Cannot read property 'flags' of undefined(3.2.x)

[xiaocaibird]

TypeScript Version: 3.2.x

Search Terms: Cannot read property 'flags' of undefined

Code

First of all, I am sorry. This is an internal project of our company, I can't provide a git url.
And because of the large amount of code, I still can't find the wrong code snippet.
Our project is still working in the previous version(3.1.x).
I found this problem in 3.2.1,and I found some related issues at the time.
I was hoping it could be fixed together, but no.

Expected behavior: Compile

Actual behavior:
TypeError: Cannot read property 'flags' of undefined
at isFreshLiteralType (/project/news-manage/node_modules/typescript/lib/tsc.js:33326:28)
at isTypeRelatedTo (/project/news-manage/node_modules/typescript/lib/tsc.js:34425:17)
at isTypeComparableTo (/project/news-manage/node_modules/typescript/lib/tsc.js:33930:20)
at /project/news-manage/node_modules/typescript/lib/tsc.js:37851:102
at Object.filter (/project/news-manage/node_modules/typescript/lib/tsc.js:340:31)
at filterType (/project/news-manage/node_modules/typescript/lib/tsc.js:37422:35)
at narrowTypeByDiscriminant (/project/news-manage/node_modules/typescript/lib/tsc.js:37851:63)
at narrowTypeByTruthiness (/project/news-manage/node_modules/typescript/lib/tsc.js:37858:28)
at narrowType (/project/news-manage/node_modules/typescript/lib/tsc.js:38161:32)
at getTypeAtFlowCondition (/project/news-manage/node_modules/typescript/lib/tsc.js:37730:36)

Playground Link:

Related Issues:

[DanielRosenwasser]

narrowTypeByDiscriminant is the call that has two type assertions

https://github.com/Microsoft/TypeScript/blob/c2898db9dd58c9b0681d6131ed6076d71d89e6b5/src/compiler/checker.ts#L15656

return propType === narrowedPropType ? type : filterType(type, t => isTypeComparableTo(getTypeOfPropertyOfType(t, propName)!, narrowedPropType!));

[xiaocaibird]

@DanielRosenwasser
Thanks.
But, how can I solve this problem.

[DanielRosenwasser]

That comment was meant more for anyone who ends up assigned to this issue 😃

[ahejlsberg]

Here's a repro that crashes with a similar call stack:

type Foo = { tag: true, x: number } | { tag: false, y: number } | { [x: string]: string };

function test(foo: Foo) {
    if (!foo.tag) {
        foo;
    }
}

The issue is that we assume that each constituent has a discriminant property when it is possible that some don't, but rather have a string index signature.

[ahejlsberg]

@xiaocaibird Just merged what I think is a fix to your issue. Try pulling the next nightly build and let us know what you find.

[zedfight]

+1 same issue here

[DanielRosenwasser]

Have you tried the nightly build? npm install typescript@next

[zedfight]

Have you tried the nightly build? npm install typescript@next

Fix. Thanks!!

[DanielRosenwasser]

Great! Glad we could fix it quickly.