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Preserve type parameter constraint in emitted mapped types while preserving their distributivity (#54759)

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This commit is contained in:
Mateusz Burzyński
2025-05-12 10:54:34 -07:00
committed by GitHub
parent 7156300cee
commit 0fb5e3a8cf
11 changed files with 528 additions and 29 deletions
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src/compiler/checker.ts
+16 -4
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@@ -6963,6 +6963,8 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
const questionToken = type.declaration.questionToken ? factory.createToken(type.declaration.questionToken.kind) as QuestionToken | PlusToken | MinusToken : undefined;
let appropriateConstraintTypeNode: TypeNode;
let newTypeVariable: TypeReferenceNode | undefined;
let templateType = getTemplateTypeFromMappedType(type);
const typeParameter = getTypeParameterFromMappedType(type);
// If the mapped type isn't `keyof` constraint-declared, _but_ still has modifiers preserved, and its naive instantiation won't preserve modifiers because its constraint isn't `keyof` constrained, we have work to do
const needsModifierPreservingWrapper = !isMappedTypeWithKeyofConstraintDeclaration(type)
&& !(getModifiersTypeFromMappedType(type).flags & TypeFlags.Unknown)
@@ -6972,9 +6974,14 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
// We have a { [P in keyof T]: X }
// We do this to ensure we retain the toplevel keyof-ness of the type which may be lost due to keyof distribution during `getConstraintTypeFromMappedType`
if (isHomomorphicMappedTypeWithNonHomomorphicInstantiation(type) && context.flags & NodeBuilderFlags.GenerateNamesForShadowedTypeParams) {
const newParam = createTypeParameter(createSymbol(SymbolFlags.TypeParameter, "T" as __String));
const name = typeParameterToName(newParam, context);
const newConstraintParam = createTypeParameter(createSymbol(SymbolFlags.TypeParameter, "T" as __String));
const name = typeParameterToName(newConstraintParam, context);
const target = type.target as MappedType;
newTypeVariable = factory.createTypeReferenceNode(name);
templateType = instantiateType(
getTemplateTypeFromMappedType(target),
makeArrayTypeMapper([getTypeParameterFromMappedType(target), getModifiersTypeFromMappedType(target)], [typeParameter, newConstraintParam]),
);
}
appropriateConstraintTypeNode = factory.createTypeOperatorNode(SyntaxKind.KeyOfKeyword, newTypeVariable || typeToTypeNodeHelper(getModifiersTypeFromMappedType(type), context));
}
@@ -6989,9 +6996,14 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
else {
appropriateConstraintTypeNode = typeToTypeNodeHelper(getConstraintTypeFromMappedType(type), context);
}
const typeParameterNode = typeParameterToDeclarationWithConstraint(getTypeParameterFromMappedType(type), context, appropriateConstraintTypeNode);
const typeParameterNode = typeParameterToDeclarationWithConstraint(typeParameter, context, appropriateConstraintTypeNode);
// nameType and templateType nodes have to be in the new scope
const cleanup = enterNewScope(context, type.declaration, /*expandedParams*/ undefined, [getDeclaredTypeOfTypeParameter(getSymbolOfDeclaration(type.declaration.typeParameter))]);
const nameTypeNode = type.declaration.nameType ? typeToTypeNodeHelper(getNameTypeFromMappedType(type)!, context) : undefined;
const templateTypeNode = typeToTypeNodeHelper(removeMissingType(getTemplateTypeFromMappedType(type), !!(getMappedTypeModifiers(type) & MappedTypeModifiers.IncludeOptional)), context);
const templateTypeNode = typeToTypeNodeHelper(removeMissingType(templateType, !!(getMappedTypeModifiers(type) & MappedTypeModifiers.IncludeOptional)), context);
cleanup();
const mappedTypeNode = factory.createMappedTypeNode(readonlyToken, typeParameterNode, nameTypeNode, questionToken, templateTypeNode, /*members*/ undefined);
context.approximateLength += 10;
const result = setEmitFlags(mappedTypeNode, EmitFlags.SingleLine);