src/main/java/com/google/devtools/build/lib/syntax/FuncallExpression.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.annotations.VisibleForTesting;
import com.google.common.base.Joiner;
import com.google.common.base.Preconditions;
import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSortedMap;
import com.google.common.collect.Iterables;
import com.google.devtools.build.lib.events.Location;
import com.google.devtools.build.lib.skylarkinterface.SkylarkCallable;
import com.google.devtools.build.lib.skylarkinterface.SkylarkInterfaceUtils;
import com.google.devtools.build.lib.skylarkinterface.SkylarkModule;
import com.google.devtools.build.lib.syntax.Runtime.NoneType;
import com.google.devtools.build.lib.syntax.SkylarkList.Tuple;
import com.google.devtools.build.lib.syntax.StarlarkSemantics.FlagIdentifier;
import java.io.IOException;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashSet;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.Optional;
import java.util.Set;
import java.util.concurrent.ExecutionException;
import java.util.stream.Collectors;
import javax.annotation.Nullable;

/** Syntax node for a function call expression. */
public final class FuncallExpression extends Expression {

  /**
   * Cache key for callable method lookup of skylark types. The key consists of the class of the
   * skylark type, and a skylark semantics object. The semantics object is required as part of the
   * key as certain methods of the class may be unavailable if certain semantics flags are flipped.
   */
  private static final class MethodDescriptorKey {
    private final Class<?> clazz;
    private final StarlarkSemantics semantics;

    private MethodDescriptorKey(Class<?> clazz, StarlarkSemantics semantics) {
      this.clazz = clazz;
      this.semantics = semantics;
    }

    public Class<?> getClazz() {
      return clazz;
    }

    public StarlarkSemantics getSemantics() {
      return semantics;
    }

    @Override
    public boolean equals(Object o) {
      if (this == o) {
        return true;
      }
      if (o == null || getClass() != o.getClass()) {
        return false;
      }
      MethodDescriptorKey that = (MethodDescriptorKey) o;
      return Objects.equals(clazz, that.clazz) && Objects.equals(semantics, that.semantics);
    }

    @Override
    public int hashCode() {
      return Objects.hash(clazz, semantics);
    }
  }

  private static final LoadingCache<MethodDescriptorKey, Optional<MethodDescriptor>> selfCallCache =
      CacheBuilder.newBuilder()
          .build(
              new CacheLoader<MethodDescriptorKey, Optional<MethodDescriptor>>() {
                @Override
                public Optional<MethodDescriptor> load(MethodDescriptorKey key) throws Exception {
                  Class<?> keyClass = key.getClazz();
                  StarlarkSemantics semantics = key.getSemantics();
                  MethodDescriptor returnValue = null;
                  for (Method method : sortMethodArrayByMethodName(keyClass.getMethods())) {
                    // Synthetic methods lead to false multiple matches
                    if (method.isSynthetic()) {
                      continue;
                    }
                    SkylarkCallable callable = SkylarkInterfaceUtils.getSkylarkCallable(method);
                    if (callable != null && callable.selfCall()) {
                      if (returnValue != null) {
                        throw new IllegalArgumentException(
                            String.format(
                                "Class %s has two selfCall methods defined", keyClass.getName()));
                      }
                      if (semantics.isFeatureEnabledBasedOnTogglingFlags(
                          callable.enableOnlyWithFlag(), callable.disableWithFlag())) {
                        returnValue = MethodDescriptor.of(method, callable, semantics);
                      }
                    }
                  }
                  return Optional.ofNullable(returnValue);
                }
              });

  private static final LoadingCache<MethodDescriptorKey, Map<String, MethodDescriptor>>
      methodCache =
          CacheBuilder.newBuilder()
              .build(
                  new CacheLoader<MethodDescriptorKey, Map<String, MethodDescriptor>>() {

                    @Override
                    public Map<String, MethodDescriptor> load(MethodDescriptorKey key)
                        throws Exception {
                      Class<?> keyClass = key.getClazz();
                      StarlarkSemantics semantics = key.getSemantics();
                      ImmutableMap.Builder<String, MethodDescriptor> methodMap =
                          ImmutableMap.builder();
                      for (Method method : sortMethodArrayByMethodName(keyClass.getMethods())) {
                        // Synthetic methods lead to false multiple matches
                        if (method.isSynthetic()) {
                          continue;
                        }
                        SkylarkCallable callable = SkylarkInterfaceUtils.getSkylarkCallable(method);
                        if (callable == null) {
                          continue;
                        }
                        if (callable.selfCall()) {
                          // Self-call java methods are not treated as methods of the skylark value.
                          continue;
                        }
                        if (semantics.isFeatureEnabledBasedOnTogglingFlags(
                            callable.enableOnlyWithFlag(), callable.disableWithFlag())) {
                          methodMap.put(
                              callable.name(), MethodDescriptor.of(method, callable, semantics));
                        }
                      }
                      return methodMap.build();
                    }
                  });

  private static final LoadingCache<MethodDescriptorKey, Map<String, MethodDescriptor>> fieldCache =
      CacheBuilder.newBuilder()
          .build(
              new CacheLoader<MethodDescriptorKey, Map<String, MethodDescriptor>>() {

