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MichaelMitchell-at
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Make identity comparison reflexive across unions or intersections of the same type
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5 files changed

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‎src/compiler/checker.ts

+16-1
Original file line numberDiff line numberDiff line change
@@ -22158,7 +22158,22 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
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if (source === target) return Ternary.True;
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if (relation === identityRelation) {
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if (source.flags !== target.flags) return Ternary.False;
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if (source.flags !== target.flags) {
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// Since normalization doesn't perform subtype reduction, unions and intersections might have duplicates, so
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// one of the types might be a union or intersection whose constituents are all identical to the other type.
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const eachSourceAndTarget: [UnionOrIntersectionType, Type] | undefined =
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source.flags & TypeFlags.Union ? [source as UnionOrIntersectionType, target]
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: target.flags & TypeFlags.Union ? [target as UnionOrIntersectionType, source]
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: source.flags & TypeFlags.Intersection ? [source as UnionOrIntersectionType, target]
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: target.flags & TypeFlags.Intersection ? [target as UnionOrIntersectionType, source]
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: undefined;
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if (eachSourceAndTarget) {
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traceUnionsOrIntersectionsTooLarge(...eachSourceAndTarget);
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return eachTypeRelatedToType(...eachSourceAndTarget, reportErrors, IntersectionState.None);
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}
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return Ternary.False;
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}
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if (source.flags & TypeFlags.Singleton) return Ternary.True;
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traceUnionsOrIntersectionsTooLarge(source, target);
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return recursiveTypeRelatedTo(source, target, /*reportErrors*/ false, IntersectionState.None, recursionFlags);

‎tests/baselines/reference/reflexiveIdentityRelation.js

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//// [tests/cases/compiler/reflexiveIdentityRelation.ts] ////
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//// [reflexiveIdentityRelation.ts]
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namespace reflexiveIdentityRelation {
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type Equals<A, B> = (<T>() => T extends B ? 1 : 0) extends (<T>() => T extends A ? 1 : 0) ? true : false;
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type Intersection = Equals<{a: 1} & {a: 1}, {a: 1}>; // true
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type Union = Equals<{a: 1} | {a: 1}, {a: 1}>; // true
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type UnionOfIntersection = Equals<{a: 1} & {b: 2} | {a: 1} & {b: 2}, {a: 1} & {b: 2}>; // true
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// The intersection distributes to `{a: 1} & {a: 1} | {a: 1} & {b: 2} | {b: 2} & {a: 1} | {b: 2} & {b: 2}`
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// which is not identical to `{a: 1} | {b: 2}`
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type IntersectionOfUnion = Equals<({a: 1} | {b: 2}) & ({a: 1} | {b: 2}), {a: 1} | {b: 2}>; // false
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}
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//// [reflexiveIdentityRelation.js]
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"use strict";
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//// [reflexiveIdentityRelation.d.ts]
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declare namespace reflexiveIdentityRelation {
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}

‎tests/baselines/reference/reflexiveIdentityRelation.symbols

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//// [tests/cases/compiler/reflexiveIdentityRelation.ts] ////
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=== reflexiveIdentityRelation.ts ===
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namespace reflexiveIdentityRelation {
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>reflexiveIdentityRelation : Symbol(reflexiveIdentityRelation, Decl(reflexiveIdentityRelation.ts, 0, 0))
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type Equals<A, B> = (<T>() => T extends B ? 1 : 0) extends (<T>() => T extends A ? 1 : 0) ? true : false;
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>Equals : Symbol(Equals, Decl(reflexiveIdentityRelation.ts, 0, 37))
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>A : Symbol(A, Decl(reflexiveIdentityRelation.ts, 1, 16))
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>B : Symbol(B, Decl(reflexiveIdentityRelation.ts, 1, 18))
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>T : Symbol(T, Decl(reflexiveIdentityRelation.ts, 1, 26))
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>T : Symbol(T, Decl(reflexiveIdentityRelation.ts, 1, 26))
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>B : Symbol(B, Decl(reflexiveIdentityRelation.ts, 1, 18))
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>T : Symbol(T, Decl(reflexiveIdentityRelation.ts, 1, 65))
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>T : Symbol(T, Decl(reflexiveIdentityRelation.ts, 1, 65))
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>A : Symbol(A, Decl(reflexiveIdentityRelation.ts, 1, 16))
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type Intersection = Equals<{a: 1} & {a: 1}, {a: 1}>; // true
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>Intersection : Symbol(Intersection, Decl(reflexiveIdentityRelation.ts, 1, 109))
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>Equals : Symbol(Equals, Decl(reflexiveIdentityRelation.ts, 0, 37))
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>a : Symbol(a, Decl(reflexiveIdentityRelation.ts, 3, 32))
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>a : Symbol(a, Decl(reflexiveIdentityRelation.ts, 3, 41))
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>a : Symbol(a, Decl(reflexiveIdentityRelation.ts, 3, 49))
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type Union = Equals<{a: 1} | {a: 1}, {a: 1}>; // true
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>Union : Symbol(Union, Decl(reflexiveIdentityRelation.ts, 3, 56))
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>Equals : Symbol(Equals, Decl(reflexiveIdentityRelation.ts, 0, 37))
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>a : Symbol(a, Decl(reflexiveIdentityRelation.ts, 4, 25))
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>a : Symbol(a, Decl(reflexiveIdentityRelation.ts, 4, 34))
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>a : Symbol(a, Decl(reflexiveIdentityRelation.ts, 4, 42))
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type UnionOfIntersection = Equals<{a: 1} & {b: 2} | {a: 1} & {b: 2}, {a: 1} & {b: 2}>; // true
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>UnionOfIntersection : Symbol(UnionOfIntersection, Decl(reflexiveIdentityRelation.ts, 4, 49))
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>Equals : Symbol(Equals, Decl(reflexiveIdentityRelation.ts, 0, 37))
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>a : Symbol(a, Decl(reflexiveIdentityRelation.ts, 5, 39))
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>b : Symbol(b, Decl(reflexiveIdentityRelation.ts, 5, 48))
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>a : Symbol(a, Decl(reflexiveIdentityRelation.ts, 5, 57))
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>b : Symbol(b, Decl(reflexiveIdentityRelation.ts, 5, 66))
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>a : Symbol(a, Decl(reflexiveIdentityRelation.ts, 5, 74))
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>b : Symbol(b, Decl(reflexiveIdentityRelation.ts, 5, 83))
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// The intersection distributes to `{a: 1} & {a: 1} | {a: 1} & {b: 2} | {b: 2} & {a: 1} | {b: 2} & {b: 2}`
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// which is not identical to `{a: 1} | {b: 2}`
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type IntersectionOfUnion = Equals<({a: 1} | {b: 2}) & ({a: 1} | {b: 2}), {a: 1} | {b: 2}>; // false
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>IntersectionOfUnion : Symbol(IntersectionOfUnion, Decl(reflexiveIdentityRelation.ts, 5, 90))
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>Equals : Symbol(Equals, Decl(reflexiveIdentityRelation.ts, 0, 37))
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>a : Symbol(a, Decl(reflexiveIdentityRelation.ts, 9, 40))
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>b : Symbol(b, Decl(reflexiveIdentityRelation.ts, 9, 49))
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>a : Symbol(a, Decl(reflexiveIdentityRelation.ts, 9, 60))
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>b : Symbol(b, Decl(reflexiveIdentityRelation.ts, 9, 69))
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>a : Symbol(a, Decl(reflexiveIdentityRelation.ts, 9, 78))
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>b : Symbol(b, Decl(reflexiveIdentityRelation.ts, 9, 87))
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}
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‎tests/baselines/reference/reflexiveIdentityRelation.types

