com.google.javascript.rhino.jstype.UnionType Maven / Gradle / Ivy
/*
*
* ***** BEGIN LICENSE BLOCK *****
* Version: MPL 1.1/GPL 2.0
*
* The contents of this file are subject to the Mozilla Public License Version
* 1.1 (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.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
* for the specific language governing rights and limitations under the
* License.
*
* The Original Code is Rhino code, released
* May 6, 1999.
*
* The Initial Developer of the Original Code is
* Netscape Communications Corporation.
* Portions created by the Initial Developer are Copyright (C) 1997-1999
* the Initial Developer. All Rights Reserved.
*
* Contributor(s):
* Bob Jervis
* Google Inc.
*
* Alternatively, the contents of this file may be used under the terms of
* the GNU General Public License Version 2 or later (the "GPL"), in which
* case the provisions of the GPL are applicable instead of those above. If
* you wish to allow use of your version of this file only under the terms of
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* MPL, indicate your decision by deleting the provisions above and replacing
* them with the notice and other provisions required by the GPL. If you do
* not delete the provisions above, a recipient may use your version of this
* file under either the MPL or the GPL.
*
* ***** END LICENSE BLOCK ***** */
package com.google.javascript.rhino.jstype;
import static com.google.common.base.Preconditions.checkState;
import static com.google.javascript.rhino.jstype.JSTypeIterations.allTypesMatch;
import static com.google.javascript.rhino.jstype.JSTypeIterations.anyTypeMatches;
import static com.google.javascript.rhino.jstype.JSTypeIterations.mapTypes;
import static com.google.javascript.rhino.jstype.JSTypeNative.ALL_TYPE;
import static com.google.javascript.rhino.jstype.JSTypeNative.CHECKED_UNKNOWN_TYPE;
import static com.google.javascript.rhino.jstype.JSTypeNative.NO_TYPE;
import static com.google.javascript.rhino.jstype.JSTypeNative.UNKNOWN_TYPE;
import static com.google.javascript.rhino.jstype.JSTypeNative.VOID_TYPE;
import static com.google.javascript.rhino.jstype.TernaryValue.UNKNOWN;
import com.google.common.collect.ImmutableList;
import com.google.javascript.rhino.ErrorReporter;
import com.google.javascript.rhino.Outcome;
import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
import java.util.TreeSet;
import javax.annotation.Nullable;
/**
* A type that may be any one of a set of types, and thus has the intersection of the properties of
* those types.
*
* The {@code UnionType} implements a common JavaScript idiom in which the code is specifically
* designed to work with multiple input types. Because JavaScript always knows the run-time type of
* an object value, this is safer than a C union.
*
*
For instance, values of the union type {@code (String,boolean)} can be of type {@code String}
* or of type {@code boolean}. The commutativity of the statement is captured by making {@code
* (String,boolean)} and {@code (boolean,String)} equal.
*
*
The implementation of this class prevents the creation of nested unions.
*/
public class UnionType extends JSType {
private static final JSTypeClass TYPE_CLASS = JSTypeClass.UNION;
/**
* Generally, if the best we can do is say "this object is one of thirty things", then we should
* just give up and admit that we have no clue.
*/
private static final int MAX_UNION_SIZE = 30;
/**
* The types that are unioned.
*
*
We use a List rather than a Set so that we can iterate by index. This is substantially more
* efficient than using the for-each idiom due to the overhead of allocating iterators. All loops
* over this collection should be indexed.
*/
private ImmutableList alternates;
/**
* Creates a union.
*
* This ctor is private because all instances are created using a {@link Builder}. The builder
* is also responsible for setting the alternates, which is why they aren't passed as a parameter.
*/
private UnionType(JSTypeRegistry registry, ImmutableList alternates) {
super(registry);
this.setAlternates(alternates);
registry.getResolver().resolveIfClosed(this, TYPE_CLASS);
}
@Override
JSTypeClass getTypeClass() {
return TYPE_CLASS;
}
/** Creates a {@link Builder} for a new {@link UnionType}. */
public static Builder builder(JSTypeRegistry registry) {
return new Builder(registry);
}
/**
* Gets the alternate types of this union type.