                @Override
                public Map<String, MethodDescriptor> load(MethodDescriptorKey key)
                    throws Exception {
                  ImmutableMap.Builder<String, MethodDescriptor> fieldMap = ImmutableMap.builder();
                  HashSet<String> fieldNamesForCollisions = new HashSet<>();
                  List<MethodDescriptor> fieldMethods =
                      methodCache.get(key).values().stream()
                          .filter(MethodDescriptor::isStructField)
                          .collect(Collectors.toList());

                  for (MethodDescriptor fieldMethod : fieldMethods) {
                    String name = fieldMethod.getName();
                    // TODO(b/72113542): Validate with annotation processor instead of at runtime.
                    if (!fieldNamesForCollisions.add(name)) {
                      throw new IllegalArgumentException(
                          String.format(
                              "Class %s has two structField methods named %s defined",
                              key.getClazz().getName(), name));
                    }
                    fieldMap.put(name, fieldMethod);
                  }
                  return fieldMap.build();
                }
              });

  // *args, **kwargs, location, ast, environment, skylark semantics
  private static final int EXTRA_ARGS_COUNT = 6;

  /**
   * Returns a map of methods and corresponding SkylarkCallable annotations of the methods of the
   * classObj class reachable from Skylark.
   */
  public static ImmutableMap<Method, SkylarkCallable> collectSkylarkMethodsWithAnnotation(
      Class<?> classObj) {
    ImmutableSortedMap.Builder<Method, SkylarkCallable> methodMap
        = ImmutableSortedMap.orderedBy(Comparator.comparing(Object::toString));
    for (Method method : sortMethodArrayByMethodName(classObj.getMethods())) {
      // Synthetic methods lead to false multiple matches
      if (!method.isSynthetic()) {
        SkylarkCallable annotation = SkylarkInterfaceUtils.getSkylarkCallable(classObj, method);
        if (annotation != null) {
          methodMap.put(method, annotation);
        }
      }
    }
    return methodMap.build();
  }

  /** Sort Method arrays by their name for a deterministic ordering */
  private static Method[] sortMethodArrayByMethodName(Method[] methods) {
    Arrays.sort(methods, Comparator.comparing(Method::getName));
    return methods;
  }

  /**
   * An exception class to handle exceptions in direct Java API calls.
   */
  public static final class FuncallException extends Exception {

    public FuncallException(String msg) {
      super(msg);
    }
  }

  private final Expression function;

  private final ImmutableList<Argument.Passed> arguments;

  private final int numPositionalArgs;

  public FuncallExpression(Expression function, ImmutableList<Argument.Passed> arguments) {
    this.function = Preconditions.checkNotNull(function);
    this.arguments = Preconditions.checkNotNull(arguments);
    this.numPositionalArgs = countPositionalArguments();
  }

  /** Returns the function that is called. */
  public Expression getFunction() {
    return this.function;
  }

  /**
   * Returns the number of positional arguments.
   */
  private int countPositionalArguments() {
    int num = 0;
    for (Argument.Passed arg : arguments) {
      if (arg.isPositional()) {
        num++;
      }
    }
    return num;
  }

  /**
   * Returns an (immutable, ordered) list of function arguments. The first n are
   * positional and the remaining ones are keyword args, where n =
   * getNumPositionalArguments().
   */
  public List<Argument.Passed> getArguments() {
    return Collections.unmodifiableList(arguments);
  }

  /**
   * Returns the number of arguments which are positional; the remainder are
   * keyword arguments.
   */
  public int getNumPositionalArguments() {
    return numPositionalArgs;
  }

  @Override
  public void prettyPrint(Appendable buffer) throws IOException {
    function.prettyPrint(buffer);
    buffer.append('(');
    String sep = "";
    for (Argument.Passed arg : arguments) {
      buffer.append(sep);
      arg.prettyPrint(buffer);
      sep = ", ";
    }
    buffer.append(')');
  }

  @Override
  public String toString() {
    Printer.LengthLimitedPrinter printer = new Printer.LengthLimitedPrinter();
    printer.append(function.toString());
    printer.printAbbreviatedList(arguments, "(", ", ", ")", null,
        Printer.SUGGESTED_CRITICAL_LIST_ELEMENTS_COUNT,
        Printer.SUGGESTED_CRITICAL_LIST_ELEMENTS_STRING_LENGTH);
    return printer.toString();
  }

