From d54cd23615362bbbc87e04260814f6567cd352d1 Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Fri, 1 Sep 2023 09:55:56 +0200
Subject: [PATCH] LibWeb: Never blockify HTML <br> elements

This is a bit iffy, but since <br> elements can't be implemented in
"just CSS" today, we should also exclude them from the blockification
algorithm. This is important, since <br> is expected to always have
inline-like behavior.
---
 Userland/Libraries/LibWeb/CSS/StyleComputer.cpp | 7 +++++++
 Userland/Libraries/LibWeb/DOM/Node.h            | 1 +
 Userland/Libraries/LibWeb/HTML/HTMLBRElement.h  | 7 +++++++
 3 files changed, 15 insertions(+)

diff --git a/Userland/Libraries/LibWeb/CSS/StyleComputer.cpp b/Userland/Libraries/LibWeb/CSS/StyleComputer.cpp
index b90a9bfca5..f65f4a66c2 100644
--- a/Userland/Libraries/LibWeb/CSS/StyleComputer.cpp
+++ b/Userland/Libraries/LibWeb/CSS/StyleComputer.cpp
@@ -68,6 +68,7 @@
 #include <LibWeb/DOM/Document.h>
 #include <LibWeb/DOM/Element.h>
 #include <LibWeb/FontCache.h>
+#include <LibWeb/HTML/HTMLBRElement.h>
 #include <LibWeb/HTML/HTMLHtmlElement.h>
 #include <LibWeb/Layout/Node.h>
 #include <LibWeb/Loader/ResourceLoader.h>
@@ -2427,6 +2428,12 @@ enum class BoxTypeTransformation {
 
 static BoxTypeTransformation required_box_type_transformation(StyleProperties const& style, DOM::Element const& element, Optional<CSS::Selector::PseudoElement> const& pseudo_element)
 {
+    // NOTE: We never blockify <br> elements. They are always inline.
+    //       There is currently no way to express in CSS how a <br> element really behaves.
+    //       Spec issue: https://github.com/whatwg/html/issues/2291
+    if (is<HTML::HTMLBRElement>(element))
+        return BoxTypeTransformation::None;
+
     // Absolute positioning or floating an element blockifies the box’s display type. [CSS2]
     if (style.position() == CSS::Position::Absolute || style.position() == CSS::Position::Fixed || style.float_() != CSS::Float::None)
         return BoxTypeTransformation::Blockify;
diff --git a/Userland/Libraries/LibWeb/DOM/Node.h b/Userland/Libraries/LibWeb/DOM/Node.h
index f9be9fc584..859c18b115 100644
--- a/Userland/Libraries/LibWeb/DOM/Node.h
+++ b/Userland/Libraries/LibWeb/DOM/Node.h
@@ -99,6 +99,7 @@ public:
     virtual bool is_html_table_section_element() const { return false; }
     virtual bool is_html_table_row_element() const { return false; }
     virtual bool is_html_table_cell_element() const { return false; }
+    virtual bool is_html_br_element() const { return false; }
     virtual bool is_navigable_container() const { return false; }
 
     WebIDL::ExceptionOr<JS::NonnullGCPtr<Node>> pre_insert(JS::NonnullGCPtr<Node>, JS::GCPtr<Node>);
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLBRElement.h b/Userland/Libraries/LibWeb/HTML/HTMLBRElement.h
index f6b1cf2f7e..221474262f 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLBRElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLBRElement.h
@@ -19,9 +19,16 @@ public:
     virtual JS::GCPtr<Layout::Node> create_layout_node(NonnullRefPtr<CSS::StyleProperties>) override;
 
 private:
+    virtual bool is_html_br_element() const override { return true; }
+
     HTMLBRElement(DOM::Document&, DOM::QualifiedName);
 
     virtual void initialize(JS::Realm&) override;
 };
 
 }
+
+namespace Web::DOM {
+template<>
+inline bool Node::fast_is<HTML::HTMLBRElement>() const { return is_html_br_element(); }
+}