File editor extension does not add a launcher card when a spec is added after launch

[jtpio]

Description

Currently the @jupyterlab/fileeditor-extension adds new cards to the launcher for some known types to create new Python, R and Julia files:

jupyterlab/packages/fileeditor-extension/src/index.ts

Lines 392 to 406 in 7160c30

	// Use available kernels to determine which common file types should have 'Create New' options in the Launcher, File Editor palette, and File menu
	const getAvailableKernelFileTypes = async (): Promise<Set<IFileTypeData>> => {
	const specsManager = app.serviceManager.kernelspecs;
	await specsManager.ready;
	let fileTypes = new Set<IFileTypeData>();
	const specs = specsManager.specs?.kernelspecs ?? {};
	Object.keys(specs).forEach(spec => {
	const specModel = specs[spec];
	if (specModel) {
	const exts = commonLanguageFileTypeData.get(specModel.language);
	exts?.forEach(ext => fileTypes.add(ext));
	}
	});
	return fileTypes;
	};

This function is used here in the plugin:

jupyterlab/packages/fileeditor-extension/src/index.ts

Lines 568 to 592 in 7160c30

	getAvailableKernelFileTypes()
	.then(availableKernelFileTypes => {
	if (launcher) {
	Commands.addKernelLanguageLauncherItems(
	launcher,
	trans,
	availableKernelFileTypes
	);
	}
	if (palette) {
	Commands.addKernelLanguagePaletteItems(
	palette,
	trans,
	availableKernelFileTypes
	);
	}
	if (menu) {
	Commands.addKernelLanguageMenuItems(menu, availableKernelFileTypes);
	}
	})
	.catch((reason: Error) => {
	console.error(reason.message);
	});

However it does not react to specs added later via the specsChanged signal. So only the notebook and console sections are correctly updated when a new spec is available.

Reproduce

1. Uninstall ipykernel
2. Start JupyterLab. The launcher does not have a way to create Python files and notebooks
3. Install ipykernel
4. Wait for the kernel specs to automatically refresh
5. Only the notebook and console sections have the python card

jupyterlab-dynamic-launcher-card-python.mp4

Expected behavior

The "Other" category should also have the Python card after the specs have been refreshed.

Context

Noticed downstream in jupyterlite/jupyterlite#1642 (via jupyterlite/pyodide-kernel#177) with the Pyodide kernel being added after the launcher plugin has been activated.

[jtpio]

For reference the notebook extension properly handles new kernel specs:

jupyterlab/packages/notebook-extension/src/index.ts

Lines 2017 to 2056 in 7160c30

	// Add a launcher item if the launcher is available.
	if (launcher) {
	void services.ready.then(() => {
	let disposables: DisposableSet | null = null;
	const onSpecsChanged = () => {
	if (disposables) {
	disposables.dispose();
	disposables = null;
	}
	const specs = services.kernelspecs.specs;
	if (!specs) {
	return;
	}
	disposables = new DisposableSet();
	for (const name in specs.kernelspecs) {
	const rank = name === specs.default ? 0 : Infinity;
	const spec = specs.kernelspecs[name]!;
	const kernelIconUrl =
	spec.resources['logo-svg'] || spec.resources['logo-64x64'];
	disposables.add(
	launcher.add({
	command: CommandIDs.createNew,
	args: { isLauncher: true, kernelName: name },
	category: trans.__('Notebook'),
	rank,
	kernelIconUrl,
	metadata: {
	kernel: JSONExt.deepCopy(
	spec.metadata || {}
	) as ReadonlyJSONValue
	}
	})
	);
	}
	};
	onSpecsChanged();
	services.kernelspecs.specsChanged.connect(onSpecsChanged);
	});
	}