Versioned::use_session Fallback breaks page editing

[Cheddam]

The use_session fallback introduced in SilverStripe 4.2 is intended to maintain the existing behaviour of the framework / CMS, by storing the stage in the session as before.

When this fallback is enabled and silverstripe-versioned-admin is installed (as a dependency of silverstripe-elemental in my case), attempting to open a page for editing in the CMS results in the following error:

[Emergency] Uncaught InvalidArgumentException: Invalid stage name ""
GET /admin/pages/edit/show/9018
Line 160 in /var/www/mysite/www/vendor/silverstripe/versioned/src/ReadingMode.php

Source
151 
152     /**
153      * Validate the stage is valid, throwing an exception if it's not
154      *
155      * @param string $stage
156      */
157     public static function validateStage($stage)
158     {
159         if (!in_array($stage, [Versioned::LIVE, Versioned::DRAFT])) {
160             throw new InvalidArgumentException("Invalid stage name \"{$stage}\"");
161         }
162     }
163 }
Trace
SilverStripe\Versioned\ReadingMode::validateStage() 
Versioned.php:2148
SilverStripe\Versioned\Versioned::set_stage() 
HistoryControllerFactory.php:35
SilverStripe\VersionedAdmin\Controllers\HistoryControllerFactory->create(SilverStripe\CMS\Controllers\CMSPageHistoryController, Array) 
Injector.php:585
SilverStripe\Core\Injector\Injector->instantiate(Array, SilverStripe\CMS\Controllers\CMSPageHistoryController, singleton) 
Injector.php:993
SilverStripe\Core\Injector\Injector->getNamedService(SilverStripe\CMS\Controllers\CMSPageHistoryController, 1, Array) 
Injector.php:946
SilverStripe\Core\Injector\Injector->get(SilverStripe\CMS\Controllers\CMSPageHistoryController) 
LeftAndMain.php:290
SilverStripe\Admin\LeftAndMain->getCombinedClientConfig() 
LeftAndMain.php:673
SilverStripe\Admin\LeftAndMain->init() 
CMSMain.php:179
...

This issue can be temporarily alleviated by appending the stage to the URL (e.g. ?stage=Stage).

A somewhat similar issue with the asset-admin module has been raised here.

[robbieaverill]

@Cheddam could you add steps to reproduce please?

[Cheddam]

@robbieaverill Slightly trickier than I'd thought:

1. Fresh install of SS 4.2 + Elemental 3
2. Add Elemental <-> Page config and use_session setting to app/_config/mysite.yml:

Page:
  extensions:
    - DNADesign\Elemental\Extensions\ElementalPageExtension

SilverStripe\Versioned\Versioned:
  use_session: true

3. dev/build, open CMS
4. Open a page and edit it... switch between different pages for a bit until you get the first 500 response
5. Observe constant 500s from page edit view loads unless a stage GET param is passed

[robbieaverill]

Thanks!

[dhensby]

Yeah, we became a lot less forgiving with stage names in that fix, I think... which has caused a little bit of pain here and there.

[ScopeyNZ]

We fixed a bunch of issues with tests that threw this exception after the 4.2 release. This section:

https://github.com/silverstripe/silverstripe-versioned-admin/blob/master/src/Controllers/HistoryControllerFactory.php#L32-L35

Will need to use SiteTree::get_one_by_stage instead... I'll PR this tomorrow unless somebody beats me to it.

[ScopeyNZ]

PR at #52