src/main/java/com/google/devtools/build/lib/syntax/DotExpression.java

// Copyright 2014 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.syntax;

import com.google.common.base.Predicate;
import com.google.common.collect.Iterables;
import com.google.devtools.build.lib.events.Location;
import com.google.devtools.build.lib.syntax.FuncallExpression.MethodDescriptor;
import com.google.devtools.build.lib.syntax.compiler.ByteCodeUtils;
import com.google.devtools.build.lib.syntax.compiler.DebugInfo;
import com.google.devtools.build.lib.syntax.compiler.VariableScope;
import java.util.ArrayList;
import java.util.List;
import net.bytebuddy.implementation.bytecode.ByteCodeAppender;
import net.bytebuddy.implementation.bytecode.Duplication;
import net.bytebuddy.implementation.bytecode.constant.TextConstant;

/** Syntax node for a dot expression. e.g. obj.field, but not obj.method() */
public final class DotExpression extends Expression {

  private final Expression obj;

  private final Identifier field;

  public DotExpression(Expression obj, Identifier field) {
    this.obj = obj;
    this.field = field;
  }

  public Expression getObj() {
    return obj;
  }

  public Identifier getField() {
    return field;
  }

  @Override
  public String toString() {
    return obj + "." + field;
  }

  @Override
  Object doEval(Environment env) throws EvalException, InterruptedException {
    Object objValue = obj.eval(env);
    String name = field.getName();
    Object result = eval(objValue, name, getLocation(), env);
    return checkResult(objValue, result, name, getLocation());
  }

  /**
   * Throws the correct error message if the result is null depending on the objValue.
   */
  public static Object checkResult(Object objValue, Object result, String name, Location loc)
      throws EvalException {
    if (result == null) {
      if (objValue instanceof ClassObject) {
        String customErrorMessage = ((ClassObject) objValue).errorMessage(name);
        if (customErrorMessage != null) {
          throw new EvalException(loc, customErrorMessage);
        }
      }
      throw new EvalException(
          loc,
          Printer.format(
              "Object of type '%s' has no field %r", EvalUtils.getDataTypeName(objValue), name));
    }
    return result;
  }

  /**
   * Returns the field of the given name of the struct objValue, or null if no such field exists.
   */
  public static Object eval(Object objValue, String name,
      Location loc, Environment env) throws EvalException {
    if (objValue instanceof ClassObject) {
      Object result = null;
      try {
        result = ((ClassObject) objValue).getValue(name);
      } catch (IllegalArgumentException ex) {
        throw new EvalException(loc, ex);
      }
      // ClassObjects may have fields that are annotated with @SkylarkCallable.
      // Since getValue() does not know about those, we cannot expect that result is a valid object.
      if (result != null) {
        result = SkylarkType.convertToSkylark(result, env);
        // If we access NestedSets using ClassObject.getValue() we won't know the generic type,
        // so we have to disable it. This should not happen.
        SkylarkType.checkTypeAllowedInSkylark(result, loc);
        return result;
      }
    }

    Iterable<MethodDescriptor> methods = objValue instanceof Class<?>
        ? FuncallExpression.getMethods((Class<?>) objValue, name, loc)
        : FuncallExpression.getMethods(objValue.getClass(), name, loc);

    if (methods != null) {
      methods =
          Iterables.filter(
              methods,
              new Predicate<MethodDescriptor>() {
                @Override
                public boolean apply(MethodDescriptor methodDescriptor) {
                  return methodDescriptor.getAnnotation().structField();
                }
              });
      if (methods.iterator().hasNext()) {
        MethodDescriptor method = Iterables.getOnlyElement(methods);
        if (method.getAnnotation().structField()) {
          return FuncallExpression.callMethod(method, name, objValue, new Object[] {}, loc, env);
        }
      }
    }

    return null;
  }

  @Override
  public void accept(SyntaxTreeVisitor visitor) {
    visitor.visit(this);
  }

  @Override
  void validate(ValidationEnvironment env) throws EvalException {
    obj.validate(env);
  }

  @Override
  ByteCodeAppender compile(VariableScope scope, DebugInfo debugInfo) throws EvalException {
    List<ByteCodeAppender> code = new ArrayList<>();
    code.add(obj.compile(scope, debugInfo));
    TextConstant name = new TextConstant(field.getName());
    ByteCodeUtils.append(
        code,
        Duplication.SINGLE,
        name,
        debugInfo.add(this).loadLocation,
        scope.loadEnvironment(),
        ByteCodeUtils.invoke(
            DotExpression.class,
            "eval",
            Object.class,
            String.class,
            Location.class,
            Environment.class),
        // at this point we have the value of obj and the result of eval on the stack
        name,
        debugInfo.add(this).loadLocation,
        ByteCodeUtils.invoke(
            DotExpression.class,
            "checkResult",
            Object.class,
            Object.class,
            String.class,
            Location.class));
    return ByteCodeUtils.compoundAppender(code);
  }
}