Errors from black are shown as 'undefined'

[lassik]

Using black natively:

$ echo 'if True:print 1' | black -
if True:print 1
error: cannot format -: cannot use --safe with this file; failed to parse source file with Python 3.7's builtin AST. Re-run with --fast or stop using deprecated Python 2 syntax. AST error message: Missing parentheses in call to 'print'. Did you mean print(1)? (<unknown>, line 1)
All done! 💥 💔 💥
1 file failed to reformat.

Same code using Unibeautify:

$ echo 'if True:print 1' | unibeautify --language Python
undefined

[Glavin001]

Does black have a non-zero exit code?

$ echo 'if True:print 1' | black -
$ echo $?

And do you know if black uses stderr or is the error in stdout instead?

Looks like error handling is implemented but not tested: https://github.com/Unibeautify/beautifier-black/blob/master/src/index.ts#L85-L86

If black beautifier is working correctly this may be a Unibeautify CLI bug.

[lassik]

It should use non-zero exit codes properly and write errors to stderr. I don't have any special handling for it in the Emacs format-all package. I just call it as black -q -.

[Glavin001]

[Black] should use non-zero exit codes properly and write errors to stderr.

Sounds like the problem is with Unibeautify CLI then not passing errors up.