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ahejlsbergahejlsberg
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Merge pull request microsoft#20882 from Microsoft/fixNarrowTypeBySwitch
Fix narrowing of type variable in switch statement
2 parents 9e9d7d5 + d1befef commit ff4f03c

5 files changed

Lines changed: 105 additions & 1 deletion

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‎src/compiler/checker.ts‎

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@@ -12923,7 +12923,7 @@ namespace ts {
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const discriminantType = getUnionType(clauseTypes);
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const caseType =
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discriminantType.flags & TypeFlags.Never ? neverType :
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replacePrimitivesWithLiterals(filterType(type, t => isTypeComparableTo(discriminantType, t)), discriminantType);
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replacePrimitivesWithLiterals(filterType(type, t => areTypesComparable(discriminantType, t)), discriminantType);
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if (!hasDefaultClause) {
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return caseType;
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}

‎tests/baselines/reference/switchWithConstrainedTypeVariable.js‎

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//// [switchWithConstrainedTypeVariable.ts]
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// Repro from #20840
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function function1<T extends 'a' | 'b'>(key: T) {
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switch (key) {
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case 'a':
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key.toLowerCase();
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break;
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default:
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key.toLowerCase();
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break;
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}
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}
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//// [switchWithConstrainedTypeVariable.js]
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"use strict";
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// Repro from #20840
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function function1(key) {
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switch (key) {
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case 'a':
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key.toLowerCase();
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break;
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default:
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key.toLowerCase();
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break;
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}
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}

‎tests/baselines/reference/switchWithConstrainedTypeVariable.symbols‎

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@@ -0,0 +1,29 @@
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=== tests/cases/conformance/controlFlow/switchWithConstrainedTypeVariable.ts ===
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// Repro from #20840
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function function1<T extends 'a' | 'b'>(key: T) {
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>function1 : Symbol(function1, Decl(switchWithConstrainedTypeVariable.ts, 0, 0))
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>T : Symbol(T, Decl(switchWithConstrainedTypeVariable.ts, 2, 19))
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>key : Symbol(key, Decl(switchWithConstrainedTypeVariable.ts, 2, 40))
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>T : Symbol(T, Decl(switchWithConstrainedTypeVariable.ts, 2, 19))
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switch (key) {
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>key : Symbol(key, Decl(switchWithConstrainedTypeVariable.ts, 2, 40))
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case 'a':
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key.toLowerCase();
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>key.toLowerCase : Symbol(String.toLowerCase, Decl(lib.d.ts, --, --))
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>key : Symbol(key, Decl(switchWithConstrainedTypeVariable.ts, 2, 40))
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>toLowerCase : Symbol(String.toLowerCase, Decl(lib.d.ts, --, --))
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break;
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default:
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key.toLowerCase();
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>key.toLowerCase : Symbol(String.toLowerCase, Decl(lib.d.ts, --, --))
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>key : Symbol(key, Decl(switchWithConstrainedTypeVariable.ts, 2, 40))
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>toLowerCase : Symbol(String.toLowerCase, Decl(lib.d.ts, --, --))
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break;
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}
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}
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‎tests/baselines/reference/switchWithConstrainedTypeVariable.types‎

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=== tests/cases/conformance/controlFlow/switchWithConstrainedTypeVariable.ts ===
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// Repro from #20840
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function function1<T extends 'a' | 'b'>(key: T) {
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>function1 : <T extends "a" | "b">(key: T) => void
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>T : T
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>key : T
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>T : T
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switch (key) {
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>key : T
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case 'a':
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>'a' : "a"
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key.toLowerCase();
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>key.toLowerCase() : string
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>key.toLowerCase : () => string
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>key : T
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>toLowerCase : () => string
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break;
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default:
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key.toLowerCase();
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>key.toLowerCase() : string
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>key.toLowerCase : () => string
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>key : T
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>toLowerCase : () => string
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break;
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}
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}
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‎tests/cases/conformance/controlFlow/switchWithConstrainedTypeVariable.ts‎

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// @strict: true
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// Repro from #20840
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function function1<T extends 'a' | 'b'>(key: T) {
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switch (key) {
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case 'a':
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key.toLowerCase();
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break;
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default:
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key.toLowerCase();
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break;
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}
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}

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