src/vs/workbench/common/contextkeys.ts/ResourceContextKey/_setLangId
class ResourceContextKey:	private _setLangId(): void {
		const value = this.get();
		if (!value) {
			this._langIdKey.set(null);
			return;
		}
		const langId = this._modelService.getModel(value)?.getLanguageId() ?? this._languageService.guessLanguageIdByFilepathOrFirstLine(value);
		this._langIdKey.set(langId);
	}