LibWeb: Stop changing width of block-level flex containers during layout

If the parent BFC can come up with a nice stretch-fit width for the flex
container, it will have already done so *before* even entering flex
layout. There's no need to do it again, midway through the flex layout
algorithm.

This wasn't just unnecessary, but we were also doing it incorrectly and
not taking margins into account when calculating the amount of available
space for stretch-fit. This led to oversized flex containers in the
presence of negative margins.

Fixes #18614

1 files changed, 3 insertions, 2 deletions

diff --git a/Userland/Libraries/LibWeb/Layout/BlockFormattingContext.cpp b/Userland/Libraries/LibWeb/Layout/BlockFormattingContext.cpp
index 39b5ce67bb..2a92319614 100644
--- a/Userland/Libraries/LibWeb/Layout/BlockFormattingContext.cpp
+++ b/Userland/Libraries/LibWeb/Layout/BlockFormattingContext.cpp
@@ -1056,9 +1056,10 @@ CSSPixels BlockFormattingContext::greatest_child_width(Box const& box) const
     return max_width;
 }
 
-void BlockFormattingContext::determine_width_of_child(Box const& box, AvailableSpace const& available_space)
+void BlockFormattingContext::determine_width_of_child(Box const&, AvailableSpace const&)
 {
-    compute_width(box, available_space);
+    // NOTE: We don't do anything here, since we'll have already determined the width of the child
+    //       before recursing into nested layout within the child.
 }
 
 void BlockFormattingContext::determine_height_of_child(Box const& box, AvailableSpace const& available_space)