  /**
   * Returns either the class itself or, if the class is {@link String}, the proxy class
   * containing all 'string' methods.
   */
  private static Class<?> getClassOrProxyClass(Class<?> clazz) {
    return String.class.isAssignableFrom(clazz)
        ? StringModule.class
        : clazz;
  }

  /**
   * Returns the Skylark callable Method of objClass with structField=true and the given name.
   *
   * @deprecated use {@link #getStructField(StarlarkSemantics, Class, String)} instead
   */
  @Deprecated
  public static MethodDescriptor getStructField(Class<?> objClass, String methodName) {
    return getStructField(StarlarkSemantics.DEFAULT_SEMANTICS, objClass, methodName);
  }

  /** Returns the Skylark callable Method of objClass with structField=true and the given name. */
  public static MethodDescriptor getStructField(
      StarlarkSemantics semantics, Class<?> objClass, String methodName) {
    try {
      return fieldCache
          .get(new MethodDescriptorKey(getClassOrProxyClass(objClass), semantics))
          .get(methodName);
    } catch (ExecutionException e) {
      throw new IllegalStateException("Method loading failed: " + e);
    }
  }

  /**
   * Returns the list of names of Skylark callable Methods of objClass with structField=true.
   *
   * @deprecated use {@link #getStructFieldNames(StarlarkSemantics, Class)} instead
   */
  @Deprecated
  public static Set<String> getStructFieldNames(Class<?> objClass) {
    return getStructFieldNames(StarlarkSemantics.DEFAULT_SEMANTICS, objClass);
  }

  /** Returns the list of names of Skylark callable Methods of objClass with structField=true. */
  public static Set<String> getStructFieldNames(StarlarkSemantics semantics, Class<?> objClass) {
    try {
      return fieldCache
          .get(new MethodDescriptorKey(getClassOrProxyClass(objClass), semantics))
          .keySet();
    } catch (ExecutionException e) {
      throw new IllegalStateException("Method loading failed: " + e);
    }
  }

  /**
   * Returns the list of Skylark callable Methods of objClass with the given name.
   *
   * @deprecated use {@link #getMethods(StarlarkSemantics, Class, String)} instead
   */
  @Deprecated
  public static MethodDescriptor getMethod(Class<?> objClass, String methodName) {
    return getMethod(StarlarkSemantics.DEFAULT_SEMANTICS, objClass, methodName);
  }

  /** Returns the list of Skylark callable Methods of objClass with the given name. */
  public static MethodDescriptor getMethod(
      StarlarkSemantics semantics, Class<?> objClass, String methodName) {
    try {
      return methodCache
          .get(new MethodDescriptorKey(getClassOrProxyClass(objClass), semantics))
          .get(methodName);
    } catch (ExecutionException e) {
      throw new IllegalStateException("Method loading failed: " + e);
    }
  }

  /**
   * Returns a set of the Skylark name of all Skylark callable methods for object of type {@code
   * objClass}.
   *
   * @deprecated use {@link #getMethodNames(StarlarkSemantics, Class)} instead
   */
  @Deprecated
  public static Set<String> getMethodNames(Class<?> objClass) {
    return getMethodNames(StarlarkSemantics.DEFAULT_SEMANTICS, objClass);
  }

  /**
   * Returns a set of the Skylark name of all Skylark callable methods for object of type {@code
   * objClass}.
   */
  public static Set<String> getMethodNames(StarlarkSemantics semantics, Class<?> objClass) {
    try {
      return methodCache
          .get(new MethodDescriptorKey(getClassOrProxyClass(objClass), semantics))
          .keySet();
    } catch (ExecutionException e) {
      throw new IllegalStateException("Method loading failed: " + e);
    }
  }

  /**
   * Returns true if the given class has a method annotated with {@link SkylarkCallable} with {@link
   * SkylarkCallable#selfCall()} set to true.
   */
  public static boolean hasSelfCallMethod(StarlarkSemantics semantics, Class<?> objClass) {
    try {
      return selfCallCache.get(new MethodDescriptorKey(objClass, semantics)).isPresent();
    } catch (ExecutionException e) {
      throw new IllegalStateException("Method loading failed: " + e);
    }
  }

  /**
   * Returns a {@link MethodDescriptor} object representing a function which calls the selfCall java
   * method of the given object (the {@link SkylarkCallable} method with {@link
   * SkylarkCallable#selfCall()} set to true).
   *
   * @throws IllegalStateException if no such method exists for the object
   */
  public static MethodDescriptor getSelfCallMethodDescriptor(
      StarlarkSemantics semantics, Object obj) {
    try {
      Optional<MethodDescriptor> selfCallDescriptor =
          selfCallCache.get(new MethodDescriptorKey(obj.getClass(), semantics));
      if (!selfCallDescriptor.isPresent()) {
        throw new IllegalStateException("Class " + obj.getClass() + " has no selfCall method");
      }
      return selfCallDescriptor.get();
    } catch (ExecutionException e) {
      throw new IllegalStateException("Method loading failed: " + e);
    }
  }

