From 0d79831ead51bda2fd38dd169e0bf04a0cdb4e72 Mon Sep 17 00:00:00 2001 From: Jack Williams <jw@jackw.io> Date: Tue, 13 Feb 2018 01:14:47 +0000 Subject: [PATCH] Add typeof-for-switch Initial draft that works for union types First draft of PR ready code with tests Revert changed line for testing Add exhaustiveness checking and move narrowByTypeOfWitnesses Try caching mechanism Comment out exhaustiveness checking to find perf regression Re-enable exhaustiveness checking for typeof switches Check if changes to narrowByTypeOfWitnesses fix perf alone. Improve switch narrowing: + Take into account repeated clauses in the switch. + Handle unions of constrained type parameters. Add more tests Comments Revert back to if-like behaviour Remove redundant checks and simplify exhaustiveness checks Change comment for narrowBySwitchOnTypeOf Reduce implied type with getAssignmentReducedType Remove any annotations --- src/compiler/binder.ts | 2 + src/compiler/checker.ts | 119 +++ .../reference/narrowingByTypeofInSwitch.js | 427 +++++++++++ .../narrowingByTypeofInSwitch.symbols | 542 ++++++++++++++ .../reference/narrowingByTypeofInSwitch.types | 695 ++++++++++++++++++ .../compiler/narrowingByTypeofInSwitch.ts | 190 +++++ 6 files changed, 1975 insertions(+) create mode 100644 tests/baselines/reference/narrowingByTypeofInSwitch.js create mode 100644 tests/baselines/reference/narrowingByTypeofInSwitch.symbols create mode 100644 tests/baselines/reference/narrowingByTypeofInSwitch.types create mode 100644 tests/cases/compiler/narrowingByTypeofInSwitch.ts diff --git a/src/compiler/binder.ts b/src/compiler/binder.ts index e6e3364840dc9..555c13f1f61e3 100644 --- a/src/compiler/binder.ts +++ b/src/compiler/binder.ts @@ -737,6 +737,8 @@ namespace ts { return isNarrowingBinaryExpression(<BinaryExpression>expr); case SyntaxKind.PrefixUnaryExpression: return (<PrefixUnaryExpression>expr).operator === SyntaxKind.ExclamationToken && isNarrowingExpression((<PrefixUnaryExpression>expr).operand); + case SyntaxKind.TypeOfExpression: + return isNarrowingExpression((<TypeOfExpression>expr).expression); } return false; } diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts index f497ba82e47a8..ab2cc1f3b8519 100644 --- a/src/compiler/checker.ts +++ b/src/compiler/checker.ts @@ -12840,6 +12840,21 @@ namespace ts { return links.switchTypes; } + function getSwitchClauseTypeOfWitnesses(switchStatement: SwitchStatement): (string | undefined)[] { + const witnesses: (string | undefined)[] = []; + for (const clause of switchStatement.caseBlock.clauses) { + if (clause.kind === SyntaxKind.CaseClause) { + if (clause.expression.kind === SyntaxKind.StringLiteral) { + witnesses.push((clause.expression as StringLiteral).text); + continue; + } + return emptyArray; + } + witnesses.push(/*explicitDefaultStatement*/ undefined); + } + return witnesses; + } + function eachTypeContainedIn(source: Type, types: Type[]) { return source.flags & TypeFlags.Union ? !forEach((<UnionType>source).types, t => !contains(types, t)) : contains(types, source); } @@ -13253,6 +13268,9 @@ namespace ts { else if (isMatchingReferenceDiscriminant(expr, type)) { type = narrowTypeByDiscriminant(type, <PropertyAccessExpression>expr, t => narrowTypeBySwitchOnDiscriminant(t, flow.switchStatement, flow.clauseStart, flow.clauseEnd)); } + else if (expr.kind === SyntaxKind.TypeOfExpression && isMatchingReference(reference, (expr as TypeOfExpression).expression)) { + type = narrowBySwitchOnTypeOf(type, flow.switchStatement, flow.clauseStart, flow.clauseEnd); + } return createFlowType(type, isIncomplete(flowType)); } @@ -13549,6 +13567,57 @@ namespace ts { return caseType.flags & TypeFlags.Never ? defaultType : getUnionType([caseType, defaultType]); } + function narrowBySwitchOnTypeOf(type: Type, switchStatement: SwitchStatement, clauseStart: number, clauseEnd: number): Type { + const switchWitnesses = getSwitchClauseTypeOfWitnesses(switchStatement); + if (!switchWitnesses.length) { + return type; + } + const clauseWitnesses = switchWitnesses.slice(clauseStart, clauseEnd); + // Equal start and end denotes implicit fallthrough; undefined marks explicit default clause + const hasDefaultClause = clauseStart === clauseEnd || contains(clauseWitnesses, /*explicitDefaultStatement*/ undefined); + const switchFacts = getFactsFromTypeofSwitch(clauseStart, clauseEnd, switchWitnesses, hasDefaultClause); + // The implied type is the raw type suggested by a + // value being caught in this clause. + // - If there is a default the implied type is not used. + // - Otherwise, take the union of the types in the + // clause. We narrow the union using facts to remove + // types that appear multiple types and are + // unreachable. + // Example: + // + // switch (typeof x) { + // case 'number': + // case 'string': break; + // default: break; + // case 'number': + // case 'boolean': break + // } + // + // The implied type of the first clause number | string. + // The implied type of the second clause is string (but this doesn't get used). + // The implied type of the third clause is boolean (number has already be caught). + if (!(hasDefaultClause || (type.flags & TypeFlags.Union))) { + let impliedType = getTypeWithFacts(getUnionType(clauseWitnesses.map(text => typeofTypesByName.get(text) || neverType)), switchFacts); + if (impliedType.flags & TypeFlags.Union) { + impliedType = getAssignmentReducedType(impliedType as UnionType, getBaseConstraintOfType(type) || type); + } + if (!(impliedType.flags & TypeFlags.Never)) { + if (isTypeSubtypeOf(impliedType, type)) { + return impliedType; + } + if (type.flags & TypeFlags.Instantiable) { + const constraint = getBaseConstraintOfType(type) || anyType; + if (isTypeSubtypeOf(impliedType, constraint)) { + return getIntersectionType([type, impliedType]); + } + } + } + } + return hasDefaultClause ? + filterType(type, t => (getTypeFacts(t) & switchFacts) === switchFacts) : + getTypeWithFacts(type, switchFacts); + } + function narrowTypeByInstanceof(type: Type, expr: BinaryExpression, assumeTrue: boolean): Type { const left = getReferenceCandidate(expr.left); if (!isMatchingReference(reference, left)) { @@ -18944,10 +19013,60 @@ namespace ts { : Diagnostics.Type_of_yield_operand_in_an_async_generator_must_either_be_a_valid_promise_or_must_not_contain_a_callable_then_member); } + /** + * Collect the TypeFacts learned from a typeof switch with + * total clauses `witnesses`, and the active clause ranging + * from `start` to `end`. Parameter `hasDefault` denotes + * whether the active clause contains a default clause. + */ + function getFactsFromTypeofSwitch(start: number, end: number, witnesses: (string | undefined)[], hasDefault: boolean): TypeFacts { + let facts: TypeFacts = TypeFacts.None; + // When in the default we only collect inequality facts + // because default is 'in theory' a set of infinite + // equalities. + if (hasDefault) { + // Value is not equal to any types after the active clause. + for (let i = end; i < witnesses.length; i++) { + facts |= typeofNEFacts.get(witnesses[i]) || TypeFacts.TypeofNEHostObject; + } + // Remove inequalities for types that appear in the + // active clause because they appear before other + // types collected so far. + for (let i = start; i < end; i++) { + facts &= ~(typeofNEFacts.get(witnesses[i]) || 0); + } + // Add inequalities for types before the active clause unconditionally. + for (let i = 0; i < start; i++) { + facts |= typeofNEFacts.get(witnesses[i]) || TypeFacts.TypeofNEHostObject; + } + } + // When in an active clause without default the set of + // equalities is finite. + else { + // Add equalities for all types in the active clause. + for (let i = start; i < end; i++) { + facts |= typeofEQFacts.get(witnesses[i]) || TypeFacts.TypeofEQHostObject; + } + // Remove equalities for types that appear before the + // active clause. + for (let i = 0; i < start; i++) { + facts &= ~(typeofEQFacts.get(witnesses[i]) || 0); + } + } + return facts; + } + function isExhaustiveSwitchStatement(node: SwitchStatement): boolean { if (!node.possiblyExhaustive) { return false; } + if (node.expression.kind === SyntaxKind.TypeOfExpression) { + const operandType = getTypeOfExpression((node.expression as TypeOfExpression).expression); + // Type is not equal to every type in the switch. + const notEqualFacts = getFactsFromTypeofSwitch(0, 0, getSwitchClauseTypeOfWitnesses(node), /*hasDefault*/ true); + const type = getBaseConstraintOfType(operandType) || operandType; + return !!