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Higher order type relations for mapped types #12351

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Nov 18, 2016
Merged

Higher order type relations for mapped types #12351

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2646828
Type relations for generic mapped types
ahejlsberg Nov 18, 2016
63387bb
Error on circular constraints in mapped types
ahejlsberg Nov 18, 2016
79bdc26
Accept new baselines
ahejlsberg Nov 18, 2016
075a3eb
Add new tests
ahejlsberg Nov 18, 2016
2376e30
Support apparent types for T[K] indexed access types
ahejlsberg Nov 18, 2016
a789990
Add tests
ahejlsberg Nov 18, 2016
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126 changes: 97 additions & 29 deletions src/compiler/checker.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -120,6 +120,7 @@ namespace ts {
const intersectionTypes = createMap<IntersectionType>();
const stringLiteralTypes = createMap<LiteralType>();
const numericLiteralTypes = createMap<LiteralType>();
const indexedAccessTypes = createMap<IndexedAccessType>();
const evolvingArrayTypes: EvolvingArrayType[] = [];

const unknownSymbol = createSymbol(SymbolFlags.Property | SymbolFlags.Transient, "unknown");
Expand Down Expand Up @@ -4665,13 +4666,22 @@ namespace ts {
return type.resolvedApparentType;
}

/**
* The apparent type of an indexed access T[K] is the type of T's string index signature, if any.
*/
function getApparentTypeOfIndexedAccess(type: IndexedAccessType) {
return getIndexTypeOfType(getApparentType(type.objectType), IndexKind.String) || type;
}

/**
* For a type parameter, return the base constraint of the type parameter. For the string, number,
* boolean, and symbol primitive types, return the corresponding object types. Otherwise return the
* type itself. Note that the apparent type of a union type is the union type itself.
*/
function getApparentType(type: Type): Type {
const t = type.flags & TypeFlags.TypeParameter ? getApparentTypeOfTypeParameter(<TypeParameter>type) : type;
const t = type.flags & TypeFlags.TypeParameter ? getApparentTypeOfTypeParameter(<TypeParameter>type) :
type.flags & TypeFlags.IndexedAccess ? getApparentTypeOfIndexedAccess(<IndexedAccessType>type) :
type;
return t.flags & TypeFlags.StringLike ? globalStringType :
t.flags & TypeFlags.NumberLike ? globalNumberType :
t.flags & TypeFlags.BooleanLike ? globalBooleanType :
Expand Down Expand Up @@ -5907,6 +5917,7 @@ namespace ts {

function getIndexType(type: Type): Type {
return type.flags & TypeFlags.TypeParameter ? getIndexTypeForTypeParameter(<TypeParameter>type) :
getObjectFlags(type) & ObjectFlags.Mapped ? getConstraintTypeFromMappedType(<MappedType>type) :
type.flags & TypeFlags.Any || getIndexInfoOfType(type, IndexKind.String) ? stringOrNumberType :
getIndexInfoOfType(type, IndexKind.Number) ? getUnionType([numberType, getLiteralTypeFromPropertyNames(type)]) :
getLiteralTypeFromPropertyNames(type);
Expand All @@ -5920,18 +5931,13 @@ namespace ts {
return links.resolvedType;
}

function createIndexedAccessType(objectType: Type, indexType: TypeParameter) {
function createIndexedAccessType(objectType: Type, indexType: Type) {
const type = <IndexedAccessType>createType(TypeFlags.IndexedAccess);
type.objectType = objectType;
type.indexType = indexType;
return type;
}

function getIndexedAccessTypeForTypeParameter(objectType: Type, indexType: TypeParameter) {
const indexedAccessTypes = indexType.resolvedIndexedAccessTypes || (indexType.resolvedIndexedAccessTypes = []);
return indexedAccessTypes[objectType.id] || (indexedAccessTypes[objectType.id] = createIndexedAccessType(objectType, indexType));
}

function getPropertyTypeForIndexType(objectType: Type, indexType: Type, accessNode: ElementAccessExpression | IndexedAccessTypeNode, cacheSymbol: boolean) {
const accessExpression = accessNode && accessNode.kind === SyntaxKind.ElementAccessExpression ? <ElementAccessExpression>accessNode : undefined;
const propName = indexType.flags & (TypeFlags.StringLiteral | TypeFlags.NumberLiteral | TypeFlags.EnumLiteral) ?
Expand Down Expand Up @@ -5995,13 +6001,41 @@ namespace ts {
return unknownType;
}

