From f67ca69e054c76775049cc57501105eed99e890f Mon Sep 17 00:00:00 2001
From: Karl Seguin <k@openmymind.io>
Date: Thu, 19 Feb 2026 17:22:12 +0800
Subject: [PATCH] FormData recognizes (and skips over) disabled fieldsets

---
 src/browser/tests/net/form_data.html | 108 +++++++++++++++++++++++++++
 src/browser/webapi/net/FormData.zig  |  41 ++++++++++
 2 files changed, 149 insertions(+)

diff --git a/src/browser/tests/net/form_data.html b/src/browser/tests/net/form_data.html
index 97814209..12363038 100644
--- a/src/browser/tests/net/form_data.html
+++ b/src/browser/tests/net/form_data.html
@@ -602,6 +602,114 @@
 }
 </script>
 
+<script id=disabledFieldset>
+{
+  // Elements inside a disabled fieldset should not be included
+  const form = document.createElement('form');
+
+  const fieldset = document.createElement('fieldset');
+  fieldset.disabled = true;
+
+  const inside = document.createElement('input');
+  inside.name = 'inside';
+  inside.value = 'nope';
+  fieldset.appendChild(inside);
+
+  const outside = document.createElement('input');
+  outside.name = 'outside';
+  outside.value = 'yes';
+
+  form.appendChild(fieldset);
+  form.appendChild(outside);
+
+  const fd = new FormData(form);
+  testing.expectEqual(null, fd.get('inside'));
+  testing.expectEqual('yes', fd.get('outside'));
+}
+</script>
+
+<script id=disabledFieldsetLegendExemption>
+{
+  // Elements inside the FIRST legend of a disabled fieldset are NOT disabled
+  const form = document.createElement('form');
+
+  const fieldset = document.createElement('fieldset');
+  fieldset.disabled = true;
+
+  const legend = document.createElement('legend');
+  const inLegend = document.createElement('input');
+  inLegend.name = 'in-legend';
+  inLegend.value = 'exempt';
+  legend.appendChild(inLegend);
+
+  const notInLegend = document.createElement('input');
+  notInLegend.name = 'not-in-legend';
+  notInLegend.value = 'nope';
+
+  fieldset.appendChild(legend);
+  fieldset.appendChild(notInLegend);
+  form.appendChild(fieldset);
+
+  const fd = new FormData(form);
+  testing.expectEqual('exempt', fd.get('in-legend'));
+  testing.expectEqual(null, fd.get('not-in-legend'));
+}
+</script>
+
+<script id=disabledFieldsetSecondLegend>
+{
+  // Only the FIRST legend gets the exemption; second legend inputs are still disabled
+  const form = document.createElement('form');
+
+  const fieldset = document.createElement('fieldset');
+  fieldset.disabled = true;
+
+  const legend1 = document.createElement('legend');
+  const inLegend1 = document.createElement('input');
+  inLegend1.name = 'first-legend';
+  inLegend1.value = 'exempt';
+  legend1.appendChild(inLegend1);
+
+  const legend2 = document.createElement('legend');
+  const inLegend2 = document.createElement('input');
+  inLegend2.name = 'second-legend';
+  inLegend2.value = 'nope';
+  legend2.appendChild(inLegend2);
+
+  fieldset.appendChild(legend1);
+  fieldset.appendChild(legend2);
+  form.appendChild(fieldset);
+
+  const fd = new FormData(form);
+  testing.expectEqual('exempt', fd.get('first-legend'));
+  testing.expectEqual(null, fd.get('second-legend'));
+}
+</script>
+
+<script id=disabledFieldsetNested>
+{
+  // Outer fieldset disabled: inner enabled fieldset's elements are still disabled
+  const form = document.createElement('form');
+
+  const outer = document.createElement('fieldset');
+  outer.disabled = true;
+
+  const inner = document.createElement('fieldset');
+  // inner is NOT disabled itself
+
+  const input = document.createElement('input');
+  input.name = 'deep';
+  input.value = 'nope';
+  inner.appendChild(input);
+
+  outer.appendChild(inner);
+  form.appendChild(outer);
+
+  const fd = new FormData(form);
+  testing.expectEqual(null, fd.get('deep'));
+}
+</script>
+
 <script id=imageWithoutName>
 {
   // Test that image input without name still submits x and y coordinates
diff --git a/src/browser/webapi/net/FormData.zig b/src/browser/webapi/net/FormData.zig
index 1e869411..48b8d0af 100644
--- a/src/browser/webapi/net/FormData.zig
+++ b/src/browser/webapi/net/FormData.zig
@@ -22,6 +22,7 @@ const log = @import("../../../log.zig");
 
 const js = @import("../../js/js.zig");
 const Page = @import("../../Page.zig");
+const Node = @import("../Node.zig");
 const Form = @import("../element/html/Form.zig");
 const Element = @import("../Element.zig");
 const KeyValueList = @import("../KeyValueList.zig");
@@ -124,12 +125,17 @@ fn collectForm(arena: Allocator, form_: ?*Form, submitter_: ?*Element, page: *Pa
     var list: KeyValueList = .empty;
     const form = form_ orelse return list;
 
+    const form_node = form.asNode();
+
     var elements = try form.getElements(page);
     var it = try elements.iterator();
     while (it.next()) |element| {
         if (element.getAttributeSafe(comptime .wrap("disabled")) != null) {
             continue;
         }
+        if (isDisabledByFieldset(element, form_node)) {
+            continue;
+        }
 
         // Handle image submitters first - they can submit without a name
         if (element.is(Form.Input)) |input| {
@@ -196,6 +202,41 @@ fn collectForm(arena: Allocator, form_: ?*Form, submitter_: ?*Element, page: *Pa
     return list;
 }
 
+// Returns true if `element` is disabled by an ancestor <fieldset disabled>,
+// stopping the upward walk when the form node is reached.
+// Per spec, elements inside the first <legend> child of a disabled fieldset
+// are NOT disabled by that fieldset.
+fn isDisabledByFieldset(element: *Element, form_node: *Node) bool {
+    const element_node = element.asNode();
+    var current: ?*Node = element_node._parent;
+    while (current) |node| {
+        // Stop at the form boundary (common case optimisation)
+        if (node == form_node) {
+            return false;
+        }
+
+        current = node._parent;
+        const el = node.is(Element) orelse continue;
+
+        if (el.getTag() == .fieldset and el.getAttributeSafe(comptime .wrap("disabled")) != null) {
+            // Check if `element` is inside the first <legend> child of this fieldset
+            var child = el.firstElementChild();
+            while (child) |c| {
+                if (c.getTag() == .legend) {
+                    // Found the first legend; exempt if element is a descendant
+                    if (c.asNode().contains(element_node)) {
+                        return false;
+                    }
+                    break;
+                }
+                child = c.nextElementSibling();
+            }
+            return true;
+        }
+    }
+    return false;
+}
+
 pub const JsApi = struct {
     pub const bridge = js.Bridge(FormData);