core: remember last pick status in no real stream

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

@@ -129,8 +129,9 @@ public final ClientStream newStream(
         if (state.shutdownStatus != null) {
           return new FailingClientStream(state.shutdownStatus, tracers);
         }
+        PickResult pickResult = null;
         if (state.lastPicker != null) {
-          PickResult pickResult = state.lastPicker.pickSubchannel(args);
+          pickResult = state.lastPicker.pickSubchannel(args);
           callOptions = args.getCallOptions();
           // User code provided authority takes precedence over the LB provided one.
           if (callOptions.getAuthority() == null
@@ -156,7 +157,7 @@ public final ClientStream newStream(
         synchronized (lock) {
           PickerState newerState = pickerState;
           if (state == newerState) {
-            return createPendingStream(args, tracers);
+            return createPendingStream(args, tracers, pickResult);
           }
           state = newerState;
         }
@@ -171,9 +172,12 @@ public final ClientStream newStream(
    * schedule tasks on syncContext.
    */
   @GuardedBy("lock")
-  private PendingStream createPendingStream(
-      PickSubchannelArgs args, ClientStreamTracer[] tracers) {
+  private PendingStream createPendingStream(PickSubchannelArgs args, ClientStreamTracer[] tracers,
+      PickResult pickResult) {
     PendingStream pendingStream = new PendingStream(args, tracers);
+    if (args.getCallOptions().isWaitForReady() && pickResult != null && pickResult.hasResult()) {
+      pendingStream.lastPickStatus = pickResult.getStatus();
+    }
     pendingStreams.add(pendingStream);
     if (getPendingStreamsCount() == 1) {
       syncContext.executeLater(reportTransportInUse);
@@ -293,6 +297,9 @@ final void reprocess(@Nullable SubchannelPicker picker) {
     for (final PendingStream stream : toProcess) {
       PickResult pickResult = picker.pickSubchannel(stream.args);
       CallOptions callOptions = stream.args.getCallOptions();
+      if (callOptions.isWaitForReady() && pickResult.hasResult()) {
+        stream.lastPickStatus = pickResult.getStatus();
+      }
       final ClientTransport transport = GrpcUtil.getTransportFromPickResult(pickResult,
           callOptions.isWaitForReady());
       if (transport != null) {
@@ -349,6 +356,7 @@ private class PendingStream extends DelayedStream {
     private final PickSubchannelArgs args;
     private final Context context = Context.current();
     private final ClientStreamTracer[] tracers;
+    private volatile Status lastPickStatus;
 
     private PendingStream(PickSubchannelArgs args, ClientStreamTracer[] tracers) {
       this.args = args;
@@ -405,6 +413,10 @@ protected void onEarlyCancellation(Status reason) {
     public void appendTimeoutInsight(InsightBuilder insight) {
       if (args.getCallOptions().isWaitForReady()) {
         insight.append("wait_for_ready");
+        Status status = lastPickStatus;
+        if (status != null && !status.isOk()) {
+          insight.appendKeyValue("Last Pick Failure", status);
+        }
       }
       super.appendTimeoutInsight(insight);
     }

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

@@ -745,6 +745,23 @@ public void pendingStream_appendTimeoutInsight_waitForReady() {
         .matches("\\[wait_for_ready, buffered_nanos=[0-9]+\\, waiting_for_connection]");
   }
 
+  @Test
+  public void pendingStream_appendTimeoutInsight_waitForReady_withLastPickFailure() {
+    ClientStream stream = delayedTransport.newStream(
+        method, headers, callOptions.withWaitForReady(), tracers);
+    stream.start(streamListener);
+    SubchannelPicker picker = mock(SubchannelPicker.class);
+    when(picker.pickSubchannel(any(PickSubchannelArgs.class)))
+        .thenReturn(PickResult.withError(Status.PERMISSION_DENIED));
+    delayedTransport.reprocess(picker);
+    InsightBuilder insight = new InsightBuilder();
+    stream.appendTimeoutInsight(insight);
+    assertThat(insight.toString())
+        .matches("\\[wait_for_ready, "
+            + "Last Pick Failure=Status\\{code=PERMISSION_DENIED, description=null, cause=null\\},"
+            + " buffered_nanos=[0-9]+, waiting_for_connection]");
+  }
+
   private static TransportProvider newTransportProvider(final ClientTransport transport) {
     return new TransportProvider() {
       @Override