Last 3.x minor | Hard deprecate all sniffs which will be removed in 4.0

[jrfnl]

It was previously already announced that the 4.0 release will drop support for:

• JavaScript and CSS tokenizers, which also means the JS and CSS specific sniffs will be removed.
• The MySource standard.

Additionally, the Squiz.WhiteSpace.LanguageConstructSpacing sniff was (soft) deprecated in PHPCS 3.3.0 and the Generic.Formatting.NoSpaceAfterCast sniff in PHPCS 3.4.0.

Providing #164 (PHPCS native handling of sniff deprecations) gets build and included in PHPCS ahead of 4.0, I propose to hard deprecate the sniffs affected by the above mentioned changes in the last PHPCS 3.x minor release.

Terminology used

Soft deprecation: deprecation via changelog mention and/or announcement only.
Hard deprecation: a deprecation notice will be shown at runtime, but will not affect the exit code of PHPCS.

Additional notes

• Sniffs which support both PHP as well as JS/CSS will not be removed in PHPCS 4.0 (only the JS/CSS support will be removed), so those sniffs are not included in this proposal.

Policy

I also propose to adhere to this as a policy for PHP_CodeSniffer for the future :

• Soft deprecate sniffs over the lifetime of a major release.
• Hard deprecate sniffs in the last minor of that same major.

I considered always using hard deprecation, but that will be noisier than necessary and will cause additional support questions for external standards using a deprecated sniff, but supporting a range of (minor) PHP_CodeSniffer versions.

[kczx3]

It might be worth linking to squizlabs/PHP_CodeSniffer#2448 for context. Being someone that is new to this tool, I was unaware of the previously announced removal of the tokenizers.

[jrfnl]

@kczx3 Thanks for adding the link. And yes, increasing awareness about these changes is exactly what this issue is about ;-)

[jrfnl]

Related #58: proposed removal of the Zend.Debug.CodeAnalyzer sniff in 4.0. If this PR proceeds, the sniff should be included in the sniffs to get a deprecation notice in the last 3.x minor.