*
* @return The alternate types of this union type. The returned set is immutable.
*/
public ImmutableList getAlternates() {
if (!this.isResolved() && anyTypeMatches(JSType::isUnionType, this.alternates)) {
rebuildAlternates();
}
return alternates;
}
/** Use a {@link Builder} to rebuild the list of alternates. */
private void rebuildAlternates() {
setAlternates(new Builder(this).addAlternates(this.alternates).buildInternal());
}
private UnionType setAlternates(ImmutableList alternates) {
checkState(!alternates.isEmpty());
this.alternates = alternates;
return this;
}
/**
* This predicate is used to test whether a given type can appear in a
* numeric context, such as an operand of a multiply operator.
*
* @return true if the type can appear in a numeric context.
*/
@Override
public boolean matchesNumberContext() {
// TODO(user): Reverse this logic to make it correct instead of generous.
return anyTypeMatches(JSType::matchesNumberContext, this);
}
/**
* This predicate is used to test whether a given type can appear in a
* {@code String} context, such as an operand of a string concat ({@code +})
* operator.
*
* All types have at least the potential for converting to {@code String}.
* When we add externally defined types, such as a browser OM, we may choose
* to add types that do not automatically convert to {@code String}.
*
* @return {@code true} if not {@link VoidType}
*/
@Override
public boolean matchesStringContext() {
// TODO(user): Reverse this logic to make it correct instead of generous.
return anyTypeMatches(JSType::matchesStringContext, this);
}
/**
* This predicate is used to test whether a given type can appear in a {@code Symbol} context
*
* @return {@code true} if not it maybe a symbol or Symbol object
*/
@Override
public boolean matchesSymbolContext() {
// TODO(user): Reverse this logic to make it correct instead of generous.
return anyTypeMatches(JSType::matchesSymbolContext, this);
}
/**
* This predicate is used to test whether a given type can appear in an
* {@code Object} context, such as the expression in a {@code with}
* statement.
*
* Most types we will encounter, except notably {@code null}, have at least
* the potential for converting to {@code Object}. Host defined objects can
* get peculiar.
*
* VOID type is included here because while it is not part of the JavaScript
* language, functions returning 'void' type can't be used as operands of
* any operator or statement.
*
* @return {@code true} if the type is not {@link NullType} or
* {@link VoidType}
*/
@Override
public boolean matchesObjectContext() {
// TODO(user): Reverse this logic to make it correct instead of generous.
return anyTypeMatches(JSType::matchesObjectContext, this);
}
@Override
protected JSType findPropertyTypeWithoutConsideringTemplateTypes(String propertyName) {
JSType propertyType = null;
for (JSType alternate : alternates) {
// Filter out the null/undefined type.
if (alternate.isNullType() || alternate.isVoidType()) {
continue;
}
JSType altPropertyType = alternate.findPropertyType(propertyName);
if (altPropertyType == null) {
continue;
}
if (propertyType == null) {
propertyType = altPropertyType;
} else {
propertyType = propertyType.getLeastSupertype(altPropertyType);
}
}
return propertyType;
}
@Override
public boolean canBeCalled() {
return allTypesMatch(JSType::canBeCalled, this);
}
@Override
public JSType autobox() {
return mapTypes(JSType::autobox, this);
}
@Override
public JSType restrictByNotNullOrUndefined() {
return mapTypes(JSType::restrictByNotNullOrUndefined, this);
}
@Override
public JSType restrictByNotUndefined() {
return mapTypes(JSType::restrictByNotUndefined, this);
}
@Override
public JSType restrictByNotNull() {
return mapTypes(JSType::restrictByNotNull, this);
}
@Override
public TernaryValue testForEquality(JSType that) {
TernaryValue result = null;
for (int i = 0; i < alternates.size(); i++) {
JSType t = alternates.get(i);
TernaryValue test = t.testForEquality(that);
if (result == null) {
result = test;
} else if (!result.equals(test)) {
return UNKNOWN;
}
}
return result;
}
/**
* This predicate determines whether objects of this type can have the
* {@code null} value, and therefore can appear in contexts where
* {@code null} is expected.
