If an incoming break token is past block-end, so is the outgoing one.

mstensho · chromium-wpt-export-bot · commit faa42db3e490 · 2025-05-14T09:48:46.000-07:00
This was failing for column balancing at a fragment that was for a resumed node that had already overflowed, and had a forced break inside. For this to happen, we need a balanced multicol container inside another fragmentation context, and break in the outer fragmentation context, then attempt to rebalance the inner while inside a resumed overflowed node. This fixes crashes, but simply avoiding those would leave a correctness issue behind (since a break inside a parallel flow would have incorrect impact on the outside). Hence a (rather complicated) correctness test for this. Without this fix, the test would both fail a DCHECK and (if bypassed) a CHECK. Bug: 396176635 Change-Id: I08e4a6ca2832e027daf02f5a7e38e5b3c632a4ff Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6545960 Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org> Commit-Queue: Morten Stenshorne <mstensho@chromium.org> Cr-Commit-Position: refs/heads/main@{#1460130}
diff --git a/css/css-multicol/multicol-fill-balance-030.html b/css/css-multicol/multicol-fill-balance-030.html
@@ -0,0 +1,22 @@
+<!DOCTYPE html>
+<title>Nested balanced multicol with forced break inside overflowed container</title>
+<link rel="author" title="Morten Stenshorne" href="mailto:mstensho@chromium.org">
+<link rel="help" href="https://issues.chromium.org/issues/396176635">
+<link rel="match" href="../reference/ref-filled-green-100px-square.xht">
+<p>Test passes if there is a filled green square and <strong>no red</strong>.</p>
+<div style="columns:2; gap:0; column-fill:auto; width:80px; border-right:20px solid green; height:100px; background:red;">
+  <div style="columns:2; gap:0;">
+    <div style="height:40px; background:green;"></div>
+    <div style="height:10px; background:red;">
+      <div style="margin-left:auto; width:50%; height:180px; background:green;">
+        <div style="height:10px; width:100%; margin-left:-100%; background:green;"></div>
+      </div>
+      <div style="break-before:column; height:10px; background:red;"></div>
+    </div>
+    <div style="width:50%; height:250px;">
+      <div style="height:170px; background:green;"></div>
+      <div style="width:200%; height:80px; background:green;"></div>
+    </div>
+    <div style="height:100px; background:green;"></div>
+  </div>
+</div>
