Add C# source generator for ScriptPathAttribute

[neikeq]

This source generator adds a newly introduced attribute, ScriptPath to all classes that:

• Are top-level classes (not inner/nested).
• Have the partial modifier.
• Inherit Godot.Object.
• The class name matches the file name.

A build error is thrown if the generator finds a class that meets these conditions but is not declared partial, unless the class is annotated with the DisableGodotGenerators attribute.

We also generate an AssemblyHasScripts assembly attribute which Godot uses to get all the script classes in the assembly, eliminating the need for Godot to search them. We can also avoid searching in assemblies that don't have this attribute. This will be good for performance in the future once we support multiple assemblies with Godot script classes.

This is an example of what the generated code looks like:

using Godot;
namespace Foo {
	[ScriptPathAttribute("res://Player.cs")]
	// Multiple partial declarations are allowed
	[ScriptPathAttribute("res://Foo/Player.cs")]
	partial class Player {}
}

[assembly:AssemblyHasScripts(new System.Type[] { typeof(Foo.Player) })]

The new attributes replace script metadata which we were generating by determining the namespace of script classes with a very simple parser.
This fixes several issues with the old approach related to parser errors and conditional compilation.
It also makes the task part of the MSBuild project build, rather than a separate step executed by the Godot editor.

[neikeq]

NOTE: We use CompilerVisibleProperty to expose MSBuild properties to our source generator. Rider doesn't support this yet:
https://youtrack.jetbrains.com/issue/RIDER-55242
https://youtrack.jetbrains.com/issue/RIDER-58080

I found no problems with VSCode's C# (OmniSharp) extension.

[akien-mga]

To fix the clang-format issues, you likely need to update your local version to clang-format 11 (they changed the logic for alignment of ternary operators in that version, going from "bad" to "still bad but different"...).

[neikeq]

I don't get it, I have the black format precommit hook (version is the same as in the CI)...

[akien-mga]

Try to run it manually with black -l 120 path/to/files. I think the pre-commit hook might fail in some circumstance (e.g. git commit --amend).

[neikeq]

Try to run it manually with black -l 120 path/to/files.

Thanks, that did it.

I think the pre-commit hook might fail in some circumstance (e.g. git commit --amend).

I was suspicious of git commit --amend being the problem and thus tried a soft reset and re-commit, yet same problem.

[akien-mga]

Is it intended to have version 4.0.0-dev4 instead of 4.0.0-dev1?

[aaronfranke]

Yes, since these are the versions of each package, dev1 to dev3 have already been used. It does seem a bit strange that they're out of sync, so maybe the source generators package should just start at 4.0.0-dev4.

[neikeq]

For stable releases they should be the same version, but during development there will be new additions to the source generator while the Sdk may remain the same. Technically we can release an unchanged new version of the Sdk to keep the version in sync with the other package, but that doesn't feel right. The only case where that would be appropriate is when going from rc to stable without changes in the packages.

[akien-mga]

Thanks!