*
* @return {@code true} for everything but {@code Number} and
* {@code Boolean} types.
*/
@Override
public boolean isNullable() {
return anyTypeMatches(JSType::isNullable, this);
}
/**
* Tests whether this type is voidable.
*/
@Override
public boolean isVoidable() {
return anyTypeMatches(JSType::isVoidable, this);
}
/** Tests whether this type explicitly allows undefined (as opposed to ? or *). */
@Override
public boolean isExplicitlyVoidable() {
return anyTypeMatches(JSType::isExplicitlyVoidable, this);
}
@Override
public boolean isUnknownType() {
return anyTypeMatches(JSType::isUnknownType, this);
}
@Override
public boolean isStruct() {
return anyTypeMatches(JSType::isStruct, this);
}
@Override
public boolean isDict() {
return anyTypeMatches(JSType::isDict, this);
}
@Override
public JSType getLeastSupertype(JSType that) {
if (!that.isUnknownType() && !that.isUnionType()) {
for (int i = 0; i < alternates.size(); i++) {
JSType alternate = alternates.get(i);
if (!alternate.isUnknownType() && that.isSubtypeOf(alternate)) {
return this;
}
}
}
return JSType.getLeastSupertype(this, that);
}
static JSType getGreatestSubtype(UnionType union, JSType that) {
// This method is implemented as a static because we don't want polymorphism. Ideally all the
// `greatestSubtype` code would be in one place. Until then, using static calls minimizes
// confusion.
JSTypeRegistry registry = union.registry;
Builder builder = builder(registry);
for (int i = 0; i < union.alternates.size(); i++) {
JSType alternate = union.alternates.get(i);
if (alternate.isSubtypeOf(that)) {
builder.addAlternate(alternate);
}
}
if (that.isUnionType()) {
List thoseAlternates = that.toMaybeUnionType().getAlternates();
for (int i = 0; i < thoseAlternates.size(); i++) {
JSType otherAlternate = thoseAlternates.get(i);
if (otherAlternate.isSubtypeOf(union)) {
builder.addAlternate(otherAlternate);
}
}
} else if (that.isSubtypeOf(union)) {
builder.addAlternate(that);
}
JSType result = builder.build();
if (!result.isNoType()) {
return result;
} else if (union.isObject() && (that.isObject() && !that.isNoType())) {
return registry.getNativeType(JSTypeNative.NO_OBJECT_TYPE);
} else {
return registry.getNativeType(JSTypeNative.NO_TYPE);
}
}
@Override
public HasPropertyKind getPropertyKind(String pname, boolean autobox) {
boolean found = false;
boolean always = true;
for (int i = 0; i < alternates.size(); i++) {
JSType alternate = alternates.get(i);
if (alternate.isNullType() || alternate.isVoidType()) {
continue;
}
switch (alternate.getPropertyKind(pname, autobox)) {
case KNOWN_PRESENT:
found = true;
break;
case ABSENT:
always = false;
break;
case MAYBE_PRESENT:
found = true;
always = false;
break;
}
if (found && !always) {
break;
}
}
return found
? (always ? HasPropertyKind.KNOWN_PRESENT : HasPropertyKind.MAYBE_PRESENT)
: HasPropertyKind.ABSENT;
}
@Override
final int recursionUnsafeHashCode() {
int hashCode = alternates.size();
for (int i = 0; i < alternates.size(); i++) {
// To be determinisitic this aggregation must be order-independent. Using a commutative
// operatator (multiplication) allows us to achieve that without sorting. Multiplication also
// has some nice properties about reducing collisions compared to addition or xor.
hashCode *= alternates.get(i).hashCode();
}
return hashCode;
}
@Override
public UnionType toMaybeUnionType() {
return this;
}
@Override
public boolean isObject() {
return allTypesMatch(JSType::isObject, this);
}
/**
* A {@link UnionType} contains a given type (alternate) iff the member
* vector contains it.
