Don't crash processing classes in the default packages

Fixes https://github.com/google/auto/issues/745

RELNOTES=n/a

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=262160859

4 files changed, 63 insertions, 1 deletions

diff --git a/factory/src/main/java/com/google/auto/factory/processor/FactoryWriter.java b/factory/src/main/java/com/google/auto/factory/processor/FactoryWriter.java
index 8037a831..e084eb0e 100644
--- a/factory/src/main/java/com/google/auto/factory/processor/FactoryWriter.java
+++ b/factory/src/main/java/com/google/auto/factory/processor/FactoryWriter.java
@@ -257,7 +257,7 @@ final class FactoryWriter {
 
   private static String getPackage(CharSequence fullyQualifiedName) {
     int lastDot = lastIndexOf(fullyQualifiedName, '.');
-    return fullyQualifiedName.subSequence(0, lastDot).toString();
+    return lastDot == -1 ? "" : fullyQualifiedName.subSequence(0, lastDot).toString();
   }
 
   private static int lastIndexOf(CharSequence charSequence, char c) {
diff --git a/factory/src/test/java/com/google/auto/factory/processor/AutoFactoryProcessorTest.java b/factory/src/test/java/com/google/auto/factory/processor/AutoFactoryProcessorTest.java
index 671ddd3f..853be12c 100644
--- a/factory/src/test/java/com/google/auto/factory/processor/AutoFactoryProcessorTest.java
+++ b/factory/src/test/java/com/google/auto/factory/processor/AutoFactoryProcessorTest.java
@@ -433,6 +433,17 @@ public class AutoFactoryProcessorTest {
         .generatesSources(loadExpectedFile("expected/OnlyPrimitivesFactory.java"));
   }
 
+  @Test
+  public void defaultPackage() {
+    JavaFileObject file = JavaFileObjects.forResource("good/DefaultPackage.java");
+    assertAbout(javaSource())
+        .that(file)
+        .processedWith(new AutoFactoryProcessor())
+        .compilesWithoutError()
+        .and()
+        .generatesSources(loadExpectedFile("expected/DefaultPackageFactory.java"));
+  }
+
   private JavaFileObject loadExpectedFile(String resourceName) {
     try {
       List<String> sourceLines = Resources.readLines(Resources.getResource(resourceName), UTF_8);
diff --git a/factory/src/test/resources/expected/DefaultPackageFactory.java b/factory/src/test/resources/expected/DefaultPackageFactory.java
new file mode 100644
index 00000000..d1d4cc85
--- /dev/null
+++ b/factory/src/test/resources/expected/DefaultPackageFactory.java
@@ -0,0 +1,31 @@
+/*
+ * Copyright 2019 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import javax.annotation.processing.Generated;
+import javax.inject.Inject;
+
+@Generated(
+    value = "com.google.auto.factory.processor.AutoFactoryProcessor",
+    comments = "https://github.com/google/auto/tree/master/factory"
+    )
+public final class DefaultPackageFactory {
+  @Inject
+  public DefaultPackageFactory() {}
+
+  public DefaultPackage create() {
+    return new DefaultPackage();
+  }
+}
diff --git a/factory/src/test/resources/good/DefaultPackage.java b/factory/src/test/resources/good/DefaultPackage.java
new file mode 100644
index 00000000..f4efee68
--- /dev/null
+++ b/factory/src/test/resources/good/DefaultPackage.java
@@ -0,0 +1,20 @@
+/*
+ * Copyright 2019 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import com.google.auto.factory.AutoFactory;
+
+@AutoFactory
+public final class DefaultPackage {}