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Fix structural identity relations #21839

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Merged
Anders Hejlsberg (ahejlsberg) merged 4 commits into from
Feb 11, 2018
Merged

Fix structural identity relations #21839

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57351e8
Add higher order structural identity relations
ahejlsberg Feb 9, 2018
35f1fcb
Add tests
ahejlsberg Feb 9, 2018
d9a0334
Accept new baselines
ahejlsberg Feb 9, 2018
fadf031
Merge branch 'master' into fixStructuralIdentity
ahejlsberg Feb 10, 2018
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66 changes: 55 additions & 11 deletions src/compiler/checker.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -6096,11 +6096,13 @@ namespace ts {
// with its constraint. We do this because if the constraint is a union type it will be distributed
// over the conditional type and possibly reduced. For example, 'T extends undefined ? never : T'
// removes 'undefined' from T.
const checkType = type.checkType;
if (checkType.flags & TypeFlags.TypeParameter) {
const constraint = getConstraintOfTypeParameter(<TypeParameter>checkType);
if (isDistributiveConditionalType(type)) {
const constraint = getConstraintOfType(type.checkType);
if (constraint) {
return instantiateType(type, createTypeMapper([<TypeParameter>checkType], [constraint]));
const target = type.target || type;
const mapper = createTypeMapper([<TypeParameter>target.checkType], [constraint]);
const combinedMapper = type.mapper ? combineTypeMappers(mapper, type.mapper) : mapper;
return instantiateType(target, combinedMapper);
}
}
return undefined;
Expand Down Expand Up @@ -8237,6 +8239,10 @@ namespace ts {
return result;
}

function isDistributiveConditionalType(type: ConditionalType) {
return !!((type.target || type).checkType.flags & TypeFlags.TypeParameter);
}

function getInferTypeParameters(node: ConditionalTypeNode): TypeParameter[] {
let result: TypeParameter[];
if (node.locals) {
Expand Down Expand Up @@ -8849,9 +8855,9 @@ namespace ts {
// Check if we have a conditional type where the check type is a naked type parameter. If so,
// the conditional type is distributive over union types and when T is instantiated to a union
// type A | B, we produce (A extends U ? X : Y) | (B extends U ? X : Y).
const checkType = target.checkType;
if (checkType.flags & TypeFlags.TypeParameter) {
const instantiatedType = combinedMapper(<TypeParameter>checkType);
if (isDistributiveConditionalType(target)) {
const checkType = <TypeParameter>target.checkType;
const instantiatedType = combinedMapper(checkType);
if (checkType !== instantiatedType && instantiatedType.flags & TypeFlags.Union) {
return mapType(instantiatedType, t => instantiateConditionalType(target, createReplacementMapper(checkType, t, combinedMapper)));
}
Expand Down Expand Up @@ -9628,17 +9634,43 @@ namespace ts {

function isIdenticalTo(source: Type, target: Type): Ternary {
let result: Ternary;
if (source.flags & TypeFlags.Object && target.flags & TypeFlags.Object) {
const flags = source.flags & target.flags;
if (flags & TypeFlags.Object) {
return recursiveTypeRelatedTo(source, target, /*reportErrors*/ false);
}
if (source.flags & TypeFlags.Union && target.flags & TypeFlags.Union ||
source.flags & TypeFlags.Intersection && target.flags & TypeFlags.Intersection) {
if (flags & (TypeFlags.Union | TypeFlags.Intersection)) {
if (result = eachTypeRelatedToSomeType(<UnionOrIntersectionType>source, <UnionOrIntersectionType>target)) {
if (result &= eachTypeRelatedToSomeType(<UnionOrIntersectionType>target, <UnionOrIntersectionType>source)) {
return result;
}
}
}
if (flags & TypeFlags.Index) {
return isRelatedTo((<IndexType>source).type, (<IndexType>target).type, /*reportErrors*/ false);

@sandersn Nathan Shively-Sanders (sandersn) Feb 9, 2018

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Does it make sense for isIdenticalTo to call back into isRelatedTo? isRelatedTo will use whatever the current relation is, which won't necessarily be identityRelation

@sandersn Nathan Shively-Sanders (sandersn) Feb 9, 2018

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Now that I've read all of isIdenticalTo, I think that it should actually be called isStructurallyIdenticalTo (for the single level at which it's called). I'm not sure that matches the intent of any of its callers.

@ahejlsberg Anders Hejlsberg (ahejlsberg) Feb 9, 2018

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The only way we could be in the isIdenticalTo function is if the current relation is identityRelation. We need to call back to isRelatedTo because it handles primtives, etc.

@sandersn Nathan Shively-Sanders (sandersn) Feb 9, 2018

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OK, that was the piece that I was missing.

}
if (flags & TypeFlags.IndexedAccess) {
if (result = isRelatedTo((<IndexedAccessType>source).objectType, (<IndexedAccessType>target).objectType, /*reportErrors*/ false)) {
if (result &= isRelatedTo((<IndexedAccessType>source).indexType, (<IndexedAccessType>target).indexType, /*reportErrors*/ false)) {
return result;
}
}
}
if (flags & TypeFlags.Conditional) {
if (result = isRelatedTo((<ConditionalType>source).checkType, (<ConditionalType>target).checkType, /*reportErrors*/ false)) {
if (result &= isRelatedTo((<ConditionalType>source).extendsType, (<ConditionalType>target).extendsType, /*reportErrors*/ false)) {
if (result &= isRelatedTo((<ConditionalType>source).trueType, (<ConditionalType>target).trueType, /*reportErrors*/ false)) {
if (result &= isRelatedTo((<ConditionalType>source).falseType, (<ConditionalType>target).falseType, /*reportErrors*/ false)) {
if (isDistributiveConditionalType(<ConditionalType>source) === isDistributiveConditionalType(<ConditionalType>target)) {

@mhegazy Mohamed Hegazy (mhegazy) Feb 10, 2018

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why not check this one first, seems the cheapest.

@ahejlsberg Anders Hejlsberg (ahejlsberg) Feb 11, 2018

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Yes, but it is also the least selective. Practically all conditional types are distributive.

return result;
}
}
}
}
}
}
if (flags & TypeFlags.Substitution) {
return isRelatedTo((<SubstitutionType>source).substitute, (<SubstitutionType>target).substitute, /*reportErrors*/ false);
}
return Ternary.False;
}

Expand Down Expand Up @@ -10024,7 +10056,19 @@ namespace ts {
}
}
}
if (result = isRelatedTo(getDefaultConstraintOfConditionalType(<ConditionalType>source), target, reportErrors)) {
if (target.flags & TypeFlags.Conditional) {
if (isTypeIdenticalTo((<ConditionalType>source).checkType, (<ConditionalType>target).checkType) &&
isTypeIdenticalTo((<ConditionalType>source).extendsType, (<ConditionalType>target).extendsType)) {
if (result = isRelatedTo((<ConditionalType>source).trueType, (<ConditionalType>target).trueType, reportErrors)) {
result &= isRelatedTo((<ConditionalType>source).falseType, (<ConditionalType>target).falseType, reportErrors);
}
if (result) {
errorInfo = saveErrorInfo;
return result;
}
}
}
else if (result = isRelatedTo(getDefaultConstraintOfConditionalType(<ConditionalType>source), target, reportErrors)) {
errorInfo = saveErrorInfo;
return result;
}
Expand Down
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