Trigger the DOMContentLoaded on the Window

This is hacky, but it's inspired by how NetSurf does it. While the Window isn't
the parent of the Document, many events should bubble from the Document to the
Window. libdom simply doesn't handle this (it has no concept of a Window, and
the Document has no parent).

We potentially need to do this for multiple event types (NetSurf only does it
for the 'load' event as far as I can tell). It would be nice to find a generic
way to do this...maybe intercept any addEventListener on the body and
registering special events on the Window? For now, `DOMContentLoaded` is the
blocking (for finance.yahoo.com) and we can see if this is really an issue for
other event types.

src/browser/html/document.zig

@@ -278,15 +278,17 @@ pub const HTMLDocument = struct {
         const state = try page.getOrCreateNodeState(@alignCast(@ptrCast(self)));
         state.ready_state = .interactive;
 
-        const evt = try parser.eventCreate();
-        defer parser.eventDestroy(evt);
-
         log.debug(.script_event, "dispatch event", .{
             .type = "DOMContentLoaded",
             .source = "document",
         });
+
+        const evt = try parser.eventCreate();
+        defer parser.eventDestroy(evt);
         try parser.eventInit(evt, "DOMContentLoaded", .{ .bubbles = true, .cancelable = true });
         _ = try parser.eventTargetDispatchEvent(parser.toEventTarget(parser.DocumentHTML, self), evt);
+
+        try page.window.dispatchForDocumentTarget(evt);
     }
 
     pub fn documentIsComplete(self: *parser.DocumentHTML, page: *Page) !void {

src/browser/html/window.zig

@@ -334,6 +334,23 @@ pub const Window = struct {
             );
         }
     }
+
+    // libdom's document doesn't have a parent, which is correct, but
+    // breaks the event bubbling that happens for many events from
+    // document -> window.
+    // We need to force dispatch this event on the window, with the
+    // document target.
+    // In theory, we should do this for a lot of events and might need
+    // to come up with a good way to solve this more generically. But
+    // this specific event, and maybe a few others in the near future,
+    // are blockers.
+    // Worth noting that NetSurf itself appears to do something similar:
+    // https://github.com/netsurf-browser/netsurf/blob/a32e1a03e1c91ee9f0aa211937dbae7a96831149/content/handlers/html/html.c#L380
+    pub fn dispatchForDocumentTarget(self: *Window, evt: *parser.Event) !void {
+        // we assume that this evt has already been dispatched on the document
+        // and thus the target has already been set to the document.
+        return self.base.redispatchEvent(evt);
+    }
 };
 
 const TimerCallback = struct {
@@ -491,4 +508,21 @@ test "Browser.HTML.Window" {
         .{ "var qm = false; window.queueMicrotask(() => {qm = true });", null },
         .{ "qm", "true" },
     }, .{});
+
+    {
+        try runner.testCases(&.{
+            .{
+                \\ let dcl = false;
+                \\ window.addEventListener('DOMContentLoaded', (e) => {
+                \\   dcl = e.target == document;
+                \\ });
+                ,
+                null,
+            },
+        }, .{});
+        try runner.dispatchDOMContentLoaded();
+        try runner.testCases(&.{
+            .{ "dcl", "true" },
+        }, .{});
+    }
 }

src/browser/netsurf.zig

@@ -846,6 +846,14 @@ pub const EventTargetTBase = extern struct {
         internal_type_.* = @intFromEnum(self.internal_target_type);
         return c.DOM_NO_ERR;
     }
+
+    // Called to simulate bubbling from a libdom node (e.g. the Document) to a
+    // Zig instance (e.g. the Window).
+    pub fn redispatchEvent(self: *EventTargetTBase, evt: *Event) !void {
+        var res: bool = undefined;
+        const err = c._dom_event_target_dispatch(@ptrCast(self), &self.eti, evt, c.DOM_BUBBLING_PHASE, &res);
+        try DOMErr(err);
+    }
 };
 
 // MouseEvent

src/testing.zig

@@ -474,6 +474,12 @@ pub const JsRunner = struct {
             return err;
         };
     }
+
+    pub fn dispatchDOMContentLoaded(self: *JsRunner) !void {
+        const HTMLDocument = @import("browser/html/document.zig").HTMLDocument;
+        const html_doc = self.page.window.document;
+        try HTMLDocument.documentIsLoaded(html_doc, self.page);
+    }
 };
 
 const RunnerOpts = struct {