(filterType(type, t => (getTypeFacts(t) & notEqualFacts) === notEqualFacts).flags & TypeFlags.Never); + } const type = getTypeOfExpression(node.expression); if (!isLiteralType(type)) { return false; diff --git a/tests/baselines/reference/narrowingByTypeofInSwitch.js b/tests/baselines/reference/narrowingByTypeofInSwitch.js new file mode 100644 index 0000000000000..2cf4b9027c2c8 --- /dev/null +++ b/tests/baselines/reference/narrowingByTypeofInSwitch.js @@ -0,0 +1,427 @@ +//// [narrowingByTypeofInSwitch.ts] +function assertNever(x: never) { + return x; +} + +function assertNumber(x: number) { + return x; +} + +function assertBoolean(x: boolean) { + return x; +} + +function assertString(x: string) { + return x; +} + +function assertSymbol(x: symbol) { + return x; +} + +function assertFunction(x: Function) { + return x; +} + +function assertObject(x: object) { + return x; +} + +function assertUndefined(x: undefined) { + return x; +} + +function assertAll(x: Basic) { + return x; +} + +type Basic = number | boolean | string | symbol | object | Function | undefined; + +function testUnion(x: Basic) { + switch (typeof x) { + case 'number': assertNumber(x); return; + case 'boolean': assertBoolean(x); return; + case 'function': assertFunction(x); return; + case 'symbol': assertSymbol(x); return; + case 'object': assertObject(x); return; + case 'string': assertString(x); return; + case 'undefined': assertUndefined(x); return; + } + assertNever(x); +} + +function testExtendsUnion<T extends Basic>(x: T) { + switch (typeof x) { + case 'number': assertNumber(x); return; + case 'boolean': assertBoolean(x); return; + case 'function': assertAll(x); return; + case 'symbol': assertSymbol(x); return; + case 'object': assertAll(x); return; + case 'string': assertString(x); return; + case 'undefined': assertUndefined(x); return; + } + assertAll(x); +} + +function testAny(x: any) { + switch (typeof x) { + case 'number': assertNumber(x); return; + case 'boolean': assertBoolean(x); return; + case 'function': assertFunction(x); return; + case 'symbol': assertSymbol(x); return; + case 'object': assertObject(x); return; + case 'string': assertString(x); return; + case 'undefined': assertUndefined(x); return; + } + assertAll(x); // is any +} + +function a1(x: string | object | undefined) { + return x; +} + +function testUnionExplicitDefault(x: Basic) { + switch (typeof x) { + case 'number': assertNumber(x); return; + case 'boolean': assertBoolean(x); return; + case 'function': assertFunction(x); return; + case 'symbol': assertSymbol(x); return; + default: a1(x); return; + } +} + +function testUnionImplicitDefault(x: Basic) { + switch (typeof x) { + case 'number': assertNumber(x); return; + case 'boolean': assertBoolean(x); return; + case 'function': assertFunction(x); return; + case 'symbol': assertSymbol(x); return; + } + return a1(x); +} + +function testExtendsExplicitDefault<T extends Basic>(x: T) { + switch (typeof x) { + case 'number': assertNumber(x); return; + case 'boolean': assertBoolean(x); return; + case 'function': assertAll(x); return; + case 'symbol': assertSymbol(x); return; + default: assertAll(x); return; + + } +} + +function testExtendsImplicitDefault<T extends Basic>(x: T) { + switch (typeof x) { + case 'number': assertNumber(x); return; + case 'boolean': assertBoolean(x); return; + case 'function': assertAll(x); return; + case 'symbol': assertSymbol(x); return; + } + return assertAll(x); +} + +type L = (x: number) => string; +type R = { x: string, y: number } + +function exhaustiveChecks(x: number | string | L | R): string { + switch (typeof x) { + case 'number': return x.toString(2); + case 'string': return x; + case 'function': return x(42); + case 'object': return x.x; + } +} + +function exhaustiveChecksGenerics<T extends L | R | number | string>(x: T): string { + switch (typeof x) { + case 'number': return x.toString(2); + case 'string': return x; + case 'function': return (x as L)(42); // Can't narrow generic + case 'object': return (x as R).x; // Can't narrow generic + } +} + +function multipleGeneric<X extends L, Y extends R>(xy: X | Y): [X, string] | [Y, number] { + switch (typeof xy) { + case 'function': return [xy, xy(42)]; + case 'object': return [xy, xy.y]; + default: return assertNever(xy); + } +} + +function multipleGenericFuse<X extends L | number, Y extends R | number>(xy: X | Y): [X, number] | [Y, string] | [(X | Y)] { + switch (typeof xy) { + case 'function': return [xy, 1]; + case 'object': return [xy, 'two']; + case 'number': return [xy] + } +} + +function multipleGenericExhaustive<X extends L, Y extends R>(xy: X | Y): [X, string] | [Y, number] { + switch (typeof xy) { + case 'object': return [xy, xy.y]; + case 'function': return [xy, xy(42)]; + } +} + +function switchOrdering(x: string | number | boolean) { + switch (typeof x) { + case 'string': return assertString(x); + case 'number': return assertNumber(x); + case 'boolean': return assertBoolean(x); + case 'number': return assertNever(x); + } +} + +function switchOrderingWithDefault(x: string | number | boolean) { + function local(y: string | number | boolean) { + return x; + } + switch (typeof x) { + case 'string': + case 'number': + default: return local(x) + case 'string': return assertNever(x); + case 'number': return assertNever(x); + } +} + + +//// [narrowingByTypeofInSwitch.js] +function assertNever(x) { + return x; +} +function assertNumber(x) { + return x; +} +function assertBoolean(x) { + return x; +} +function assertString(x) { + return x; +} +function assertSymbol(x) { + return x; +} +function assertFunction(x) { + return x; +} +function assertObject(x) { + return x; +} +function assertUndefined(x) { + return x; +} +function assertAll(x) { + return x; +} +function testUnion(x) { + switch (typeof x) { + case 'number': + assertNumber(x); + return; + case 'boolean': + assertBoolean(x); + return; + case 'function': + assertFunction(x); + return; + case 'symbol': + assertSymbol(x); + return; + case 'object': + assertObject(x); + return; + case 'string': + assertString(x); + return; + case 'undefined': + assertUndefined(x); + return; + } + assertNever(x); +} +function testExtendsUnion(x) { + switch (typeof x) { + case 'number': + assertNumber(x); + return; + case 'boolean': + assertBoolean(x); + return; + case 'function': + assertAll(x); + return; + case 'symbol': + assertSymbol(x); + return; + case 'object': + assertAll(x); + return; + case 'string': + assertString(x); + return; + case 'undefined': + assertUndefined(x); + return; + } + assertAll(x); +} +function testAny(x) { + switch (typeof x) { + case 'number': + assertNumber(x); + return; + case 'boolean': + assertBoolean(x); + return; + case 'function': + assertFunction(x); + return; + case 'symbol': + assertSymbol(x); + return; + case 'object': + assertObject(x); + return; + case 'string': + assertString(x); + return; + case 'undefined': + assertUndefined(x); + return; + } + assertAll(x); // is any +} +function a1(x) { + return x; +} +function testUnionExplicitDefault(x) { + switch (typeof x) { + case 'number': + assertNumber(x); + return; + case 'boolean': + assertBoolean(x); + return; + case 'function': + assertFunction(x); + return; + case 'symbol': + assertSymbol(x); + return; + default: + a1(x); + return; + } +} +function