Add MinSdk annotation.

Bug: 177884215
Test: m modules-annotation-minsdk-soong
Change-Id: I8bf4d5c05450e8255daa2b291373ecf32775f8a8

java/com/android/modules/annotation/Android.bp

@@ -0,0 +1,28 @@
+/*
+ * Copyright (C) 2021 The Android Open Source Project
+ *
+ * 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.
+ */
+
+java_library {
+    name: "modules-annotation-minsdk",
+    host_supported: true,
+    srcs: [
+        "MinSdk.java",
+    ],
+    sdk_version: "29",
+    visibility: ["//visibility:public"],
+    apex_available: [
+        "//apex_available:anyapex",
+    ],
+}

java/com/android/modules/annotation/MinSdk.java

@@ -0,0 +1,57 @@
+/*
+ * Copyright (C) 2021 The Android Open Source Project
+ *
+ * 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.android.modules.annotation;
+
+import static java.lang.annotation.ElementType.CONSTRUCTOR;
+import static java.lang.annotation.ElementType.FIELD;
+import static java.lang.annotation.ElementType.METHOD;
+import static java.lang.annotation.ElementType.TYPE;
+import static java.lang.annotation.RetentionPolicy.CLASS;
+
+import java.lang.annotation.Repeatable;
+import java.lang.annotation.Retention;
+import java.lang.annotation.Target;
+
+/**
+ * Indicates than an API is only supported on platform versions of at least the given value and
+ * later.
+ *
+ * Currently, this annotations is purely informational. The exact meaning of this annotation depends
+ * on it's context:
+ * <ul>
+ *     <li>On a public SDK method, it means that the member should only be included in the SDK of
+ *     the given version or later</li>
+ *     <li>On a module API, it will mean that it should only be called when running on a device with
+ *     the given SDK or later</li>
+ * </ul>
+ *
+ * In future, the annotation will acquire further semantics:
+ * <ul>
+ *     <li>Classes annotated with this will only be classloaded on devices running the given SDK
+ *     version or later.</li>
+ *     <li>It will be used to ensure API safety at build time in the context of a codebase with
+ *     different parts having different min SDK versions.</li>
+ * </ul>
+ *
+ * This annotation should only be used on code that exports an API (either public SDK or
+ * {@code @SystemApi}. For code that just calls APIs that only exist on newer platform versions
+ * use {@code androidx.annotation.RequiresApi} instead.
+ */
+@Retention(CLASS)
+@Target({CONSTRUCTOR, METHOD, FIELD, TYPE})
+public @interface MinSdk {
+    int value();
+}