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ahejlsbergahejlsberg
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Preserve special intersections in mapped types (#50704)
* Preserve special intersections in mapped types * Add regression test
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6 files changed

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‎src/compiler/checker.ts

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@@ -11780,6 +11780,12 @@ namespace ts {
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return mapType(type as UnionType, getLowerBoundOfKeyType);
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}
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if (type.flags & TypeFlags.Intersection) {
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// Similarly to getTypeFromIntersectionTypeNode, we preserve the special string & {}, number & {},
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// and bigint & {} intersections that are used to prevent subtype reduction in union types.
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const types = (type as IntersectionType).types;
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if (types.length === 2 && !!(types[0].flags & (TypeFlags.String | TypeFlags.Number | TypeFlags.BigInt)) && types[1] === emptyTypeLiteralType) {
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return type;
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}
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return getIntersectionType(sameMap((type as UnionType).types, getLowerBoundOfKeyType));
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}
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return type;

‎tests/baselines/reference/specialIntersectionsInMappedTypes.errors.txt

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tests/cases/compiler/specialIntersectionsInMappedTypes.ts(14,1): error TS2532: Object is possibly 'undefined'.
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==== tests/cases/compiler/specialIntersectionsInMappedTypes.ts (1 errors) ====
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// Repro from #50683
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type Alignment = (string & {}) | "left" | "center" | "right";
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type Alignments = Record<Alignment, string>;
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const a: Alignments = {
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left: "align-left",
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center: "align-center",
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right: "align-right",
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other: "align-other",
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};
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a.left.length;
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a.other.length; // Error expected here
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~~~~~~~
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!!! error TS2532: Object is possibly 'undefined'.
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‎tests/baselines/reference/specialIntersectionsInMappedTypes.js

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//// [specialIntersectionsInMappedTypes.ts]
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// Repro from #50683
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type Alignment = (string & {}) | "left" | "center" | "right";
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type Alignments = Record<Alignment, string>;
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const a: Alignments = {
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left: "align-left",
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center: "align-center",
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right: "align-right",
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other: "align-other",
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};
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a.left.length;
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a.other.length; // Error expected here
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//// [specialIntersectionsInMappedTypes.js]
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"use strict";
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// Repro from #50683
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var a = {
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left: "align-left",
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center: "align-center",
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right: "align-right",
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other: "align-other"
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};
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a.left.length;
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a.other.length; // Error expected here

‎tests/baselines/reference/specialIntersectionsInMappedTypes.symbols

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=== tests/cases/compiler/specialIntersectionsInMappedTypes.ts ===
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// Repro from #50683
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type Alignment = (string & {}) | "left" | "center" | "right";
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>Alignment : Symbol(Alignment, Decl(specialIntersectionsInMappedTypes.ts, 0, 0))
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type Alignments = Record<Alignment, string>;
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>Alignments : Symbol(Alignments, Decl(specialIntersectionsInMappedTypes.ts, 2, 61))
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>Record : Symbol(Record, Decl(lib.es5.d.ts, --, --))
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>Alignment : Symbol(Alignment, Decl(specialIntersectionsInMappedTypes.ts, 0, 0))
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const a: Alignments = {
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>a : Symbol(a, Decl(specialIntersectionsInMappedTypes.ts, 5, 5))
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>Alignments : Symbol(Alignments, Decl(specialIntersectionsInMappedTypes.ts, 2, 61))
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left: "align-left",
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>left : Symbol(left, Decl(specialIntersectionsInMappedTypes.ts, 5, 23))
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center: "align-center",
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>center : Symbol(center, Decl(specialIntersectionsInMappedTypes.ts, 6, 23))
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right: "align-right",
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>right : Symbol(right, Decl(specialIntersectionsInMappedTypes.ts, 7, 27))
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other: "align-other",
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>other : Symbol(other, Decl(specialIntersectionsInMappedTypes.ts, 8, 25))
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};
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a.left.length;
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>a.left.length : Symbol(String.length, Decl(lib.es5.d.ts, --, --))
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>a.left : Symbol(left)
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>a : Symbol(a, Decl(specialIntersectionsInMappedTypes.ts, 5, 5))
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>left : Symbol(left)
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>length : Symbol(String.length, Decl(lib.es5.d.ts, --, --))
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a.other.length; // Error expected here
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>a.other.length : Symbol(String.length, Decl(lib.es5.d.ts, --, --))
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>a : Symbol(a, Decl(specialIntersectionsInMappedTypes.ts, 5, 5))
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>length : Symbol(String.length, Decl(lib.es5.d.ts, --, --))
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‎tests/baselines/reference/specialIntersectionsInMappedTypes.types

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=== tests/cases/compiler/specialIntersectionsInMappedTypes.ts ===
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// Repro from #50683
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type Alignment = (string & {}) | "left" | "center" | "right";
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>Alignment : (string & {}) | "left" | "center" | "right"
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type Alignments = Record<Alignment, string>;
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>Alignments : { [x: string & {}]: string; left: string; center: string; right: string; }
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const a: Alignments = {
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>a : Alignments
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>{ left: "align-left", center: "align-center", right: "align-right", other: "align-other",} : { left: string; center: string; right: string; other: string; }
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left: "align-left",
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>left : string
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>"align-left" : "align-left"
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center: "align-center",
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>center : string
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>"align-center" : "align-center"
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right: "align-right",
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>right : string
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>"align-right" : "align-right"
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other: "align-other",
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>other : string
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>"align-other" : "align-other"
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};
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a.left.length;
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>a.left.length : number
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>a.left : string
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>a : Alignments
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>left : string
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>length : number
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a.other.length; // Error expected here
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>a.other.length : number
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>a.other : string | undefined
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>a : Alignments
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>other : string | undefined
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>length : number
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‎tests/cases/compiler/specialIntersectionsInMappedTypes.ts

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// @strict: true
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// @noUncheckedIndexedAccess: true
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// Repro from #50683
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type Alignment = (string & {}) | "left" | "center" | "right";
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type Alignments = Record<Alignment, string>;
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const a: Alignments = {
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left: "align-left",
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center: "align-center",
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right: "align-right",
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other: "align-other",
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};
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a.left.length;
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a.other.length; // Error expected here

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