), pickerCaptor.capture());
+    SubchannelPicker initialPicker = pickerCaptor.getAllValues().get(0);
+    PickResult result = initialPicker.pickSubchannel(mock(PickSubchannelArgs.class));
+
+    assertThat(result.getDelayType()).isEqualTo("connecting");
+    assertThat(result.getDelayReason()).isEqualTo(
+        "priority child state uninitialized");
+  }
+
   private void assertLatestConnectivityState(ConnectivityState expectedState) {
     verify(helper, atLeastOnce())
         .updateBalancingState(connectivityStateCaptor.capture(), pickerCaptor.capture());