From ad89079a44dc195d1d495dc0207364f03f870589 Mon Sep 17 00:00:00 2001
From: "C. Scott Ananian" <cscott@cscott.net>
Date: Wed, 20 Mar 2019 16:37:49 -0400
Subject: [PATCH] Avoid counting input lines twice in BlockLevelPass::execute()

In T208070 / I120ca25a77b7b933de4afddd1d458e36a95e26da we added a
check whether we were processing the last line of input, in order
to avoid emitting extra trailing newlines.  But if the number of
input lines is large, StringUtils::explode() will return an
iterator which doesn't implement Countable for efficiency.
I22eebb70af1b19d7c25241fc78bfcced4470e78a fixed this, but at the
cost of scanning the string twice: once just to count the number
of newlines before we begin to iterate over the lines.

This patch uses Iterator::valid() to determine if we're on the
last iteration without having to scan the string twice.

Bug: T208070
Bug: T218817
Change-Id: I41a45266d266195aa6002d3854e018cacf052ca6
---
 includes/parser/BlockLevelPass.php | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/includes/parser/BlockLevelPass.php b/includes/parser/BlockLevelPass.php
index 6d6af7716c..f925038302 100644
--- a/includes/parser/BlockLevelPass.php
+++ b/includes/parser/BlockLevelPass.php
@@ -192,8 +192,6 @@ class BlockLevelPass {
 		# happening here is handling of block-level elements p, pre,
 		# and making lists from lines starting with * # : etc.
 		$textLines = StringUtils::explode( "\n", $text );
-		# Count this way because $textLines could be an ExplodeIterator
-		$lineCount = substr_count( $text, "\n" ) + 1;
 
 		$lastPrefix = $output = '';
 		$this->DTopen = $inBlockElem = false;
@@ -201,9 +199,11 @@ class BlockLevelPass {
 		$pendingPTag = false;
 		$inBlockquote = false;
 
-		$nextLineNum = 0;
-		foreach ( $textLines as $inputLine ) {
-			$nextLineNum += 1;
+		for ( $textLines->rewind(); $textLines->valid(); ) {
+			$inputLine = $textLines->current();
+			$textLines->next();
+			$notLastLine = $textLines->valid();
+
 			# Fix up $lineStart
 			if ( !$this->lineStart ) {
 				$output .= $inputLine;
@@ -410,7 +410,7 @@ class BlockLevelPass {
 					$output .= $t;
 					// Add a newline if there's an open paragraph
 					// or we've yet to reach the last line.
-					if ( $nextLineNum < $lineCount || $this->hasOpenParagraph() ) {
+					if ( $notLastLine || $this->hasOpenParagraph() ) {
 						$output .= "\n";
 					}
 				} else {
-- 
2.20.1