*
* @param type The alternate which might be in this union.
*
* @return {@code true} if the alternate is in the union
*/
public boolean contains(JSType type) {
return anyTypeMatches(type::equals, this);
}
/**
* Returns a more restricted union type than {@code this} one, in which all
* subtypes of {@code type} have been removed.
*
* Examples:
*
* - {@code (number,string)} restricted by {@code number} is
* {@code string}
* - {@code (null, EvalError, URIError)} restricted by
* {@code Error} is {@code null}
*
*
* @param type the supertype of the types to remove from this union type
*/
public JSType getRestrictedUnion(JSType type) {
Builder restricted = builder(registry);
for (int i = 0; i < alternates.size(); i++) {
JSType t = alternates.get(i);
// Keep all unknown/unresolved types.
if (t.isUnknownType() || t.isNoResolvedType() || !t.isSubtypeOf(type)) {
restricted.addAlternate(t);
}
}
return restricted.build();
}
@Override
void appendTo(TypeStringBuilder sb) {
sb.append("(");
// Sort types by stringification to get deterministic behaviour.
TreeSet sortedNames = new TreeSet<>();
for (JSType alt : this.alternates) {
// Clone the config to preserve indentation.
sortedNames.add(sb.cloneWithConfig().append(alt).build());
}
sb.appendAll(sortedNames, "|");
sb.append(")");
}
@Override
public JSType getRestrictedTypeGivenOutcome(
Outcome outcome) {
return mapTypes((t) -> t.getRestrictedTypeGivenOutcome(outcome), this);
}
@Override
public BooleanLiteralSet getPossibleToBooleanOutcomes() {
BooleanLiteralSet literals = BooleanLiteralSet.EMPTY;
for (int i = 0; i < alternates.size(); i++) {
JSType element = alternates.get(i);
literals = literals.union(element.getPossibleToBooleanOutcomes());
if (literals == BooleanLiteralSet.BOTH) {
break;
}
}
return literals;
}
@Override
public TypePair getTypesUnderEquality(JSType that) {
Builder thisRestricted = builder(registry);
Builder thatRestricted = builder(registry);
for (int i = 0; i < alternates.size(); i++) {
JSType element = alternates.get(i);
TypePair p = element.getTypesUnderEquality(that);
if (p.typeA != null) {
thisRestricted.addAlternate(p.typeA);
}
if (p.typeB != null) {
thatRestricted.addAlternate(p.typeB);
}
}
return new TypePair(
thisRestricted.build(),
thatRestricted.build());
}
@Override
public TypePair getTypesUnderInequality(JSType that) {
Builder thisRestricted = builder(registry);
Builder thatRestricted = builder(registry);
for (int i = 0; i < alternates.size(); i++) {
JSType element = alternates.get(i);
TypePair p = element.getTypesUnderInequality(that);
if (p.typeA != null) {
thisRestricted.addAlternate(p.typeA);
}
if (p.typeB != null) {
thatRestricted.addAlternate(p.typeB);
}
}
return new TypePair(
thisRestricted.build(),
thatRestricted.build());
}
@Override
public TypePair getTypesUnderShallowInequality(JSType that) {
Builder thisRestricted = builder(registry);
Builder thatRestricted = builder(registry);
for (int i = 0; i < alternates.size(); i++) {
JSType element = alternates.get(i);
TypePair p = element.getTypesUnderShallowInequality(that);
if (p.typeA != null) {
thisRestricted.addAlternate(p.typeA);
}
if (p.typeB != null) {
thatRestricted.addAlternate(p.typeB);
}
}
return new TypePair(
thisRestricted.build(),
thatRestricted.build());
}
@Override
public T visit(Visitor visitor) {
return visitor.caseUnionType(this);
}
@Override T visit(RelationshipVisitor visitor, JSType that) {
return visitor.caseUnionType(this, that);
}
@Override
JSType resolveInternal(ErrorReporter reporter) {
for (int i = 0; i < alternates.size(); i++) {
JSType alternate = alternates.get(i);
alternate.resolve(reporter);
}
// Ensure the union is in a normalized state.
