Compile error using TypeScript "ReturnType"

[jmagaram]

I'm submitting a...

[ ] Regression (a behavior that used to work and stopped working in a new release)
[x] Bug report  
[ ] Performance issue
[ ] Feature request
[ ] Documentation issue or request
[ ] Support request => Please do not submit support request here, instead see https://github.com/angular/angular/blob/master/CONTRIBUTING.md#question
[ ] Other... Please describe:

Current behavior

Create a brand new Angular app. Open in VS Code. Compiles and works fine. Add the following legal TypeScript to a new .ts file in the app folder.

const f = () => 'abc';
type T = ReturnType<typeof f>;

Run npm build. Error I receive is `error TS2304: Cannot find name 'ReturnType'. Works fine in an old create-react-app project. The VS Code editor is happy with the code (no red squigglies) but the build process isn't. The status bar shows using TypeScript 2.91.

Expected behavior

No build error.

Minimal reproduction of the problem with instructions

ng new ang-app
cd ang-app
ng serve --open

VS Code 1.24
Open folder ang-app
Run build task - no problems

In the app folder, add a file rt.ts with code as shown above
npm build
Error as described above

What is the motivation / use case for changing the behavior?

ReturnType is useful for generating strongly-typed actions (like Redux) with less boilerplate.

Environment

Angular version: 6.03 


Browser:
n/a
 
For Tooling issues:
- Node version: 5.60
- Platform:  Windows 10
- VS Code 1.24

Others:

[jmagaram]

Did npm install -g typescript and then tsc --version and it shows 2.9.2. Restarted VS Code. Same problem. In package.json I set the devDependency of TypeScript to 2.9.2. Restarted VS Code. Same problem. Also tried this...

let s: NonNullable = 7;

And get the same error. Cannot find name 'NonNullable'. These are all part of conditional types

[jmagaram]

I think the features I want are part of TypeScript 2.8. I have installed the latest TypeScript as described above. Within VS Code when I'm editing a TypeScript file I see in the status bar below 2.9.2. If I click on it I get a choice of whether to use VS Code's version 2.9.2 or the workspace version 2.7.2, which is in the node/modules folder. I've chosen the more recent version.

[jmagaram]

Just found this StackOverflow comment

If you want to use TS 2.8 you need to use cli version 6.1.0-beta.0

[jmagaram]

Duplicate of #23779

[sandeep2]

What fixed this issue for you ?

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