From c2e8f505c12ace6af42161bf9930d483b1721f2e Mon Sep 17 00:00:00 2001
From: =?utf8?q?Bartosz=20Dziewo=C5=84ski?= <matma.rex@gmail.com>
Date: Mon, 28 Sep 2015 19:12:06 +0200
Subject: [PATCH] Work around IE9's broken handling of .styleSheet.cssText

IE9 drops @media queries from .styleSheet.cssText when that property
is read. Therefore we can't trust it to contain what we put there
previously.

Bug: T108727
Change-Id: Ic4f553966e48e3fc608a47ef193df923227ceb96
---
 resources/src/mediawiki/mediawiki.js | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/resources/src/mediawiki/mediawiki.js b/resources/src/mediawiki/mediawiki.js
index 5dd2acbd81..1577fff0e2 100644
--- a/resources/src/mediawiki/mediawiki.js
+++ b/resources/src/mediawiki/mediawiki.js
@@ -924,14 +924,22 @@
 					// Verify that the element before the marker actually is a
 					// <style> tag and one that came from ResourceLoader
 					// (not some other style tag or even a `<meta>` or `<script>`).
-					if ( $style.data( 'ResourceLoaderDynamicStyleTag' ) === true ) {
+					if ( $style.data( 'ResourceLoaderDynamicStyleTag' ) ) {
 						// There's already a dynamic <style> tag present and
 						// we are able to append more to it.
 						styleEl = $style.get( 0 );
 						// Support: IE6-10
 						if ( styleEl.styleSheet ) {
 							try {
-								styleEl.styleSheet.cssText += cssText;
+								// Support: IE9
+								// We can't do styleSheet.cssText += cssText, since IE9 mangles this property on
+								// write, dropping @media queries from the CSS text. If we read it and used its
+								// value, we would accidentally apply @media-specific styles to all media. (T108727)
+								if ( document.documentMode === 9 ) {
+									styleEl.styleSheet.cssText = $style.data( 'ResourceLoaderDynamicStyleTag' ) + cssText;
+								} else {
+									styleEl.styleSheet.cssText += cssText;
+								}
 							} catch ( e ) {
 								mw.track( 'resourceloader.exception', { exception: e, source: 'stylesheet' } );
 							}
@@ -943,7 +951,15 @@
 					}
 				}
 
-				$( newStyleTag( cssText, getMarker() ) ).data( 'ResourceLoaderDynamicStyleTag', true );
+				$style = $( newStyleTag( cssText, getMarker() ) );
+
+				if ( document.documentMode === 9 ) {
+					// Support: IE9
+					// Preserve original CSS text because IE9 mangles it on write
+					$style.data( 'ResourceLoaderDynamicStyleTag', cssText );
+				} else {
+					$style.data( 'ResourceLoaderDynamicStyleTag', true );
+				}
 
 				fireCallbacks();
 			}
-- 
2.20.1