process.stdout.isTTY is undefined when git-bash (on Windows) invokes node via a shell script

[daiplusplus]

Version

14.17.4 (also reproduces on 16.4)

Platform

Microsoft Windows NT 10.0.19042.0 x64

Subsystem

No response

What steps will reproduce the bug?

This was discovered while investigating this issue: angular/angular-cli#21512

1. Save this script (ttytest.js) somewhere:

   process.stdout.write("typeof stdout.isTTY === '" + typeof process.stdout.isTTY + "'\n");
   if( typeof process.stdout.isTTY === 'boolean' ) {
       process.stdout.write( "process.stdout.isTTY == " + process.stdout.isTTY ? 'true' : 'false' );
   }
   else if( typeof process.stdout.isTTY === 'undefined' ) {
       process.stdout.write( "process.stdout.isTTY is undefined " );
   }
   else if( typeof process.stdout.isTTY === 'object' && process.stdout.isTTY === null ) {
       process.stdout.write( "process.stdout.isTTY is null" );
   }
   else {
       process.stdout.write( "process.stdout.isTTY.toString() == \"" + process.stdout.isTTY.toString() + "\"" );
   }

2. Open a Windows cmd prompt (with node in the PATH) and run the script:

   C:\>node "C:\Users\Me\Desktop\2021\2021-08\ttytest.js"
   typeof stdout.isTTY === 'boolean'
   process.stdout.isTTY == true
   

   So far, so good.

3. Open a git-bash prompt and run the script:

   me@cube MINGW64 /c/users/David/Desktop
   $ node /c/users/David/Desktop/2021/2021-08/ttytest.js
   typeof stdout.isTTY === 'boolean'
   process.stdout.isTTY == true
   

   Also good.

4. Run the script via a cmd batch file:

   Save this to indirect-cmd.cmd

   node ttytest.js
   

   This also works fine:

   C:\Users\me\Desktop\2021\2021-08>indirect-cmd.cmd
   
   C:\Users\me\Desktop\2021\2021-08>node ttytest.js
   typeof stdout.isTTY === 'boolean'
   process.stdout.isTTY == true
   C:\Users\me\Desktop\2021\2021-08>
   

5. However, do the same for bash and it fails

   Save this to indirect-bash.sh

   node ttytest.js

   And run it:

   me@cube MINGW64 /c/users/me/Desktop/2021/2021-08
   $ /c/users/me/Desktop/2021/2021-08/indirect.sh
   typeof stdout.isTTY === 'undefined'
   process.stdout.isTTY is undefined
   

6. It is also undefined when node is invoked using exec:

   Save this to indirect-exec-bash.sh

   exec node ttytest.js

   And run it:

   me@cube MINGW64 /c/users/me/Desktop/2021/2021-08
   $ ./indirect-bash.sh
   typeof stdout.isTTY === 'undefined'
   process.stdout.isTTY is undefined
   

How often does it reproduce? Is there a required condition?

Always.

What is the expected behavior?

I expect isTTY to never be undefined.

What do you see instead?

No response

Additional information

No response

[devsnek]

You'll need to run node using winpty.

[daiplusplus]

@devsnek Right - I know that works-around the issue, but I feel that isTTY being undefined is a bug, surely?

The documentation for writeStream.isTTY says:

A boolean that is always true.

...yet I've demonstrated that it can sometimes be undefined and not true.

So either:

1. The documentation is incorrect and should be updated to state that it can return undefined and under what circumstances it will be undefined.
2. There's a bug in isTTY that causes it to incorrectly return undefined when it should return false - the fact winpty was - or was not used - is irrelevant to the current incongruence.

[devsnek]

If stdout is not a tty, it won't be an instance of tty.WriteStream, it will just be a normal socket stream, which has no isTTY property. The documentation also recommends using Boolean(process.stdout.isTTY) because of this. https://nodejs.org/api/process.html#process_a_note_on_process_i_o

[daiplusplus]

My mistake - I realise that the tty module adds isTTY to WriteStream as a bool literal rather than extending WriteStream with a proper getter/setter property for isTTY.

I was thinking that isTTY was always a defined member of process.stdout.

[daiplusplus]

For reference, and for anyone else encountering the same issue, it's the same as these issues/problems:

• Yarn throws "stdout is not a tty" in Git Bash yarnpkg/yarn#2591
• https://stackoverflow.com/questions/45890339/stdout-is-not-a-tty-using-bash-for-node-tape-tap-spec

[davidmurdoch]

Related issue with the Definitely Typed TypeScript types definitions: DefinitelyTyped/DefinitelyTyped#68299