More flexible submenus?

[krassowski]

Currently, the menu widgets are either:

• commands,
• separators, or
• submenus

however, the developer API is not as convenient to use for submenus as it is for commands. For example, one can create a callback for a command to be asked about its visibility (isVisible) or state (isEnabled), but this does not seem to be possible for submenus:

lumino/packages/widgets/src/menu.ts

Lines 1871 to 1879 in 77ec35c

	get isVisible(): boolean {
	if (this.type === 'command') {
	return this._commands.isVisible(this.command, this.args);
	}
	if (this.type === 'submenu') {
	return this.submenu !== null;
	}
	return true;
	}

Lack of callbacks also means that the we do not have an easy way to:

• dynamically change the name of the submenu
• dynamically generate its content

This led me to use some quirky workarounds when implementing spellcheck suggestions.

One lazy way of getting what I want would be (pseudo-code follows):

type ItemType = 'command' | 'submenu' | 'separator' | 'subcommand';    // ← added

IItemOptions: {
    type?: ItemType;
    command?: string;
    args?: ReadonlyJSONObject;
    submenu?: Menu | null;
    subcommand?: string;   // ← added
}

this.app.commands.addCommand(
    'spellchecker:suggestions',
   {
        label: () => anySuggestions() ? 'Adjust to' : 'No suggestions',
        isEnabled: () => anySuggestions(),
        /* provides the menu items options; command defaults to subcommand */
        execute: () => getSuggestions().map(suggestion => {args: {name: suggestion}}) as IItemOptions[],
   }
)

this.app.commands.addCommand(
    'spellchecker:use-suggestion',
   {
        label: (args) => args.name as string,
        execute: (args) => replaceToken(args.name as string),
   }
)

this.app.contextMenu.addItem({
    selector: '.cm-spell-error',
    command: 'spellchecker:suggestions',
    subcommand: 'spellchecker:use-suggestion',
    type: 'subcommand'
});

Not sure how good it would be; the trick with re-using execute seems elegant but sadly the type checking would not be of much use here... Unless we would have additional addSubCommand method with items instead of execute.

Also, if I am the only one struggling with this it might not be worth introducing extra complexity.