  /**
   * Returns a {@link BuiltinCallable} representing a {@link SkylarkCallable}-annotated instance
   * method of a given object with the given method name.
   */
  public static BuiltinCallable getBuiltinCallable(Object obj, String methodName) {
    Class<?> objClass = obj.getClass();
    MethodDescriptor methodDescriptor = getMethod(objClass, methodName);
    if (methodDescriptor == null) {
      throw new IllegalStateException(String.format(
          "Expected a method named '%s' in %s, but found none",
          methodName, objClass));
    }
    return new BuiltinCallable(obj, methodName);
  }

  /**
   * Invokes the given structField=true method and returns the result.
   *
   * <p>The given method must <b>not</b> require extra-interpreter parameters, such as
   * {@link Environment}. This method throws {@link IllegalArgumentException} for violations.</p>
   *
   * @param methodDescriptor the descriptor of the method to invoke
   * @param fieldName the name of the struct field
   * @param obj the object on which to invoke the method
   * @return the method return value
   * @throws EvalException if there was an issue evaluating the method
   */
  public static Object invokeStructField(
      MethodDescriptor methodDescriptor, String fieldName, Object obj)
      throws EvalException, InterruptedException {
    Preconditions.checkArgument(
        methodDescriptor.isStructField(), "Can only be invoked on structField callables");
    Preconditions.checkArgument(
        !methodDescriptor.isUseEnvironment()
            || !methodDescriptor.isUseSkylarkSemantics()
            || !methodDescriptor.isUseLocation()
            || !methodDescriptor.isUseContext(),
        "Cannot be invoked on structField callables with extra interpreter params");
    return methodDescriptor.call(obj, new Object[0], Location.BUILTIN, null);
  }

  /**
   * Converts Starlark-defined arguments to an array of argument {@link Object}s that may be passed
   * to a given callable-from-Starlark Java method.
   *
   * @param method a descriptor for a java method callable from Starlark
   * @param objClass the class of the java object on which to invoke this method
   * @param args a list of positional Starlark arguments
   * @param kwargs a map of keyword Starlark arguments; keys are the used keyword, and values are
   *     their corresponding values in the method call
   * @param environment the current Starlark environment
   * @return the array of arguments which may be passed to {@link MethodDescriptor#call}
   * @throws EvalException if the given set of arguments are invalid for the given method. For
   *     example, if any arguments are of unexpected type, or not all mandatory parameters are
   *     specified by the user
   */
  public Object[] convertStarlarkArgumentsToJavaMethodArguments(
      MethodDescriptor method,
      Class<?> objClass,
      List<Object> args,
      Map<String, Object> kwargs,
      Environment environment)
      throws EvalException {
    Preconditions.checkArgument(!method.isStructField(),
        "struct field methods should be handled by DotExpression separately");

    ImmutableList<ParamDescriptor> parameters = method.getParameters();
    ImmutableList.Builder<Object> builder =
        ImmutableList.builderWithExpectedSize(parameters.size() + EXTRA_ARGS_COUNT);
    boolean acceptsExtraArgs = method.isAcceptsExtraArgs();
    boolean acceptsExtraKwargs = method.isAcceptsExtraKwargs();

    int argIndex = 0;

    // Process parameters specified in callable.parameters()
    Set<String> keys = new LinkedHashSet<>(kwargs.keySet());
    // Positional parameters are always enumerated before non-positional parameters,
    // And default-valued positional parameters are always enumerated after other positional
    // parameters. These invariants are validated by the SkylarkCallable annotation processor.
    // Index is used deliberately, since usage of iterators adds a significant overhead
    for (int i = 0; i < parameters.size(); ++i) {
      ParamDescriptor param = parameters.get(i);
      SkylarkType type = param.getSkylarkType();
      Object value;

      if (param.isDisabledInCurrentSemantics()) {
        value =
            SkylarkSignatureProcessor.getDefaultValue(
                param.getName(), param.getValueOverride(), null);
        builder.add(value);
        continue;
      }

