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fix(50340): typeof ... === "undefined" check on discriminated union of undefined and object type doesn't narrow correctly (#50344)
* fix(50340): narrow type by discriminant in typeof * add additional test cases
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5 files changed

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‎src/compiler/checker.ts

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@@ -25328,11 +25328,19 @@ namespace ts {
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}
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const target = getReferenceCandidate(typeOfExpr.expression);
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if (!isMatchingReference(reference, target)) {
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const propertyAccess = getDiscriminantPropertyAccess(typeOfExpr.expression, type);
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if (propertyAccess) {
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return narrowTypeByDiscriminant(type, propertyAccess, t => narrowTypeByLiteralExpression(t, literal, assumeTrue));
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}
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if (strictNullChecks && optionalChainContainsReference(target, reference) && assumeTrue === (literal.text !== "undefined")) {
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return getAdjustedTypeWithFacts(type, TypeFacts.NEUndefinedOrNull);
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}
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return type;
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}
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return narrowTypeByLiteralExpression(type, literal, assumeTrue);
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}
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function narrowTypeByLiteralExpression(type: Type, literal: LiteralExpression, assumeTrue: boolean) {
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return assumeTrue ?
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narrowTypeByTypeName(type, literal.text) :
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getTypeWithFacts(type, typeofNEFacts.get(literal.text) || TypeFacts.TypeofNEHostObject);

‎tests/baselines/reference/narrowingTypeofUndefined.js

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//// [narrowingTypeofUndefined.ts]
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declare const a: { error: { prop: string }, result: undefined } | { error: undefined, result: { prop: number } }
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if (typeof a.error === 'undefined') {
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a.result.prop; // number
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}
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else {
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a.error.prop; // string
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}
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if (typeof a.error !== 'undefined') {
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a.error.prop; // string
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}
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else {
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a.result.prop; // number
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}
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//// [narrowingTypeofUndefined.js]
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if (typeof a.error === 'undefined') {
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a.result.prop; // number
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}
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else {
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a.error.prop; // string
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}
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if (typeof a.error !== 'undefined') {
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a.error.prop; // string
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}
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else {
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a.result.prop; // number
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}

‎tests/baselines/reference/narrowingTypeofUndefined.symbols

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=== tests/cases/compiler/narrowingTypeofUndefined.ts ===
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declare const a: { error: { prop: string }, result: undefined } | { error: undefined, result: { prop: number } }
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>a : Symbol(a, Decl(narrowingTypeofUndefined.ts, 0, 13))
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>error : Symbol(error, Decl(narrowingTypeofUndefined.ts, 0, 18))
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>prop : Symbol(prop, Decl(narrowingTypeofUndefined.ts, 0, 27))
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>result : Symbol(result, Decl(narrowingTypeofUndefined.ts, 0, 43))
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>error : Symbol(error, Decl(narrowingTypeofUndefined.ts, 0, 67))
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>result : Symbol(result, Decl(narrowingTypeofUndefined.ts, 0, 85))
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>prop : Symbol(prop, Decl(narrowingTypeofUndefined.ts, 0, 95))
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if (typeof a.error === 'undefined') {
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>a.error : Symbol(error, Decl(narrowingTypeofUndefined.ts, 0, 18), Decl(narrowingTypeofUndefined.ts, 0, 67))
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>a : Symbol(a, Decl(narrowingTypeofUndefined.ts, 0, 13))
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>error : Symbol(error, Decl(narrowingTypeofUndefined.ts, 0, 18), Decl(narrowingTypeofUndefined.ts, 0, 67))
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a.result.prop; // number
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>a.result.prop : Symbol(prop, Decl(narrowingTypeofUndefined.ts, 0, 95))
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>a.result : Symbol(result, Decl(narrowingTypeofUndefined.ts, 0, 43), Decl(narrowingTypeofUndefined.ts, 0, 85))
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>a : Symbol(a, Decl(narrowingTypeofUndefined.ts, 0, 13))
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>result : Symbol(result, Decl(narrowingTypeofUndefined.ts, 0, 43), Decl(narrowingTypeofUndefined.ts, 0, 85))
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>prop : Symbol(prop, Decl(narrowingTypeofUndefined.ts, 0, 95))
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}
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else {
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a.error.prop; // string
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>a.error.prop : Symbol(prop, Decl(narrowingTypeofUndefined.ts, 0, 27))
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>a.error : Symbol(error, Decl(narrowingTypeofUndefined.ts, 0, 18), Decl(narrowingTypeofUndefined.ts, 0, 67))
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>a : Symbol(a, Decl(narrowingTypeofUndefined.ts, 0, 13))
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>error : Symbol(error, Decl(narrowingTypeofUndefined.ts, 0, 18), Decl(narrowingTypeofUndefined.ts, 0, 67))
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>prop : Symbol(prop, Decl(narrowingTypeofUndefined.ts, 0, 27))
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}
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if (typeof a.error !== 'undefined') {
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>a.error : Symbol(error, Decl(narrowingTypeofUndefined.ts, 0, 18), Decl(narrowingTypeofUndefined.ts, 0, 67))
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>a : Symbol(a, Decl(narrowingTypeofUndefined.ts, 0, 13))
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>error : Symbol(error, Decl(narrowingTypeofUndefined.ts, 0, 18), Decl(narrowingTypeofUndefined.ts, 0, 67))
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a.error.prop; // string
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>a.error.prop : Symbol(prop, Decl(narrowingTypeofUndefined.ts, 0, 27))
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>a.error : Symbol(error, Decl(narrowingTypeofUndefined.ts, 0, 18), Decl(narrowingTypeofUndefined.ts, 0, 67))
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>a : Symbol(a, Decl(narrowingTypeofUndefined.ts, 0, 13))
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>error : Symbol(error, Decl(narrowingTypeofUndefined.ts, 0, 18), Decl(narrowingTypeofUndefined.ts, 0, 67))
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>prop : Symbol(prop, Decl(narrowingTypeofUndefined.ts, 0, 27))
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}
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else {
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a.result.prop; // number
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>a.result.prop : Symbol(prop, Decl(narrowingTypeofUndefined.ts, 0, 95))
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>a.result : Symbol(result, Decl(narrowingTypeofUndefined.ts, 0, 43), Decl(narrowingTypeofUndefined.ts, 0, 85))
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>a : Symbol(a, Decl(narrowingTypeofUndefined.ts, 0, 13))
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>result : Symbol(result, Decl(narrowingTypeofUndefined.ts, 0, 43), Decl(narrowingTypeofUndefined.ts, 0, 85))
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>prop : Symbol(prop, Decl(narrowingTypeofUndefined.ts, 0, 95))
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}
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‎tests/baselines/reference/narrowingTypeofUndefined.types

