4.0 | Revise exit codes for PHPCS and PHPCBF commands

[jrfnl]

Repost from https://github.com/squizlabs/PHP_CodeSniffer/issues/2898 by @gsherwood:

Version 4 is a good time to review the exit codes that both scripts produce to ensure that success cases all use 0 and that all failure cases have codes that make sense. Documentation in the wiki to describe the new exist codes should be an output of this work.

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Additional info posted by @jrfnl:

Loosely related open issues:

• squizlabs/PHP_CodeSniffer#1818
• squizlabs/PHP_CodeSniffer#2412 (discoverability of availability of exit code related CLI arguments)

And some related closed issues:

• https://github.com/squizlabs/PHP_CodeSniffer/issues/2954
• https://github.com/squizlabs/PHP_CodeSniffer/issues/3057
• https://github.com/squizlabs/PHP_CodeSniffer/issues/3367
• https://github.com/squizlabs/PHP_CodeSniffer/pull/3541

And the following open PR is also related:

• https://github.com/squizlabs/PHP_CodeSniffer/pull/3696

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Related remark posted by @nelson6e65:

Param --runtime-set ignore_warnings_on_exit 1 works on phpcs, but it does not for phpcbf.

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Question by @dfelton:

Is there any documentation somewhere that lists all non 0 or 1 exit codes that exist, and the meaning of them?

Today was the first time I discovered an exit code of 3 is used for when and invalid standard is given. It'd be nice to be able to read a compiled list of what exit codes there are, and I cannot seem to find any information on the wiki on this topic.

Reply by @jrfnl:

I think this is what you are looking for: https://github.com/squizlabs/PHP_CodeSniffer/issues/930#issuecomment-229562566