Don't run RootProcessingStep#postProcess if no root element was detec…

…ted.

RELNOTES=n/a
PiperOrigin-RevId: 560887928

java/dagger/hilt/processor/internal/root/RootProcessingStep.java

@@ -57,6 +57,9 @@
 public final class RootProcessingStep extends BaseProcessingStep {
 
   private boolean processed;
+  // TODO(b/297889547) do not run preProcess and postProcess if supported annotation isn't present
+  // in the environment.
+  private boolean hasElementsToProcess = false;
   private GeneratesRootInputs generatesRootInputs;
 
   public RootProcessingStep(XProcessingEnv env) {
@@ -75,6 +78,7 @@ protected ImmutableSet<ClassName> annotationClassNames() {
 
   @Override
   public void processEach(ClassName annotation, XElement element) throws Exception {
+    hasElementsToProcess = true;
     XTypeElement rootElement = XElements.asTypeElement(element);
     // TODO(bcorso): Move this logic into a separate isolating processor to avoid regenerating it
     // for unrelated changes in Gradle.
@@ -93,6 +97,9 @@ rootElement, originatingRootElement, processingEnv().requireTypeElement(annotati
 
   @Override
   protected void postProcess(XProcessingEnv env, XRoundEnv roundEnv) throws Exception {
+    if (!hasElementsToProcess) {
+      return;
+    }
     if (!useAggregatingRootProcessor(processingEnv())) {
       return;
     }