function getIndexedAccessForMappedType(type: MappedType, indexType: Type, accessNode?: ElementAccessExpression | IndexedAccessTypeNode) {
const accessExpression = accessNode && accessNode.kind === SyntaxKind.ElementAccessExpression ? <ElementAccessExpression>accessNode : undefined;
if (accessExpression && isAssignmentTarget(accessExpression) && type.declaration.readonlyToken) {
error(accessExpression, Diagnostics.Index_signature_in_type_0_only_permits_reading, typeToString(type));
return unknownType;
}
const mapper = createUnaryTypeMapper(getTypeParameterFromMappedType(type), indexType);
const templateMapper = type.mapper ? combineTypeMappers(type.mapper, mapper) : mapper;
return addOptionality(instantiateType(getTemplateTypeFromMappedType(type), templateMapper), !!type.declaration.questionToken);
}

function getIndexedAccessType(objectType: Type, indexType: Type, accessNode?: ElementAccessExpression | IndexedAccessTypeNode) {
if (indexType.flags & TypeFlags.TypeParameter) {
if (accessNode && !isTypeAssignableTo(getConstraintOfTypeParameter(<TypeParameter>indexType) || emptyObjectType, getIndexType(objectType))) {
error(accessNode, Diagnostics.Type_0_is_not_constrained_to_keyof_1, typeToString(indexType), typeToString(objectType));
return unknownType;
if (indexType.flags & TypeFlags.TypeParameter ||
objectType.flags & TypeFlags.TypeParameter && indexType.flags & TypeFlags.Index ||
isGenericMappedType(objectType)) {
// If either the object type or the index type are type parameters, or if the object type is a mapped
// type with a generic constraint, we are performing a higher-order index access where we cannot
// meaningfully access the properties of the object type. In those cases, we first check that the
// index type is assignable to 'keyof T' for the object type.
if (accessNode) {
const keyType = indexType.flags & TypeFlags.TypeParameter ? getConstraintOfTypeParameter(<TypeParameter>indexType) || emptyObjectType : indexType;
if (!isTypeAssignableTo(keyType, getIndexType(objectType))) {
error(accessNode, Diagnostics.Type_0_cannot_be_used_to_index_type_1, typeToString(indexType), typeToString(objectType));
return unknownType;
}
}
// If the object type is a mapped type { [P in K]: E }, we instantiate E using a mapper that substitutes
// the index type for P. For example, for an index access { [P in K]: Box<T[P]> }[X], we construct the
// type Box<T[X]>.
if (isGenericMappedType(objectType)) {
return getIndexedAccessForMappedType(<MappedType>objectType, indexType, accessNode);
}
return getIndexedAccessTypeForTypeParameter(objectType, <TypeParameter>indexType);
// Otherwise we defer the operation by creating an indexed access type.
const id = objectType.id + "," + indexType.id;
return indexedAccessTypes[id] || (indexedAccessTypes[id] = createIndexedAccessType(objectType, indexType));
}
const apparentType = getApparentType(objectType);
if (indexType.flags & TypeFlags.Union && !(indexType.flags & TypeFlags.Primitive)) {
Expand Down Expand Up @@ -6034,6 +6068,9 @@ namespace ts {
type.aliasSymbol = getAliasSymbolForTypeNode(node);
type.aliasTypeArguments = getAliasTypeArgumentsForTypeNode(node);
links.resolvedType = type;
// Eagerly resolve the constraint type which forces an error if the constraint type circularly
// references itself through one or more type aliases.
getConstraintTypeFromMappedType(type);
}
return links.resolvedType;
}
Expand Down Expand Up @@ -7153,12 +7190,24 @@ namespace ts {
}

