Add sniff to detect consecutive empty lines in a file

This is an edited version of the 'EmptyLines' part of
Squiz.WhiteSpace.SuperfluousWhitespace sniff (which only looks inside
functions).

Squiz.WhiteSpace.SuperfluousWhitespace.EmptyLines has also been excluded
from the standard.

Bug: T120570
Change-Id: I556b209f2660590b007f332307a171ab6099b6ad

MediaWiki/Sniffs/WhiteSpace/MultipleEmptyLinesSniff.php

@@ -0,0 +1,50 @@
+<?php
+/**
+ * Check multiple consecutive newlines in a file.
+ */
+// @codingStandardsIgnoreStart
+class MediaWiki_Sniffs_WhiteSpace_MultipleEmptyLinesSniff
+	implements PHP_CodeSniffer_Sniff {
+	// @codingStandardsIgnoreEnd
+	public function register() {
+		return array(
+			T_WHITESPACE
+		);
+	}
+
+	public function process( PHP_CodeSniffer_File $phpcsFile, $stackPtr ) {
+		$tokens = $phpcsFile->getTokens();
+
+		if ( $stackPtr > 2
+			&& $tokens[$stackPtr - 1]['line'] < $tokens[$stackPtr]['line']
+			&& $tokens[$stackPtr - 2]['line'] === $tokens[$stackPtr - 1]['line']
+			) {
+				// This is the first whitespace token on a line
+				// and the line before this one is not empty,
+				// so this could be the start of a multiple empty line block.
+				$next = $phpcsFile->findNext( T_WHITESPACE, $stackPtr, null, true );
+				$lines = ( $tokens[$next]['line'] - $tokens[$stackPtr]['line'] );
+				if ( $lines > 1 ) {
+					// If the next non T_WHITESPACE token is more than 1 line away,
+					// then there were multiple empty lines.
+					$error = 'Multiple empty lines should not exist in a row; found %s consecutive empty lines';
+					$fix   = $phpcsFile->addFixableError(
+						$error,
+						$stackPtr,
+						'MultipleEmptyLines',
+						array( $lines )
+					);
+					if ( $fix === true ) {
+						$phpcsFile->fixer->beginChangeset();
+						$i = $stackPtr;
+						while ( $tokens[$i]['line'] !== $tokens[$next]['line'] ) {
+							$phpcsFile->fixer->replaceToken( $i, '' );
+							$i++;
+						}
+						$phpcsFile->fixer->addNewlineBefore( $i );
+						$phpcsFile->fixer->endChangeset();
+					}
+				}
+		}
+	}
+}

MediaWiki/Tests/files/WhiteSpace/multiple_empty_lines_fail.php

@@ -0,0 +1,12 @@
+<?php
+$a = true;
+
+
+$b = false;
+
+function wfFoo() {
+	$a = 1;
+
+
+	$b = 2;
+}

MediaWiki/Tests/files/WhiteSpace/multiple_empty_lines_pass.php

@@ -0,0 +1,10 @@
+<?php
+$a = true;
+
+$b = false;
+
+function wfFoo() {
+	$a = 1;
+
+	$b = 2;
+}

MediaWiki/ruleset.xml

@@ -102,7 +102,10 @@
 	<rule ref="Squiz.WhiteSpace.ScopeClosingBrace" />
 	<rule ref="Squiz.WhiteSpace.ScopeKeywordSpacing" />
 	<rule ref="Squiz.WhiteSpace.SemicolonSpacing" />
-	<rule ref="Squiz.WhiteSpace.SuperfluousWhitespace" />
+	<rule ref="Squiz.WhiteSpace.SuperfluousWhitespace">
+		<!-- Implemented as MediaWiki.WhiteSpace.MultipleEmptyLines -->
+		<exclude name="Squiz.WhiteSpace.SuperfluousWhitespace.EmptyLines" />
+	</rule>
 
 	<rule ref="Zend.Files.ClosingTag" />
 </ruleset>