Two performance fixes without which the build takes minutes in the configuration phase for multi-module projects with a lot of cross-references.

1. Loads the plugin just one time, instead of loading separately for each module. Debug logging showed that sometimes, this operations takes 10 sec (on some machines at least).

2. The more critical issue was in `recursiveDependenciesOf`. Without caching of the results, the same operations are repeated over and over again and it takes minutes to configure.

For a work project I have, with 16 modules, with a lot of cross-references, adding the scoverage plugin without these fixes takes 5-10 mins. The worst of it is that this is the wait time for each change in any build.gradle (e.g. adding a new dependency), which makes the work nearly impossible. After applying the fixes, there is no significant difference with the time taken without the scoverage plugin.

Author: tpetrov-rms

src/main/groovy/org/scoverage/ScoveragePlugin.groovy

@@ -10,6 +10,7 @@ import org.gradle.api.tasks.SourceSet
 import org.gradle.api.tasks.scala.ScalaCompile
 
 import java.nio.file.Files
+import java.util.concurrent.ConcurrentHashMap
 
 import static groovy.io.FileType.FILES
 
@@ -23,6 +24,9 @@ class ScoveragePlugin implements Plugin<PluginAware> {
 
     static final String DEFAULT_REPORT_DIR = 'reports' + File.separatorChar + 'scoverage'
 
+    private volatile File pluginFile = null
+    private ConcurrentHashMap<Task, Set<? extends Task>> taskDependencies = new ConcurrentHashMap<>();
+
     @Override
     void apply(PluginAware pluginAware) {
         if (pluginAware instanceof Project) {
@@ -174,9 +178,12 @@ class ScoveragePlugin implements Plugin<PluginAware> {
             }
 
             compileTask.configure {
-                File pluginFile = project.configurations[CONFIGURATION_NAME].find {
-                    it.name.startsWith("scalac-scoverage-plugin")
+                if (pluginFile == null) {
+                    pluginFile = project.configurations[CONFIGURATION_NAME].find {
+                        it.name.startsWith("scalac-scoverage-plugin")
+                    }
                 }
+
                 List<String> parameters = ['-Xplugin:' + pluginFile.absolutePath]
                 List<String> existingParameters = scalaCompileOptions.additionalParameters
                 if (existingParameters) {
@@ -269,9 +276,15 @@ class ScoveragePlugin implements Plugin<PluginAware> {
     }
 
     private Set<? extends Task> recursiveDependenciesOf(Task task) {
+        if (!taskDependencies.containsKey(task)) {
+            def directDependencies = task.getTaskDependencies().getDependencies(task)
+            def nestedDependencies = directDependencies.collect {recursiveDependenciesOf(it) }.flatten()
+            def dependencies = directDependencies + nestedDependencies
 
-        def directDependencies = task.getTaskDependencies().getDependencies(task)
-        def nestedDependencies = directDependencies.collect {recursiveDependenciesOf(it) }.flatten()
-        return directDependencies + nestedDependencies
+            taskDependencies.put(task, dependencies)
+            return dependencies
+        } else {
+            return taskDependencies.get(task)
+        }
     }
 }