arrow function emit emit error

[basarat]

TypeScript Version: nightly latest

Code

{
 "compilerOptions": {
 "module": "commonjs",
 "target": "es5",
 "noImplicitAny": false,
 "sourceMap": false,
 "lib": [
 "es6", "dom"
 ]
 },
 "exclude": [
 "node_modules"
 ]
}

const foo = (x: string) => null;

Expected behavior:

Gives js

var foo = function (x) { return null; };

Actual behavior:

var foo = function (x: string) { return null; };

[mhegazy]

Ron Buckton (@rbuckton) can you take a look.

[rbuckton]

Basarat Ali Syed (@basarat) Is this the entire set of repro steps? I tried this locally and cannot repro this.

[basarat]

Is this the entire set of repro steps?

Sadly no. Seems to be an issue one with language service compile on save, stuff like semicolons etc can be used to trigger it to come in and go out. Same code can give different output depending on how the edits were made :-/

Made a quick video : https://www.youtube.com/watch?v=N4EgtjRnZGE 🌹

[rbuckton]

Thanks, I'll take a look at it.

[rbuckton]

In the video it looks like you're using VSCode. Are you using a .vscode/tasks.json and compiling with tsc in watch mode, or are you using grunt or gulp with a plugin? So far I'm still unable to reproduce this issue.

[rbuckton]

Or rather, is this Atom?

[jesseschalken]

Ron Buckton (@rbuckton) I think it's https://github.com/alm-tools/alm

[basarat]

I think it's https://github.com/alm-tools/alm

Yup.

[basarat]

Basically compileOnSave. This is my build function is simply : https://github.com/alm-tools/alm/blob/c98ffc247078c5f6308548cdcc79f8f8f90c50b0/src/server/workers/lang/modules/building.ts#L35-L43 🌹

[basarat]

I can repro in alm with just const foo = (x: string) => null => const foo = (x) => null;

With a simple tsconfig.json

{
 "compilerOptions": {
 "module": "commonjs",
 "target": "es5"
 }
}

That said I ran the same with tsc -w and it doesn't happen, does that use languageService. getEmitOutput? 🌹