From 1f9aa57a0816bb66908334648838b8b305fd8fbe Mon Sep 17 00:00:00 2001
From: roytam1 <roytam@gmail.com>
Date: Thu, 14 Apr 2022 15:05:27 +0800
Subject: [PATCH] import from UXP: Bug 1419762 - Return the inline continuation
 of an IB split when appending (fc8fcfc0)

---
 layout/base/crashtests/1419762.html    | 15 +++++++++++++++
 layout/base/crashtests/crashtests.list |  1 +
 layout/base/nsCSSFrameConstructor.cpp  |  7 ++++---
 3 files changed, 20 insertions(+), 3 deletions(-)
 create mode 100644 layout/base/crashtests/1419762.html

diff --git a/layout/base/crashtests/1419762.html b/layout/base/crashtests/1419762.html
new file mode 100644
index 000000000..08a56106d
--- /dev/null
+++ b/layout/base/crashtests/1419762.html
@@ -0,0 +1,15 @@
+<style id='style_1'>
+  :first-child { display: table-column-group; }
+</style>
+<script>
+  try { o1 = document.createElement('isindex') } catch(e) { }
+  try { o2 = document.createElement('input') } catch(e) { }
+  try { o3 = document.createElement('optgroup') } catch(e) { }
+  try { o4 = document.createElement('col') } catch(e) { }
+  try { document.documentElement.appendChild(o1) } catch(e) { }
+  try { o1.appendChild(o2) } catch(e) { }
+  try { o1.appendChild(o3) } catch(e) { }
+  try { document.documentElement.offsetTop; } catch (e) { }
+  try { document.documentElement.appendChild(o4) } catch(e) { }
+  try { document.styleSheets[0].insertRule('optgroup::first-line { list-style-type: japanese-formal; }', 0); } catch(e) { }
+</script>
diff --git a/layout/base/crashtests/crashtests.list b/layout/base/crashtests/crashtests.list
index cb935dac5..7539fc06a 100644
--- a/layout/base/crashtests/crashtests.list
+++ b/layout/base/crashtests/crashtests.list
@@ -485,3 +485,4 @@ load 1308848-2.html
 asserts(0-1) load 1343606.html # bug 1343948
 load 1404789-1.html
 load 1404789-2.html
+load 1419762.html
diff --git a/layout/base/nsCSSFrameConstructor.cpp b/layout/base/nsCSSFrameConstructor.cpp
index eb7362320..2d69f1576 100644
--- a/layout/base/nsCSSFrameConstructor.cpp
+++ b/layout/base/nsCSSFrameConstructor.cpp
@@ -6796,10 +6796,11 @@ nsCSSFrameConstructor::GetInsertionPrevSibling(InsertionPoint* aInsertion,
       *aIsAppend = true;
       if (IsFramePartOfIBSplit(aInsertion->mParentFrame)) {
         // Since we're appending, we'll walk to the last anonymous frame
-        // that was created for the broken inline frame.  But don't walk
-        // to the trailing inline if it's empty; stop at the block.
+        // that was created for the broken inline frame. We can walk to the
+        // trailing inline, since we know this is a real append, and not an
+        // insert (that would've been handled by `FindNextSibling`).
         aInsertion->mParentFrame =
-          GetLastIBSplitSibling(aInsertion->mParentFrame, false);
+          GetLastIBSplitSibling(aInsertion->mParentFrame, true);
       }
       // Get continuation that parents the last child.
       aInsertion->mParentFrame =