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=== tests/cases/compiler/narrowingTypeofUndefined.ts ===
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declare const a: { error: { prop: string }, result: undefined } | { error: undefined, result: { prop: number } }
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>a : { error: { prop: string;}; result: undefined; } | { error: undefined; result: { prop: number;}; }
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>error : { prop: string; }
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>prop : string
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>result : undefined
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>error : undefined
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>result : { prop: number; }
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>prop : number
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if (typeof a.error === 'undefined') {
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>typeof a.error === 'undefined' : boolean
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>typeof a.error : "string" | "number" | "bigint" | "boolean" | "symbol" | "undefined" | "object" | "function"
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>a.error : { prop: string; }
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>a : { error: { prop: string; }; result: undefined; } | { error: undefined; result: { prop: number; }; }
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>error : { prop: string; }
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>'undefined' : "undefined"
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a.result.prop; // number
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>a.result.prop : number
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>a.result : { prop: number; }
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>a : { error: { prop: string; }; result: undefined; } | { error: undefined; result: { prop: number; }; }
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>result : { prop: number; }
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>prop : number
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}
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else {
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a.error.prop; // string
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>a.error.prop : string
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>a.error : { prop: string; }
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>a : { error: { prop: string; }; result: undefined; } | { error: undefined; result: { prop: number; }; }
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>error : { prop: string; }
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>prop : string
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}
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if (typeof a.error !== 'undefined') {
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>typeof a.error !== 'undefined' : boolean
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>typeof a.error : "string" | "number" | "bigint" | "boolean" | "symbol" | "undefined" | "object" | "function"
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>a.error : { prop: string; }
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>a : { error: { prop: string; }; result: undefined; } | { error: undefined; result: { prop: number; }; }
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>error : { prop: string; }
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>'undefined' : "undefined"
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a.error.prop; // string
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>a.error.prop : string
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>a.error : { prop: string; }
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>a : { error: { prop: string; }; result: undefined; } | { error: undefined; result: { prop: number; }; }
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>error : { prop: string; }
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>prop : string
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}
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else {
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a.result.prop; // number
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>a.result.prop : number
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>a.result : { prop: number; }
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>a : { error: { prop: string; }; result: undefined; } | { error: undefined; result: { prop: number; }; }
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>result : { prop: number; }
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>prop : number
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}
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‎tests/cases/compiler/narrowingTypeofUndefined.ts

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declare const a: { error: { prop: string }, result: undefined } | { error: undefined, result: { prop: number } }
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if (typeof a.error === 'undefined') {
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a.result.prop; // number
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}
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else {
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a.error.prop; // string
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}
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if (typeof a.error !== 'undefined') {
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a.error.prop; // string
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}
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else {
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a.result.prop; // number
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}

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