      if (argIndex < args.size() && param.isPositional()) { // Positional args and params remain.
        value = args.get(argIndex);
        if (!type.contains(value)) {
          throw argumentMismatchException(
              String.format(
                  "expected value of type '%s' for parameter '%s'", type, param.getName()),
              method,
              objClass);
        }
        if (param.isNamed() && keys.contains(param.getName())) {
          throw argumentMismatchException(
              String.format("got multiple values for keyword argument '%s'", param.getName()),
              method,
              objClass);
        }
        argIndex++;
      } else { // No more positional arguments, or no more positional parameters.
        if (param.isNamed() && keys.remove(param.getName())) {
          // Param specified by keyword argument.
          value = kwargs.get(param.getName());
          if (!type.contains(value)) {
            throw argumentMismatchException(
                String.format(
                    "expected value of type '%s' for parameter '%s'", type, param.getName()),
                method,
                objClass);
          }
        } else { // Param not specified by user. Use default value.
          if (param.getDefaultValue().isEmpty()) {
            throw argumentMismatchException(
                String.format("parameter '%s' has no default value", param.getName()),
                method,
                objClass);
          }
          value =
              SkylarkSignatureProcessor.getDefaultValue(
                  param.getName(), param.getDefaultValue(), null);
        }
      }
      if (!param.isNoneable() && value instanceof NoneType) {
        throw argumentMismatchException(
            String.format("parameter '%s' cannot be None", param.getName()), method, objClass);
      }
      builder.add(value);
    }

    ImmutableList<Object> extraArgs = ImmutableList.of();
    if (argIndex < args.size()) {
      if (acceptsExtraArgs) {
        ImmutableList.Builder<Object> extraArgsBuilder =
            ImmutableList.builderWithExpectedSize(args.size() - argIndex);
        for (; argIndex < args.size(); argIndex++) {
          extraArgsBuilder.add(args.get(argIndex));
        }
        extraArgs = extraArgsBuilder.build();
      } else {
        throw argumentMismatchException(
            String.format(
                "expected no more than %s positional arguments, but got %s", argIndex, args.size()),
            method,
            objClass);
      }
    }
    ImmutableMap<String, Object> extraKwargs = ImmutableMap.of();
    if (!keys.isEmpty()) {
      if (acceptsExtraKwargs) {
        ImmutableMap.Builder<String, Object> extraKwargsBuilder =
            ImmutableMap.builderWithExpectedSize(keys.size());
        for (String key : keys) {
          extraKwargsBuilder.put(key, kwargs.get(key));
        }
        extraKwargs = extraKwargsBuilder.build();
      } else {
        throw unexpectedKeywordArgumentException(keys, method, objClass, environment);
      }
    }

    // Then add any skylark-interpreter arguments (for example kwargs or the Environment).
    if (acceptsExtraArgs) {
      builder.add(Tuple.copyOf(extraArgs));
    }
    if (acceptsExtraKwargs) {
      builder.add(SkylarkDict.copyOf(environment, extraKwargs));
    }
    appendExtraInterpreterArgs(builder, method, this, getLocation(), environment);

    return builder.build().toArray();
  }

  private EvalException unexpectedKeywordArgumentException(
      Set<String> unexpectedKeywords,
      MethodDescriptor method,
      Class<?> objClass,
      Environment env) {
    // Check if any of the unexpected keywords are for parameters which are disabled by the
    // current semantic flags. Throwing an error with information about the misconfigured
    // semantic flag is likely far more helpful.
    for (ParamDescriptor param : method.getParameters()) {
      if (param.isDisabledInCurrentSemantics() && unexpectedKeywords.contains(param.getName())) {
        FlagIdentifier flagIdentifier = param.getFlagResponsibleForDisable();
        // If the flag is True, it must be a deprecation flag. Otherwise it's an experimental flag.
        if (env.getSemantics().flagValue(flagIdentifier)) {
          return new EvalException(
              getLocation(),
              String.format(
                  "parameter '%s' is deprecated and will be removed soon. It may be "
                      + "temporarily re-enabled by setting --%s=false",
                  param.getName(), flagIdentifier.getFlagName()));
        } else {
          return new EvalException(
              getLocation(),
              String.format(
                  "parameter '%s' is experimental and thus unavailable with the current "
                      + "flags. It may be enabled by setting --%s",
                  param.getName(), flagIdentifier.getFlagName()));
        }
      }
    }

    return argumentMismatchException(
        String.format(
            "unexpected keyword%s %s",
            unexpectedKeywords.size() > 1 ? "s" : "",
            Joiner.on(",").join(Iterables.transform(unexpectedKeywords, s -> "'" + s + "'"))),
        method,
        objClass);
  }

  private EvalException argumentMismatchException(
      String errorDescription, MethodDescriptor methodDescriptor, Class<?> objClass) {
    if (methodDescriptor.isSelfCall() || SkylarkInterfaceUtils.hasSkylarkGlobalLibrary(objClass)) {
      return new EvalException(
          getLocation(),
          String.format(
              "%s, for call to function %s",
              errorDescription, formatMethod(objClass, methodDescriptor)));
    } else {
      return new EvalException(
          getLocation(),
          String.format(
              "%s, for call to method %s of '%s'",
              errorDescription,
              formatMethod(objClass, methodDescriptor),
              EvalUtils.getDataTypeNameFromClass(objClass)));
    }
  }

  private EvalException missingMethodException(Class<?> objClass, String methodName) {
    return new EvalException(
        getLocation(),
        String.format(
            "type '%s' has no method %s()",
            EvalUtils.getDataTypeNameFromClass(objClass), methodName));
  }

