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Allow assertion signatures to narrow by discriminant (#37310)
1 parent ac3dc0c commit 667f3b4

5 files changed

+204
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lines changed

‎src/compiler/checker.ts

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@@ -20641,7 +20641,10 @@ namespace ts {
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}
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if (strictNullChecks && assumeTrue && optionalChainContainsReference(predicateArgument, reference) &&
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!(getTypeFacts(predicate.type) & TypeFacts.EQUndefined)) {
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return getTypeWithFacts(type, TypeFacts.NEUndefinedOrNull);
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type = getTypeWithFacts(type, TypeFacts.NEUndefinedOrNull);
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}
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if (isMatchingReferenceDiscriminant(predicateArgument, declaredType)) {
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return narrowTypeByDiscriminant(type, predicateArgument as AccessExpression, t => getNarrowedType(t, predicate.type!, assumeTrue, isTypeSubtypeOf));
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}
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}
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}

‎tests/baselines/reference/assertionFunctionsCanNarrowByDiscriminant.js

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//// [assertionFunctionsCanNarrowByDiscriminant.ts]
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interface Cat {
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type: 'cat';
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canMeow: true;
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}
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interface Dog {
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type: 'dog';
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canBark: true;
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}
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type Animal = Cat | Dog;
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declare function assertEqual<T>(value: any, type: T): asserts value is T;
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const animal = { type: 'cat', canMeow: true } as Animal;
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assertEqual(animal.type, 'cat' as const);
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animal.canMeow; // since is cat, should not be an error
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const animalOrUndef = { type: 'cat', canMeow: true } as Animal | undefined;
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assertEqual(animalOrUndef?.type, 'cat' as const);
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animalOrUndef.canMeow; // since is cat, should not be an error
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//// [assertionFunctionsCanNarrowByDiscriminant.js]
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"use strict";
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var animal = { type: 'cat', canMeow: true };
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assertEqual(animal.type, 'cat');
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animal.canMeow; // since is cat, should not be an error
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var animalOrUndef = { type: 'cat', canMeow: true };
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assertEqual(animalOrUndef === null || animalOrUndef === void 0 ? void 0 : animalOrUndef.type, 'cat');
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animalOrUndef.canMeow; // since is cat, should not be an error

‎tests/baselines/reference/assertionFunctionsCanNarrowByDiscriminant.symbols

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=== tests/cases/compiler/assertionFunctionsCanNarrowByDiscriminant.ts ===
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interface Cat {
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>Cat : Symbol(Cat, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 0, 0))
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type: 'cat';
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>type : Symbol(Cat.type, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 0, 15))
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canMeow: true;
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>canMeow : Symbol(Cat.canMeow, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 1, 16))
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}
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interface Dog {
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>Dog : Symbol(Dog, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 3, 1))
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type: 'dog';
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>type : Symbol(Dog.type, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 5, 15))
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canBark: true;
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>canBark : Symbol(Dog.canBark, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 6, 16))
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}
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type Animal = Cat | Dog;
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>Animal : Symbol(Animal, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 8, 1))
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>Cat : Symbol(Cat, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 0, 0))
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>Dog : Symbol(Dog, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 3, 1))
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declare function assertEqual<T>(value: any, type: T): asserts value is T;
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>assertEqual : Symbol(assertEqual, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 10, 24))
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>T : Symbol(T, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 12, 29))
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>value : Symbol(value, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 12, 32))
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>type : Symbol(type, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 12, 43))
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>T : Symbol(T, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 12, 29))
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>value : Symbol(value, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 12, 32))
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>T : Symbol(T, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 12, 29))
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const animal = { type: 'cat', canMeow: true } as Animal;
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>animal : Symbol(animal, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 14, 5))
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>type : Symbol(type, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 14, 16))
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>canMeow : Symbol(canMeow, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 14, 29))
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>Animal : Symbol(Animal, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 8, 1))
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assertEqual(animal.type, 'cat' as const);
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>assertEqual : Symbol(assertEqual, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 10, 24))
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>animal.type : Symbol(type, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 0, 15), Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 5, 15))
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>animal : Symbol(animal, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 14, 5))
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>type : Symbol(type, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 0, 15), Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 5, 15))
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animal.canMeow; // since is cat, should not be an error
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>animal.canMeow : Symbol(Cat.canMeow, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 1, 16))
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>animal : Symbol(animal, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 14, 5))
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>canMeow : Symbol(Cat.canMeow, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 1, 16))
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const animalOrUndef = { type: 'cat', canMeow: true } as Animal | undefined;
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>animalOrUndef : Symbol(animalOrUndef, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 19, 5))
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>type : Symbol(type, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 19, 23))
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>canMeow : Symbol(canMeow, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 19, 36))
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>Animal : Symbol(Animal, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 8, 1))
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assertEqual(animalOrUndef?.type, 'cat' as const);
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>assertEqual : Symbol(assertEqual, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 10, 24))
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>animalOrUndef?.type : Symbol(type, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 0, 15), Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 5, 15))
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>animalOrUndef : Symbol(animalOrUndef, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 19, 5))
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>type : Symbol(type, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 0, 15), Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 5, 15))
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animalOrUndef.canMeow; // since is cat, should not be an error
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>animalOrUndef.canMeow : Symbol(Cat.canMeow, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 1, 16))
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>animalOrUndef : Symbol(animalOrUndef, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 19, 5))
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>canMeow : Symbol(Cat.canMeow, Decl(assertionFunctionsCanNarrowByDiscriminant.ts, 1, 16))
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‎tests/baselines/reference/assertionFunctionsCanNarrowByDiscriminant.types

