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Code Flow analysis truthy checks not working for literal booleans #12939

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basarat opened this issue Dec 15, 2016 · 3 comments

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Working as Intended

Contributor

basarat commented Dec 15, 2016 •

edited

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TypeScript Version: nightly (2.2.0-dev.201xxxxx)

Code

The following does not work

declare let foo: { hasError: true } | { hasError: false, value: any };
function test() {
  if (foo.hasError) return;
  foo.value; // Error
}

But the following does:

declare let foo: { hasError: true } | { hasError: false, value: any };
function test() {
  if (foo.hasError == true) return;
  foo.value; // Error
}

Expected behavior:
No error in both examples

Proof

BTW. Just wanted to say ... not related to this ... loving mapped types. So .. much .. power 🌹

Contributor

gcnew commented Dec 15, 2016 •

edited

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I've run into this as well. It happens only if strictNullChecks is off. See #10564.

RyanCavanaugh added the Working as Intended label

Member

RyanCavanaugh commented Dec 21, 2016

strictNullChecks is needed for this code to work because we can't rule out null or undefined as hasError values and thus can't narrow in the remainder of the function body

Contributor Author

basarat commented Dec 21, 2016

Closing in favor of #10564 🌹

basarat closed this as completed

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