testUnionImplicitDefault(x) { + switch (typeof x) { + case 'number': + assertNumber(x); + return; + case 'boolean': + assertBoolean(x); + return; + case 'function': + assertFunction(x); + return; + case 'symbol': + assertSymbol(x); + return; + } + return a1(x); +} +function testExtendsExplicitDefault(x) { + switch (typeof x) { + case 'number': + assertNumber(x); + return; + case 'boolean': + assertBoolean(x); + return; + case 'function': + assertAll(x); + return; + case 'symbol': + assertSymbol(x); + return; + default: + assertAll(x); + return; + } +} +function testExtendsImplicitDefault(x) { + switch (typeof x) { + case 'number': + assertNumber(x); + return; + case 'boolean': + assertBoolean(x); + return; + case 'function': + assertAll(x); + return; + case 'symbol': + assertSymbol(x); + return; + } + return assertAll(x); +} +function exhaustiveChecks(x) { + switch (typeof x) { + case 'number': return x.toString(2); + case 'string': return x; + case 'function': return x(42); + case 'object': return x.x; + } +} +function exhaustiveChecksGenerics(x) { + switch (typeof x) { + case 'number': return x.toString(2); + case 'string': return x; + case 'function': return x(42); // Can't narrow generic + case 'object': return x.x; // Can't narrow generic + } +} +function multipleGeneric(xy) { + switch (typeof xy) { + case 'function': return [xy, xy(42)]; + case 'object': return [xy, xy.y]; + default: return assertNever(xy); + } +} +function multipleGenericFuse(xy) { + switch (typeof xy) { + case 'function': return [xy, 1]; + case 'object': return [xy, 'two']; + case 'number': return [xy]; + } +} +function multipleGenericExhaustive(xy) { + switch (typeof xy) { + case 'object': return [xy, xy.y]; + case 'function': return [xy, xy(42)]; + } +} +function switchOrdering(x) { + switch (typeof x) { + case 'string': return assertString(x); + case 'number': return assertNumber(x); + case 'boolean': return assertBoolean(x); + case 'number': return assertNever(x); + } +} +function switchOrderingWithDefault(x) { + function local(y) { + return x; + } + switch (typeof x) { + case 'string': + case 'number': + default: return local(x); + case 'string': return assertNever(x); + case 'number': return assertNever(x); + } +} diff --git a/tests/baselines/reference/narrowingByTypeofInSwitch.symbols b/tests/baselines/reference/narrowingByTypeofInSwitch.symbols new file mode 100644 index 0000000000000..2d1bd06baba98 --- /dev/null +++ b/tests/baselines/reference/narrowingByTypeofInSwitch.symbols @@ -0,0 +1,542 @@ +=== tests/cases/compiler/narrowingByTypeofInSwitch.ts === +function assertNever(x: never) { +>assertNever : Symbol(assertNever, Decl(narrowingByTypeofInSwitch.ts, 0, 0)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 0, 21)) + + return x; +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 0, 21)) +} + +function assertNumber(x: number) { +>assertNumber : Symbol(assertNumber, Decl(narrowingByTypeofInSwitch.ts, 2, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 4, 22)) + + return x; +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 4, 22)) +} + +function assertBoolean(x: boolean) { +>assertBoolean : Symbol(assertBoolean, Decl(narrowingByTypeofInSwitch.ts, 6, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 8, 23)) + + return x; +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 8, 23)) +} + +function assertString(x: string) { +>assertString : Symbol(assertString, Decl(narrowingByTypeofInSwitch.ts, 10, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 12, 22)) + + return x; +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 12, 22)) +} + +function assertSymbol(x: symbol) { +>assertSymbol : Symbol(assertSymbol, Decl(narrowingByTypeofInSwitch.ts, 14, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 16, 22)) + + return x; +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 16, 22)) +} + +function assertFunction(x: Function) { +>assertFunction : Symbol(assertFunction, Decl(narrowingByTypeofInSwitch.ts, 18, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 20, 24)) +>Function : Symbol(Function, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --)) + + return x; +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 20, 24)) +} + +function assertObject(x: object) { +>assertObject : Symbol(assertObject, Decl(narrowingByTypeofInSwitch.ts, 22, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 24, 22)) + + return x; +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 24, 22)) +} + +function assertUndefined(x: undefined) { +>assertUndefined : Symbol(assertUndefined, Decl(narrowingByTypeofInSwitch.ts, 26, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 28, 25)) + + return x; +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 28, 25)) +} + +function assertAll(x: Basic) { +>assertAll : Symbol(assertAll, Decl(narrowingByTypeofInSwitch.ts, 30, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 32, 19)) +>Basic : Symbol(Basic, Decl(narrowingByTypeofInSwitch.ts, 34, 1)) + + return x; +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 32, 19)) +} + +type Basic = number | boolean | string | symbol | object | Function | undefined; +>Basic : Symbol(Basic, Decl(narrowingByTypeofInSwitch.ts, 34, 1)) +>Function : Symbol(Function, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --)) + +function testUnion(x: Basic) { +>testUnion : Symbol(testUnion, Decl(narrowingByTypeofInSwitch.ts, 36, 80)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 38, 19)) +>Basic : Symbol(Basic, Decl(narrowingByTypeofInSwitch.ts, 34, 1)) + + switch (typeof x) { +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 38, 19)) + + case 'number': assertNumber(x); return; +>assertNumber : Symbol(assertNumber, Decl(narrowingByTypeofInSwitch.ts, 2, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 38, 19)) + + case 'boolean': assertBoolean(x); return; +>assertBoolean : Symbol(assertBoolean, Decl(narrowingByTypeofInSwitch.ts, 6, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 38, 19)) + + case 'function': assertFunction(x); return; +>assertFunction : Symbol(assertFunction, Decl(narrowingByTypeofInSwitch.ts, 18, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 38, 19)) + + case 'symbol': assertSymbol(x); return; +>assertSymbol : Symbol(assertSymbol, Decl(narrowingByTypeofInSwitch.ts, 14, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 38, 19)) + + case 'object': assertObject(x); return; +>assertObject : Symbol(assertObject, Decl(narrowingByTypeofInSwitch.ts, 22, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 38, 19)) + + case 'string': assertString(x); return; +>assertString : Symbol(assertString, Decl(narrowingByTypeofInSwitch.ts, 10, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 38, 19)) + + case 'undefined': assertUndefined(x); return; +>assertUndefined : Symbol(assertUndefined, Decl(narrowingByTypeofInSwitch.ts, 26, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 38, 19)) + } + assertNever(x); +>assertNever : Symbol(assertNever, Decl(narrowingByTypeofInSwitch.ts, 0, 0)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 38, 19)) +} + +function testExtendsUnion<T extends Basic>(x: T) { +>testExtendsUnion : Symbol(testExtendsUnion, Decl(narrowingByTypeofInSwitch.ts, 49, 1)) +>T : Symbol(T, Decl(narrowingByTypeofInSwitch.ts, 51, 26)) +>Basic : Symbol(Basic, Decl(narrowingByTypeofInSwitch.ts, 34, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 51, 43)) +>T : Symbol(T, Decl(narrowingByTypeofInSwitch.ts, 51, 26)) + + switch (typeof x) { +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 51, 43)) + + case 'number': assertNumber(x); return; +>assertNumber : Symbol(assertNumber, Decl(narrowingByTypeofInSwitch.ts, 2, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 51, 43)) + + case 'boolean': assertBoolean(x); return; +>assertBoolean : Symbol(assertBoolean, Decl(narrowingByTypeofInSwitch.ts, 6, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 