Don't run the builder if there's no dirty files

jps-plugin/src/org/jetbrains/jet/jps/build/KotlinBuilder.java

@@ -72,8 +72,11 @@ public class KotlinBuilder extends ModuleLevelBuilder {
         ModuleBuildTarget representativeTarget = chunk.representativeTarget();
 
         // For non-incremental build: take all sources
+        if (!KotlinSourceFileCollector.hasDirtyFiles(dirtyFilesHolder)) {
+            return ExitCode.NOTHING_DONE;
+        }
         List<File> sourceFiles = KotlinSourceFileCollector.getAllKotlinSourceFiles(representativeTarget);
-        //List<File> sourceFiles = getDirtySourceFiles(dirtyFilesHolder);
+        //List<File> sourceFiles = KotlinSourceFileCollector.getDirtySourceFiles(dirtyFilesHolder);
 
         if (sourceFiles.isEmpty()) {
             return ExitCode.NOTHING_DONE;

jps-plugin/src/org/jetbrains/jet/jps/build/KotlinSourceFileCollector.java

@@ -16,6 +16,7 @@
 
 package org.jetbrains.jet.jps.build;
 
+import com.intellij.openapi.util.Ref;
 import com.intellij.openapi.util.io.FileUtil;
 import com.intellij.util.Processor;
 import com.intellij.util.containers.ContainerUtil;
@@ -50,6 +51,21 @@ public class KotlinSourceFileCollector {
         return sourceFiles;
     }
 
+    // For incremental compilation
+    public static boolean hasDirtyFiles(DirtyFilesHolder<JavaSourceRootDescriptor, ModuleBuildTarget> dirtyFilesHolder)
+            throws IOException {
+        final Ref<Boolean> result = Ref.create(false);
+
+        dirtyFilesHolder.processDirtyFiles(new FileProcessor<JavaSourceRootDescriptor, ModuleBuildTarget>() {
+            @Override
+            public boolean apply(ModuleBuildTarget target, File file, JavaSourceRootDescriptor root) throws IOException {
+                result.set(true);
+                return false;
+            }
+        });
+        return result.get();
+    }
+
     @NotNull
     public static List<File> getAllKotlinSourceFiles(@NotNull ModuleBuildTarget target) {
         final List<File> result = ContainerUtil.newArrayList();