Reduce the number of metrics exported to stackdriver. (#311)

The change only exports metrics for "public" gradle tasks. The reason
for doing this is that we are hitting maximim quota limit of active
timeseries, which causes failure to upload metrics.

Author: vkryachko

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;
+  }
 }