extensions/css-language-features/client/src/customData.ts/collect
function getCustomDataPathsInAllWorkspaces(): string[] {
	const workspaceFolders = workspace.workspaceFolders;

	const dataPaths: string[] = [];

	if (!workspaceFolders) {
		return dataPaths;
	}

	const collect = (paths: string[] | undefined, rootFolder: Uri) => {
		if (Array.isArray(paths)) {
			for (const path of paths) {
				if (typeof path === 'string') {
					dataPaths.push(Utils.resolvePath(rootFolder, path).toString());
				}
			}
		}
	};

	for (let i = 0; i < workspaceFolders.length; i++) {
		const folderUri = workspaceFolders[i].uri;
		const allCssConfig = workspace.getConfiguration('css', folderUri);
		const customDataInspect = allCssConfig.inspect<string[]>('customData');
		if (customDataInspect) {
			collect(customDataInspect.workspaceFolderValue, folderUri);
			if (i === 0) {
				if (workspace.workspaceFile) {
					collect(customDataInspect.workspaceValue, workspace.workspaceFile);
				}
				collect(customDataInspect.globalValue, folderUri);
			}
		}

	}
	return dataPaths;
}