Error CS0246: Are you missing a using directive or an assembly reference?

[NickVas]

Backstory:
I was trying to implement Unity Push Notifications SDK, messing with analytics and firebase… something went wrong, and I’ve got this error first:

Package com.unity.render-pipelines.lightweight@2.0.3-preview has invalid dependencies:
com.unity.render-pipelines.core: Version [2.0.3-preview] is incompatible with the selected version [2.0.0-preview]
One or more packages could not be added to the local file system:
com.unity.render-pipelines.core: Package [com.unity.render-pipelines.core@2.0.0-preview] cannot be found

Next: I’ve found on web that to resolve that I can go Help > Reset Packages to defaults
(I’m working with Plastic SCM - so I relied on it, thinking I can restore everything back anyway) so I pressed on it… and got 200+ errors, like this:

Assets/_DEV/Scripts/LevelsScripts/LevelController.cs(37,12): error CS0246: The type or namespace name 'TextMeshProUGUI' could not be found (are you missing a using directive or an assembly reference?)

I’ve tried to revert my game using version control…but the errors not gone (how can it be?)

Tried to remove manifest.json and packages-lock.json files, so Unity can rebuild them - didn’t help.

Opened another unity project - there is everything ok.

I’m still noob with Unity… tried to resolve this by my self, searching web - without a result…

[NickVas]

[Kurt-Dekker]

At a minimum you need to doublecheck you have TextMeshPro in game.

Here’s more things to check:

Extra unwanted packages in new projects (collab, testing, rider and other junk):

Temp/UnityEngine.TestRunner.dll Error

Recent versions of unity have an annoying habit of crapping useless packages into your project. When those packages inevitably have errors, this sort of thing happens. I have railed about it before. Go into the package manager and remove crap you don’t need, like the entire test runner and collab and whatnot. If you feel brave you can hand-edit the Packages/manifest.json file a lot faster than using the laggy package manager interface that only lets you remove one package at a time: [7287748-…

About the fastest way I have found to make a project and avoid all this noise is to create the project, then as soon as you see the files appear, FORCE-STOP (hard-kill) Unity (with the Activity Manager or Task Manager), then go hand-edit the Packages/manifest.json file as outlined in the above post, then reopen Unity.

Sometimes the package system gets borked from all this unnecessary churn and requires the package cache to be cleared:

Unity3D Package Cache errors(?)

[NickVas]

I’ve re-imported packages…and problem solved!