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=== tests/cases/compiler/assertionFunctionsCanNarrowByDiscriminant.ts ===
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interface Cat {
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type: 'cat';
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>type : "cat"
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canMeow: true;
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>canMeow : true
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>true : true
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}
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interface Dog {
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type: 'dog';
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>type : "dog"
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canBark: true;
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>canBark : true
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>true : true
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}
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type Animal = Cat | Dog;
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>Animal : Animal
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declare function assertEqual<T>(value: any, type: T): asserts value is T;
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>assertEqual : <T>(value: any, type: T) => asserts value is T
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>value : any
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>type : T
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const animal = { type: 'cat', canMeow: true } as Animal;
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>animal : Animal
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>{ type: 'cat', canMeow: true } as Animal : Animal
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>{ type: 'cat', canMeow: true } : { type: "cat"; canMeow: true; }
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>type : "cat"
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>'cat' : "cat"
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>canMeow : true
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>true : true
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assertEqual(animal.type, 'cat' as const);
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>assertEqual(animal.type, 'cat' as const) : void
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>assertEqual : <T>(value: any, type: T) => asserts value is T
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>animal.type : "cat" | "dog"
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>animal : Animal
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>type : "cat" | "dog"
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>'cat' as const : "cat"
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>'cat' : "cat"
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animal.canMeow; // since is cat, should not be an error
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>animal.canMeow : true
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>animal : Cat
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>canMeow : true
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const animalOrUndef = { type: 'cat', canMeow: true } as Animal | undefined;
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>animalOrUndef : Cat | Dog | undefined
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>{ type: 'cat', canMeow: true } as Animal | undefined : Cat | Dog | undefined
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>{ type: 'cat', canMeow: true } : { type: "cat"; canMeow: true; }
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>type : "cat"
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>'cat' : "cat"
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>canMeow : true
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>true : true
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assertEqual(animalOrUndef?.type, 'cat' as const);
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>assertEqual(animalOrUndef?.type, 'cat' as const) : void
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>assertEqual : <T>(value: any, type: T) => asserts value is T
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>animalOrUndef?.type : "cat" | "dog" | undefined
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>animalOrUndef : Cat | Dog | undefined
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>type : "cat" | "dog" | undefined
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>'cat' as const : "cat"
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>'cat' : "cat"
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animalOrUndef.canMeow; // since is cat, should not be an error
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>animalOrUndef.canMeow : true
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>animalOrUndef : Cat
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>canMeow : true
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‎tests/cases/compiler/assertionFunctionsCanNarrowByDiscriminant.ts

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// @strict: true
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interface Cat {
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type: 'cat';
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canMeow: true;
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}
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interface Dog {
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type: 'dog';
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canBark: true;
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}
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type Animal = Cat | Dog;
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declare function assertEqual<T>(value: any, type: T): asserts value is T;
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const animal = { type: 'cat', canMeow: true } as Animal;
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assertEqual(animal.type, 'cat' as const);
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animal.canMeow; // since is cat, should not be an error
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const animalOrUndef = { type: 'cat', canMeow: true } as Animal | undefined;
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assertEqual(animalOrUndef?.type, 'cat' as const);
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animalOrUndef.canMeow; // since is cat, should not be an error

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