Incorrect dynamic Field asset upload folder results in "Could not resolve the subpath"

[kr37]

Description

This is not a huge problem, just an ungraceful degradation relating to bad user input.

When adding a field to a global set, the control panel gives an error: Could not resolve the subpath "branding/{siteHandle}"

The immediate solution (for me) was to correct to branding/{site} and it works fine, but I thought you'd want craft to check for this more gracefully.

Steps to reproduce

1. Create a field with type 'asset', and set the upload folder incorrectly, such as branding/{siteHandle}
2. On Settings->Globals, add the field and try to save. An error will be displayed.

Additional info

craft\errors\InvalidSubpathException: Could not resolve the subpath “branding/{siteHandle}”. in /var/www/craft3/vendor/craftcms/cms/src/fields/Assets.php:542
Stack trace:
#0 /var/www/craft3/vendor/craftcms/cms/src/fields/Assets.php(626): craft\fields\Assets->_resolveVolumePathToFolderId('folder:1', 'branding/{siteH...', Object(craft\elements\GlobalSet), true)
#1 /var/www/craft3/vendor/craftcms/cms/src/fields/Assets.php(278): craft\fields\Assets->_determineUploadFolderId(Object(craft\elements\GlobalSet))
#2 /var/www/craft3/vendor/craftcms/cms/src/base/Element.php(1723): craft\fields\Assets->afterElementSave(Object(craft\elements\GlobalSet), false)
#3 /var/www/craft3/vendor/craftcms/cms/src/services/Elements.php(459): craft\base\Element->afterSave(false)
#4 /var/www/craft3/vendor/craftcms/cms/src/services/Globals.php(282): craft\services\Elements->saveElement(Object(craft\elements\GlobalSet), false)
#5 /var/www/craft3/vendor/craftcms/cms/src/controllers/GlobalsController.php(82): craft\services\Globals->saveSet(Object(craft\elements\GlobalSet))
#6 [internal function]: craft\controllers\GlobalsController->actionSaveSet()
#7 /var/www/craft3/vendor/yiisoft/yii2/base/InlineAction.php(57): call_user_func_array(Array, Array)
#8 /var/www/craft3/vendor/yiisoft/yii2/base/Controller.php(157): yii\base\InlineAction->runWithParams(Array)
#9 /var/www/craft3/vendor/craftcms/cms/src/web/Controller.php(74): yii\base\Controller->runAction('save-set', Array)
#10 /var/www/craft3/vendor/yiisoft/yii2/base/Module.php(528): craft\web\Controller->runAction('save-set', Array)
#11 /var/www/craft3/vendor/craftcms/cms/src/web/Application.php(237): yii\base\Module->runAction('globals/save-se...', Array)
#12 /var/www/craft3/vendor/craftcms/cms/src/web/Application.php(445): craft\web\Application->runAction('globals/save-se...', Array)
#13 /var/www/craft3/vendor/craftcms/cms/src/web/Application.php(221): craft\web\Application->_processActionRequest(Object(craft\web\Request))
#14 /var/www/craft3/vendor/yiisoft/yii2/base/Application.php(386): craft\web\Application->handleRequest(Object(craft\web\Request))
#15 /var/www/html/index.php(24): yii\base\Application->run()
#16 {main}

• Craft version: Personal 3.0.0-RC14
• PHP version: 7.1.15
• Database driver & version: MySQL 5.5.59
• Plugins & versions: Redactor 1.0.1 (Pixel & Tonic), Importable 1.0.1 (Mark Drzycimski), Amazon S3 1.0.8 (Pixel & Tonic), Calendar Links 1.0.0 (Superbig), Wordsmith 3.0.2 (Michael Rog), Environment Label 3.1.2 (Top Shelf Craft (Michael Rog))
  Domain: http://localhost

[andris-sevcenko]

Since the actual subpath resolution happens after the element has been saved, it's not possible to add any validation errors or bail out of global set (which is an element) saving.

So, throwing an exception is the most appropriate way - if it looked like the global set had saved and an error message (which would be hacky to add), was not noticed, it might be pretty misleading to the user.

Taking all of that into account, it's probably best to leave the behavior as it is currently.