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//// [tests/cases/compiler/reflexiveIdentityRelation.ts] ////
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=== reflexiveIdentityRelation.ts ===
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namespace reflexiveIdentityRelation {
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type Equals<A, B> = (<T>() => T extends B ? 1 : 0) extends (<T>() => T extends A ? 1 : 0) ? true : false;
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>Equals : Equals<A, B>
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> : ^^^^^^^^^^^^
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>true : true
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> : ^^^^
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>false : false
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> : ^^^^^
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type Intersection = Equals<{a: 1} & {a: 1}, {a: 1}>; // true
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>Intersection : true
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> : ^^^^
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>a : 1
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> : ^
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>a : 1
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> : ^
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>a : 1
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> : ^
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type Union = Equals<{a: 1} | {a: 1}, {a: 1}>; // true
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>Union : true
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> : ^^^^
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>a : 1
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> : ^
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>a : 1
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> : ^
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>a : 1
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> : ^
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type UnionOfIntersection = Equals<{a: 1} & {b: 2} | {a: 1} & {b: 2}, {a: 1} & {b: 2}>; // true
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>UnionOfIntersection : true
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> : ^^^^
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>a : 1
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> : ^
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>b : 2
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> : ^
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>a : 1
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> : ^
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>b : 2
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> : ^
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>a : 1
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> : ^
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>b : 2
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> : ^
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// The intersection distributes to `{a: 1} & {a: 1} | {a: 1} & {b: 2} | {b: 2} & {a: 1} | {b: 2} & {b: 2}`
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// which is not identical to `{a: 1} | {b: 2}`
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type IntersectionOfUnion = Equals<({a: 1} | {b: 2}) & ({a: 1} | {b: 2}), {a: 1} | {b: 2}>; // false
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>IntersectionOfUnion : false
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> : ^^^^^
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>a : 1
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> : ^
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>b : 2
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> : ^
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>a : 1
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> : ^
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>b : 2
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> : ^
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>a : 1
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> : ^
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>b : 2
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> : ^
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}
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‎tests/cases/compiler/reflexiveIdentityRelation.ts

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// @strict: true
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// @declaration: true
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namespace reflexiveIdentityRelation {
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type Equals<A, B> = (<T>() => T extends B ? 1 : 0) extends (<T>() => T extends A ? 1 : 0) ? true : false;
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type Intersection = Equals<{a: 1} & {a: 1}, {a: 1}>; // true
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type Union = Equals<{a: 1} | {a: 1}, {a: 1}>; // true
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type UnionOfIntersection = Equals<{a: 1} & {b: 2} | {a: 1} & {b: 2}, {a: 1} & {b: 2}>; // true
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// The intersection distributes to `{a: 1} & {a: 1} | {a: 1} & {b: 2} | {b: 2} & {a: 1} | {b: 2} & {b: 2}`
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// which is not identical to `{a: 1} | {b: 2}`
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type IntersectionOfUnion = Equals<({a: 1} | {b: 2}) & ({a: 1} | {b: 2}), {a: 1} | {b: 2}>; // false
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}

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