Allow creating GDExtension plugins from inside the Godot editor

[aaronfranke]

This PR implements godotengine/godot-proposals#3367 and godotengine/godot-proposals#9306 (not exactly as the proposals describe, but solves the same problem).

The status quo for GDExtension development is really unfortunate. For the most part the only easy way to get started is to edit the GDExtension template project, or copy-paste an existing GDExtension project and use it as a template. If you don't do this, you'd need to follow the documentation, which is a massive behemoth that manually explains to the user how to create each file from scratch, and it would take a user hours to follow this guide.

Really, I believe it should be as simple as making a GDScript plugin:

• Click a button to open a wizard to make an extension.
• Give your extension a name.
• Select a language from the dropdown menu.
• Click Create.

This is what this PR implements. Just go into Project Settings -> GDExtension:

Next, click Create GDExtension, type in a base name, click "Create", and then it will create and compile an extension.

The library name and path are optional. If you do not specify these, they will be determined automatically.

The dialog includes hover tooltips if you hover over the boxes, which explain what each field is and what the values you write in it should be.

The language system is designed to be completely language-agnostic. The dialogs have no clue about the existence of C++ or SCons. All of the C++ and SCons specific code is isolated in one class, and in the future we can allow editor plugins to extend this. It's not exposed as of this PR in case we want to iterate on the internal code first, but we can expose it whenever, preferably in a future PR to avoid this one becoming too big.

As mentioned by proposal godotengine/godot-proposals#3367, this sets up the build system with a build command (scons), the .gitignore files, the .gdextension file, the type registration boilerplate, and it even git clones godot-cpp. By default, it will also initiate scons to compile the extension, but this does take awhile, so you can skip this step by unchecking the "Compile now?" box.

Note that this PR does not include setting up system-level dependencies, such as installing a C++ compiler, installing Git, installing SCons, etc. This varies widely by operating system and it would be a slippery slope to try and have that. This PR is purely focused on the files that go in your project, not the system-wide dependencies. This PR does not try to detect a C++ compiler, but it will warn the user if either Git or SCons is not found on their system.

When you create a GDExtension plugin with this PR, one example node is provided called ExampleNode. Like the Blender default cube, this is expected to be replaced by users as soon as possible. However, its existence is useful to both new and experienced users, since it serves 2 functions: 1) As a reference for how to make a node type, including the code, registration, docs, icon, etc, and 2) A minimal test to check if your GDExtension plugin works (don't see it in the editor? It's not working).

Assuming you have the system-wide dependencies installed, and you leave the "Compile now?" checkbox enabled, and you wait for it to finish, the extension immediately works. No fuss, the example node is just there.

Assuming it was compiled, it will show up in a list of GDExtensions. This list will contain every loaded GDExtension, regardless of whether it was been created by the create dialog. It gets this list from GDExtensionManager, so it will not include any non-compiled or otherwise broken extensions.

If you change the code, you just need to run scons in either the extension folder or the project root. A future idea would be to detect this in projects and provide a "Build" button in the editor UI like we already do for C#, but that is technically separate from what this PR does.

The files look like this:

The SConstruct at the project root is extremely barebones, it is only one line to call into another SConstruct. It is designed to be simple enough so that more GDExtension plugins can be added to the same Godot project with no manual work. The _ensure_file_contains helper function in this PR completely handles the merging of more calls into this file. You can just make 2 plugins back-to-back with no conflicts. If you want to have 20 GDExtension plugins, this PR will let you do that just fine, with one call to scons in the root folder able to compile all of them at once.

This PR provides 2 options for making a GDExtension plugin: "C++ with SCons, GDExtension only" or "C++ with SCons, GDExtension and engine module". The former creates a standalone GDExtension C++ plugin, with the only files stored in the root of the project being a .gitignore and barebones SConstruct.

The engine module option provides a few more files like SCsub and config.py, provides lots of #ifdef directives to support both GDExtensions and modules, and places most of the C++ code in the root of the folder, which is more suitable for making a Godot engine module. This way if users want to target both GDExtension and modules with one codebase, they can do this as easily as selecting it from the dropdown. This option turns the project's root folder into a module, so only one module is allowed per project.

When in this mode, you can either compile for GDExtension the same as with the "only" option, or you can copy-paste the entire Godot project into the engine modules folder, naming the folder the same as the addon folder name, and it works.

The source files are designed to handle the extension+module case, but are automatically simplified by this PR's project generator when making a non-module extension, including by looking at the #if preprocessor directives to determine which lines of code to exclude.

In the extension list, you can click the pencil button on any of these items to open a menu to edit the GDExtension.

Like the create dialog, the dialog includes hover tooltips which describe each field. However, for the Libraries and Icons fields, the hover tooltips are placed on the Label nodes instead of the Dictionary editors.

