From 9ce047439890d507b9e2e69e425a960a0b9983c0 Mon Sep 17 00:00:00 2001
From: Xidorn Quan <me@upsuper.org>
Date: Thu, 28 Sep 2017 16:19:45 +1000
Subject: [PATCH] Bug 1402094 - Blacklist about:reader from using stylo.
 r=bholley

MozReview-Commit-ID: 6cG1x1tcOwn

--HG--
extra : rebase_source : dce6a0b1828f8388952e5ff1993424dff782d3d5
---
 dom/base/nsDocument.cpp | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/dom/base/nsDocument.cpp b/dom/base/nsDocument.cpp
index afa7fac21670..471b38680181 100644
--- a/dom/base/nsDocument.cpp
+++ b/dom/base/nsDocument.cpp
@@ -13608,6 +13608,27 @@ nsIDocument::ReportHasScrollLinkedEffect()
                                   "ScrollLinkedEffectFound2");
 }
 
+// URL-based blacklist for stylo.
+static bool
+ShouldUseGeckoBackend(nsIURI* aDocumentURI)
+{
+  if (!aDocumentURI) {
+    return false;
+  }
+  bool isScheme = false;
+  if (NS_SUCCEEDED(aDocumentURI->SchemeIs("about", &isScheme))) {
+    nsAutoCString path;
+    aDocumentURI->GetFilePath(path);
+    // about:reader requires support of :scope pseudo-class so we have
+    // to use Gecko backend for now. See bug 1402094.
+    // This should be fixed by bug 1204818.
+    if (path.EqualsLiteral("reader")) {
+      return true;
+    }
+  }
+  return false;
+}
+
 void
 nsIDocument::UpdateStyleBackendType()
 {
@@ -13626,7 +13647,7 @@ nsIDocument::UpdateStyleBackendType()
     // Note that, since tests can have XUL support, we still need to
     // explicitly exclude XUL documents here.
     if (!nsContentUtils::IsSystemPrincipal(NodePrincipal()) &&
-        !IsXULDocument()) {
+        !IsXULDocument() && !ShouldUseGeckoBackend(mDocumentURI)) {
       mStyleBackendType = StyleBackendType::Servo;
     }
   }