Type narrowing doesn't work with mutable variables in closures

[falsandtru]

Includes arguments.

TypeScript Version: 2.9.0-dev.201xxxxx

Search Terms:

Code

declare const a: {} | void;
if (a instanceof Object) a; // {}
if (a instanceof Object) () => a; // {}
declare let b: {} | void;
if (b instanceof Object) b; // {}
if (b instanceof Object) () => b;

Expected behavior:

if (b instanceof Object) () => b; // {}

Actual behavior:

if (b instanceof Object) () => b; // void | {}

Playground Link:

Related Issues:

[falsandtru]

Seems like it also breaks colorization.

[ghost]

Duplicate of #9998
Could you explain the problem with colorization?

[falsandtru]

Indeed.

On the colorization, the last return keyword is white, should be blue.

    if (process instanceof Coroutine) return this.register(
      name,
      {
        init: state => state,
        main: (param, state) =>
          (process as Coroutine<R, R, P>)[Coroutine.port].send(param)
            .then<Supervisor.Process.Result<R, S>>(({ value: reply, done }) =>
              done
                ? void this.kill(name, undefined) ||
                  (process as Coroutine<R, R, P>).then<Supervisor.Process.Result<R, S>>(reply =>
                    [reply, state])
                : [reply, state,]),
        exit: reason => void process[Coroutine.terminator](reason),
      },
      state,
      reason);
    return super.register(name, process, state);

https://github.com/falsandtru/spica/blob/v0.0.167/src/supervisor.es2018.ts#L29

[ghost]

@falsandtru What editor? I see colorized return when pasting that example into vscode. (With or without the latest grammar installed.)

[falsandtru]

Hm, I'm using VSCode v1.22.2 on Win10.

[ghost]

What's your color scheme?

[falsandtru]

Dark (Visual Studio).

[ghost]

I'm on windows, on the latest vscode-insiders, with the dark color scheme and latest grammar installed, and both returns are colored blue:

[falsandtru]

Oh No! Please open and check https://github.com/falsandtru/spica/blob/v0.0.167/src/supervisor.es2018.ts#L29 via vscode!

[ghost]

Looks like the error is only present in vscode non-insiders without the latest grammar installed.

[falsandtru]

This is my screenshot.

[falsandtru]

Looks like the error is only present in vscode non-insiders without the latest grammar installed.

I see, I wait for the next release. Currently, this is not a serious problem for me.

[ghost]

You can also open the extensions sidebar and search for "latest typescript and javascript grammar".

[falsandtru]

Resolved, thanks for letting me know!