Upgrade to typescript 3.5.1

[jasongrout]

References

Code changes

Upgrade to Typescript 3.5.1

User-facing changes

Backwards-incompatible changes

None, other than our dependencies change.

[jupyterlab-dev-mode]

Thanks for making a pull request to JupyterLab!

To try out this branch on binder, follow this link:

[blink1073]

Thanks!

[blink1073]

$ tsc -b
../fileeditor-extension/src/index.ts(237,7): error TS2322: Type 'string | number | boolean | number[]' is not assignable to type 'never'.
  Type 'string' is not assignable to type 'never'.
../notebook-extension/src/index.ts(602,7): error TS2322: Type 'string | number | boolean | number[]' is not assignable to type 'never'.
  Type 'string' is not assignable to type 'never'.
../notebook-extension/src/index.ts(612,7): error TS2322: Type 'string | number | boolean | number[]' is not assignable to type 'never'.
  Type 'string' is not assignable to type 'never'.
../notebook-extension/src/index.ts(622,7): error TS2322: Type 'string | number | boolean | number[]' is not assignable to type 'never'.
  Type 'string' is not assignable to type 'never'.
../terminal-extension/src/index.ts(120,7): error TS2322: Type 'JSONPrimitive' is not assignable to type 'never'.
  Type 'string' is not assignable to type 'never'.

[blink1073]

Uh oh, the Windows JS build succeeded but actually had the same error as above...

[jasongrout]

We are running into problems where we have the following pattern:

interface IMy {
  a: number;
  b: string;
  c: boolean;
}

let x: IMy = {
  a: 5,
  b: 'hello',
  c: true
};

Object.keys(x).forEach((k: keyof IMy) => {
  x[k] = 'a';
});

That assignment x[k] = 'a' works fine in TS 3.4, but TS 3.5 is smarter about the keyof union, and realizes that nothing could ever satisfy the type conditions for 'a' | 'b' | 'c' (which is the keyof type), so x[keyof x] is type never, so assigning something to it never works.

I think this is related to https://github.com/Microsoft/TypeScript/wiki/Breaking-Changes#fixes-to-unsound-writes-to-indexed-access-types

[jasongrout]

Looks like the test failure is something to be fixed in ts-loader: TypeStrong/ts-loader#939, TypeStrong/ts-loader#942

[blink1073]

I'd say wait for the patch release of ts-loader since it looks to be imminent.

[jasongrout]

I'd say wait for the patch release of ts-loader since it looks to be imminent.

Yep, I was on the fence about changing this vs waiting for a ts-loader release. At least we'll see if there are any other issues.

[jasongrout]

Looks like the updated ts-loader made all of our tests happy now!

[blink1073]

LGTM, thanks!

[jasongrout]

Thanks @vidartf and @blink1073 for the reviews.

[lock]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related discussion.