Add firebase-annotations module. (#2167)

* Add firebase-annotations module.

* Fix copyright

Author: vkryachko

firebase-annotations/firebase-annotations.gradle

@@ -0,0 +1,31 @@
+// Copyright 2020 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.
+
+plugins {
+    id 'firebase-java-library'
+}
+
+firebaseLibrary {
+    publishSources = true
+    publishJavadoc = false
+}
+
+java {
+    sourceCompatibility JavaVersion.VERSION_1_8
+    targetCompatibility JavaVersion.VERSION_1_8
+}
+
+tasks.withType(JavaCompile) {
+    options.compilerArgs << "-Werror"
+}

firebase-annotations/gradle.properties

@@ -0,0 +1,15 @@
+# Copyright 2020 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.
+
+version=16.0.0

firebase-annotations/src/main/java/com/google/firebase/annotations/DeferredApi.java

@@ -0,0 +1,32 @@
+// Copyright 2020 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.
+
+package com.google.firebase.annotations;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Inherited;
+import java.lang.annotation.Target;
+
+/**
+ * Indicates that the annotated symbol should be called from a {@code Deferred<T>} dependency.
+ *
+ * <p>This is particularly important for callback-style APIs in the context of <a
+ * href="https://developer.android.com/guide/app-bundle/play-feature-delivery">dynamically loaded
+ * modules</a>.
+ *
+ * @hide
+ */
+@Target({ElementType.METHOD, ElementType.CONSTRUCTOR})
+@Inherited
+public @interface DeferredApi {}

subprojects.cfg

@@ -1,4 +1,5 @@
 firebase-abt
+firebase-annotations
 firebase-common
 firebase-common:data-collection-tests
 firebase-common:ktx