Adding compile time checks to the options parser.

Keeping this simple for now, just checking that the options are declared in accepted places. Will convert static, annotation-content based checks to be done here instead of at runtime in a later change.

TESTED: Added an option in a non-OptionBase, and verified that it failed to compile.
PiperOrigin-RevId: 166126408

2 files changed, 121 insertions, 0 deletions

diff --git a/src/main/java/com/google/devtools/common/options/BUILD b/src/main/java/com/google/devtools/common/options/BUILD
index 949720187b..42cdff3eae 100644
--- a/src/main/java/com/google/devtools/common/options/BUILD
+++ b/src/main/java/com/google/devtools/common/options/BUILD
@@ -20,6 +20,23 @@ java_library(
 
 java_library(
     name = "options",
+    exported_plugins = [":options_preprocessor"],
+    exports = [":options_internal"],
+)
+
+java_plugin(
+    name = "options_preprocessor",
+    srcs = [
+        "OptionProcessor.java",
+    ],
+    processor_class = "com.google.devtools.common.options.OptionProcessor",
+    deps = [
+        ":options_internal",
+    ],
+)
+
+java_library(
+    name = "options_internal",
     srcs = glob(
         ["*.java"],
         exclude = [
diff --git a/src/main/java/com/google/devtools/common/options/OptionProcessor.java b/src/main/java/com/google/devtools/common/options/OptionProcessor.java
new file mode 100644
index 0000000000..c2ef64409b
--- /dev/null
+++ b/src/main/java/com/google/devtools/common/options/OptionProcessor.java
@@ -0,0 +1,104 @@
+// Copyright 2017 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.common.options;
+
+import java.util.Set;
+import javax.annotation.processing.AbstractProcessor;
+import javax.annotation.processing.Messager;
+import javax.annotation.processing.ProcessingEnvironment;
+import javax.annotation.processing.RoundEnvironment;
+import javax.annotation.processing.SupportedAnnotationTypes;
+import javax.annotation.processing.SupportedSourceVersion;
+import javax.lang.model.SourceVersion;
+import javax.lang.model.element.Element;
+import javax.lang.model.element.ElementKind;
+import javax.lang.model.element.TypeElement;
+import javax.lang.model.type.TypeMirror;
+import javax.lang.model.util.Elements;
+import javax.lang.model.util.Types;
+import javax.tools.Diagnostic;
+
+/**
+ * Annotation processor for {@link Option}.
+ *
+ * <p>The {@link OptionsParser} only accepts publicly declared options in {@link
+ * OptionsBase}-inheriting classes, and there is no support for {@link Option} annotated fields
+ * declared elsewhere or privately. Prevent such uses from compiling.
+ */
+@SupportedAnnotationTypes({"com.google.devtools.common.options.Option"})
+@SupportedSourceVersion(SourceVersion.RELEASE_8)
+public final class OptionProcessor extends AbstractProcessor {
+
+  private Types typeUtils;
+  private Elements elementUtils;
+  private Messager messager;
+
+  @Override
+  public synchronized void init(ProcessingEnvironment processingEnv) {
+    super.init(processingEnv);
+    typeUtils = processingEnv.getTypeUtils();
+    elementUtils = processingEnv.getElementUtils();
+    messager = processingEnv.getMessager();
+  }
+
+  private static class OptionProcessorException extends Exception {
+    private Element elementInError;
+
+    OptionProcessorException(Element element, String message) {
+      super(message);
+      elementInError = element;
+    }
+  }
+
+  /** Check that the Option variables only occur in OptionBase-inheriting classes. */
+  private void checkInOptionBase(Element annotatedElement) throws OptionProcessorException {
+    if (annotatedElement.getEnclosingElement().getKind() != ElementKind.CLASS) {
+      throw new OptionProcessorException(annotatedElement, "The field should belong to a class.");
+    }
+    TypeMirror thisOptionClass = annotatedElement.getEnclosingElement().asType();
+    TypeMirror optionsBase =
+        elementUtils.getTypeElement("com.google.devtools.common.options.OptionsBase").asType();
+    if (!typeUtils.isAssignable(thisOptionClass, optionsBase)) {
+      throw new OptionProcessorException(
+          annotatedElement,
+          "@Option annotated fields can only be in classes that inherit from OptionsBase.");
+    }
+  }
+
+  @Override
+  public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {
+    try {
+      for (Element annotatedElement : roundEnv.getElementsAnnotatedWith(Option.class)) {
+        // Only fields are annotated with Option, this should already be checked by the
+        // @Target(ElementType.FIELD) annotation.
+
+        checkInOptionBase(annotatedElement);
+      }
+    } catch (OptionProcessorException e) {
+      error(e.elementInError, e.getMessage());
+    }
+    // Claim all Option annotated fields.
+    return true;
+  }
+
+  /**
+   * Prints an error message & fails the compilation.
+   *
+   * @param e The element which has caused the error. Can be null
+   * @param msg The error message
+   */
+  public void error(Element e, String msg) {
+    messager.printMessage(Diagnostic.Kind.ERROR, msg, e);
+  }
+}