1946904 - `window` argument to `devtools.panels.ExtensionSidebarPane.onShown` listeners is `undefined`

Status: NEW

(WebExtensions :: Developer Tools, defect)

Description

[Bramus]

Steps to reproduce:

This is a follow-up to https://bugzilla.mozilla.org/show_bug.cgi?id=1852246, in which it was surfaced that the first and only argument to listeners passed into browser.devtools.panels.onShown.addListener and browser.devtools.panels.onHidden.addListener is always undefined.

Demo REPO: https://github.com/bramus/devtools-extension-bug-sidebarpane-events

This extension logs the x argument of the listener and also the global window object.

const initSidebarPanel = (sidebarPane) => {
    sidebarPane.setPage('devtools.html');

    sidebarPane.onShown.addListener((x) => {
        console.log('onShown', x, window);
    });

    sidebarPane.onHidden.addListener((x) => {
        console.log('onHidden', x, window);
    });
};

Actual results:

The logged value for x is always undefined.

Expected results:

According to https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/devtools/panels/ExtensionSidebarPane/onShown this value should be “The window object of the sidebar page, if a page was set with setPage().”

Comment 1

[Alex Cornestean]

Hello,

I reproduced the issue on the latest Nightly (137.0a1/20250209212051), Beta (136.0b3/20250207091649) and Release (135.0/20250130195129) on Windows 10 and Ubuntu 24.04 LTS.

After loading the extensions via about:debugging I opened a page in a new tab (Wikipedia) and opened devtools.
From the “Inspector” tab I selected an element and then from the sidebar I selected POC. Below is what was logged to console:
onShown undefined Window moz-extension://0df11701-5c4e-4481-90cc-419dec62416f/devtools-page.html devtools.js:5:17

After that, I selected something else from the sidebar. This was logged to console:
onHidden undefined Window moz-extension://0df11701-5c4e-4481-90cc-419dec62416f/devtools-page.html devtools.js:9:17

Comment 2

[Rob Wu [:robwu]]

The implementation is at https://searchfox.org/mozilla-central/rev/7b3f3fb5fd2cad8f348131498a35a91bef68b47b/browser/components/extensions/child/ext-devtools-panels.js#189-196

          const listener = (eventName, panelContentWindow) => {
            fire.asyncWithoutClone(panelContentWindow);
          };
          this.on("shown", listener);

(this implementation seems to have been copied from the devtools.panels.onShown implementation at https://searchfox.org/mozilla-central/rev/7b3f3fb5fd2cad8f348131498a35a91bef68b47b/browser/components/extensions/child/ext-devtools-panels.js#91-98)

... but the internal shown event is never passed a window:
https://searchfox.org/mozilla-central/rev/7b3f3fb5fd2cad8f348131498a35a91bef68b47b/browser/components/extensions/child/ext-devtools-panels.js#156-158

  recvInspectorSidebarShown() {
    // TODO: wait and emit sidebar contentWindow once sidebar.setPage is supported.
    this.emit("shown");

The setPage method was added later in bug 1398734.

Luca: do you recall why the window is missing? Can this be fixed easily?