Reduce the number of metrics exported to stackdriver.

buildSrc/src/main/groovy/com/google/firebase/gradle/plugins/ci/metrics/Metrics.java

@@ -14,7 +14,10 @@
 
 package com.google.firebase.gradle.plugins.ci.metrics;
 
+import java.util.function.Predicate;
 import org.gradle.api.Task;
+import org.gradle.api.logging.LogLevel;
+import org.gradle.api.logging.Logger;
 
 /** Provides methods for measuring various parts of the build. */
 interface Metrics {
@@ -23,4 +26,41 @@ interface Metrics {
 
   /** Measure task execution failure. */
   void measureFailure(Task task);
+
+  /**
+   * Creates a {@link Metrics} implementation that uses a {@code predicate} to determine whether to
+   * emit measurements for it.
+   */
+  static Metrics filtered(Metrics metrics, Predicate<Task> predicate) {
+    return new Metrics() {
+      @Override
+      public void measureSuccess(Task task, long elapsedTime) {
+        if (predicate.test(task)) {
+          metrics.measureSuccess(task, elapsedTime);
+        }
+      }
+
+      @Override
+      public void measureFailure(Task task) {
+        if (predicate.test(task)) {
+          metrics.measureFailure(task);
+        }
+      }
+    };
+  }
+
+  /** Creates a {@link Metrics} implementation that logs results at the specified level. */
+  static Metrics toLog(Logger toLogger, LogLevel level) {
+    return new Metrics() {
+      @Override
+      public void measureSuccess(Task task, long elapsedTime) {
+        toLogger.log(level, "[METRICS] Task {} took {}ms.", task.getPath(), elapsedTime);
+      }
+
+      @Override
+      public void measureFailure(Task task) {
+        toLogger.log(level, "[METRICS] Task {} failed.", task.getPath());
+      }
+    };
+  }
 }

buildSrc/src/main/groovy/com/google/firebase/gradle/plugins/ci/metrics/MetricsPlugin.java

@@ -16,26 +16,39 @@
 
 import org.gradle.api.Plugin;
 import org.gradle.api.Project;
+import org.gradle.api.Task;
 import org.gradle.api.execution.TaskExecutionGraph;
+import org.gradle.api.logging.LogLevel;
 
 /** Instruments Gradle to measure latency and success rate of all executed tasks. */
 public class MetricsPlugin implements Plugin<Project> {
   @Override
   public void apply(Project project) {
-    if (!isCollectionEnabled()) {
-      project.getLogger().lifecycle("Metrics collection is disabled.");
-      return;
-    }
-    project.getLogger().lifecycle("Metrics collection is enabled.");
 
-    Metrics metrics = new StackdriverMetrics(project.getGradle(), project.getLogger());
+    Metrics metrics = Metrics.filtered(initializeMetrics(project), MetricsPlugin::isTaskPublic);
 
     TaskExecutionGraph taskGraph = project.getGradle().getTaskGraph();
     taskGraph.addTaskExecutionListener(new MeasuringTaskExecutionListener(metrics, taskGraph));
   }
 
+  private static Metrics initializeMetrics(Project project) {
+    if (!isCollectionEnabled()) {
+      project.getLogger().lifecycle("Metrics collection is disabled. Logging to stdout...");
+      return Metrics.toLog(project.getLogger(), LogLevel.LIFECYCLE);
+    }
+    project.getLogger().lifecycle("Metrics collection is enabled.");
+    return new StackdriverMetrics(project.getGradle(), project.getLogger());
+  }
+
   private static boolean isCollectionEnabled() {
     String enabled = System.getenv("FIREBASE_ENABLE_METRICS");
     return enabled != null && enabled.equals("1");
   }
+
+  /**
+   * Determines whether a given gradle {@link Task} is "public", e.g. visible with `gradle tasks`.
+   */
+  private static boolean isTaskPublic(Task task) {
+    return task.getGroup() != null;
+  }
 }