51, 43)) + + case 'function': assertAll(x); return; +>assertAll : Symbol(assertAll, Decl(narrowingByTypeofInSwitch.ts, 30, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 51, 43)) + + case 'symbol': assertSymbol(x); return; +>assertSymbol : Symbol(assertSymbol, Decl(narrowingByTypeofInSwitch.ts, 14, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 51, 43)) + + case 'object': assertAll(x); return; +>assertAll : Symbol(assertAll, Decl(narrowingByTypeofInSwitch.ts, 30, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 51, 43)) + + case 'string': assertString(x); return; +>assertString : Symbol(assertString, Decl(narrowingByTypeofInSwitch.ts, 10, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 51, 43)) + + case 'undefined': assertUndefined(x); return; +>assertUndefined : Symbol(assertUndefined, Decl(narrowingByTypeofInSwitch.ts, 26, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 51, 43)) + } + assertAll(x); +>assertAll : Symbol(assertAll, Decl(narrowingByTypeofInSwitch.ts, 30, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 51, 43)) +} + +function testAny(x: any) { +>testAny : Symbol(testAny, Decl(narrowingByTypeofInSwitch.ts, 62, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 64, 17)) + + switch (typeof x) { +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 64, 17)) + + case 'number': assertNumber(x); return; +>assertNumber : Symbol(assertNumber, Decl(narrowingByTypeofInSwitch.ts, 2, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 64, 17)) + + case 'boolean': assertBoolean(x); return; +>assertBoolean : Symbol(assertBoolean, Decl(narrowingByTypeofInSwitch.ts, 6, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 64, 17)) + + case 'function': assertFunction(x); return; +>assertFunction : Symbol(assertFunction, Decl(narrowingByTypeofInSwitch.ts, 18, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 64, 17)) + + case 'symbol': assertSymbol(x); return; +>assertSymbol : Symbol(assertSymbol, Decl(narrowingByTypeofInSwitch.ts, 14, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 64, 17)) + + case 'object': assertObject(x); return; +>assertObject : Symbol(assertObject, Decl(narrowingByTypeofInSwitch.ts, 22, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 64, 17)) + + case 'string': assertString(x); return; +>assertString : Symbol(assertString, Decl(narrowingByTypeofInSwitch.ts, 10, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 64, 17)) + + case 'undefined': assertUndefined(x); return; +>assertUndefined : Symbol(assertUndefined, Decl(narrowingByTypeofInSwitch.ts, 26, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 64, 17)) + } + assertAll(x); // is any +>assertAll : Symbol(assertAll, Decl(narrowingByTypeofInSwitch.ts, 30, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 64, 17)) +} + +function a1(x: string | object | undefined) { +>a1 : Symbol(a1, Decl(narrowingByTypeofInSwitch.ts, 75, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 77, 12)) + + return x; +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 77, 12)) +} + +function testUnionExplicitDefault(x: Basic) { +>testUnionExplicitDefault : Symbol(testUnionExplicitDefault, Decl(narrowingByTypeofInSwitch.ts, 79, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 81, 34)) +>Basic : Symbol(Basic, Decl(narrowingByTypeofInSwitch.ts, 34, 1)) + + switch (typeof x) { +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 81, 34)) + + case 'number': assertNumber(x); return; +>assertNumber : Symbol(assertNumber, Decl(narrowingByTypeofInSwitch.ts, 2, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 81, 34)) + + case 'boolean': assertBoolean(x); return; +>assertBoolean : Symbol(assertBoolean, Decl(narrowingByTypeofInSwitch.ts, 6, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 81, 34)) + + case 'function': assertFunction(x); return; +>assertFunction : Symbol(assertFunction, Decl(narrowingByTypeofInSwitch.ts, 18, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 81, 34)) + + case 'symbol': assertSymbol(x); return; +>assertSymbol : Symbol(assertSymbol, Decl(narrowingByTypeofInSwitch.ts, 14, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 81, 34)) + + default: a1(x); return; +>a1 : Symbol(a1, Decl(narrowingByTypeofInSwitch.ts, 75, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 81, 34)) + } +} + +function testUnionImplicitDefault(x: Basic) { +>testUnionImplicitDefault : Symbol(testUnionImplicitDefault, Decl(narrowingByTypeofInSwitch.ts, 89, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 91, 34)) +>Basic : Symbol(Basic, Decl(narrowingByTypeofInSwitch.ts, 34, 1)) + + switch (typeof x) { +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 91, 34)) + + case 'number': assertNumber(x); return; +>assertNumber : Symbol(assertNumber, Decl(narrowingByTypeofInSwitch.ts, 2, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 91, 34)) + + case 'boolean': assertBoolean(x); return; +>assertBoolean : Symbol(assertBoolean, Decl(narrowingByTypeofInSwitch.ts, 6, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 91, 34)) + + case 'function': assertFunction(x); return; +>assertFunction : Symbol(assertFunction, Decl(narrowingByTypeofInSwitch.ts, 18, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 91, 34)) + + case 'symbol': assertSymbol(x); return; +>assertSymbol : Symbol(assertSymbol, Decl(narrowingByTypeofInSwitch.ts, 14, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 91, 34)) + } + return a1(x); +>a1 : Symbol(a1, Decl(narrowingByTypeofInSwitch.ts, 75, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 91, 34)) +} + +function testExtendsExplicitDefault<T extends Basic>(x: T) { +>testExtendsExplicitDefault : Symbol(testExtendsExplicitDefault, Decl(narrowingByTypeofInSwitch.ts, 99, 1)) +>T : Symbol(T, Decl(narrowingByTypeofInSwitch.ts, 101, 36)) +>Basic : Symbol(Basic, Decl(narrowingByTypeofInSwitch.ts, 34, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 101, 53)) +>T : Symbol(T, Decl(narrowingByTypeofInSwitch.ts, 101, 36)) + + switch (typeof x) { +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 101, 53)) + + case 'number': assertNumber(x); return; +>assertNumber : Symbol(assertNumber, Decl(narrowingByTypeofInSwitch.ts, 2, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 101, 53)) + + case 'boolean': assertBoolean(x); return; +>assertBoolean : Symbol(assertBoolean, Decl(narrowingByTypeofInSwitch.ts, 6, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 101, 53)) + + case 'function': assertAll(x); return; +>assertAll : Symbol(assertAll, Decl(narrowingByTypeofInSwitch.ts, 30, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 101, 53)) + + case 'symbol': assertSymbol(x); return; +>assertSymbol : Symbol(assertSymbol, Decl(narrowingByTypeofInSwitch.ts, 14, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 101, 53)) + + default: assertAll(x); return; +>assertAll : Symbol(assertAll, Decl(narrowingByTypeofInSwitch.ts, 30, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 101, 53)) + + } +} + +function testExtendsImplicitDefault<T extends Basic>(x: T) { +>testExtendsImplicitDefault : Symbol(testExtendsImplicitDefault, Decl(narrowingByTypeofInSwitch.ts, 110, 1)) +>T : Symbol(T, Decl(narrowingByTypeofInSwitch.ts, 112, 36)) +>Basic : Symbol(Basic, Decl(narrowingByTypeofInSwitch.ts, 34, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 112, 53)) +>T : Symbol(T, Decl(narrowingByTypeofInSwitch.ts, 112, 36)) + + switch (typeof x) { +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 112, 53)) + + case 'number': assertNumber(x); return; +>assertNumber : Symbol(assertNumber, Decl(narrowingByTypeofInSwitch.ts, 2, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 112, 53)) + + case 'boolean': assertBoolean(x); return; +>assertBoolean : Symbol(assertBoolean, Decl(narrowingByTypeofInSwitch.ts, 6, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 112, 53)) + + case 