rebuildAlternates();
if (alternates.size() == 1) {
return alternates.get(0);
}
return this;
}
@Override
public JSType collapseUnion() {
JSType currentValue = null;
ObjectType currentCommonSuper = null;
for (int i = 0; i < alternates.size(); i++) {
JSType a = alternates.get(i);
if (a.isUnknownType()) {
return getNativeType(JSTypeNative.UNKNOWN_TYPE);
}
ObjectType obj = a.toObjectType();
if (obj == null) {
if (currentValue == null && currentCommonSuper == null) {
// If obj is not an object, then it must be a value.
currentValue = a;
} else {
// Multiple values and objects will always collapse to the ALL_TYPE.
return getNativeType(JSTypeNative.ALL_TYPE);
}
} else if (currentValue != null) {
// Values and objects will always collapse to the ALL_TYPE.
return getNativeType(JSTypeNative.ALL_TYPE);
} else if (currentCommonSuper == null) {
currentCommonSuper = obj;
} else {
currentCommonSuper =
registry.findCommonSuperObject(currentCommonSuper, obj);
}
}
return currentCommonSuper;
}
@Override
public void matchConstraint(JSType constraint) {
for (int i = 0; i < alternates.size(); i++) {
JSType alternate = alternates.get(i);
alternate.matchConstraint(constraint);
}
}
@Override
public boolean hasAnyTemplateTypesInternal() {
return anyTypeMatches(JSType::hasAnyTemplateTypes, this);
}
/**
* Implements type unioning logic, since {@link UnionType}s only actually need to perform unioning
* operations when being (re)built.
*
* {@link Builder}s exist in two forms. One for assembing a new union and one for updating an
* existing union. Only the former is exposed.
*
*
Most users of this class should prefer {@link JSTypeRegistry#createUnionType} instead.
*/
public static final class Builder {
private final UnionType rebuildTarget;
private final JSTypeRegistry registry;
private final List alternates = new ArrayList<>();
// If a union has ? or *, we do not care about any other types, except for undefined (for
// optional
// properties).
private boolean containsVoidType = false;
private boolean isAllType = false;
private boolean isNativeUnknownType = false;
private boolean areAllUnknownsChecked = true;
// Every UnionType may have at most one structural function in it.
//
// NOTE(nicksantos): I've read some literature that says that type-inferenced
// languages are fundamentally incompatible with union types. I refuse
// to believe this. But they do make the type lattice much more complicated.
//
// For this reason, when we deal with function types, we actually merge some
// nodes on the lattice, and treat them as fundamentally equivalent.
// For example, we treat
// function(): string | function(): number
// as equivalent to
// function(): (string|number)
// and normalize the first type into the second type.
//
// To perform this normalization, we've modified Builder to disallow
// multiple structural functions in a union. We always delegate to
// FunctionType::getLeastSupertype, which either merges the functions into
// one structural function, or just bails out and uses the top function type.
private int functionTypePosition = -1;
private boolean hasBuilt = false;
/** Creates a builder for a new union. */
private Builder(JSTypeRegistry registry) {
this.rebuildTarget = null;
this.registry = registry;
}
/** Creates a re-builder for an existing union. */
private Builder(UnionType rebuildTarget) {
this.rebuildTarget = rebuildTarget;
this.registry = rebuildTarget.registry;
}
private static boolean isSubtype(JSType rightType, JSType leftType) {
return rightType.isSubtypeWithoutStructuralTyping(leftType);
}
public Builder addAlternates(Collection c) {
for (JSType type : c) {
addAlternate(type);
}
return this;
}
// A specific override that avoid creating an iterator. This version is currently used when
// adding a union as an alternate.
public Builder addAlternates(List list) {
for (int i = 0; i < list.size(); i++) {
addAlternate(list.get(i));
}
return this;
}
/**
* Adds an alternate to the union type under construction.
