Microsoft/TypeScript
Voir sur GitHubAssertion signature on generics doesn't narrow
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#60 130 ouverte le 3 oct. 2024
BugDomain: check: Control FlowHelp Wanted
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Description
🔎 Search Terms
Assertion AND signature
🕗 Version & Regression Information
- This is the behavior in every version I tried, and I reviewed the FAQ for entries about Assertion Signatures, Generics.
⏯ Playground Link
💻 Code
// "Good assert": makes destructuring succeed
// function assert(c: unknown): asserts c {
// if (!c) {
// throw new TypeError('Assertion failed');
// }
// }
// "Bad assert": destructuring error
function assert<C>(c: C): asserts c {
if (!c) {
throw new TypeError('Assertion failed');
}
}
export function test(lines: string[]): string[] {
let func: {
name: string;
lines: string[];
} | null = null;
for (const line of lines) {
if (Math.random() < 0.5) {
func = {
name: "qwer",
lines: [line],
};
} else {
assert(func);
const {name, lines} = func; // <=== ERROR HERE: 'name' implicitly has type 'any'
lines.push(line);
assert(name !== 'abc');
}
}
if (func)
return func.lines;
return lines;
}
🙁 Actual behavior
When the generic-assert implementation is active, the line -
const {name, lines} = func;
errors with 'name' implicitly has type 'any'.
When the unknown assert implementation is active, types are properly inferred.
🙂 Expected behavior
Both assert versions contain assertion signature, and both should be able to narrow the type.
Additional information about the issue
No response