PSR-12 not reporting error for empty lines with only whitespace

[nereusz]

Describe the bug
PSR-2 includes requirement: "There MUST NOT be trailing whitespace at the end of non-blank lines.".
But in PSR-12 requirement changed to: "There MUST NOT be trailing whitespace at the end of lines.". Any line. Not only blank ones.
PHPCS seems to still use PSR-2 requirement, even if call it with PSR-12 standard.

Code sample (test.php)

<?php

// some irrelevant code
  
echo "There are only two spaces in previous line";
//  
echo "There are two slashes and two spaces in previous line";

To reproduce
Steps to reproduce the behavior:

1. Create a file called test.php with the code sample above...
2. Run phpcs --standard=PSR12 -vvv test.php
3. See error message displayed

[...]
[PHP => 15 tokens in 7 lines]... 
        *** START TOKEN PROCESSING ***
                Process token 0: T_OPEN_TAG => <?php\n
                        Processing PHP_CodeSniffer\Standards\PSR12\Sniffs\Files\OpenTagSniff... DONE in 0 seconds
                        Processing PHP_CodeSniffer\Standards\PSR12\Sniffs\Files\FileHeaderSniff... DONE in 0.0001 seconds
                        Processing PHP_CodeSniffer\Standards\PSR1\Sniffs\Files\SideEffectsSniff... DONE in 0.0001 seconds
                        Processing PHP_CodeSniffer\Standards\Generic\Sniffs\PHP\DisallowAlternativePHPTagsSniff... DONE in 0 seconds
                        Processing PHP_CodeSniffer\Standards\Generic\Sniffs\PHP\DisallowShortOpenTagSniff... DONE in 0 seconds
                        Processing PHP_CodeSniffer\Standards\Generic\Sniffs\Files\LineEndingsSniff... DONE in 0 seconds
                        Processing PHP_CodeSniffer\Standards\PSR2\Sniffs\Files\EndFileNewlineSniff... DONE in 0 seconds
                        Processing PHP_CodeSniffer\Standards\PSR2\Sniffs\Files\ClosingTagSniff... DONE in 0 seconds
                        Processing PHP_CodeSniffer\Standards\Generic\Sniffs\Files\LineLengthSniff... DONE in 0.0001 seconds
                        Processing PHP_CodeSniffer\Standards\Squiz\Sniffs\WhiteSpace\SuperfluousWhitespaceSniff... DONE in 0 seconds
                        Processing PHP_CodeSniffer\Standards\Generic\Sniffs\WhiteSpace\ScopeIndentSniff... DONE in 0.0002 seconds
                        Processing PHP_CodeSniffer\Standards\Generic\Sniffs\WhiteSpace\DisallowTabIndentSniff... DONE in 0.0001 seconds
                Process token 1: T_WHITESPACE => \n
                        Processing PHP_CodeSniffer\Standards\Squiz\Sniffs\WhiteSpace\SuperfluousWhitespaceSniff... DONE in 0 seconds
                Process token 2: T_COMMENT => //·some·irrelevant·code\n
                        Processing PHP_CodeSniffer\Standards\Squiz\Sniffs\WhiteSpace\SuperfluousWhitespaceSniff... DONE in 0 seconds
                Process token 3: T_WHITESPACE => ··\n
                        Processing PHP_CodeSniffer\Standards\Squiz\Sniffs\WhiteSpace\SuperfluousWhitespaceSniff... DONE in 0 seconds
                Process token 4: T_ECHO => echo
                        Processing PHP_CodeSniffer\Standards\Generic\Sniffs\PHP\LowerCaseKeywordSniff... DONE in 0 seconds
                Process token 5: T_WHITESPACE => ·
                        Processing PHP_CodeSniffer\Standards\Squiz\Sniffs\WhiteSpace\SuperfluousWhitespaceSniff... DONE in 0 seconds
                Process token 6: T_CONSTANT_ENCAPSED_STRING => "There·are·only·two·spaces·in·previous·line"
                Process token 7: T_SEMICOLON => ;
                        Processing PHP_CodeSniffer\Standards\Generic\Sniffs\Formatting\DisallowMultipleStatementsSniff... DONE in 0 seconds
                Process token 8: T_WHITESPACE => \n
                        Processing PHP_CodeSniffer\Standards\Squiz\Sniffs\WhiteSpace\SuperfluousWhitespaceSniff... DONE in 0 seconds
                Process token 9: T_COMMENT => //··\n
                        Processing PHP_CodeSniffer\Standards\Squiz\Sniffs\WhiteSpace\SuperfluousWhitespaceSniff... DONE in 0.0001 seconds
                Process token 10: T_ECHO => echo
                        Processing PHP_CodeSniffer\Standards\Generic\Sniffs\PHP\LowerCaseKeywordSniff... DONE in 0 seconds
                Process token 11: T_WHITESPACE => ·
                        Processing PHP_CodeSniffer\Standards\Squiz\Sniffs\WhiteSpace\SuperfluousWhitespaceSniff... DONE in 0 seconds
                Process token 12: T_CONSTANT_ENCAPSED_STRING => "There·are·two·slashes·and·two·spaces·in·previous·line"
                Process token 13: T_SEMICOLON => ;
                        Processing PHP_CodeSniffer\Standards\Generic\Sniffs\Formatting\DisallowMultipleStatementsSniff... DONE in 0 seconds
                Process token 14: T_WHITESPACE => \n
                        Processing PHP_CodeSniffer\Standards\Squiz\Sniffs\WhiteSpace\SuperfluousWhitespaceSniff... DONE in 0 seconds
        *** END TOKEN PROCESSING ***

[...]
----------------------------------------------------------------------
FOUND 1 ERROR AFFECTING 1 LINE
----------------------------------------------------------------------
 6 | ERROR | [x] Whitespace found at end of line
----------------------------------------------------------------------
[...]

Expected behavior
In output summary, there should be another error indicated in the line 4 with the same (similar?) message: Whitespace found at end of line

Versions:

• OS: Linux (Debian)
• PHP: 5.6 and 7.2
• PHPCS: 3.5.6
• Standard: PSR12

Additional info
What is worth mentioning, using Squiz standard there's no such behaviour and line 4 is marked as "Whitespace found at end of line", so it's somehow possible. Tested on the same file with only changing standard to Squiz.

[gsherwood]

Went back to see if this was an intentional change, and it appears to be: php-fig/fig-standards@d3a3d23

It doesn't reference a reason for the change, besides the wording being confusing. That leads me to believe that the author believed they were keeping the intended message from PSR-2, but making the wording clearer. I have no idea if that's correct, but the commit does say "Trailing whitespace is not allowed in any situation", so I think that is clear enough to ban it on lines that only contain whitespace.

[gsherwood]

I've pushed up the fix for this. Thanks for pointing out that PSR-12 had modified this rule from PSR-2.