Yarn fails under git-bash: Can't answer a question unless a user TTY

[jmathew]

Do you want to request a feature or report a bug?
Bug.

What is the current behavior?
Running yarn init yields:

$ yarn init
yarn init v1.0.2
error An unexpected error occurred: "Can't answer a question unless a user TTY".

What is the expected behavior?
Standard init process.

Please mention your node.js, yarn and operating system version.
Versions:

Git-bash
You are downloading the latest (2.14.1) 64-bit version of Git for Windows. 

Which seems to install MinTTY 2.7.7

$ node -v
v8.1.4

$ npm -v
5.0.3

$ yarn -v
1.0.2

$ bash --version
GNU bash, version 4.4.12(1)-release (x86_64-pc-msys)
Copyright (C) 2016 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>

This is free software; you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Background Research

The problem was previously noted in:
#743

This yielded a fix that tried to autodetect mintty and use winpty:
#2243

That fix worked for interactive operations but breaks any sort of piping.

This fix was removed in favor a explicit environment variable in:
#2998

The reason being yarn shell commands seemed to fail because of winpty when used in a pipe. And there appears to be some terminal output that shows git bash working without the need for winpty. This is not consistent with my experience.

Technical details

I believe yarn uses isTTY to check for an interactive terminal. The discussion attributed the issue to be caused by winpty however running node by itself can produce that error:

$  node -p -e "Boolean(process.stdout.isTTY)"
true

$  node -p -e "Boolean(process.stdout.isTTY)" | cat
stdout is not a tty

I think that's the check that's actually causing the issue when any yarn command is involved in a pipe. But weirdly using yarn in a pipe works for commands that are not interactive like --version.

Below is a bunch of commands I ran on the terminal that I hope help diagnose the issue.

$ yarn --version | cat
1.0.2

$ yarn init
yarn init v1.0.2
error An unexpected error occurred: "Can't answer a question unless a user TTY".
info If you think this is a bug, please open a bug report with the information provided in "C:\\Users\\jmathew\\work\\FatGolem\\yarn-error.log".
info Visit https://yarnpkg.com/en/docs/cli/init for documentation about this command.

$ YARN_FORCE_WINPTY=1 yarn --version
1.0.2

$ YARN_FORCE_WINPTY=1 yarn --version  | cat
stdout is not a tty

$ bash -c 'yarn install'
yarn install v1.0.2
info No lockfile found.
[1/4] Resolving packages...
[2/4] Fetching packages...
[3/4] Linking dependencies...
[4/4] Building fresh packages...
info Lockfile not saved, no dependencies.
Done in 0.05s.

$ bash -c 'YARN_FORCE_WINPTY=1 yarn install'
yarn install v1.0.2
info No lockfile found.
[1/4] Resolving packages...
[2/4] Fetching packages...
[3/4] Linking dependencies...
[4/4] Building fresh packages...

info Lockfile not saved, no dependencies.
Done in 0.05s.

There's a lot of moving pieces so its hard for me to understand the cause and effect here. So I'm not sure of a good solution that keeps this interactive terminal check.

My initial thought is that this check for interactive terminal isn't really worth the hassle of keeping around. If you design a script that has yarn init and fail to provide input or redirect properly and it spins forever waiting that should be on you right? Npm doesn't do this and I suspect its because of these kinds of problems.

Summary

It would seem that I have to use the YARN_FORCE_WINPTY when using an interactive command in git bash and specifically not use that when trying to do any piping.

Further, YARN_FORCE_WINPTY isn't documented anywhere as far as I know. Other than the old issues and the script itself. Maybe add that to the error message?

Regardless of all that I just want to be able to type yarn init and have it work consistently without having to do anything special to make it work on windows.

[BYK]

This looks a lot like a duplicate of #2591 so closing in favor of that. Reopen if you don't agree.

[alancnet]

Please consider reopening. #2591 may have fixed a related issue, but this issue is still present today (or is present again).

@BYK @jmathew

[yu-sssss]

Use PowerShell instead.

[alancnet]

I'm not satisfied that this thread ends with "You should use my preferred tool instead of your preferred tool". This is still a problem. NPM works, Yarn doesn't. How about some action here?

@kittens @bestander @arcanis @sebmck @BYK @Daniel15 @rally25rs @zertosh @voxsim

[BYK]

@alancnet sure, we always accept well-written and tested PRs

[alancnet]

My apologies @BYK, it seems this issue has been resolved in v1.17.0. It is still an issue in v1.16.0 which is what is published. I look forward to the next release.

[BYK]

@alancnet don't really see anything that could have fixed this since 1.16.0: v1.16.0...master

Are you sure this is not something else?

[alancnet]

@BYK You're right. When you npm install yarn, the yarn shim is ignored, and a cmd-shim is created instead. The yarn shim has code that executes yarn with winpty. There is no functionality in npm to customize the shim.

Do you think it would be appropriate to add a postinstall script to replace the shim?

[BYK]

@alancnet ooh, interesting find! I wonder why they diverge and I'd say this is a bug. So you have no issues when installing from npm but have issues when you install it from another place(which place btw, can you share)?

If so we should file a new bug to align them.

[alancnet]

@BYK The shim shown on the left of my screenshot is when installing from npm:

[lanseria]

[BYK]

@alancnet sorry for the late response! I definitely remember hitting this issue. So when Yarn detects winpty it simply uses that without a way to turn off. I think there should be an option to turn it off or the automatic enabling should use a better test (not in git-bash for instance?).

Did some digging and seems like this behavior was introduced in #4577 to fix this exact issue and the code responsible lives in https://github.com/thetrompf/yarn/blob/master/bin/yarn

I'm reopening the issue. Would you like to try fixing this and submitting a PR to become the hero of all these people :) I am also using Windows and I'd be happy to assist you in the PR journey. Once it is merged, it'll be available in the nightly builds pretty quickly.