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isTypeReadonly.ts
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isTypeReadonly.ts
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import {
isObjectType,
isUnionType,
isUnionOrIntersectionType,
unionTypeParts,
isPropertyReadonlyInType,
} from 'tsutils';
import * as ts from 'typescript';
import { nullThrows, NullThrowsReasons } from '.';
/**
* Returns:
* - null if the type is not an array or tuple,
* - true if the type is a readonly array or readonly tuple,
* - false if the type is a mutable array or mutable tuple.
*/
function isTypeReadonlyArrayOrTuple(
checker: ts.TypeChecker,
type: ts.Type,
): boolean | null {
function checkTypeArguments(arrayType: ts.TypeReference): boolean {
const typeArguments = checker.getTypeArguments(arrayType);
/* istanbul ignore if */ if (typeArguments.length === 0) {
// this shouldn't happen in reality as:
// - tuples require at least 1 type argument
// - ReadonlyArray requires at least 1 type argument
return true;
}
// validate the element types are also readonly
if (typeArguments.some(typeArg => !isTypeReadonly(checker, typeArg))) {
return false;
}
return true;
}
if (checker.isArrayType(type)) {
const symbol = nullThrows(
type.getSymbol(),
NullThrowsReasons.MissingToken('symbol', 'array type'),
);
const escapedName = symbol.getEscapedName();
if (escapedName === 'Array' && escapedName !== 'ReadonlyArray') {
return false;
}
return checkTypeArguments(type);
}
if (checker.isTupleType(type)) {
if (!type.target.readonly) {
return false;
}
return checkTypeArguments(type);
}
return null;
}
/**
* Returns:
* - null if the type is not an object,
* - true if the type is an object with only readonly props,
* - false if the type is an object with at least one mutable prop.
*/
function isTypeReadonlyObject(
checker: ts.TypeChecker,
type: ts.Type,
): boolean | null {
function checkIndexSignature(kind: ts.IndexKind): boolean | null {
const indexInfo = checker.getIndexInfoOfType(type, kind);
if (indexInfo) {
return indexInfo.isReadonly ? true : false;
}
return null;
}
const properties = type.getProperties();
if (properties.length) {
// ensure the properties are marked as readonly
for (const property of properties) {
if (!isPropertyReadonlyInType(type, property.getEscapedName(), checker)) {
return false;
}
}
// all properties were readonly
// now ensure that all of the values are readonly also.
// do this after checking property readonly-ness as a perf optimization,
// as we might be able to bail out early due to a mutable property before
// doing this deep, potentially expensive check.
for (const property of properties) {
const propertyType = nullThrows(
checker.getTypeOfPropertyOfType(type, property.getName()),
NullThrowsReasons.MissingToken(`property "${property.name}"`, 'type'),
);
if (!isTypeReadonly(checker, propertyType)) {
return false;
}
}
}
const isStringIndexSigReadonly = checkIndexSignature(ts.IndexKind.String);
if (isStringIndexSigReadonly === false) {
return isStringIndexSigReadonly;
}
const isNumberIndexSigReadonly = checkIndexSignature(ts.IndexKind.Number);
if (isNumberIndexSigReadonly === false) {
return isNumberIndexSigReadonly;
}
return true;
}
/**
* Checks if the given type is readonly
*/
function isTypeReadonly(checker: ts.TypeChecker, type: ts.Type): boolean {
if (isUnionType(type)) {
// all types in the union must be readonly
return unionTypeParts(type).every(t => isTypeReadonly(checker, t));
}
// all non-object, non-intersection types are readonly.
// this should only be primitive types
if (!isObjectType(type) && !isUnionOrIntersectionType(type)) {
return true;
}
// pure function types are readonly
if (
type.getCallSignatures().length > 0 &&
type.getProperties().length === 0
) {
return true;
}
const isReadonlyArray = isTypeReadonlyArrayOrTuple(checker, type);
if (isReadonlyArray !== null) {
return isReadonlyArray;
}
const isReadonlyObject = isTypeReadonlyObject(checker, type);
/* istanbul ignore else */ if (isReadonlyObject !== null) {
return isReadonlyObject;
}
throw new Error('Unhandled type');
}
export { isTypeReadonly };