'function': assertAll(x); return; +>assertAll : Symbol(assertAll, Decl(narrowingByTypeofInSwitch.ts, 30, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 112, 53)) + + case 'symbol': assertSymbol(x); return; +>assertSymbol : Symbol(assertSymbol, Decl(narrowingByTypeofInSwitch.ts, 14, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 112, 53)) + } + return assertAll(x); +>assertAll : Symbol(assertAll, Decl(narrowingByTypeofInSwitch.ts, 30, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 112, 53)) +} + +type L = (x: number) => string; +>L : Symbol(L, Decl(narrowingByTypeofInSwitch.ts, 120, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 122, 10)) + +type R = { x: string, y: number } +>R : Symbol(R, Decl(narrowingByTypeofInSwitch.ts, 122, 31)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 123, 10)) +>y : Symbol(y, Decl(narrowingByTypeofInSwitch.ts, 123, 21)) + +function exhaustiveChecks(x: number | string | L | R): string { +>exhaustiveChecks : Symbol(exhaustiveChecks, Decl(narrowingByTypeofInSwitch.ts, 123, 33)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 125, 26)) +>L : Symbol(L, Decl(narrowingByTypeofInSwitch.ts, 120, 1)) +>R : Symbol(R, Decl(narrowingByTypeofInSwitch.ts, 122, 31)) + + switch (typeof x) { +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 125, 26)) + + case 'number': return x.toString(2); +>x.toString : Symbol(Number.toString, Decl(lib.d.ts, --, --)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 125, 26)) +>toString : Symbol(Number.toString, Decl(lib.d.ts, --, --)) + + case 'string': return x; +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 125, 26)) + + case 'function': return x(42); +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 125, 26)) + + case 'object': return x.x; +>x.x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 123, 10)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 125, 26)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 123, 10)) + } +} + +function exhaustiveChecksGenerics<T extends L | R | number | string>(x: T): string { +>exhaustiveChecksGenerics : Symbol(exhaustiveChecksGenerics, Decl(narrowingByTypeofInSwitch.ts, 132, 1)) +>T : Symbol(T, Decl(narrowingByTypeofInSwitch.ts, 134, 34)) +>L : Symbol(L, Decl(narrowingByTypeofInSwitch.ts, 120, 1)) +>R : Symbol(R, Decl(narrowingByTypeofInSwitch.ts, 122, 31)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 134, 69)) +>T : Symbol(T, Decl(narrowingByTypeofInSwitch.ts, 134, 34)) + + switch (typeof x) { +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 134, 69)) + + case 'number': return x.toString(2); +>x.toString : Symbol(toString, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --) ... and 2 more) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 134, 69)) +>toString : Symbol(toString, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --) ... and 2 more) + + case 'string': return x; +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 134, 69)) + + case 'function': return (x as L)(42); // Can't narrow generic +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 134, 69)) +>L : Symbol(L, Decl(narrowingByTypeofInSwitch.ts, 120, 1)) + + case 'object': return (x as R).x; // Can't narrow generic +>(x as R).x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 123, 10)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 134, 69)) +>R : Symbol(R, Decl(narrowingByTypeofInSwitch.ts, 122, 31)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 123, 10)) + } +} + +function multipleGeneric<X extends L, Y extends R>(xy: X | Y): [X, string] | [Y, number] { +>multipleGeneric : Symbol(multipleGeneric, Decl(narrowingByTypeofInSwitch.ts, 141, 1)) +>X : Symbol(X, Decl(narrowingByTypeofInSwitch.ts, 143, 25)) +>L : Symbol(L, Decl(narrowingByTypeofInSwitch.ts, 120, 1)) +>Y : Symbol(Y, Decl(narrowingByTypeofInSwitch.ts, 143, 37)) +>R : Symbol(R, Decl(narrowingByTypeofInSwitch.ts, 122, 31)) +>xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 143, 51)) +>X : Symbol(X, Decl(narrowingByTypeofInSwitch.ts, 143, 25)) +>Y : Symbol(Y, Decl(narrowingByTypeofInSwitch.ts, 143, 37)) +>X : Symbol(X, Decl(narrowingByTypeofInSwitch.ts, 143, 25)) +>Y : Symbol(Y, Decl(narrowingByTypeofInSwitch.ts, 143, 37)) + + switch (typeof xy) { +>xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 143, 51)) + + case 'function': return [xy, xy(42)]; +>xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 143, 51)) +>xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 143, 51)) + + case 'object': return [xy, xy.y]; +>xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 143, 51)) +>xy.y : Symbol(y, Decl(narrowingByTypeofInSwitch.ts, 123, 21)) +>xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 143, 51)) +>y : Symbol(y, Decl(narrowingByTypeofInSwitch.ts, 123, 21)) + + default: return assertNever(xy); +>assertNever : Symbol(assertNever, Decl(narrowingByTypeofInSwitch.ts, 0, 0)) +>xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 143, 51)) + } +} + +function multipleGenericFuse<X extends L | number, Y extends R | number>(xy: X | Y): [X, number] | [Y, string] | [(X | Y)] { +>multipleGenericFuse : Symbol(multipleGenericFuse, Decl(narrowingByTypeofInSwitch.ts, 149, 1)) +>X : Symbol(X, Decl(narrowingByTypeofInSwitch.ts, 151, 29)) +>L : Symbol(L, Decl(narrowingByTypeofInSwitch.ts, 120, 1)) +>Y : Symbol(Y, Decl(narrowingByTypeofInSwitch.ts, 151, 50)) +>R : Symbol(R, Decl(narrowingByTypeofInSwitch.ts, 122, 31)) +>xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 151, 73)) +>X : Symbol(X, Decl(narrowingByTypeofInSwitch.ts, 151, 29)) +>Y : Symbol(Y, Decl(narrowingByTypeofInSwitch.ts, 151, 50)) +>X : Symbol(X, Decl(narrowingByTypeofInSwitch.ts, 151, 29)) +>Y : Symbol(Y, Decl(narrowingByTypeofInSwitch.ts, 151, 50)) +>X : Symbol(X, Decl(narrowingByTypeofInSwitch.ts, 151, 29)) +>Y : Symbol(Y, Decl(narrowingByTypeofInSwitch.ts, 151, 50)) + + switch (typeof xy) { +>xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 151, 73)) + + case 'function': return [xy, 1]; +>xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 151, 73)) + + case 'object': return [xy, 'two']; +>xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 151, 73)) + + case 'number': return [xy] +>xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 151, 73)) + } +} + +function multipleGenericExhaustive<X extends L, Y extends R>(xy: X | Y): [X, string] | [Y, number] { +>multipleGenericExhaustive : Symbol(multipleGenericExhaustive, Decl(narrowingByTypeofInSwitch.ts, 157, 1)) +>X : Symbol(X, Decl(narrowingByTypeofInSwitch.ts, 159, 35)) +>L : Symbol(L, Decl(narrowingByTypeofInSwitch.ts, 120, 1)) +>Y : Symbol(Y, Decl(narrowingByTypeofInSwitch.ts, 159, 47)) +>R : Symbol(R, Decl(narrowingByTypeofInSwitch.ts, 122, 31)) +>xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 159, 61)) +>X : Symbol(X, Decl(narrowingByTypeofInSwitch.ts, 159, 35)) +>Y : Symbol(Y, Decl(narrowingByTypeofInSwitch.ts, 159, 47)) +>X : Symbol(X, Decl(narrowingByTypeofInSwitch.ts, 159, 35)) +>Y : Symbol(Y, Decl(narrowingByTypeofInSwitch.ts, 159, 47)) + + switch (typeof xy) { +>xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 159, 61)) + + case 'object': return [xy, xy.y]; +>xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 159, 61)) +>xy.y : Symbol(y, Decl(narrowingByTypeofInSwitch.ts, 123, 21)) +>xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 159, 61)) +>y : Symbol(y, Decl(narrowingByTypeofInSwitch.ts, 123, 21)) + + case 'function': return [xy, xy(42)]; +>xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 159, 61)) +>xy : Symbol(xy, Decl(narrowingByTypeofInSwitch.ts, 159, 61)) + } +} + +function switchOrdering(x: string | number | boolean) { +>switchOrdering : Symbol(switchOrdering, Decl(narrowingByTypeofInSwitch.ts, 164, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 166, 24)) + + switch (typeof x) { +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 