  /**
   * Returns the extra interpreter arguments for the given {@link SkylarkCallable}, to be added at
   * the end of the argument list for the callable.
   *
   * <p>This method accepts null {@code ast} only if {@code callable.useAst()} is false. It is up to
   * the caller to validate this invariant.
   */
  public static List<Object> extraInterpreterArgs(
      MethodDescriptor method, @Nullable FuncallExpression ast, Location loc, Environment env) {
    ImmutableList.Builder<Object> builder = ImmutableList.builder();
    appendExtraInterpreterArgs(builder, method, ast, loc, env);
    return builder.build();
  }

  /**
   * Same as {@link #extraInterpreterArgs(MethodDescriptor, FuncallExpression, Location,
   * Environment)} but appends args to a passed {@code builder} to avoid unnecessary allocations of
   * intermediate instances.
   *
   * @see #extraInterpreterArgs(MethodDescriptor, FuncallExpression, Location, Environment)
   */
  private static void appendExtraInterpreterArgs(
      ImmutableList.Builder<Object> builder,
      MethodDescriptor method,
      @Nullable FuncallExpression ast,
      Location loc,
      Environment env) {
    if (method.isUseLocation()) {
      builder.add(loc);
    }
    if (method.isUseAst()) {
      if (ast == null) {
        throw new IllegalArgumentException("Callable expects to receive ast: " + method.getName());
      }
      builder.add(ast);
    }
    if (method.isUseEnvironment()) {
      builder.add(env);
    }
    if (method.isUseSkylarkSemantics()) {
      builder.add(env.getSemantics());
    }
    if (method.isUseContext()) {
      builder.add(env.getStarlarkContext());
    }
  }

  private static String formatMethod(Class<?> objClass, MethodDescriptor methodDescriptor) {
    ImmutableList.Builder<String> argTokens = ImmutableList.builder();
    // Skip first parameter ('self') for StringModule, as its a special case.
    Iterable<ParamDescriptor> parameters =
        objClass == StringModule.class
            ? Iterables.skip(methodDescriptor.getParameters(), 1)
            : methodDescriptor.getParameters();

    for (ParamDescriptor paramDescriptor : parameters) {
      if (!paramDescriptor.isDisabledInCurrentSemantics()) {
        if (paramDescriptor.getDefaultValue().isEmpty()) {
          argTokens.add(paramDescriptor.getName());
        } else {
          argTokens.add(paramDescriptor.getName() + " = " + paramDescriptor.getDefaultValue());
        }
      }
    }
    if (methodDescriptor.isAcceptsExtraArgs()) {
      argTokens.add("*args");
    }
    if (methodDescriptor.isAcceptsExtraKwargs()) {
      argTokens.add("**kwargs");
    }
    return methodDescriptor.getName() + "(" + Joiner.on(", ").join(argTokens.build()) + ")";
  }

  /**
   * Add one named argument to the keyword map, and returns whether that name has been encountered
   * before.
   */
  private static boolean addKeywordArgAndCheckIfDuplicate(
      Map<String, Object> kwargs,
      String name,
      Object value) {
    return kwargs.put(name, value) != null;
  }

  /**
   * Add multiple arguments to the keyword map (**kwargs), and returns all the names of those
   * arguments that have been encountered before or {@code null} if there are no such names.
   */
  @Nullable
  private static ImmutableList<String> addKeywordArgsAndReturnDuplicates(
      Map<String, Object> kwargs,
      Object items,
      Location location)
      throws EvalException {
    if (!(items instanceof Map<?, ?>)) {
      throw new EvalException(
          location,
          "argument after ** must be a dictionary, not '" + EvalUtils.getDataTypeName(items) + "'");
    }
    ImmutableList.Builder<String> duplicatesBuilder = null;
    for (Map.Entry<?, ?> entry : ((Map<?, ?>) items).entrySet()) {
      if (!(entry.getKey() instanceof String)) {
        throw new EvalException(
            location,
            "keywords must be strings, not '" + EvalUtils.getDataTypeName(entry.getKey()) + "'");
      }
      String argName = (String) entry.getKey();
      if (addKeywordArgAndCheckIfDuplicate(kwargs, argName, entry.getValue())) {
        if (duplicatesBuilder == null) {
          duplicatesBuilder = ImmutableList.builder();
        }
        duplicatesBuilder.add(argName);
      }
    }
    return duplicatesBuilder == null ? null : duplicatesBuilder.build();
  }

