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Simplify relationship check for conditional type on target side #46429

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merged 5 commits into from Oct 22, 2021
Merged

Simplify relationship check for conditional type on target side #46429

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9ea685b
Simplify relationship check for conditional type on target side
ahejlsberg Oct 19, 2021
75ab347
Accept new baselines
ahejlsberg Oct 19, 2021
3012d35
Better support for non-distribution-dependent types
ahejlsberg Oct 21, 2021
45a0113
Accept new API baselines
ahejlsberg Oct 21, 2021
dc9da80
Accept new baselines
ahejlsberg Oct 21, 2021
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56 changes: 21 additions & 35 deletions src/compiler/checker.ts
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Expand Up @@ -15315,13 +15315,6 @@ namespace ts {
return type[cache] = type;
}

function isConditionalTypeAlwaysTrueDisregardingInferTypes(type: ConditionalType) {
const extendsInferParamMapper = type.root.inferTypeParameters && createTypeMapper(type.root.inferTypeParameters, map(type.root.inferTypeParameters, () => wildcardType));
const checkType = type.checkType;
const extendsType = type.extendsType;
return isTypeAssignableTo(getRestrictiveInstantiation(checkType), getRestrictiveInstantiation(instantiateType(extendsType, extendsInferParamMapper)));
}

function getSimplifiedConditionalType(type: ConditionalType, writing: boolean) {
const checkType = type.checkType;
const extendsType = type.extendsType;
Expand Down Expand Up @@ -15649,6 +15642,10 @@ namespace ts {
const links = getNodeLinks(node);
if (!links.resolvedType) {
const checkType = getTypeFromTypeNode(node.checkType);
const isDistributive = !!(checkType.flags & TypeFlags.TypeParameter);
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I know this code was already put in place - but don't we distribute on indexed access types or something like that as well?

const isDistributionDependent = isDistributive && (
isTypeParameterPossiblyReferenced(checkType as TypeParameter, node.trueType) ||
isTypeParameterPossiblyReferenced(checkType as TypeParameter, node.falseType));
const aliasSymbol = getAliasSymbolForTypeNode(node);
const aliasTypeArguments = getTypeArgumentsForAliasSymbol(aliasSymbol);
const allOuterTypeParameters = getOuterTypeParameters(node, /*includeThisTypes*/ true);
Expand All @@ -15657,7 +15654,8 @@ namespace ts {
node,
checkType,
extendsType: getTypeFromTypeNode(node.extendsType),
isDistributive: !!(checkType.flags & TypeFlags.TypeParameter),
isDistributive,
isDistributionDependent,
inferTypeParameters: getInferTypeParameters(node),
outerTypeParameters,
instantiations: undefined,
Expand Down Expand Up @@ -19031,33 +19029,21 @@ namespace ts {
return Ternary.Maybe;
}
const c = target as ConditionalType;
// Check if the conditional is always true or always false but still deferred for distribution purposes
const skipTrue = !isTypeAssignableTo(getPermissiveInstantiation(c.checkType), getPermissiveInstantiation(c.extendsType));
const skipFalse = !skipTrue && isConditionalTypeAlwaysTrueDisregardingInferTypes(c);

// Instantiate with a replacement mapper if the conditional is distributive, replacing the check type with a clone of itself,
// this way {x: string | number, y: string | number} -> (T extends T ? { x: T, y: T } : never) appropriately _fails_ when
// T = string | number (since that will end up distributing and producing `{x: string, y: string} | {x: number, y: number}`,
// to which `{x: string | number, y: string | number}` isn't assignable)
let distributionMapper: TypeMapper | undefined;
const checkVar = getActualTypeVariable(c.root.checkType);
if (c.root.isDistributive && checkVar.flags & TypeFlags.TypeParameter) {
const newParam = cloneTypeParameter(checkVar);
distributionMapper = prependTypeMapping(checkVar, newParam, c.mapper);
newParam.mapper = distributionMapper;
}

// TODO: Find a nice way to include potential conditional type breakdowns in error output, if they seem good (they usually don't)
const expanding = isDeeplyNestedType(target, targetStack, targetDepth);
let localResult: Ternary | undefined = expanding ? Ternary.Maybe : undefined;
if (skipTrue || expanding || (localResult = isRelatedTo(source, distributionMapper ? instantiateType(getTypeFromTypeNode(c.root.node.trueType), distributionMapper) : getTrueTypeFromConditionalType(c), RecursionFlags.Target, /*reportErrors*/ false))) {
if (!skipFalse && !expanding) {
localResult = (localResult || Ternary.Maybe) & isRelatedTo(source, distributionMapper ? instantiateType(getTypeFromTypeNode(c.root.node.falseType), distributionMapper) : getFalseTypeFromConditionalType(c), RecursionFlags.Target, /*reportErrors*/ false);
}
}
if (localResult) {
resetErrorInfo(saveErrorInfo);
return localResult;
// We check for a relationship to a conditional type target only when the conditional type has no
// 'infer' positions and is not distributive or is distributive but doesn't reference the check type
// parameter in either of the result types.
if (!c.root.inferTypeParameters && !c.root.isDistributionDependent) {
// Check if the conditional is always true or always false but still deferred for distribution purposes.
const skipTrue = !isTypeAssignableTo(getPermissiveInstantiation(c.checkType), getPermissiveInstantiation(c.extendsType));
const skipFalse = !skipTrue && isTypeAssignableTo(getRestrictiveInstantiation(c.checkType), getRestrictiveInstantiation(c.extendsType));
// TODO: Find a nice way to include potential conditional type breakdowns in error output, if they seem good (they usually don't)
if (result = skipTrue ? Ternary.True : isRelatedTo(source, getTrueTypeFromConditionalType(c), RecursionFlags.Target, /*reportErrors*/ false)) {
result &= skipFalse ? Ternary.True : isRelatedTo(source, getFalseTypeFromConditionalType(c), RecursionFlags.Target, /*reportErrors*/ false);
if (result) {
resetErrorInfo(saveErrorInfo);
return result;
}
}
}
}
else if (target.flags & TypeFlags.TemplateLiteral) {
Expand Down
1 change: 1 addition & 0 deletions src/compiler/types.ts
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Expand Up @@ -5648,6 +5648,7 @@ namespace ts {
checkType: Type;
extendsType: Type;
isDistributive: boolean;
isDistributionDependent: boolean;
inferTypeParameters?: TypeParameter[];
outerTypeParameters?: TypeParameter[];
instantiations?: Map<Type>;
Expand Down
1 change: 1 addition & 0 deletions tests/baselines/reference/api/tsserverlibrary.d.ts
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Expand Up @@ -2747,6 +2747,7 @@ declare namespace ts {
checkType: Type;
extendsType: Type;
isDistributive: boolean;
isDistributionDependent: boolean;
inferTypeParameters?: TypeParameter[];
outerTypeParameters?: TypeParameter[];
instantiations?: Map<Type>;
Expand Down
1 change: 1 addition & 0 deletions tests/baselines/reference/api/typescript.d.ts
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Expand Up @@ -2747,6 +2747,7 @@ declare namespace ts {
checkType: Type;
extendsType: Type;
isDistributive: boolean;
isDistributionDependent: boolean;
inferTypeParameters?: TypeParameter[];
outerTypeParameters?: TypeParameter[];
instantiations?: Map<Type>;
Expand Down