From baab085b322c67877ef9507255d1faf953bb98b8 Mon Sep 17 00:00:00 2001
From: =?utf8?q?Bartosz=20Dziewo=C5=84ski?= <matma.rex@gmail.com>
Date: Tue, 23 May 2017 14:48:32 +0200
Subject: [PATCH] Parser: Better debugging of lock errors ("Did you call
 Parser::parse recursively?")

Save the backtrace when locking, so that if some code tries locking again,
we can print the lock owner's backtrace for easier debugging.

Change-Id: I6e352b4aa5e7cb35825a66592f6c066d9e8b95c9
---
 includes/parser/Parser.php | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/includes/parser/Parser.php b/includes/parser/Parser.php
index ecee0e22d3..11392dea4e 100644
--- a/includes/parser/Parser.php
+++ b/includes/parser/Parser.php
@@ -245,7 +245,7 @@ class Parser {
 	public $currentRevisionCache;
 
 	/**
-	 * @var bool Recursive call protection.
+	 * @var bool|string Recursive call protection.
 	 * This variable should be treated as if it were private.
 	 */
 	public $mInParse = false;
@@ -6073,9 +6073,13 @@ class Parser {
 	protected function lock() {
 		if ( $this->mInParse ) {
 			throw new MWException( "Parser state cleared while parsing. "
-				. "Did you call Parser::parse recursively?" );
+				. "Did you call Parser::parse recursively? Lock is held by: " . $this->mInParse );
 		}
-		$this->mInParse = true;
+
+		// Save the backtrace when locking, so that if some code tries locking again,
+		// we can print the lock owner's backtrace for easier debugging
+		$e = new Exception;
+		$this->mInParse = $e->getTraceAsString();
 
 		$recursiveCheck = new ScopedCallback( function() {
 			$this->mInParse = false;
-- 
2.20.1