  /**
   * Evaluate this FuncallExpression's arguments, and put the resulting evaluated expressions
   * into the given {@code posargs} and {@code kwargs} collections.
   *
   * @param posargs a list to which all positional arguments will be added
   * @param kwargs a mutable map to which all keyword arguments will be added. A mutable map
   *     is used here instead of an immutable map builder to deal with duplicates
   *     without memory overhead
   * @param env the current environment
   */
  @SuppressWarnings("unchecked")
  private void evalArguments(
      List<Object> posargs, Map<String, Object> kwargs, Environment env)
      throws EvalException, InterruptedException {

    // Optimize allocations for the common case where they are no duplicates.
    ImmutableList.Builder<String> duplicatesBuilder = null;
    // Iterate over the arguments. We assume all positional arguments come before any keyword
    // or star arguments, because the argument list was already validated by
    // Argument#validateFuncallArguments, as called by the Parser,
    // which should be the only place that build FuncallExpression-s.
    // Argument lists are typically short and functions are frequently called, so go by index
    // (O(1) for ImmutableList) to avoid the iterator overhead.
    for (int i = 0; i < arguments.size(); i++) {
      Argument.Passed arg = arguments.get(i);
      Object value = arg.getValue().eval(env);
      if (arg.isPositional()) {
        posargs.add(value);
      } else if (arg.isStar()) { // expand the starArg
        if (!(value instanceof Iterable)) {
          throw new EvalException(
              getLocation(),
              "argument after * must be an iterable, not " + EvalUtils.getDataTypeName(value));
        }
        for (Object starArgUnit : (Iterable<Object>) value) {
          posargs.add(starArgUnit);
        }
      } else if (arg.isStarStar()) { // expand the kwargs
        ImmutableList<String> duplicates =
            addKeywordArgsAndReturnDuplicates(kwargs, value, getLocation());
        if (duplicates != null) {
          if (duplicatesBuilder == null) {
            duplicatesBuilder = ImmutableList.builder();
          }
          duplicatesBuilder.addAll(duplicates);
        }
      } else {
        if (addKeywordArgAndCheckIfDuplicate(kwargs, arg.getName(), value)) {
          if (duplicatesBuilder == null) {
            duplicatesBuilder = ImmutableList.builder();
          }
          duplicatesBuilder.add(arg.getName());
        }
      }
    }
    if (duplicatesBuilder != null) {
      ImmutableList<String> dups = duplicatesBuilder.build();
      throw new EvalException(
          getLocation(),
          "duplicate keyword"
              + (dups.size() > 1 ? "s" : "")
              + " '"
              + Joiner.on("', '").join(dups)
              + "' in call to "
              + function);
    }
  }

  @VisibleForTesting
  public static boolean isNamespace(Class<?> classObject) {
    return classObject.isAnnotationPresent(SkylarkModule.class)
        && classObject.getAnnotation(SkylarkModule.class).namespace();
  }

  @Override
  Object doEval(Environment env) throws EvalException, InterruptedException {
    // This is a hack which provides some performance improvement over the alternative:
    // Consider 'foo.bar()'. Without this hack, the parser would evaluate the DotExpression
    // 'foo.bar' first, determine that 'foo.bar' is a callable object, and then invoke the
    // callable object. If 'foo' is a java object, however, the parser would need to create a
    // new function object to represent 'foo.bar' *just* so it could invoke method 'bar' of 'foo'.
    // Constructing throwaway function objects would be a performance hit, so instead this code
    // effectively 'looks ahead' to invoke an object method directly.
    if (function instanceof DotExpression) {
      return invokeObjectMethod(env, (DotExpression) function);
    }
    Object funcValue = function.eval(env);
    ArrayList<Object> posargs = new ArrayList<>();
    Map<String, Object> kwargs = new LinkedHashMap<>();
    evalArguments(posargs, kwargs, env);
    return callFunction(funcValue, posargs, kwargs, env);
  }

  /** Invokes object.function() and returns the result. */
  private Object invokeObjectMethod(Environment env, DotExpression dot)
      throws EvalException, InterruptedException {
    Object objValue = dot.getObject().eval(env);
    String methodName = dot.getField().getName();
    ArrayList<Object> posargs = new ArrayList<>();
    Map<String, Object> kwargs = new LinkedHashMap<>();
    evalArguments(posargs, kwargs, env);

    // Case 1: Object is a String. String is an unusual special case.
    if (objValue instanceof String) {
      return callStringMethod((String) objValue, methodName, posargs, kwargs, env);
    }

