Create @SkylarkGlobalLibrary annotation, allowing classes/interfaces with global skylark functions to use @SkylarkCallable instead of @SkylarkSignature.

Also migrate skylark's global "rule" function to @SkylarkCallable, thus demonstrating the new feature.

RELNOTES: None.
PiperOrigin-RevId: 193085313

2 files changed, 35 insertions, 1 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/skylarkinterface/SkylarkGlobalLibrary.java b/src/main/java/com/google/devtools/build/lib/skylarkinterface/SkylarkGlobalLibrary.java
new file mode 100644
index 0000000000..1ee6388394
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/skylarkinterface/SkylarkGlobalLibrary.java
@@ -0,0 +1,32 @@
+// Copyright 2018 The Bazel Authors. All rights reserved.
+//
+// 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.devtools.build.lib.skylarkinterface;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/**
+ * An annotation to mark a class whose methods are global (top-level) Skylark functions.
+ *
+ * <p>A class or interface annotated with this annotation indicates that all of its methods
+ * which are annotated with {@link SkylarkCallable} should be treated as global top-level
+ * functions.
+ *
+ * <p>Global libraries should be stateless, and must have a public zero-arg constructor.
+ */
+@Target({ElementType.TYPE})
+@Retention(RetentionPolicy.RUNTIME)
+public @interface SkylarkGlobalLibrary {}
diff --git a/src/main/java/com/google/devtools/build/lib/skylarkinterface/SkylarkInterfaceUtils.java b/src/main/java/com/google/devtools/build/lib/skylarkinterface/SkylarkInterfaceUtils.java
index e3751a8494..2c269a74d9 100644
--- a/src/main/java/com/google/devtools/build/lib/skylarkinterface/SkylarkInterfaceUtils.java
+++ b/src/main/java/com/google/devtools/build/lib/skylarkinterface/SkylarkInterfaceUtils.java
@@ -86,7 +86,9 @@ public class SkylarkInterfaceUtils {
   public static SkylarkCallable getSkylarkCallable(Class<?> classObj, Method method) {
     try {
       Method superMethod = classObj.getMethod(method.getName(), method.getParameterTypes());
-      if (classObj.isAnnotationPresent(SkylarkModule.class)
+      boolean classAnnotatedForCallables = classObj.isAnnotationPresent(SkylarkModule.class)
+          || classObj.isAnnotationPresent(SkylarkGlobalLibrary.class);
+      if (classAnnotatedForCallables
           && superMethod.isAnnotationPresent(SkylarkCallable.class)) {
         return superMethod.getAnnotation(SkylarkCallable.class);
       }