From aac387bcc649fb8d44f1dd58d15239a2e95a053a Mon Sep 17 00:00:00 2001
From: Sam Atkins <sam@ladybird.org>
Date: Tue, 25 Nov 2025 16:06:44 +0000
Subject: [PATCH] LibWeb/DOM: Copy "allow declarative shadow roots" to template
 document

This flag defaults to false for new Documents, such as the one created
here for use by template elements' contents. Without setting it to
true, nothing inside a template can have a declarative shadow dom.

As noted, this appears to be a spec issue. I am not convinced that this
is the correct fix, but it is simple and does solve the issue without
any apparent regressions.
---
 Libraries/LibWeb/DOM/Document.cpp                     |  5 +++++
 .../shadow-dom/attachShadow-with-ShadowRoot.txt       |  5 ++---
 .../declarative/declarative-shadow-dom-basic.txt      | 11 +++++------
 3 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/Libraries/LibWeb/DOM/Document.cpp b/Libraries/LibWeb/DOM/Document.cpp
index b4c61fb3491..7e4d61d3182 100644
--- a/Libraries/LibWeb/DOM/Document.cpp
+++ b/Libraries/LibWeb/DOM/Document.cpp
@@ -4511,6 +4511,11 @@ GC::Ref<DOM::Document> Document::appropriate_template_contents_owner_document()
             if (document_type() == Type::HTML)
                 new_document->set_document_type(Type::HTML);
 
+            // AD-HOC: Copy over the "allow declarative shadow roots" flag, otherwise no elements inside templates will
+            //         be able to have declarative shadow roots.
+            // Spec issue: https://github.com/whatwg/html/issues/11955
+            new_document->set_allow_declarative_shadow_roots(allow_declarative_shadow_roots());
+
             // 3. Set doc's associated inert template document to new doc.
             m_associated_inert_template_document = new_document;
         }
diff --git a/Tests/LibWeb/Text/expected/wpt-import/shadow-dom/attachShadow-with-ShadowRoot.txt b/Tests/LibWeb/Text/expected/wpt-import/shadow-dom/attachShadow-with-ShadowRoot.txt
index 5fdd2350d47..2c70fb40664 100644
--- a/Tests/LibWeb/Text/expected/wpt-import/shadow-dom/attachShadow-with-ShadowRoot.txt
+++ b/Tests/LibWeb/Text/expected/wpt-import/shadow-dom/attachShadow-with-ShadowRoot.txt
@@ -2,7 +2,6 @@ Harness status: OK
 
 Found 2 tests
 
-1 Pass
-1 Fail
+2 Pass
 Pass	can use ShadowRoot as options for attachShadow
-Fail	can use ShadowRoot in document fragment as options for attachShadow
\ No newline at end of file
+Pass	can use ShadowRoot in document fragment as options for attachShadow
\ No newline at end of file
diff --git a/Tests/LibWeb/Text/expected/wpt-import/shadow-dom/declarative/declarative-shadow-dom-basic.txt b/Tests/LibWeb/Text/expected/wpt-import/shadow-dom/declarative/declarative-shadow-dom-basic.txt
index d543fdf7b50..bb970d7b1bc 100644
--- a/Tests/LibWeb/Text/expected/wpt-import/shadow-dom/declarative/declarative-shadow-dom-basic.txt
+++ b/Tests/LibWeb/Text/expected/wpt-import/shadow-dom/declarative/declarative-shadow-dom-basic.txt
@@ -2,8 +2,7 @@ Harness status: OK
 
 Found 22 tests
 
-18 Pass
-4 Fail
+22 Pass
 Pass	Declarative Shadow DOM: Basic test
 Pass	Declarative Shadow DOM: Feature detection
 Pass	Shadowrootmode reflection
@@ -19,10 +18,10 @@ Pass	Declarative Shadow DOM: Missing closing tag
 Pass	Declarative Shadow DOM: delegates focus attribute
 Pass	Declarative Shadow DOM: clonable attribute
 Pass	Declarative Shadow DOM: Multiple roots
-Fail	Declarative Shadow DOM: template containing declarative shadow root (with shadowrootclonable)
-Fail	Declarative Shadow DOM: template containing (deeply nested) declarative shadow root
-Fail	Declarative Shadow DOM: template containing a template containing declarative shadow root
-Fail	Declarative Shadow DOM: template containing declarative shadow root and UA shadow root
+Pass	Declarative Shadow DOM: template containing declarative shadow root (with shadowrootclonable)
+Pass	Declarative Shadow DOM: template containing (deeply nested) declarative shadow root
+Pass	Declarative Shadow DOM: template containing a template containing declarative shadow root
+Pass	Declarative Shadow DOM: template containing declarative shadow root and UA shadow root
 Pass	Declarative Shadow DOM: template containing closed declarative shadow root and UA shadow root
 Pass	Declarative Shadow DOM: declarative shadow roots are not supported by the template element
 Pass	Declarative Shadow DOM: explicit test that exceptions are not thrown
\ No newline at end of file