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Closure Compiler is a JavaScript optimizing compiler. It parses your JavaScript, analyzes it, removes dead code and rewrites and minimizes what's left. It also checks syntax, variable references, and types, and warns about common JavaScript pitfalls. It is used in many of Google's JavaScript apps, including Gmail, Google Web Search, Google Maps, and Google Docs.
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/*
 * Copyright 2017 The Closure Compiler Authors.
 *
 * 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.javascript.jscomp;

import static com.google.common.base.Preconditions.checkState;

import com.google.common.base.Supplier;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Multimap;
import com.google.javascript.rhino.ObjectTypeI;
import com.google.javascript.rhino.TypeI;
import com.google.javascript.rhino.TypeIRegistry;
import com.google.javascript.rhino.jstype.JSTypeNative;
import javax.annotation.Nullable;

/**
 * Keeps track of "invalidating types" that force type-based
 * optimizations to back off, specifically for {@link InlineProperties},
 * {@link AmbiguateProperties}, and {@link DisambiguateProperties}.
 * Note that disambiguation has slightly different behavior from the
 * other two, as pointed out in implementation comments.
 */
final class InvalidatingTypes {

  private final ImmutableSet types;
  private final boolean allowEnums;
  private final boolean allowScalars;

  private InvalidatingTypes(Builder builder) {
    this.types = builder.types.build();
    this.allowEnums = builder.allowEnums;
    this.allowScalars = builder.allowScalars;
  }

  boolean isInvalidating(TypeI type) {
    if (type == null || type.isUnknownType() || type.isBottom()) {
      return true;
    }
    if (type.isUnionType()) {
      type = type.restrictByNotNullOrUndefined();
      if (type.isUnionType()) {
        for (TypeI alt : type.getUnionMembers()) {
          if (isInvalidating(alt)) {
            return true;
          }
        }
        return false;
      }
    }

    ObjectTypeI objType = type.toMaybeObjectType();

    if (objType == null) {
      return !allowScalars;
    }
    return types.contains(objType)
        || objType.isAmbiguousObject()
        || (!allowEnums && objType.isEnumObject())
        || (!allowScalars && objType.isBoxableScalar());
  }

  static final class Builder {
    private final ImmutableSet.Builder types = ImmutableSet.builder();
    private final TypeIRegistry registry;
    private boolean allowEnums = false;
    private boolean allowScalars = false;
    @Nullable private Multimap> invalidationMap;

    Builder(TypeIRegistry registry) {
      this.registry = registry;
    }

    InvalidatingTypes build() {
      return new InvalidatingTypes(this);
    }

    // TODO(sdh): Investigate whether this can be consolidated between all three passes.
    // In particular, mutation testing suggests allowEnums=true should work everywhere.
    // We should revisit what breaks when we disallow scalars everywhere.
    Builder recordInvalidations(@Nullable Multimap> invalidationMap) {
      this.invalidationMap = invalidationMap;
      return this;
    }

    Builder allowEnumsAndScalars() {
      // Ambiguate and Inline do not allow enums or scalars.
      this.allowEnums = this.allowScalars = true;
      return this;
    }

    Builder disallowGlobalThis() {
      // Disambiguate does not invalidate global this because it
      // sets skipping explicitly for extern properties only on
      // the extern types.
      types.add(registry.getNativeType(JSTypeNative.GLOBAL_THIS));
      return this;
    }

    Builder addAllTypeMismatches(Iterable mismatches) {
      for (TypeMismatch mis : mismatches) {
        addType(mis.typeA, mis);
        addType(mis.typeB, mis);
      }
      return this;
    }

    Builder addTypesInvalidForPropertyRenaming() {
      types.addAll(
          ImmutableList.of(
              registry.getNativeType(JSTypeNative.FUNCTION_FUNCTION_TYPE),
              registry.getNativeType(JSTypeNative.FUNCTION_INSTANCE_TYPE),
              registry.getNativeType(JSTypeNative.FUNCTION_PROTOTYPE),
              registry.getNativeType(JSTypeNative.OBJECT_TYPE),
              registry.getNativeType(JSTypeNative.OBJECT_PROTOTYPE),
              registry.getNativeType(JSTypeNative.OBJECT_FUNCTION_TYPE),
              registry.getNativeType(JSTypeNative.TOP_LEVEL_PROTOTYPE)));
      return this;
    }

    /** Invalidates the given type, so that no properties on it will be inlined or renamed. */
    private Builder addType(TypeI type, TypeMismatch mismatch) {
      type = type.restrictByNotNullOrUndefined();
      if (type.isUnionType()) {
        for (TypeI alt : type.getUnionMembers()) {
          addType(alt, mismatch);
        }
      } else if (type.isEnumElement()) { // only in disamb
        addType(type.getEnumeratedTypeOfEnumElement(), mismatch);
      } else { // amb and inl both do this without the else
        checkState(!type.isUnionType());
        types.add(type);
        recordInvalidation(type, mismatch);

        ObjectTypeI objType = type.toMaybeObjectType();
        if (objType != null) {
          ObjectTypeI proto = objType.getPrototypeObject();
          if (proto != null) {
            types.add(proto);
            recordInvalidation(proto, mismatch);
          }
          if (objType.isConstructor()) {
            types.add(objType.toMaybeFunctionType().getInstanceType());
          } else if (objType.isInstanceType()) {
            types.add(objType.getConstructor());
          }
        }
      }
      return this;
    }

    private void recordInvalidation(TypeI t, TypeMismatch mis) {
      if (!t.isObjectType()) {
        return;
      }
      if (invalidationMap != null) {
        invalidationMap.put(t, mis.error);
      }
    }
  }
}