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// 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.processor;
import com.google.devtools.build.lib.skylarkinterface.Param;
import com.google.devtools.build.lib.skylarkinterface.SkylarkCallable;
import java.util.List;
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.ExecutableElement;
import javax.lang.model.element.Modifier;
import javax.lang.model.element.TypeElement;
import javax.lang.model.element.VariableElement;
import javax.tools.Diagnostic;
/**
* Annotation processor for {@link SkylarkCallable}.
*
* <p>Checks the following invariants about {@link SkylarkCallable}-annotated methods:
* <ul>
* <li>The method must be public.</li>
* <li>If structField=true, there must be zero user-supplied parameters.</li>
* <li>Method parameters must be supplied in the following order:
* <pre>method([positionals]*[other user-args](Location)(FuncallExpression)(Envrionment))</pre>
* where Location, FuncallExpression, and Environment are supplied by the interpreter if and
* only if useLocation, useAst, and useEnvironment are specified, respectively.
* </li>
* <li>
* The number of method parameters much match the number of annotation-declared parameters
* plus the number of interpreter-supplied parameters.
* </li>
* </ul>
*
* <p>These properties can be relied upon at runtime without additional checks.
*/
@SupportedAnnotationTypes({"com.google.devtools.build.lib.skylarkinterface.SkylarkCallable"})
@SupportedSourceVersion(SourceVersion.RELEASE_8)
public final class SkylarkCallableProcessor extends AbstractProcessor {
private Messager messager;
private static final String LOCATION = "com.google.devtools.build.lib.events.Location";
private static final String AST = "com.google.devtools.build.lib.syntax.FuncallExpression";
private static final String ENVIRONMENT = "com.google.devtools.build.lib.syntax.Environment";
@Override
public synchronized void init(ProcessingEnvironment processingEnv) {
super.init(processingEnv);
messager = processingEnv.getMessager();
}
@Override
public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {
for (Element element : roundEnv.getElementsAnnotatedWith(SkylarkCallable.class)) {
// Only methods are annotated with SkylarkCallable. This is verified by the
// @Target(ElementType.METHOD) annotation.
ExecutableElement methodElement = (ExecutableElement) element;
SkylarkCallable annotation = methodElement.getAnnotation(SkylarkCallable.class);
if (!methodElement.getModifiers().contains(Modifier.PUBLIC)) {
error(methodElement, "@SkylarkCallable annotated methods must be public.");
}
try {
verifyParamSemantics(methodElement, annotation);
verifyNumberOfParameters(methodElement, annotation);
verifyExtraInterpreterParams(methodElement, annotation);
} catch (SkylarkCallableProcessorException exception) {
error(exception.methodElement, exception.errorMessage);
}
}
return true;
}
private void verifyParamSemantics(ExecutableElement methodElement, SkylarkCallable annotation)
throws SkylarkCallableProcessorException {
for (Param parameter : annotation.parameters()) {
if ("None".equals(parameter.defaultValue()) && !parameter.noneable()) {
throw new SkylarkCallableProcessorException(
methodElement,
String.format("Parameter '%s' has 'None' default value but is not noneable. "
+ "(If this is intended as a mandatory parameter, leave the defaultValue field "
+ "empty)",
parameter.name()));
}
}
}
private void verifyNumberOfParameters(ExecutableElement methodElement, SkylarkCallable annotation)
throws SkylarkCallableProcessorException {
List<? extends VariableElement> methodSignatureParams = methodElement.getParameters();
int numExtraInterpreterParams = numExpectedExtraInterpreterParams(annotation);
if (annotation.parameters().length > 0 || annotation.mandatoryPositionals() >= 0) {
int numDeclaredArgs =
annotation.parameters().length + Math.max(0, annotation.mandatoryPositionals());
if (methodSignatureParams.size() != numDeclaredArgs + numExtraInterpreterParams) {
throw new SkylarkCallableProcessorException(
methodElement,
String.format(
"@SkylarkCallable annotated method has %d parameters, but annotation declared "
+ "%d user-supplied parameters and %d extra interpreter parameters.",
methodSignatureParams.size(), numDeclaredArgs, numExtraInterpreterParams));
}
}
if (annotation.structField()) {
if (methodSignatureParams.size() > 0) {
// TODO(cparsons): Allow structField methods to accept interpreter-supplied arguments.
throw new SkylarkCallableProcessorException(
methodElement,
"@SkylarkCallable annotated methods with structField=true must have zero arguments.");
}
}
}
private void verifyExtraInterpreterParams(ExecutableElement methodElement,
SkylarkCallable annotation) throws SkylarkCallableProcessorException {
List<? extends VariableElement> methodSignatureParams = methodElement.getParameters();
int currentIndex = methodSignatureParams.size() - numExpectedExtraInterpreterParams(annotation);
// TODO(cparsons): Matching by class name alone is somewhat brittle, but due to tangled
// dependencies, it is difficult for this processor to depend directy on the expected
// classes here.
if (annotation.useLocation()) {
if (!LOCATION.equals(methodSignatureParams.get(currentIndex).asType().toString())) {
throw new SkylarkCallableProcessorException(
methodElement,
String.format(
"Expected parameter index %d to be the %s type, matching useLocation, but was %s",
currentIndex,
LOCATION,
methodSignatureParams.get(currentIndex).asType().toString()));
}
currentIndex++;
}
if (annotation.useAst()) {
if (!AST.equals(methodSignatureParams.get(currentIndex).asType().toString())) {
throw new SkylarkCallableProcessorException(
methodElement,
String.format(
"Expected parameter index %d to be the %s type, matching useAst, but was %s",
currentIndex, AST, methodSignatureParams.get(currentIndex).asType().toString()));
}
currentIndex++;
}
if (annotation.useEnvironment()) {
if (!ENVIRONMENT.equals(methodSignatureParams.get(currentIndex).asType().toString())) {
throw new SkylarkCallableProcessorException(
methodElement,
String.format(
"Expected parameter index %d to be the %s type, matching useEnvironment, "
+ "but was %s",
currentIndex,
ENVIRONMENT,
methodSignatureParams.get(currentIndex).asType().toString()));
}
}
}
private int numExpectedExtraInterpreterParams(SkylarkCallable annotation) {
int numExtraInterpreterParams = 0;
numExtraInterpreterParams += annotation.useLocation() ? 1 : 0;
numExtraInterpreterParams += annotation.useAst() ? 1 : 0;
numExtraInterpreterParams += annotation.useEnvironment() ? 1 : 0;
return numExtraInterpreterParams;
}
/**
* Prints an error message & fails the compilation.
*
* @param e The element which has caused the error. Can be null
* @param msg The error message
*/
private void error(Element e, String msg) {
messager.printMessage(Diagnostic.Kind.ERROR, msg, e);
}
private static class SkylarkCallableProcessorException extends Exception {
private final ExecutableElement methodElement;
private final String errorMessage;
private SkylarkCallableProcessorException(
ExecutableElement methodElement, String errorMessage) {
this.methodElement = methodElement;
this.errorMessage = errorMessage;
}
}
}
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