Add C# source generator for a new ScriptPath attribute

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.

1 files changed, 17 insertions, 7 deletions

diff --git a/modules/mono/build_scripts/godot_net_sdk_build.py b/modules/mono/build_scripts/godot_net_sdk_build.py
index 3bfba0f0f6..8c5a60d2db 100644
--- a/modules/mono/build_scripts/godot_net_sdk_build.py
+++ b/modules/mono/build_scripts/godot_net_sdk_build.py
@@ -21,6 +21,18 @@ def build_godot_net_sdk(source, target, env):
     # No need to copy targets. The Godot.NET.Sdk csproj takes care of copying them.
 
 
+def get_nupkgs_versions(props_file):
+    import xml.etree.ElementTree as ET
+
+    tree = ET.parse(props_file)
+    root = tree.getroot()
+
+    return {
+        "Godot.NET.Sdk": root.find("./PropertyGroup/PackageVersion_Godot_NET_Sdk").text.strip(),
+        "Godot.SourceGenerators": root.find("./PropertyGroup/PackageVersion_Godot_SourceGenerators").text.strip(),
+    }
+
+
 def build(env_mono):
     assert env_mono["tools"]
 
@@ -30,14 +42,12 @@ def build(env_mono):
 
     module_dir = os.getcwd()
 
-    package_version_file = os.path.join(
-        module_dir, "editor", "Godot.NET.Sdk", "Godot.NET.Sdk", "Godot.NET.Sdk_PackageVersion.txt"
-    )
-
-    with open(package_version_file, mode="r") as f:
-        version = f.read().strip()
+    nupkgs_versions = get_nupkgs_versions(os.path.join(module_dir, "SdkPackageVersions.props"))
 
-    target_filenames = ["Godot.NET.Sdk.%s.nupkg" % version]
+    target_filenames = [
+        "Godot.NET.Sdk.%s.nupkg" % nupkgs_versions["Godot.NET.Sdk"],
+        "Godot.SourceGenerators.%s.nupkg" % nupkgs_versions["Godot.SourceGenerators"],
+    ]
 
     targets = [os.path.join(nupkgs_dir, filename) for filename in target_filenames]