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bugfix: homomorphic mapped types when T is non-generic, solves 27995 #48433

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bugfix: homomorphic mapped types when T is non-generic, solves 27995 #48433

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260708d
bugfix: homomorphic mapped types when T is non-generic, solves 27995
mikearnaldi Mar 26, 2022
3b70763
Add tests for concrete mapped tuples
Andarist Mar 26, 2022
3e203b1
fix: improve parameter constraint in case it appears in a homomorphic…
mikearnaldi Mar 26, 2022
294f5af
chore: fix lint
mikearnaldi Mar 26, 2022
fbc586a
fix: fix typo in tests
mikearnaldi Mar 27, 2022
ab725d6
chore: extract common logic
mikearnaldi Mar 27, 2022
fd8cbf8
chore: fix lint
mikearnaldi Mar 27, 2022
b0083f8
Merge branch 'main' into bugfix/issue-27995
Andarist Sep 16, 2023
e9ebeaf
Avoid creating a mapped type object altogether
Andarist Sep 18, 2023
2387a6e
Avoid the introduced check to be syntactical
Andarist Sep 18, 2023
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chore: extract common logic
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@mikearnaldi
mikearnaldi committed Mar 27, 2022
commit ab725d6f0ff343c251d7d57db3e64b6789e65c57
42 changes: 24 additions & 18 deletions src/compiler/checker.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -13340,6 +13340,18 @@ namespace ts {
return inferences && getIntersectionType(inferences);
}

function getTupleConstraintFromMappedTypeNode(node: MappedTypeNode) {
if (!node.nameType && node.typeParameter.constraint &&
isTypeOperatorNode(node.typeParameter.constraint) &&
node.typeParameter.constraint.operator === SyntaxKind.KeyOfKeyword
) {
const keyOfTarget = getTypeFromTypeNode(node.typeParameter.constraint.type);
if (isTupleType(keyOfTarget)) {
return keyOfTarget
}
}
}

/** This is a worker function. Use getConstraintOfTypeParameter which guards against circular constraints. */
function getConstraintFromTypeParameter(typeParameter: TypeParameter): Type | undefined {
if (!typeParameter.constraint) {
Expand All @@ -13355,13 +13367,10 @@ namespace ts {
else {
// Detect is the constraint is for a homomorphic mapped type to a tuple and in case return a literal union of the used tuple keys
if (constraintDeclaration.parent && constraintDeclaration.parent.parent && constraintDeclaration.parent.parent.kind === SyntaxKind.MappedType) {
const mappedTypeNode = constraintDeclaration.parent.parent as MappedTypeNode;
if (!mappedTypeNode.nameType && mappedTypeNode.typeParameter.constraint && isTypeOperatorNode(mappedTypeNode.typeParameter.constraint) && mappedTypeNode.typeParameter.constraint.operator === SyntaxKind.KeyOfKeyword) {
const keyOfTarget = getTypeFromTypeNode(mappedTypeNode.typeParameter.constraint.type);
if (isTupleType(keyOfTarget)) {
typeParameter.constraint = getUnionType(map(getTypeArguments(keyOfTarget), (_, i) => getStringLiteralType("" + i)));
return typeParameter.constraint;
}
const keyOfTarget = getTupleConstraintFromMappedTypeNode(constraintDeclaration.parent.parent as MappedTypeNode);
if (keyOfTarget) {
typeParameter.constraint = getUnionType(map(getTypeArguments(keyOfTarget), (_, i) => getStringLiteralType("" + i)));
return typeParameter.constraint;
}
}
let type = getTypeFromTypeNode(constraintDeclaration);
Expand Down Expand Up @@ -15860,17 +15869,14 @@ namespace ts {
// references itself through one or more type aliases.
getConstraintTypeFromMappedType(type);
// Detect if the mapped type should be homomorphic to a tuple by checking the declaration of the constraint if it contains a keyof over a tuple
if (!node.nameType && node.typeParameter.constraint && isTypeOperatorNode(node.typeParameter.constraint) && node.typeParameter.constraint.operator === SyntaxKind.KeyOfKeyword) {
const keyOfTarget = getTypeFromTypeNode(node.typeParameter.constraint.type);
if (isTupleType(keyOfTarget)) {
// Instantiate the mapped type over a tuple with an identity mapper
const instantiatedTupleMappedType = instantiateMappedTupleType(
keyOfTarget,
type,
makeFunctionTypeMapper(identity)
);
links.resolvedType = instantiatedTupleMappedType;
}
const keyOfTarget = getTupleConstraintFromMappedTypeNode(node);
if (keyOfTarget) {
// Instantiate the mapped type over a tuple with an identity mapper
links.resolvedType = instantiateMappedTupleType(
keyOfTarget,
type,
makeFunctionTypeMapper(identity)
);
}
}
return links.resolvedType;
Expand Down