[.NET] Avoid heap alloc when using StringNames as key in a Dictionary

[fLindahl]

StringNames in Godot C# are IEquatable, and overrides GetHashCode(), which calls godot_string_name.movable's version of that method, which was not overridden. This led to heap allocations when e.g. calling the indexer in a Dictionary with StringName type as Key.

This PR just adds the (assuming) missing method, which seems to fix the issue.

[raulsntos]

Thanks for contributing to the .NET module!

The movable types are only meant to be used to store them in classes (like StringName) where we can't store ref structs. None of them implement any API other than for conversion. So I think it was intentional to not implement GetHashCode.

However, as you noticed, we likely meant to call the godot_string_name.GetHashCode method (which is implemented) from the StringName.GetHashCode implementation. So the fix should be something like this:

diff --git a/modules/mono/glue/GodotSharp/GodotSharp/Core/StringName.cs b/modules/mono/glue/GodotSharp/GodotSharp/Core/StringName.cs
index 21d9ada127..a28230636f 100644
--- a/modules/mono/glue/GodotSharp/GodotSharp/Core/StringName.cs
+++ b/modules/mono/glue/GodotSharp/GodotSharp/Core/StringName.cs
@@ -161,7 +161,7 @@ namespace Godot
 
         public override int GetHashCode()
         {
-            return NativeValue.GetHashCode();
+            return NativeValue.DangerousSelfRef.GetHashCode();
         }
     }
 }

[fLindahl]

The movable types are only meant to be used to store them in classes (like StringName) where we can't store ref structs. None of them implement any API other than for conversion. So I think it was intentional to not implement GetHashCode.

That makes sense! I removed the GetHashCode method from movable and changed StringName to use the existing version in godot_string_name instead. Thanks!

[raulsntos]

Looks good to me, thanks!

[clayjohn]

Looks great! The final step before merging is to squash all the commits together so that the whole PR only contains 1 big commit with all your changes. We like to merge one commit at a time to keep the git history clean and navigable.

If you don't know how to do that, we have a helpful tutorial in the official documentation https://docs.godotengine.org/en/latest/community/contributing/pr_workflow.html#the-interactive-rebase