if (target.flags & TypeFlags.TypeParameter) {
// Given a type parameter K with a constraint keyof T, a type S is
// assignable to K if S is assignable to keyof T.
const constraint = getConstraintOfTypeParameter(<TypeParameter>target);
if (constraint && constraint.flags & TypeFlags.Index) {
if (result = isRelatedTo(source, constraint, reportErrors)) {
return result;
// A source type { [P in keyof T]: X } is related to a target type T if X is related to T[P].
if (getObjectFlags(source) & ObjectFlags.Mapped && getConstraintTypeFromMappedType(<MappedType>source) === getIndexType(target)) {
if (!(<MappedType>source).declaration.questionToken) {
const templateType = getTemplateTypeFromMappedType(<MappedType>source);
const indexedAccessType = getIndexedAccessType(target, getTypeParameterFromMappedType(<MappedType>source));
if (result = isRelatedTo(templateType, indexedAccessType, reportErrors)) {
return result;
}
}
}
else {
// Given a type parameter K with a constraint keyof T, a type S is
// assignable to K if S is assignable to keyof T.
const constraint = getConstraintOfTypeParameter(<TypeParameter>target);
if (constraint && constraint.flags & TypeFlags.Index) {
if (result = isRelatedTo(source, constraint, reportErrors)) {
return result;
}
}
}
}
Expand All @@ -7178,22 +7227,41 @@ namespace ts {
}
}
}
else if (target.flags & TypeFlags.IndexedAccess) {
// if we have indexed access types with identical index types, see if relationship holds for
// the two object types.
if (source.flags & TypeFlags.IndexedAccess && (<IndexedAccessType>source).indexType === (<IndexedAccessType>target).indexType) {
if (result = isRelatedTo((<IndexedAccessType>source).objectType, (<IndexedAccessType>target).objectType, reportErrors)) {
return result;
}
}
}

if (source.flags & TypeFlags.TypeParameter) {
let constraint = getConstraintOfTypeParameter(<TypeParameter>source);

if (!constraint || constraint.flags & TypeFlags.Any) {
constraint = emptyObjectType;
// A source type T is related to a target type { [P in keyof T]: X } if T[P] is related to X.
if (getObjectFlags(target) & ObjectFlags.Mapped && getConstraintTypeFromMappedType(<MappedType>target) === getIndexType(source)) {
const indexedAccessType = getIndexedAccessType(source, getTypeParameterFromMappedType(<MappedType>target));
const templateType = getTemplateTypeFromMappedType(<MappedType>target);
if (result = isRelatedTo(indexedAccessType, templateType, reportErrors)) {
return result;
}
}
else {
let constraint = getConstraintOfTypeParameter(<TypeParameter>source);

// The constraint may need to be further instantiated with its 'this' type.
constraint = getTypeWithThisArgument(constraint, source);
if (!constraint || constraint.flags & TypeFlags.Any) {
constraint = emptyObjectType;
}

// Report constraint errors only if the constraint is not the empty object type
const reportConstraintErrors = reportErrors && constraint !== emptyObjectType;
if (result = isRelatedTo(constraint, target, reportConstraintErrors)) {
errorInfo = saveErrorInfo;
return result;
// The constraint may need to be further instantiated with its 'this' type.
constraint = getTypeWithThisArgument(constraint, source);

// Report constraint errors only if the constraint is not the empty object type
const reportConstraintErrors = reportErrors && constraint !== emptyObjectType;
if (result = isRelatedTo(constraint, target, reportConstraintErrors)) {
errorInfo = saveErrorInfo;
return result;
}
}
}
else {
Expand Down
2 changes: 1 addition & 1 deletion src/compiler/diagnosticMessages.json
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Original file line number Diff line number Diff line change
Expand Up @@ -1731,7 +1731,7 @@
"category": "Error",
"code": 2535
},
"Type '{0}' is not constrained to 'keyof {1}'.": {
"Type '{0}' cannot be used to index type '{1}'.": {
"category": "Error",
"code": 2536
},
Expand Down
4 changes: 1 addition & 3 deletions src/compiler/types.ts
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Expand Up @@ -2974,8 +2974,6 @@ namespace ts {
/* @internal */
resolvedIndexType: IndexType;
/* @internal */
resolvedIndexedAccessTypes: IndexedAccessType[];
/* @internal */
isThisType?: boolean;
}

Expand All @@ -2985,7 +2983,7 @@ namespace ts {

export interface IndexedAccessType extends Type {
objectType: Type;
indexType: TypeParameter;
indexType: Type;
}

export const enum SignatureKind {
Expand Down
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