Fix structural identity relations #21839
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| 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); |
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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
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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.
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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.
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OK, that was the piece that I was missing.
# Conflicts: # tests/baselines/reference/conditionalTypes1.errors.txt # tests/baselines/reference/conditionalTypes1.js # tests/baselines/reference/conditionalTypes1.symbols # tests/baselines/reference/conditionalTypes1.types # tests/cases/conformance/types/conditional/conditionalTypes1.ts
| 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)) { |
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why not check this one first, seems the cheapest.
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Yes, but it is also the least selective. Practically all conditional types are distributive.
This PR adds several missing structural identity relations for higher order types, specifically index types, indexed access types, conditional types, and substitution types. Previously we'd only consider such types identical when they have the same object identity, now we properly check their constituents for structural identity.
This PR also more consistently handles distributive conditional types.
Finally, the PR introduces a new type relation: A conditional type
X extends Y ? S1 : S2is related to a conditional typeX extends Y ? T1 : T2ifS1is related toT1andS2is related toT2. In other words, two conditional types with identical conditions are related if their true and false branch types are pairwise related.Fixes #21823.