[Windows] [coc.nvim] error: UnhandledRejection: Cannot read property 'reader' of undefined

[ohuu]

Result from CocInfo

## versions
vim version: NVIM v0.4.3
node version: v13.12.0
coc.nvim version: 0.0.78-bcb2fe977c
term: vtpcon
platform: win32

Describe the bug

I'm using coc-metals and have raised this issue on the coc-metals repo but have been advised to report it here instead.

Installing coc-metals using :CocInstall works well but when it is preparing I receive this error:

[coc.nvim] error: UnhandledRejection: Cannot read property 'reader' of undefined
TypeError: Cannot read property 'reader' of undefined
    at C:\Users\Oliver\.nvim\plugged\coc.nvim\build\index.js:57558:48

Here are the relevant lines in index.js:

createConnection() {
    let errorHandler = (error, message, count) => {
        logger.error('connection error:', error, message);
        this.handleConnectionError(error, message, count);
    };
    let closeHandler = () => {
        this.handleConnectionClosed();
    };
    return this.createMessageTransports(this._clientOptions.stdioEncoding || 'utf8').then(transports => {
        return createConnection(transports.reader, transports.writer, errorHandler, closeHandler);
    });
}

The problem is that transports is undefined.

Reproduce the bug

On Windows 10 using Windows Terminal and Powershell 7 install coc-metals and open a scala file.

[chemzqm]

https://github.com/neoclide/coc.nvim/wiki/Debug-coc.nvim

[ohuu]

The problem is with a call to fs.existsSync. This call is made in order to see if the cmd exists. In coc-metals' case the cmd is java. The file exists but for some reason it returns false.

It may be related to this issue:
nodejs/node#17921

commenting out the existence check everything works fine so it's definitely this that's causing the problem.

[ohuu]

It turns out that fs.existsSync is failing on Windows for 2 reasons:

1. the path to cmd is in the Windows format (single \) e.g. C:\blah\blah\blah instead of C:/blah/blah/blah or C:\\blah\\blah\\blah
2. The path does not contain the file's extension. In coc-metals' case it's looking for java instead of java.exe

[oblitum]

The problem is with a call to fs.existsSync

Which call in the sources?

[chemzqm]

Should be

coc.nvim/src/language-client/index.ts

Line 425 in d9c7993

if (path.isAbsolute(cmd) && !fs.existsSync(cmd)) {

[chemzqm]

I've removed that check, it's not necessary.