From c4380b91f448a54e5a145cb48f7ef0c75fbb8548 Mon Sep 17 00:00:00 2001
From: Pierre Tachoire <pierre@lightpanda.io>
Date: Wed, 12 Nov 2025 11:02:22 +0100
Subject: [PATCH] handle template's original content

When the document fragment is called via the content method on a
templat, it must contain the original template's HTML nodes.
---
 src/browser/dom/node.zig      | 16 ++++++++++++++++
 src/browser/html/elements.zig | 15 ++++++++++++++-
 src/tests/html/template.html  | 16 ++++++++++++++++
 3 files changed, 46 insertions(+), 1 deletion(-)

diff --git a/src/browser/dom/node.zig b/src/browser/dom/node.zig
index a8f43a1f4..7eae13c9a 100644
--- a/src/browser/dom/node.zig
+++ b/src/browser/dom/node.zig
@@ -390,7 +390,23 @@ pub const Node = struct {
         return parser.nodeHasChildNodes(self);
     }
 
+    fn is_template(self: *parser.Node) !bool {
+        if (parser.nodeType(self) != .element) {
+            return false;
+        }
+
+        const e = parser.nodeToElement(self);
+        return try parser.elementTag(e) == .template;
+    }
+
     pub fn get_childNodes(self: *parser.Node, page: *Page) !NodeList {
+        // special case for template:
+        // > The Node.childNodes property of the <template> element is always empty
+        // https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/Elements/template#usage_notes
+        if (try is_template(self)) {
+            return .{};
+        }
+
         const allocator = page.arena;
         var list: NodeList = .{};
 
diff --git a/src/browser/html/elements.zig b/src/browser/html/elements.zig
index e8dfdfbdf..b5da542f6 100644
--- a/src/browser/html/elements.zig
+++ b/src/browser/html/elements.zig
@@ -33,6 +33,8 @@ const DataSet = @import("DataSet.zig");
 const StyleSheet = @import("../cssom/StyleSheet.zig");
 const CSSStyleDeclaration = @import("../cssom/CSSStyleDeclaration.zig");
 
+const WalkerChildren = @import("../dom/walker.zig").WalkerChildren;
+
 // HTMLElement interfaces
 pub const Interfaces = .{
     Element,
@@ -1200,11 +1202,22 @@ pub const HTMLTemplateElement = struct {
     pub const subtype = .node;
 
     pub fn get_content(self: *parser.Template, page: *Page) !*parser.DocumentFragment {
-        const state = try page.getOrCreateNodeState(@ptrCast(@alignCast(self)));
+        const n: *parser.Node = @ptrCast(@alignCast(self));
+        const state = try page.getOrCreateNodeState(n);
         if (state.template_content) |tc| {
             return tc;
         }
         const tc = try parser.documentCreateDocumentFragment(@ptrCast(page.window.document));
+        const ntc: *parser.Node = @ptrCast(@alignCast(tc));
+
+        // move existing template's childnodes to the fragment.
+        const walker = WalkerChildren{};
+        var next: ?*parser.Node = null;
+        while (true) {
+            next = try walker.get_next(n, next) orelse break;
+            _ = try parser.nodeAppendChild(ntc, next.?);
+        }
+
         state.template_content = tc;
         return tc;
     }
diff --git a/src/tests/html/template.html b/src/tests/html/template.html
index 30b7cf444..058c1dd32 100644
--- a/src/tests/html/template.html
+++ b/src/tests/html/template.html
@@ -20,3 +20,19 @@
   testing.expectEqual('P', t.content.childNodes[1].tagName);
   testing.expectEqual('9000!', t.content.childNodes[1].innerHTML);
 </script>
+
+<template id="hello"><p>hello, world</p></template>
+
+<script id=template_parsing>
+  const tt = document.getElementById('hello');
+  testing.expectEqual('<p>hello, world</p>', tt.innerHTML);
+
+  // > The Node.childNodes property of the <template> element is always empty
+  // https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/Elements/template#usage_notes
+  testing.expectEqual(0, tt.childNodes.length);
+
+  let out = document.createElement('div');
+  out.appendChild(tt.content.cloneNode(true));
+
+  testing.expectEqual('<p>hello, world</p>', out.innerHTML);
+</script>