Suppress emitting errors about unprocessed elements when there are already errors in the processing round. The extra errors don't add any information and end up hiding the real errors.

I found this substantially reduced the issue highlighted in b/141176717.

RELNOTES=Suppress error noise in `com.google.auto.common.BasicAnnotationProcessor`

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=270454309

2 files changed, 55 insertions, 2 deletions

diff --git a/common/src/main/java/com/google/auto/common/BasicAnnotationProcessor.java b/common/src/main/java/com/google/auto/common/BasicAnnotationProcessor.java
index 2d9c1199..8de3b817 100644
--- a/common/src/main/java/com/google/auto/common/BasicAnnotationProcessor.java
+++ b/common/src/main/java/com/google/auto/common/BasicAnnotationProcessor.java
@@ -171,10 +171,14 @@ public abstract class BasicAnnotationProcessor extends AbstractProcessor {
 
     deferredElementNames.clear();
 
-    // If this is the last round, report all of the missing elements
+    // If this is the last round, report all of the missing elements if there
+    // were no errors raised in the round; otherwise reporting the missing
+    // elements just adds noise the output.
     if (roundEnv.processingOver()) {
       postRound(roundEnv);
-      reportMissingElements(deferredElements, elementsDeferredBySteps.values());
+      if (!roundEnv.errorRaised()) {
+        reportMissingElements(deferredElements, elementsDeferredBySteps.values());
+      }
       return false;
     }
 
diff --git a/common/src/test/java/com/google/auto/common/BasicAnnotationProcessorTest.java b/common/src/test/java/com/google/auto/common/BasicAnnotationProcessorTest.java
index 0cf1075d..59a135c4 100644
--- a/common/src/test/java/com/google/auto/common/BasicAnnotationProcessorTest.java
+++ b/common/src/test/java/com/google/auto/common/BasicAnnotationProcessorTest.java
@@ -20,6 +20,7 @@ import static com.google.common.truth.Truth.assertAbout;
 import static com.google.common.truth.Truth.assertThat;
 import static com.google.testing.compile.JavaSourceSubjectFactory.javaSource;
 import static com.google.testing.compile.JavaSourcesSubjectFactory.javaSources;
+import static javax.tools.Diagnostic.Kind.ERROR;
 import static javax.tools.StandardLocation.SOURCE_OUTPUT;
 
 import com.google.common.collect.ImmutableList;
@@ -166,6 +167,37 @@ public class BasicAnnotationProcessorTest {
     }
   }
 
+  /** An annotation which causes an annotation processing error. */
+  public @interface CauseError {}
+
+  /** Report an error for any class annotated. */
+  public static class CauseErrorProcessor extends BasicAnnotationProcessor {
+    @Override
+    public SourceVersion getSupportedSourceVersion() {
+      return SourceVersion.latestSupported();
+    }
+
+    @Override
+    protected Iterable<? extends ProcessingStep> initSteps() {
+      return ImmutableSet.of(
+          new ProcessingStep() {
+            @Override
+            public Set<Element> process(
+                SetMultimap<Class<? extends Annotation>, Element> elementsByAnnotation) {
+              for (Element e : elementsByAnnotation.values()) {
+                processingEnv.getMessager().printMessage(ERROR, "purposeful error", e);
+              }
+              return ImmutableSet.copyOf(elementsByAnnotation.values());
+            }
+
+            @Override
+            public Set<? extends Class<? extends Annotation>> annotations() {
+              return ImmutableSet.of(CauseError.class);
+            }
+          });
+    }
+  }
+
   @Test public void properlyDefersProcessing_typeElement() {
     JavaFileObject classAFileObject = JavaFileObjects.forSourceLines("test.ClassA",
         "package test;",
@@ -329,6 +361,23 @@ public class BasicAnnotationProcessorTest {
         .in(classAFileObject).onLine(4);
   }
 
+  @Test
+  public void reportsMissingTypeSuppressedWhenOtherErrors() {
+    JavaFileObject classAFileObject =
+        JavaFileObjects.forSourceLines(
+            "test.ClassA",
+            "package test;",
+            "",
+            "@" + CauseError.class.getCanonicalName(),
+            "public class ClassA {}");
+    assertAbout(javaSources())
+        .that(ImmutableList.of(classAFileObject))
+        .processedWith(new CauseErrorProcessor())
+        .failsToCompile()
+        .withErrorCount(1)
+        .withErrorContaining("purposeful");
+  }
+
   private static void generateClass(Filer filer, String generatedClassName) {
     PrintWriter writer = null;
     try {