Add support for external editors with Mono/C#/.NET and/or document how to enable them

[Zishan-Rahman]

Essentially the same as flathub/org.godotengine.GodotSharp#2, but for this Godot 3 C# Flatpak instead of the Godot 4 C# Flatpak.

The suggestions from the Godot 4 C# Flatpak's relevant issue made here and here could be relevant to this Flatpak too.

[geekley]

See flathub/org.godotengine.GodotSharp#2 (comment)

The corresponding scripts for Godot3Sharp are slightly different. That's because there's no editor setting for custom exec and args in Godot 3. So the user is instead instructed to create a wrapper script in the PATH if they need the program to run in some custom way (e.g. Flatpak VSCode, etc).

/app/bin/code

#!/usr/bin/sh
flatpak-spawn --host code "$@" && exit
zenity --name='godot_editor' --class='godot' --error --title='Godot: Mono External Editor' \
	--window-icon="/app/share/icons/hicolor/scalable/apps/org.godotengine.Godot3Sharp.svg" \
	--no-wrap --text="\
Trying to run external editor <b>VS Code</b> failed: EXIT_STATUS=$?.
Ensure the <b>code</b> program is available outside Flatpak via command line.

Or provide a custom script for it in <b>~/.local/bin/code</b>, e.g.:
<i>#!/usr/bin/sh
flatpak run com.visualstudio.code \"\$@\"</i>

You can also disable this editor setting to use the internal script editor:
<b>mono/editor/external_editor</b>"

/app/bin/monodevelop

#!/usr/bin/sh
flatpak-spawn --host monodevelop "$@" && exit
zenity --name='godot_editor' --class='godot' --error --title='Godot: Mono External Editor' \
	--window-icon="/app/share/icons/hicolor/scalable/apps/org.godotengine.Godot3Sharp.svg" \
	--no-wrap --text="\
Trying to run external editor <b>MonoDevelop</b> failed: EXIT_STATUS=$?.
Ensure the <b>monodevelop</b> program is available outside Flatpak via command line.

Or provide a custom script for it in <b>~/.local/bin/monodevelop</b>, e.g.:
<i>#!/usr/bin/sh
/path/to/monodevelop \"\$@\"</i>

You can also disable this editor setting to use the internal script editor:
<b>mono/editor/external_editor</b>"

[Zishan-Rahman]

See flathub/org.godotengine.GodotSharp#2 (comment).

Given the lack of specific editor settings for Mono/C# in Godot 3, I'm more willing to entertain the idea of custom wrapper scripts here. There has to be other ways to solve this issue, though.

[geekley]

Well, if it serves as a motivation, Unity Hub's flatpak uses a wrapper script for code too (that's where I got the idea from).

But theirs needs to be much more complex because it also handles this:

In order for debugging to work, the Unity Debugger VS Code extension needs to be able to find Unity Editor's PID.

Mine is much simpler because tbh I didn't even try to use VSCode debugging with Godot (I don't even know if I can, or if Flatpak causes any issues). I know VSCode's GDScript connects to Godot-flatpak's port just fine, so I just assumed C# debugging wouldn't be an issue I guess. But it's worth testing that, in and out of Flatpak.

There has to be other ways to solve this issue, though.

IMO the most ideal way would be for it to be solved upstream, where Godot's code would detect if it's inside a flatpak by the presence of /usr/bin/flatpak-spawn and do any necessary workarounds directly in the editor's code.