*
* Returns this for easy chaining.
*/
public Builder addAlternate(JSType alternate) {
checkHasNotBuilt();
if (alternate.isUnionType()) {
addAlternates(alternate.toMaybeUnionType().getAlternates());
return this;
}
if (alternates.size() > MAX_UNION_SIZE) {
return this;
}
// Defer removing duplicate elements until all alternates in the union are resolved.
// JSType operations like equality and subtyping are not reliable pre-resolution.
if (!alternate.isResolved()) {
for (JSType current : alternates) {
if (JSType.areIdentical(current, alternate)) {
return this;
}
}
alternates.add(alternate);
return this;
}
// build() returns the bottom type by default, so we can just bail out early here.
if (alternate.isNoType()) {
return this;
}
isAllType = isAllType || alternate.isAllType();
containsVoidType = containsVoidType || alternate.isVoidType();
boolean isAlternateUnknown = alternate instanceof UnknownType;
isNativeUnknownType = isNativeUnknownType || isAlternateUnknown;
if (isAlternateUnknown) {
areAllUnknownsChecked = areAllUnknownsChecked && alternate.isCheckedUnknownType();
}
if (isAllType || isNativeUnknownType) {
return this;
}
// Function types are special, because they have their
// own bizarre sub-lattice. See the comments on
// FunctionType#supAndInf helper and above at functionTypePosition.
if (alternate.isFunctionType() && functionTypePosition != -1) {
// See the comments on functionTypePosition above.
FunctionType other = alternates.get(functionTypePosition).toMaybeFunctionType();
FunctionType supremum = alternate.toMaybeFunctionType().supAndInfHelper(other, true);
alternates.set(functionTypePosition, supremum);
return this;
}
// Look through the alternates we've got so far,
// and check if any of them are duplicates of
// one another.
for (int index = 0; index < alternates.size(); index++) {
boolean removeCurrent = false;
JSType current = alternates.get(index);
if (!current.isResolved()) { // Defer de-duplicating unresolved alternates.
continue;
}
// Unknown and NoResolved types may just be names that haven't
// been resolved yet. So keep these in the union, and just use
// equality checking for simple de-duping.
if (alternate.isUnknownType()
|| current.isUnknownType()
|| alternate.isNoResolvedType()
|| current.isNoResolvedType()
|| alternate.hasAnyTemplateTypes()
|| current.hasAnyTemplateTypes()) {
if (alternate.equals(current)) {
// Alternate is unnecessary.
return this;
}
} else if (alternate.isTemplatizedType() || current.isTemplatizedType()) {
// Because "Foo" and "Foo" are roughly equivalent
// templatized types, special care is needed when building the
// union. For example:
// Object is consider a subtype of Object
// but we want to leave "Object" not "Object" when
// building the subtype.
//
// Cases:
// 1) alternate:Array and current:Object ==> Object
// 2) alternate:Array and current:Array ==> Array
// 3) alternate:Object and
// current:Array ==> Array|Object
// 4) alternate:Object and current:Array ==> Object
// 5) alternate:Array and current:Array ==> Array
// 6) alternate:Array and
// current:Object ==> Array|Object
// 7) alternate:Array and
// current:Array ==> Array
// 8) alternate:Array and
// current:Array ==> Array
// 9) alternate:Array and
// current:Object ==> Object|Array
if (!current.isTemplatizedType()) {
if (isSubtype(alternate, current)) {
// case 1, 2
return this;
}
// case 3: leave current, add alternate
} else if (!alternate.isTemplatizedType()) {
if (isSubtype(current, alternate)) {
// case 4, 5
removeCurrent = true;
}
// case 6: leave current, add alternate
} else {
checkState(current.isTemplatizedType() && alternate.isTemplatizedType());
TemplatizedType templatizedAlternate = alternate.toMaybeTemplatizedType();
TemplatizedType templatizedCurrent = current.toMaybeTemplatizedType();
if (templatizedCurrent.wrapsSameRawType(templatizedAlternate)) {
if (current.equals(alternate)) {
// case 8
return this;
} else {
// case 7: replace with a merged alternate specialized on `?`.
