Add an option for the number of actions shown in the experimental UI

Currently, the experimental UI always shows the 3 oldest, still running actions.
While this seems a reasonable default, some users requested to be able to change
the number of actions shown. Hence replace the hard-coded value by a flag.

While there, also fix an off-by-one error in deciding when to put the ellipsis
symbol.

--
Change-Id: I037d208360fa1d3f100c99ab1ab1f5fc140138ac
Reviewed-on: https://bazel-review.googlesource.com/#/c/3811
MOS_MIGRATED_REVID=125427168

4 files changed, 56 insertions, 3 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/runtime/BlazeCommandEventHandler.java b/src/main/java/com/google/devtools/build/lib/runtime/BlazeCommandEventHandler.java
index 635a4561a0..85fb3fa45c 100644
--- a/src/main/java/com/google/devtools/build/lib/runtime/BlazeCommandEventHandler.java
+++ b/src/main/java/com/google/devtools/build/lib/runtime/BlazeCommandEventHandler.java
@@ -157,6 +157,13 @@ public class BlazeCommandEventHandler implements EventHandler {
     )
     public boolean experimentalUiDebugAllEvents;
 
+    @Option(
+      name = "experimental_ui_actions_shown",
+      defaultValue = "3",
+      category = "hidden",
+      help = "Number of concurrent actions shown in the experimental new Bazel UI."
+    )
+    public int experimentalUiActionsShown;
 
     public boolean useColor() {
       return useColorEnum == UseColor.YES || (useColorEnum == UseColor.AUTO && isATty);
diff --git a/src/main/java/com/google/devtools/build/lib/runtime/ExperimentalEventHandler.java b/src/main/java/com/google/devtools/build/lib/runtime/ExperimentalEventHandler.java
index 6ad3e531d0..2605cc277b 100644
--- a/src/main/java/com/google/devtools/build/lib/runtime/ExperimentalEventHandler.java
+++ b/src/main/java/com/google/devtools/build/lib/runtime/ExperimentalEventHandler.java
@@ -94,6 +94,7 @@ public class ExperimentalEventHandler extends BlazeCommandEventHandler {
         this.cursorControl
             ? new ExperimentalStateTracker(clock, this.terminalWidth - 2)
             : new ExperimentalStateTracker(clock);
+    this.stateTracker.setSampleSize(options.experimentalUiActionsShown);
     this.numLinesProgressBar = 0;
     this.minimalDelayMillis = Math.round(options.showProgressRateLimit * 1000);
     this.minimalUpdateInterval = Math.max(this.minimalDelayMillis, MAXIMAL_UPDATE_DELAY_MILLIS);
diff --git a/src/main/java/com/google/devtools/build/lib/runtime/ExperimentalStateTracker.java b/src/main/java/com/google/devtools/build/lib/runtime/ExperimentalStateTracker.java
index f5fb46d1bb..5343bfa19e 100644
--- a/src/main/java/com/google/devtools/build/lib/runtime/ExperimentalStateTracker.java
+++ b/src/main/java/com/google/devtools/build/lib/runtime/ExperimentalStateTracker.java
@@ -48,12 +48,13 @@ import java.util.TreeSet;
  */
 class ExperimentalStateTracker {
 
-  static final int SAMPLE_SIZE = 3;
   static final long SHOW_TIME_THRESHOLD_SECONDS = 3;
   static final String ELLIPSIS = "...";
 
   static final int NANOS_PER_SECOND = 1000000000;
 
+  private int sampleSize = 3;
+
   private String status;
   private String additionalMessage;
 
@@ -101,6 +102,13 @@ class ExperimentalStateTracker {
     this(clock, 0);
   }
 
+  /**
+   * Set the maximal number of actions shown in the progress bar.
+   */
+  void setSampleSize(int sampleSize) {
+    this.sampleSize = sampleSize;
+  }
+
   void buildStarted(BuildStartingEvent event) {
     status = "Loading";
     additionalMessage = "";
@@ -368,10 +376,11 @@ class ExperimentalStateTracker {
         continue;
       }
       count++;
-      if (count > SAMPLE_SIZE) {
+      if (count > sampleSize) {
+        totalCount--;
         break;
       }
-      int width = (count >= SAMPLE_SIZE && count < actionCount) ? targetWidth - 8 : targetWidth - 4;
+      int width = (count >= sampleSize && count < actionCount) ? targetWidth - 8 : targetWidth - 4;
       terminalWriter.newline().append("    " + describeAction(action, nanoTime, width, toSkip));
     }
     if (totalCount < actionCount) {
diff --git a/src/test/java/com/google/devtools/build/lib/runtime/ExperimentalStateTrackerTest.java b/src/test/java/com/google/devtools/build/lib/runtime/ExperimentalStateTrackerTest.java
index ead2c53e46..da25a610b9 100644
--- a/src/test/java/com/google/devtools/build/lib/runtime/ExperimentalStateTrackerTest.java
+++ b/src/test/java/com/google/devtools/build/lib/runtime/ExperimentalStateTrackerTest.java
@@ -199,6 +199,42 @@ public class ExperimentalStateTrackerTest extends FoundationTestCase {
   }
 
   @Test
+  public void testSampleSize() throws IOException {
+    // Verify that the number of actions shown in the progress bar can be set as sample size.
+    ManualClock clock = new ManualClock();
+    clock.advanceMillis(TimeUnit.SECONDS.toMillis(123));
+    ExperimentalStateTracker stateTracker = new ExperimentalStateTracker(clock);
+    clock.advanceMillis(TimeUnit.SECONDS.toMillis(2));
+
+    // Start 10 actions (numbered 0 to 9).
+    for (int i = 0; i < 10; i++) {
+      clock.advanceMillis(TimeUnit.SECONDS.toMillis(1));
+      Action action = mockAction("Performing action A" + i + ".", "action_A" + i + ".out");
+      stateTracker.actionStarted(new ActionStartedEvent(action, clock.nanoTime()));
+    }
+
+    // For various sample sizes verify the progress bar
+    for (int i = 1; i < 11; i++) {
+      stateTracker.setSampleSize(i);
+      LoggingTerminalWriter terminalWriter = new LoggingTerminalWriter(/*discardHighlight=*/ true);
+      stateTracker.writeProgressBar(terminalWriter);
+      String output = terminalWriter.getTranscript();
+      assertTrue(
+          "Action " + (i - 1) + " should still be shown in the output: '" + output,
+          output.contains("A" + (i - 1) + "."));
+      assertFalse(
+          "Action " + i + " should not be shown in the output: " + output,
+          output.contains("A" + i + "."));
+      if (i < 10) {
+        assertTrue("Ellipsis symbol should be shown in output: " + output, output.contains("..."));
+      } else {
+        assertFalse(
+            "Ellipsis symbol should not be shown in output: " + output, output.contains("..."));
+      }
+    }
+  }
+
+  @Test
   public void testTimesShown() throws IOException {
     // For sufficiently long running actions, the time that has passed since their start is shown.
     // In the short version of the progress bar, this should be true at least for the oldest action.