166, 24)) + + case 'string': return assertString(x); +>assertString : Symbol(assertString, Decl(narrowingByTypeofInSwitch.ts, 10, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 166, 24)) + + case 'number': return assertNumber(x); +>assertNumber : Symbol(assertNumber, Decl(narrowingByTypeofInSwitch.ts, 2, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 166, 24)) + + case 'boolean': return assertBoolean(x); +>assertBoolean : Symbol(assertBoolean, Decl(narrowingByTypeofInSwitch.ts, 6, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 166, 24)) + + case 'number': return assertNever(x); +>assertNever : Symbol(assertNever, Decl(narrowingByTypeofInSwitch.ts, 0, 0)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 166, 24)) + } +} + +function switchOrderingWithDefault(x: string | number | boolean) { +>switchOrderingWithDefault : Symbol(switchOrderingWithDefault, Decl(narrowingByTypeofInSwitch.ts, 173, 1)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 175, 35)) + + function local(y: string | number | boolean) { +>local : Symbol(local, Decl(narrowingByTypeofInSwitch.ts, 175, 66)) +>y : Symbol(y, Decl(narrowingByTypeofInSwitch.ts, 176, 19)) + + return x; +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 175, 35)) + } + switch (typeof x) { +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 175, 35)) + + case 'string': + case 'number': + default: return local(x) +>local : Symbol(local, Decl(narrowingByTypeofInSwitch.ts, 175, 66)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 175, 35)) + + case 'string': return assertNever(x); +>assertNever : Symbol(assertNever, Decl(narrowingByTypeofInSwitch.ts, 0, 0)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 175, 35)) + + case 'number': return assertNever(x); +>assertNever : Symbol(assertNever, Decl(narrowingByTypeofInSwitch.ts, 0, 0)) +>x : Symbol(x, Decl(narrowingByTypeofInSwitch.ts, 175, 35)) + } +} + diff --git a/tests/baselines/reference/narrowingByTypeofInSwitch.types b/tests/baselines/reference/narrowingByTypeofInSwitch.types new file mode 100644 index 0000000000000..785bdd23609d5 --- /dev/null +++ b/tests/baselines/reference/narrowingByTypeofInSwitch.types @@ -0,0 +1,695 @@ +=== tests/cases/compiler/narrowingByTypeofInSwitch.ts === +function assertNever(x: never) { +>assertNever : (x: never) => never +>x : never + + return x; +>x : never +} + +function assertNumber(x: number) { +>assertNumber : (x: number) => number +>x : number + + return x; +>x : number +} + +function assertBoolean(x: boolean) { +>assertBoolean : (x: boolean) => boolean +>x : boolean + + return x; +>x : boolean +} + +function assertString(x: string) { +>assertString : (x: string) => string +>x : string + + return x; +>x : string +} + +function assertSymbol(x: symbol) { +>assertSymbol : (x: symbol) => symbol +>x : symbol + + return x; +>x : symbol +} + +function assertFunction(x: Function) { +>assertFunction : (x: Function) => Function +>x : Function +>Function : Function + + return x; +>x : Function +} + +function assertObject(x: object) { +>assertObject : (x: object) => object +>x : object + + return x; +>x : object +} + +function assertUndefined(x: undefined) { +>assertUndefined : (x: undefined) => undefined +>x : undefined + + return x; +>x : undefined +} + +function assertAll(x: Basic) { +>assertAll : (x: Basic) => Basic +>x : Basic +>Basic : Basic + + return x; +>x : Basic +} + +type Basic = number | boolean | string | symbol | object | Function | undefined; +>Basic : Basic +>Function : Function + +function testUnion(x: Basic) { +>testUnion : (x: Basic) => void +>x : Basic +>Basic : Basic + + switch (typeof x) { +>typeof x : "string" | "number" | "boolean" | "symbol" | "undefined" | "object" | "function" +>x : Basic + + case 'number': assertNumber(x); return; +>'number' : "number" +>assertNumber(x) : number +>assertNumber : (x: number) => number +>x : number + + case 'boolean': assertBoolean(x); return; +>'boolean' : "boolean" +>assertBoolean(x) : boolean +>assertBoolean : (x: boolean) => boolean +>x : boolean + + case 'function': assertFunction(x); return; +>'function' : "function" +>assertFunction(x) : Function +>assertFunction : (x: Function) => Function +>x : Function + + case 'symbol': assertSymbol(x); return; +>'symbol' : "symbol" +>assertSymbol(x) : symbol +>assertSymbol : (x: symbol) => symbol +>x : symbol + + case 'object': assertObject(x); return; +>'object' : "object" +>assertObject(x) : object +>assertObject : (x: object) => object +>x : object + + case 'string': assertString(x); return; +>'string' : "string" +>assertString(x) : string +>assertString : (x: string) => string +>x : string + + case 'undefined': assertUndefined(x); return; +>'undefined' : "undefined" +>assertUndefined(x) : undefined +>assertUndefined : (x: undefined) => undefined +>x : undefined + } + assertNever(x); +>assertNever(x) : never +>assertNever : (x: never) => never +>x : never +} + +function testExtendsUnion<T extends Basic>(x: T) { +>testExtendsUnion : <T extends Basic>(x: T) => void +>T : T +>Basic : Basic +>x : T +>T : T + + switch (typeof x) { +>typeof x : "string" | "number" | "boolean" | "symbol" | "undefined" | "object" | "function" +>x : T + + case 'number': assertNumber(x); return; +>'number' : "number" +>assertNumber(x) : number +>assertNumber : (x: number) => number +>x : T & number + + case 'boolean': assertBoolean(x); return; +>'boolean' : "boolean" +>assertBoolean(x) : boolean +>assertBoolean : (x: boolean) => boolean +>x : (T & true) | (T & false) + + case 'function': assertAll(x); return; +>'function' : "function" +>assertAll(x) : Basic +>assertAll : (x: Basic) => Basic +>x : T + + case 'symbol': assertSymbol(x); return; +>'symbol' : "symbol" +>assertSymbol(x) : symbol +>assertSymbol : (x: symbol) => symbol +>x : T & symbol + + case 'object': assertAll(x); return; +>'object' : "object" +>assertAll(x) : Basic +>assertAll : (x: Basic) => Basic +>x : T + + case 'string': assertString(x); return; +>'string' : "string" +>assertString(x) : string +>assertString : (x: string) => string +>x : T & string + + case 'undefined': assertUndefined(x); return; +>'undefined' : "undefined" +>assertUndefined(x) : undefined +>assertUndefined : (x: undefined) => undefined +>x : T & undefined + } + assertAll(x); +>assertAll(x) : Basic +>assertAll : (x: Basic) => Basic +>x : T +} + +function testAny(x: any) { +>testAny : (x: any) => void +>x : any + + switch (typeof x) { +>typeof x : "string" | "number" | "boolean" | "symbol" | "undefined" | "object" | "function" +>x : any + + case 'number': assertNumber(x); return; +>'number' : "number" +>assertNumber(x) : number +>assertNumber : (x: number) => number +>x : number + + case 'boolean': assertBoolean(x); return; +>'boolean' : "boolean" +>assertBoolean(x) : boolean +>assertBoolean : (x: boolean) => boolean +>x : boolean + + case 'function': assertFunction(x); return; +>'function' : "function" +>assertFunction(x) : Function +>assertFunction : (x: Function) => Function +>x : any + + case 'symbol': assertSymbol(x); return; +>'symbol' : "symbol" +>assertSymbol(x) : symbol +>assertSymbol : (x: symbol) => symbol +>x : symbol + + case 'object': assertObject(x); return; +>'object' : "object" +>assertObject(x) : object +>assertObject : (x: object) => object +>x : any + + case 'string': assertString(x); return; +>'string' : "string" +>assertString(x) : string +>assertString : (x: string) => string +>x : string + + case 'undefined': assertUndefined(x); return; +>'undefined' : "undefined" +>assertUndefined(x) : undefined +>assertUndefined : (x: undefined) => undefined +>x : undefined + } + assertAll(x); // is any +>assertAll(x) : Basic +>assertAll : (x: Basic) => Basic +>x : any +} + +function a1(x: string | object | undefined) { +>a1 : (x: string | object | undefined) => string | object | undefined +>x : string | object | undefined + + return x; +>x : string | object | undefined +} + +function testUnionExplicitDefault(x: Basic) { +>testUnionExplicitDefault : (x: Basic) => void +>x : Basic +>Basic : Basic + + switch (typeof x) { +>typeof x : "string" | "number" | "boolean" | "symbol" | "undefined" | "object" | "function" +>x : Basic + + case 'number': assertNumber(x); return; +>'number' : "number" +>assertNumber(x) : number +>assertNumber : (x: number) => number +>x : number + + case 'boolean': assertBoolean(x); return; +>'boolean' : "boolean" +>assertBoolean(x) : boolean +>assertBoolean : (x: boolean) => boolean +>x : boolean + + case 'function': assertFunction(x); return; +>'function' : "function" +>assertFunction(x) : Function +>assertFunction : (x: Function) => Function +>x : Function + + case 'symbol': assertSymbol(x); return; +>'symbol' : "symbol" +>assertSymbol(x) : symbol +>assertSymbol : (x: symbol) => symbol +>x : symbol + + default: a1(x); return; +>a1(x) : string | object | undefined +>a1 : (x: string | object | undefined) => string | object | undefined +>x : string | object | undefined + } +} + +function testUnionImplicitDefault(x: Basic) { +>testUnionImplicitDefault : (x: Basic) => string | object | undefined +>x : Basic +>Basic : Basic + + switch (typeof x) { +>typeof x : "string" | "number" | "boolean" | "symbol" | "undefined" | "object" | "function" +>x : Basic + + case 'number': assertNumber(x); return; +>'number' : "number" +>assertNumber(x) : number +>assertNumber : (x: number) => number +>x : number + + case 'boolean': assertBoolean(x); return; +>'boolean' : "boolean" +>assertBoolean(x) : boolean +>assertBoolean : (x: boolean) => boolean +>x : boolean + + case 'function': assertFunction(x); return; +>'function' : "function" +>assertFunction(x) : Function +>assertFunction : (x: Function) => Function +>x : Function + + case 'symbol': assertSymbol(x); return; +>'symbol' : "symbol" +>assertSymbol(x) : symbol +>assertSymbol : (x: symbol) => symbol +>x : symbol + } + return a1(x); +>a1(x) : string | object | undefined +>a1 : (x: string | object | undefined) => string | object | undefined +>x : string | object | undefined +} + +function testExtendsExplicitDefault<T extends Basic>(x: T) { +>testExtendsExplicitDefault : <T extends Basic>(x: T) => void +>T : T +>Basic : Basic +>x : T +>T : T + + switch (typeof x) { +>typeof x : "string" | "number" | "boolean" | "symbol" | "undefined" | "object" | "function" +>x : T + + case 'number': assertNumber(x); return; +>'number' : "number" +>assertNumber(x) : number +>assertNumber : (x: number) => number +>x : T & number + + case 'boolean': assertBoolean(x); return; +>'boolean' : "boolean" +>assertBoolean(x) : boolean +>assertBoolean : (x: boolean) => boolean +>x : (T & true) | (T & false) + + case 'function': assertAll(x); return; +>'function' : "function" +>assertAll(x) : Basic +>assertAll : (x: Basic) => Basic +>x : T + + case 'symbol': assertSymbol(x); return; +>'symbol' : "symbol" +>assertSymbol(x) : symbol +>assertSymbol : (x: symbol) => symbol +>x : T & symbol + + default: assertAll(x); return; +>assertAll(x) : Basic +>assertAll : (x: Basic) => Basic +>x : T + + } +} + +function testExtendsImplicitDefault<T extends Basic>(x: T) { +>testExtendsImplicitDefault : <T extends Basic>(x: T) => string | number | boolean | symbol | object | undefined +>T : T +>Basic : Basic +>x : T +>T : T + + switch (typeof x) { +>typeof x : "string" | "number" | "boolean" | "symbol" | "undefined" | "object" | "function" +>x : T + + case 'number': assertNumber(x); return; +>'number' : "number" +>assertNumber(x) : number +>assertNumber : (x: number) => number +>x : T & number + + case 'boolean': assertBoolean(x); return; +>'boolean' : "boolean" +>assertBoolean(x) : boolean +>assertBoolean : (x: boolean) => boolean +>x : (T & true) | (T & false) + + case 'function': assertAll(x); return; +>'function' : "function" +>assertAll(x) : Basic +>assertAll : (x: Basic) => Basic +>x : T + + case 'symbol': assertSymbol(x); return; +>'symbol' : "symbol" +>assertSymbol(x) : symbol +>assertSymbol : (x: symbol) => symbol +>x : T & symbol + } + return assertAll(x); +>assertAll(x) : Basic +>assertAll : (x: Basic) => Basic +>x : T +} + +type L = (x: number) => string; +>L : L +>x : number + +type R = { x: string, y: number } +>R : R +>x : string +>y : number + +function exhaustiveChecks(x: number | string | L | R): string { +>exhaustiveChecks : (x: string | number | R | L) => string +>x : string | number | R | L +>L : L +>R : R + + switch (typeof x) { +>typeof x : "string" | "number" | "boolean" | "symbol" | "undefined" | "object" | "function" +>x : string | number | R | L + + case 'number': return x.toString(2); +>'number' : "number" +>x.toString(2) : string +>x.toString : (radix?: number | undefined) => string +>x : number +>toString : (radix?: number | undefined) => string +>2 : 2 + + case 'string': return x; +>'string' : "string" +>x : string + + case 'function': return x(42); +>'function' : "function" +>x(42) : string +>x : L +>42 : 42 + + case 'object': return x.x; +>'object' : "object" +>x.x : string +>x : R +>x : string + } +} + +function exhaustiveChecksGenerics<T extends L | R | number | string>(x: T): string { +>exhaustiveChecksGenerics : <T extends string | number | R | L>(x: T) => string +>T : T +>L : L +>R : R +>x : T +>T : T + + switch (typeof x) { +>typeof x : "string" | "number" | "boolean" | "symbol" | "undefined" | "object" | "function" +>x : T + + case 'number': return x.toString(2); +>'number' : "number" +>x.toString(2) : string +>x.toString : ((radix?: number | undefined) => string) | ((() => string) & ((radix?: number | undefined) => string)) | ((() => string) & ((radix?: number | undefined) => string)) | ((() => string) & ((radix?: number | undefined) => string)) +>x : T & number +>toString : ((radix?: number | undefined) => string) | ((() => string) & ((radix?: number | undefined) => string)) | ((() => string) & ((radix?: number | undefined) => string)) | ((() => string) & ((radix?: number | undefined) => string)) +>2 : 2 + + case 'string': return x; +>'string' : "string" +>x : T & string + + case 'function': return (x as L)(42); // Can't narrow generic +>'function' : "function" +>(x as L)(42) : string +>(x as L) : L +>x as L : L +>x : T +>L : L +>42 : 42 + + case 'object': return (x as R).x; // Can't narrow generic +>'object' : "object" +>(x as R).x : string +>(x as R) : R +>x as R : R +>x : T +>R : R +>x : string + } +} + +function multipleGeneric<X extends L, Y extends R>(xy: X | Y): [X, string] | [Y, number] { +>multipleGeneric : <X extends L, Y extends R>(xy: X | Y) => [X, string] | [Y, number] +>X : X +>L : L +>Y : Y +>R : R +>xy : X | Y +>X : X +>Y : Y +>X : X +>Y : Y + + switch (typeof xy) { +>typeof xy : "string" | "number" | "boolean" | "symbol" | "undefined" | "object" | "function" +>xy : X | Y + + case 'function': return [xy, xy(42)]; +>'function' : "function" +>[xy, xy(42)] : [X, string] +>xy : X +>xy(42) : string +>xy : X +>42 : 42 + + case 'object': return [xy, xy.y]; +>'object' : "object" +>[xy, xy.y] : [Y, number] +>xy : Y +>xy.y : number +>xy : Y +>y : number + + default: return assertNever(xy); +>assertNever(xy) : never +>assertNever : (x: never) => never +>xy : never + } +} + +function multipleGenericFuse<X extends L | number, Y extends R | number>(xy: X | Y): [X, number] | [Y, string] | [(X | Y)] { +>multipleGenericFuse : <X extends number | L, Y extends number | R>(xy: X | Y) => [X, number] | [Y, string] | [X | Y] +>X : X +>L : L +>Y : Y +>R : R +>xy : X | Y +>X : X +>Y : Y +>X : X +>Y : Y +>X : X +>Y : Y + + switch (typeof xy) { +>typeof xy : "string" | "number" | "boolean" | "symbol" | "undefined" | "object" | "function" +>xy : X | Y + + case 'function': return [xy, 1]; +>'function' : "function" +>[xy, 1] : [X, number] +>xy : X +>1 : 1 + + case 'object': return [xy, 'two']; +>'object' : "object" +>[xy, 'two'] : [Y, string] +>xy : Y +>'two' : "two" + + case 'number': return [xy] +>'number' : "number" +>[xy] : [X | Y] +>xy : X | Y + } +} + +function multipleGenericExhaustive<X extends L, Y extends R>(xy: X | Y): [X, string] | [Y, number] { +>multipleGenericExhaustive : <X extends L, Y extends R>(xy: X | Y) => [X, string] | [Y, number] +>X : X +>L : L +>Y : Y +>R : R +>xy : X | Y +>X : X +>Y : Y +>X : X +>Y : Y + + switch (typeof xy) { +>typeof xy : "string" | "number" | "boolean" | "symbol" | "undefined" | "object" | "function" +>xy : X | Y + + case 'object': return [xy, xy.y]; +>'object' : "object" +>[xy, xy.y] : [Y, number] +>xy : Y +>xy.y : number +>xy : Y +>y : number + + case 'function': return [xy, xy(42)]; +>'function' : "function" +>[xy, xy(42)] : [X, string] +>xy : X +>xy(42) : string +>xy : X +>42 : 42 + } +} + +function switchOrdering(x: string | number | boolean) { +>switchOrdering : (x: string | number | boolean) => string | number | boolean +>x : string | number | boolean + + switch (typeof x) { +>typeof x : "string" | "number" | "boolean" | "symbol" | "undefined" | "object" | "function" +>x : string | number | boolean + + case 'string': return assertString(x); +>'string' : "string" +>assertString(x) : string +>assertString : (x: string) => string +>x : string + + case 'number': return assertNumber(x); +>'number' : "number" +>assertNumber(x) : number +>assertNumber : (x: number) => number +>x : number + + case 'boolean': return assertBoolean(x); +>'boolean' : "boolean" +>assertBoolean(x) : boolean +>assertBoolean : (x: boolean) => boolean +>x : boolean + + case 'number': return assertNever(x); +>'number' : "number" +>assertNever(x) : never +>assertNever : (x: never) => never +>x : never + } +} + +function switchOrderingWithDefault(x: string | number | boolean) { +>switchOrderingWithDefault : (x: string | number | boolean) => string | number | boolean +>x : string | number | boolean + + function local(y: string | number | boolean) { +>local : (y: string | number | boolean) => string | number | boolean +>y : string | number | boolean + + return x; +>x : string | number | boolean + } + switch (typeof x) { +>typeof x : "string" | "number" | "boolean" | "symbol" | "undefined" | "object" | "function" +>x : string | number | boolean + + case 'string': +>'string' : "string" + + case 'number': +>'number' : "number" + + default: return local(x) +>local(x) : string | number | boolean +>local : (y: string | number | boolean) => string | number | boolean +>x : string | number | boolean + + case 'string': return assertNever(x); +>'string' : "string" +>assertNever(x) : never +>assertNever : (x: never) => never +>x : never + + case 'number': return assertNever(x); +>'number' : "number" +>assertNever(x) : never +>assertNever : (x: never) => never +>x : never + } +} + diff --git a/tests/cases/compiler/narrowingByTypeofInSwitch.ts b/tests/cases/compiler/narrowingByTypeofInSwitch.ts new file mode 100644 index 0000000000000..aadd351b87e00 --- /dev/null +++ b/tests/cases/compiler/narrowingByTypeofInSwitch.ts @@ -0,0 +1,190 @@ +// @strictNullChecks: true +// @strictFunctionTypes: true + +function assertNever(x: never) { + return x; +} + +function assertNumber(x: number) { + return x; +} + +function assertBoolean(x: boolean) { + return x; +} + +function assertString(x: string) { + return x; +} + +function assertSymbol(x: symbol) { + return x; +} + +function assertFunction(x: Function) { + return x; +} + +function assertObject(x: object) { + return x; +} + +function assertUndefined(x: undefined) { + return x; +} + +function assertAll(x: Basic) { + return x; +} + +type Basic = number | boolean | string | symbol | object | Function | undefined; + +function testUnion(x: Basic) { + switch (typeof x) { + case 'number': assertNumber(x); return; + case 'boolean': assertBoolean(x); return; + case 'function': assertFunction(x); return; + case 'symbol': assertSymbol(x); return; + case 'object': assertObject(x); return; + case 'string': assertString(x); return; + case 'undefined': assertUndefined(x); return; + } + assertNever(x); +} + +function testExtendsUnion<T extends Basic>(x: T) { + switch (typeof x) { + case 'number': assertNumber(x); return; + case 'boolean': assertBoolean(x); return; + case 'function': assertAll(x); return; + case 'symbol': assertSymbol(x); return; + case 'object': assertAll(x); return; + case 'string': assertString(x); return; + case 'undefined': assertUndefined(x); return; + } + assertAll(x); +} + +function testAny(x: any) { + switch (typeof x) { + case 'number': assertNumber(x); return; + case 'boolean': assertBoolean(x); return; + case 'function': assertFunction(x); return; + case 'symbol': assertSymbol(x); return; + case 'object': assertObject(x); return; + case 'string': assertString(x); return; + case 'undefined': assertUndefined(x); return; + } + assertAll(x); // is any +} + +function a1(x: string | object | undefined) { + return x; +} + +function testUnionExplicitDefault(x: Basic) { + switch (typeof x) { + case 'number': assertNumber(x); return; + case 'boolean': assertBoolean(x); return; + case 'function': assertFunction(x); return; + case 'symbol': assertSymbol(x); return; + default: a1(x); return; + } +} + +function testUnionImplicitDefault(x: Basic) { + switch (typeof x) { + case 'number': assertNumber(x); return; + case 'boolean': assertBoolean(x); return; + case 'function': assertFunction(x); return; + case 'symbol': assertSymbol(x); return; + } + return a1(x); +} + +function testExtendsExplicitDefault<T extends Basic>(x: T) { + switch (typeof x) { + case 'number': assertNumber(x); return; + case 'boolean': assertBoolean(x); return; + case 'function': assertAll(x); return; + case 'symbol': assertSymbol(x); return; + default: assertAll(x); return; + + } +} + +function testExtendsImplicitDefault<T extends Basic>(x: T) { + switch (typeof x) { + case 'number': assertNumber(x); return; + case 'boolean': assertBoolean(x); return; + case 'function': assertAll(x); return; + case 'symbol': assertSymbol(x); return; + } + return assertAll(x); +} + +type L = (x: number) => string; +type R = { x: string, y: number } + +function exhaustiveChecks(x: number | string | L | R): string { + switch (typeof x) { + case 'number': return x.toString(2); + case 'string': return x; + case 'function': return x(42); + case 'object': return x.x; + } +} + +function exhaustiveChecksGenerics<T extends L | R | number | string>(x: T): string { + switch (typeof x) { + case 'number': return x.toString(2); + case 'string': return x; + case 'function': return (x as L)(42); // Can't narrow generic + case 'object': return (x as R).x; // Can't narrow generic + } +} + +function multipleGeneric<X extends L, Y extends R>(xy: X | Y): [X, string] | [Y, number] { + switch (typeof xy) { + case 'function': return [xy, xy(42)]; + case 'object': return [xy, xy.y]; + default: return assertNever(xy); + } +} + +function multipleGenericFuse<X extends L | number, Y extends R | number>(xy: X | Y): [X, number] | [Y, string] | [(X | Y)] { + switch (typeof xy) { + case 'function': return [xy, 1]; + case 'object': return [xy, 'two']; + case 'number': return [xy] + } +} + +function multipleGenericExhaustive<X extends L, Y extends R>(xy: X | Y): [X, string] | [Y, number] { + switch (typeof xy) { + case 'object': return [xy, xy.y]; + case 'function': return [xy, xy(42)]; + } +} + +function switchOrdering(x: string | number | boolean) { + switch (typeof x) { + case 'string': return assertString(x); + case 'number': return assertNumber(x); + case 'boolean': return assertBoolean(x); + case 'number': return assertNever(x); + } +} + +function switchOrderingWithDefault(x: string | number | boolean) { + function local(y: string | number | boolean) { + return x; + } + switch (typeof x) { + case 'string': + case 'number': + default: return local(x) + case 'string': return assertNever(x); + case 'number': return assertNever(x); + } +}