Fix Form.requestSubmit(submitter) not setting SubmitEvent.submitter

Create SubmitEvent type and use it in submitForm() so that
e.submitter is correctly set when requestSubmit(submitter) is called.

Fixes #1982

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/browser/Page.zig

@@ -61,6 +61,7 @@ const IntersectionObserver = @import("webapi/IntersectionObserver.zig");
 const CustomElementDefinition = @import("webapi/CustomElementDefinition.zig");
 const storage = @import("webapi/storage/storage.zig");
 const PageTransitionEvent = @import("webapi/event/PageTransitionEvent.zig");
+const SubmitEvent = @import("webapi/event/SubmitEvent.zig");
 const NavigationKind = @import("webapi/navigation/root.zig").NavigationKind;
 const KeyboardEvent = @import("webapi/event/KeyboardEvent.zig");
 const MouseEvent = @import("webapi/event/MouseEvent.zig");
@@ -3487,7 +3488,8 @@ pub fn submitForm(self: *Page, submitter_: ?*Element, form_: ?*Element.Html.Form
     };
 
     if (submit_opts.fire_event) {
-        const submit_event = try Event.initTrusted(comptime .wrap("submit"), .{ .bubbles = true, .cancelable = true }, self);
+        const submitter_html: ?*HtmlElement = if (submitter_) |s| s.is(HtmlElement) else null;
+        const submit_event = (try SubmitEvent.initTrusted(comptime .wrap("submit"), .{ .bubbles = true, .cancelable = true, .submitter = submitter_html }, self)).asEvent();
 
         // so submit_event is still valid when we check _prevent_default
         submit_event.acquireRef();

src/browser/js/bridge.zig

@@ -850,6 +850,7 @@ pub const JsApis = flattenTypes(&.{
     @import("../webapi/event/TextEvent.zig"),
     @import("../webapi/event/InputEvent.zig"),
     @import("../webapi/event/PromiseRejectionEvent.zig"),
+    @import("../webapi/event/SubmitEvent.zig"),
     @import("../webapi/MessageChannel.zig"),
     @import("../webapi/MessagePort.zig"),
     @import("../webapi/media/MediaError.zig"),

src/browser/tests/element/html/form.html

@@ -463,3 +463,44 @@
   });
 }
 </script>
+
+<!-- Test: requestSubmit(submitter) sets SubmitEvent.submitter -->
+<form id="test_form_submitter" action="/should-not-navigate6" method="get">
+  <button id="submitter_btn" type="submit">Save</button>
+</form>
+
+<script id="requestSubmit_sets_submitter">
+{
+  const form = $('#test_form_submitter');
+  const btn = $('#submitter_btn');
+  let capturedSubmitter = undefined;
+
+  form.addEventListener('submit', (e) => {
+    e.preventDefault();
+    capturedSubmitter = e.submitter;
+  });
+
+  form.requestSubmit(btn);
+  testing.expectEqual(btn, capturedSubmitter);
+}
+</script>
+
+<!-- Test: requestSubmit() without submitter sets submitter to the form element -->
+<form id="test_form_submitter2" action="/should-not-navigate7" method="get">
+  <input type="text" name="q" value="test">
+</form>
+
+<script id="requestSubmit_default_submitter_is_form">
+{
+  const form = $('#test_form_submitter2');
+  let capturedSubmitter = undefined;
+
+  form.addEventListener('submit', (e) => {
+    e.preventDefault();
+    capturedSubmitter = e.submitter;
+  });
+
+  form.requestSubmit();
+  testing.expectEqual(form, capturedSubmitter);
+}
+</script>

src/browser/webapi/Event.zig

@@ -76,6 +76,7 @@ pub const Type = union(enum) {
     pop_state_event: *@import("event/PopStateEvent.zig"),
     ui_event: *@import("event/UIEvent.zig"),
     promise_rejection_event: *@import("event/PromiseRejectionEvent.zig"),
+    submit_event: *@import("event/SubmitEvent.zig"),
 };
 
 pub const Options = struct {

src/browser/webapi/event/SubmitEvent.zig

@@ -0,0 +1,95 @@
+// Copyright (C) 2023-2026  Lightpanda (Selecy SAS)
+//
+// Francis Bouvier <francis@lightpanda.io>
+// Pierre Tachoire <pierre@lightpanda.io>
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as
+// published by the Free Software Foundation, either version 3 of the
+// License, or (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+const std = @import("std");
+const String = @import("../../../string.zig").String;
+
+const js = @import("../../js/js.zig");
+const Page = @import("../../Page.zig");
+const Session = @import("../../Session.zig");
+const Event = @import("../Event.zig");
+const HtmlElement = @import("../element/Html.zig");
+const Allocator = std.mem.Allocator;
+
+// https://developer.mozilla.org/en-US/docs/Web/API/SubmitEvent
+const SubmitEvent = @This();
+
+_proto: *Event,
+_submitter: ?*HtmlElement,
+
+const SubmitEventOptions = struct {
+    submitter: ?*HtmlElement = null,
+};
+
+const Options = Event.inheritOptions(SubmitEvent, SubmitEventOptions);
+
+pub fn init(typ: []const u8, opts_: ?Options, page: *Page) !*SubmitEvent {
+    const arena = try page.getArena(.{ .debug = "SubmitEvent" });
+    errdefer page.releaseArena(arena);
+    const type_string = try String.init(arena, typ, .{});
+    return initWithTrusted(arena, type_string, opts_, false, page);
+}
+
+pub fn initTrusted(typ: String, _opts: ?Options, page: *Page) !*SubmitEvent {
+    const arena = try page.getArena(.{ .debug = "SubmitEvent.trusted" });
+    errdefer page.releaseArena(arena);
+    return initWithTrusted(arena, typ, _opts, true, page);
+}
+
+fn initWithTrusted(arena: Allocator, typ: String, _opts: ?Options, trusted: bool, page: *Page) !*SubmitEvent {
+    const opts = _opts orelse Options{};
+
+    const event = try page._factory.event(
+        arena,
+        typ,
+        SubmitEvent{
+            ._proto = undefined,
+            ._submitter = opts.submitter,
+        },
+    );
+
+    Event.populatePrototypes(event, opts, trusted);
+    return event;
+}
+
+pub fn deinit(self: *SubmitEvent, shutdown: bool, session: *Session) void {
+    self._proto.deinit(shutdown, session);
+}
+
+pub fn asEvent(self: *SubmitEvent) *Event {
+    return self._proto;
+}
+
+pub fn getSubmitter(self: *const SubmitEvent) ?*HtmlElement {
+    return self._submitter;
+}
+
+pub const JsApi = struct {
+    pub const bridge = js.Bridge(SubmitEvent);
+
+    pub const Meta = struct {
+        pub const name = "SubmitEvent";
+        pub const prototype_chain = bridge.prototypeChain();
+        pub var class_id: bridge.ClassId = undefined;
+        pub const weak = true;
+        pub const finalizer = bridge.finalizer(SubmitEvent.deinit);
+    };
+
+    pub const constructor = bridge.constructor(SubmitEvent.init, .{});
+    pub const submitter = bridge.accessor(SubmitEvent.getSubmitter, null, .{});
+};