Allow sources to be empty with annotation processing enabled

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=289711077

2 files changed, 37 insertions, 1 deletions

diff --git a/java/com/google/turbine/binder/Binder.java b/java/com/google/turbine/binder/Binder.java
index 76cbd99..e779748 100644
--- a/java/com/google/turbine/binder/Binder.java
+++ b/java/com/google/turbine/binder/Binder.java
@@ -97,7 +97,7 @@ public class Binder {
             classpath,
             bootclasspath,
             moduleVersion);
-    if (!processorInfo.processors().isEmpty()) {
+    if (!processorInfo.processors().isEmpty() && !units.isEmpty()) {
       br =
           Processing.process(
               log, units, classpath, processorInfo, bootclasspath, br, moduleVersion);
diff --git a/javatests/com/google/turbine/main/MainTest.java b/javatests/com/google/turbine/main/MainTest.java
index be38d97..ea6f9a8 100644
--- a/javatests/com/google/turbine/main/MainTest.java
+++ b/javatests/com/google/turbine/main/MainTest.java
@@ -54,6 +54,7 @@ import java.util.jar.JarOutputStream;
 import java.util.jar.Manifest;
 import java.util.stream.Stream;
 import javax.annotation.processing.AbstractProcessor;
+import javax.annotation.processing.ProcessingEnvironment;
 import javax.annotation.processing.RoundEnvironment;
 import javax.annotation.processing.SupportedAnnotationTypes;
 import javax.lang.model.SourceVersion;
@@ -365,4 +366,39 @@ public class MainTest {
     }
     return manifest.build();
   }
+
+  @SupportedAnnotationTypes("*")
+  public static class CrashyProcessor extends AbstractProcessor {
+
+    @Override
+    public SourceVersion getSupportedSourceVersion() {
+      return SourceVersion.latestSupported();
+    }
+
+    @Override
+    public synchronized void init(ProcessingEnvironment processingEnv) {
+      throw new AssertionError();
+    }
+
+    @Override
+    public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {
+      return false;
+    }
+  }
+
+  @Test
+  public void noSourcesProcessing() throws IOException {
+    // Compilations with no sources shouldn't initialize annotation processors.
+    File gensrc = temporaryFolder.newFile("gensrc.jar");
+    Main.compile(
+        optionsWithBootclasspath()
+            .setProcessors(ImmutableList.of(CrashyProcessor.class.getName()))
+            .setGensrcOutput(gensrc.toString())
+            .build());
+    try (JarFile jarFile = new JarFile(gensrc);
+        Stream<JarEntry> entries = jarFile.stream()) {
+      assertThat(entries.map(JarEntry::getName))
+          .containsExactly("META-INF/", "META-INF/MANIFEST.MF");
+    }
+  }
 }