    // Case 2: Object is a Java object with a matching @SkylarkCallable method.
    // This is an optimization. For 'foo.bar()' where 'foo' is a java object with a callable
    // java method 'bar()', this avoids evaluating 'foo.bar' in isolation (which would require
    // creating a throwaway function-like object).
    MethodDescriptor methodDescriptor =
        FuncallExpression.getMethod(env.getSemantics(), objValue.getClass(), methodName);
    if (methodDescriptor != null && !methodDescriptor.isStructField()) {
      Object[] javaArguments = convertStarlarkArgumentsToJavaMethodArguments(
          methodDescriptor, objValue.getClass(), posargs, kwargs, env);
      return methodDescriptor.call(objValue, javaArguments, getLocation(), env);
    }

    // Case 3: Object is a function registered with the BuiltinRegistry.
    // TODO(cparsons): The runtime builtin registry is deprecated and only used by non-Bazel users
    // of the Starlark interpreter. Remove its use.
    BaseFunction legacyRuntimeFunction =
        Runtime.getBuiltinRegistry().getFunction(objValue.getClass(), methodName);
    if (legacyRuntimeFunction != null) {
      return callLegacyBuiltinRegistryFunction(
          legacyRuntimeFunction, objValue, posargs, kwargs, env);
    }

    // Case 4: All other cases. Evaluate "foo.bar" as a dot expression, then try to invoke it
    // as a callable.
    Object functionObject = DotExpression.eval(objValue, methodName, dot.getLocation(), env);
    if (functionObject == null) {
      throw missingMethodException(objValue.getClass(), methodName);
    } else {
      return callFunction(functionObject, posargs, kwargs, env);
    }
  }

  private Object callLegacyBuiltinRegistryFunction(BaseFunction legacyRuntimeFunction,
      Object objValue, ArrayList<Object> posargs, Map<String, Object> kwargs, Environment env)
      throws EvalException, InterruptedException {
    if (!isNamespace(objValue.getClass())) {
      posargs.add(0, objValue);
    }
    return legacyRuntimeFunction.call(posargs, kwargs, this, env);
  }

  private Object callStringMethod(String objValue, String methodName,
      ArrayList<Object> posargs, Map<String, Object> kwargs, Environment env)
      throws InterruptedException, EvalException {
    // String is a special case, since it can't be subclassed. Methods on strings defer
    // to StringModule, and thus need to include the actual string as a 'self' parameter.
    posargs.add(0, objValue);

    MethodDescriptor method = getMethod(env.getSemantics(), StringModule.class, methodName);
    if (method == null) {
      throw missingMethodException(StringModule.class, methodName);
    }

    Object[] javaArguments = convertStarlarkArgumentsToJavaMethodArguments(
        method, StringModule.class, posargs, kwargs, env);
    return method.call(
        StringModule.INSTANCE, javaArguments, getLocation(), env);
  }

  /**
   * Calls a callable object {@code funcValue}.
   *
   * @throws EvalException if funcValue is not a callable object or if invalid arguments are
   *     given
   */
  private Object callFunction(Object funcValue,
      ArrayList<Object> posargs, Map<String, Object> kwargs, Environment env)
      throws EvalException, InterruptedException {

    if (funcValue instanceof StarlarkFunction) {
      StarlarkFunction function = (StarlarkFunction) funcValue;
      return function.call(posargs, ImmutableMap.copyOf(kwargs), this, env);
    } else if (hasSelfCallMethod(env.getSemantics(), funcValue.getClass())) {
      MethodDescriptor descriptor = getSelfCallMethodDescriptor(env.getSemantics(), funcValue);
      Object[] javaArguments = convertStarlarkArgumentsToJavaMethodArguments(
          descriptor, funcValue.getClass(), posargs, kwargs, env);
      return descriptor.call(funcValue, javaArguments, getLocation(), env);
    } else {
      throw new EvalException(
          getLocation(), "'" + EvalUtils.getDataTypeName(funcValue) + "' object is not callable");
    }
  }

  /**
   * Returns the value of the argument 'name' (or null if there is none).
   * This function is used to associate debugging information to rules created by skylark "macros".
   */
  @Nullable
  public String getNameArg() {
    for (Argument.Passed arg : arguments) {
      if (arg != null) {
        String name = arg.getName();
        if (name != null && name.equals("name")) {
          Expression expr = arg.getValue();
          return (expr instanceof StringLiteral) ? ((StringLiteral) expr).getValue() : null;
        }
      }
    }
    return null;
  }

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

  @Override
  public Kind kind() {
    return Kind.FUNCALL;
  }

  @Override
  protected boolean isNewScope() {
    return true;
  }
}