ObjectType rawType = templatizedCurrent.getReferencedObjTypeInternal();
// Providing no type-parameter values specializes `rawType` on `?` by default.
alternate = registry.createTemplatizedType(rawType, ImmutableList.of());
removeCurrent = true;
}
}
// case 9: leave current, add alternate
}
// Otherwise leave both templatized types.
} else if (isSubtype(alternate, current)) {
// Alternate is unnecessary.
mayRegisterDroppedProperties(alternate, current);
return this;
} else if (isSubtype(current, alternate)) {
// Alternate makes current obsolete
mayRegisterDroppedProperties(current, alternate);
removeCurrent = true;
}
if (removeCurrent) {
alternates.remove(index);
if (index == functionTypePosition) {
functionTypePosition = -1;
} else if (index < functionTypePosition) {
functionTypePosition--;
}
index--;
}
}
if (alternate.isFunctionType()) {
// See the comments on functionTypePosition above.
checkState(functionTypePosition == -1);
functionTypePosition = alternates.size();
}
alternates.add(alternate);
return this;
}
private void mayRegisterDroppedProperties(JSType subtype, JSType supertype) {
if (subtype.toMaybeRecordType() != null && supertype.toMaybeRecordType() != null) {
registry.registerDroppedPropertiesInUnion(
subtype.toMaybeRecordType(), supertype.toMaybeRecordType());
}
}
/**
* Returns a type, not necessarily a {@link UnionType}, that represents the union of the inputs.
*
* The {@link Builder} cannot be used again once this method is called.
*/
public JSType build() {
checkState(rebuildTarget == null);
ImmutableList alternates = buildInternal();
if (alternates.size() == 1) {
return alternates.get(0);
} else {
return new UnionType(registry, alternates);
}
}
/** Create the final set of alternates for either a new union or a union being rebuilt. */
private ImmutableList buildInternal() {
checkHasNotBuilt();
this.hasBuilt = true;
JSType wildcard = getNativeWildcardType();
if (wildcard != null) {
if (containsVoidType) {
return ImmutableList.of(wildcard, registry.getNativeType(VOID_TYPE));
} else {
return ImmutableList.of(wildcard);
}
}
if (alternates.isEmpty()) {
// To simplify the typesystem, empty union types are forbidden. Using a single `bottom`
// makes it essentially a proxy instead.
return ImmutableList.of(registry.getNativeType(NO_TYPE));
} else if (alternates.size() > MAX_UNION_SIZE) {
return ImmutableList.of(registry.getNativeType(UNKNOWN_TYPE));
} else {
return ImmutableList.copyOf(alternates);
}
}
/** Returns ALL_TYPE, UNKNOWN_TYPE, CHECKED_UNKNOWN_TYPE, or null as specified by the flags. */
@Nullable
private JSType getNativeWildcardType() {
if (isAllType) {
return registry.getNativeType(ALL_TYPE);
} else if (isNativeUnknownType) {
if (areAllUnknownsChecked) {
return registry.getNativeType(CHECKED_UNKNOWN_TYPE);
} else {
return registry.getNativeType(UNKNOWN_TYPE);
}
}
return null;
}
private void checkHasNotBuilt() {
checkState(!this.hasBuilt, "Cannot reuse a `UnionType.Builder` that has already filled.");
}
}
}