IssueTracker

As stated in the title, artifact collection during the MergeResources task can take a very long time for sufficiently large dependency graphs.  At Square, we are experiencing several hour long execution times for a top level app module's `mergeDebugAndroidTestResources` task.  We hooked up a debugger and discovered that the time was spent continually crawling the dependency graph during artifact collection.  We believe this was a regression introduced when converting the AGP code from Java to Kotlin (around versions 3.0.0-beta6 -> 3.0.0) in which artifact collection would revisit already visited nodes.  In a dependency graph that has common modules shared across many modules this can be very expensive while we exhaustively crawl the entire graph.

Build Info:
Gradle version: 4.9
Android Plugin Version: 3.2.1
Module Compile Sdk Version: 27
Module Build Tools Version: 28.0.3
Android SDK Tools version: 26.1.1

Bad commit: https://android.googlesource.com/platform/tools/base/+/dee879d0da071dcf93bd244e29b63f5fbd9fb7d3

Bad line: https://android.googlesource.com/platform/tools/base/+/studio-master-dev/build-system/gradle-core/src/main/java/com/android/build/gradle/internal/dependency/AndroidTestResourceArtifactCollection.kt#144

Proposed change: The return value of adding the dependency to the keptComponents set should be used to determine if we've already visited this node.  If we have, we should not traverse the node's children again.

Suggested Patch:
     private fun collect(
         keptComponents: MutableSet<ComponentIdentifier>,
         item: ResolvedDependencyResult) {
-        keptComponents.add(item.selected.id)
-        for (dependency in item.selected.dependencies) {
-            collect(keptComponents, dependency as ResolvedDependencyResult)
+        if (keptComponents.add(item.selected.id)) {
+            for (dependency in item.selected.dependencies) {
+                collect(keptComponents, dependency as ResolvedDependencyResult)
+            }
         }
     }