A hash table can only be added to another hash table about datum

[gaelcolas]

[edited]
So to the comment/question: "hash table can only be added to another hash table"
Yes, that's by design, otherwise you can't really predict how it should behave...
If it's different type (broad types, i.e. Key/Name collections/Scalar/arrays of scalar), the reference object should be used...

I will now have a look at the branch you mention (just wanted to edit my comment)

[gaelcolas]

Yep, that's a bug.

[gaelcolas]

Oh, and surprise, it seems to be an issue with the cache... That's why it was so hard to consistently reproduce!
If you look closely, the RSOP are generated fine, but the compilation fails...
If you load a fresh datum structure and tries the lookup -PropertyPath 'FilesAndFolders' -Node $Node -DatumTree $Datum it works fine...

Then try to build.ps1 (leave it to fail) and then try again that line above... it fails.
Reset the cache of the Datum module:

$m = get-module datum
&$m { $script:FileProviderDataCache = $null }
lookup -PropertyPath 'FilesAndFolders' -Node $Node -DatumTree $Datum

Now it works again...

Definitely a bug, look for the root cause, probably in the cache. Will let you know when I get an idea how to fix this...

[gaelcolas]

More specifically, it's the cache for the FileServer Role.
When it works it looks like this:

PS C:\src\DscWorkshop\DscSample> &$m { $script:FileProviderDataCache['C:\src\DscWorkshop\DscSample\DSC_ConfigData\Roles\FileServer.yml'].value.FilesAndFolders.items.ToString() }
System.Object[]

When it fails:

PS C:\src\DscWorkshop\DscSample> &$m { $script:FileProviderDataCache['C:\src\DscWorkshop\DscSample\DSC_ConfigData\Roles\FileServer.yml'].value.FilesAndFolders.items.ToString() }System.Collections.Generic.List`1[System.Object]

I wonder when this is getting "corrupted"...

Most likely, there's a Write-Output somewhere (might be implicit), that is not using -NoEnumerate.

[gaelcolas]

I've got a quick fix for that issue (I think).
Hit me up on Skype when you're available.

[gaelcolas]

Have a look there:
https://ci.appveyor.com/project/gaelcolas/datum/builds/21791313/artifacts
Unzip in your BuildOutput\modules of your project and rebuild without a resolve-dependency.

That should fix it.

[raandree]

Thanks @gaelcolas, I came up with a similar thing but did not really understand why ForEach-Object refreshed the $_ variable while .ForEach did not. do you know what happens inside of PowerShell here?

[gaelcolas]

Not really...
Even when the array was empty it was calling the Foreach method, but because there was no item, $_ did get updated with the current collection's item (should have been $null), so it used a parent loop's $_, being a scalar... That you can't merge with a hashtable...

Very weird, but I've seen that before. Just never bothered going down that rabbit hole... a bit of a shame as sending stuff through the pipeline has a cost and the Foreach method is meant to be faster, but those are rarely big merges so the impact should be minimal, even for big configs.

Those part are due for a re-write anyway, just not my priority for now as we discussed previously.

[raandree]

If you have concerns about performance, let's use the foreach keyword instead of Foreach-Object cmdlet. This should not be much slower than .foreach.