Make upgrading Godot remove existing .mono and .import directories.

[Sslaxx]

Godot version: Since the .mono and .import directories were added.

OS/device including version: N/A

Issue description: With newer versions of Godot (especially upgrades such as 3.1 to 3.2), .mono (and sometimes .import) directories, being left untouched, cause issues when building/running/exporting projects that have been upgraded from a previous version. Some mechanism for newer versions of Godot to detect this and remove the .mono and/or .import directories as required would be useful.

[neikeq]

I don't know about .import/.

For quite some time now Godot has been configured not to break when upgrading due to old .mono/. If that's not the case, please file a bug report.

[Sslaxx]

This is a bug report.

This is an issue because 3.2 will be using Mono 6.6; 3.1 (and earlier) project assemblies will therefore not work as-is if upgraded to 3.2.

From Discord:
Me
Define "work".

@akien-mga
Doesn't doesn't work :)
You can open the editor, compile a project and run it, export a project and run it.

Me
Under Win10, editor works, projects compile/run. About to try exporting.
Exporting gives an error dialogue.
"Failed to export C# project: null".

akien
So far I tried:

• Linux 64-bit editor works.
• WebAssembly debug export works (from Linux).
• Android export fails. I found out why, so I'm working on a fix for it and I'll reupload the export templates before releasing.
  Hm, I had this export error on Windows 10 in test builds, but this beta 4 is supposed to have this issue fixed :( Maybe it's another additional issue.

Me
Removing the .mono directory appears to fix the issue I had.

akien
Does the exported binary work nevertheless?

Me
Trying it now...
And it works.
Didn't try the exported binary before I removed the .mono directory, note.
Honestly, I'd have a new version of Godot always remove the .mono directory beforehand.

[neikeq]

Is the bug only the Failed to export C# project: Null error? I was discussing this one with Akien yesterday. I'll try to reproduce and fix it tomorrow, but I doubt it has anything to do with the .mono/ folder.

[neikeq]

#34464 fixes the Failed to export C# project: Null error.

[aaronfranke]

Some mechanism for newer versions of Godot to detect this

I could possibly add this to #31171 (for 4.0+). "Open anyway? All files will be re-imported."

Also, it would be nice to have #23368 solved first since these folders may be renamed.

[neikeq]

If there's any bug related to the .mono folder when upgrading, please open a new issue describing it.

[eyeEmotion]

I've got a similar issue. Using Godot Mono vers. 3.2.1 When my game is build to an exe, the game sometimes gets issues it doesn't have when testing it in Godot itself.
Other days I was able to export without an error message, or maybe another Godot window got focus so I didn't get to see the error message, but today I get them all the time. Although my game is still being exported. But I'm wondering if this error is the reason why my game is getting these glitches sometimes?

The error I get is : "Failed to export C# project" - Could not find file "path\to\my\project\.mono\metadata\scripts_metadata.release".
The export templates I have, were directly downloaded and installed from within Godot Mono itself.