---

EDIT: This PR has changed a lot since first opening. For the record, here's the old PR description:

This PR implements godotengine/godot-proposals#3367 (not exactly as that proposal describes, but solves the same problem).

The status quo for GDExtension development is really unfortunate. For the most part the only easy way to get started is to copy-paste an existing GDExtension project and use it as a template. If you don't do this, you'd need to follow the documentation, which is a massive behemoth that manually explains to the user how to create each file from scratch, and it would take a user hours to follow this guide.

Really, I believe it should be as simple as making a GDScript plugin:

• Click a button to open a wizard to make a plugin.
• Give your plugin a name.
• Select GDExtension from the dropdown menu (only step added compared to GDScript plugins).
• Click Create.

This is what this PR implements. Just go into Project Settings -> Plugins, click Create New Plugin, and select GDExtension.

As mentioned by proposal godotengine/godot-proposals#3367, this sets up the build system with a build command (scons), the .gitignore files, the .gdextension file, the type registration boilerplate, and it even git clones godot-cpp. By default, it will also initiate scons to compile the extension, but this does take awhile, so you can skip this step by unchecking the "Compile now? (slow)" box.

Note that this PR does not include setting up system-level dependencies, such as installing a C++ compiler, installing Git, installing SCons, etc. This varies widely by operating system and it would be a slippery slope to try and have that. This PR is purely focused on the files that go in your project, not the system-wide dependencies. This PR does not try to detect a C++ compiler, but it will warn the user if either Git or SCons is not found on their system.

When you create a GDExtension plugin with this PR, one example node is provided called ExampleNode. Like the Blender default cube, this is expected to be replaced by users as soon as possible. However, its existence is useful to both new and experienced users, since it serves 2 functions: 1) As a reference for how to make a node type, including the code, registration, docs, icon, etc, and 2) A minimal test to check if your GDExtension plugin works (don't see it in the editor? It's not working).

Assuming you have the system-wide dependencies installed, and you leave the "Compile now?" checkbox enabled, and you wait for it to finish, the extension immediately works. No fuss, the example node is just there:

If you change the code, you just need to run scons in the root. A future idea would be to detect this in projects and provide a "Build" button in the editor UI like we already do for C#, but that is technically separate from what this PR does.

The files look like this:

The SConstruct at the root is extremely barebones, it is only one line to call into another SConstruct. It is designed to be simple enough so that more GDExtension plugins can be added to the same Godot project with no manual work. The _ensure_file_contains helper function in this PR completely handles the merging of more calls into this file. Except for deleting the first plugin's ExampleNode, you can pretty much just make 2 plugins back-to-back with no conflicts. If you want to have 20 GDExtension plugins, this PR will let you do that just fine, with one call to scons in the root folder able to compile all of them at once.

This PR provides 2 options for making a GDExtension plugin: "GDExtension C++ only" or "GDExtension C++ and engine module". The former creates a standalone GDExtension C++ plugin, with the only files stored in the root of the project being a .gitignore and barebones SConstruct.

The engine module option provides a few more files like SCsub and config.py, provides lots of #ifdef directives to support both GDExtensions and modules, and places most of the C++ code in the root of the folder, which is more suitable for making a Godot engine module. This way if users want to target both GDExtension and modules with one codebase, they can do this as easily as selecting it from the dropdown. This option turns the project's root folder into a module, so only one module is allowed per project:

When in this mode, you can either compile for GDExtension the same as with the "only" option, or you can copy-paste the entire Godot project into the engine modules folder, naming the folder the same as the base name (the first name you entered in the Create GDExtension dialog), and it works.

The source files are designed to handle the extension+module case, but are automatically simplified by this PR's project generator when making a non-module extension, including by looking at the #if preprocessor directives to determine which lines of code to exclude.

TODO list before undrafting this PR:

• Merge PR Rename internal is_ascii_char to is_ascii_alphabet_char #90931
• Merge PR Organize existing code for editor plugins #90975
• Add support for documentation, see PR GDExtension: Add an interface for loading extra documentation #83747 and proposal A way to include in-editor class documentation for GDExtension plugins godot-proposals#8245
• Decide how we want this to work for non-C++ languages (currently the code is not designed to be plugable).
• Decide if we want this to work for non-SCons build systems.
• Get lots of feedback and testing. I'm sure this can be improved, but as-is it is already a massive improvement.

[deralmas]

Wow, this looks great! I wonder, does this also resolve godotengine/godot-proposals#9306 ? It looks like the same problem IMO.

[Naros]

This looks great, but I also definitely think its worthwhile to consider support for other build systems beyond scons. There has been a tremendous amount of work put into the cmake build in godot-cpp, and I think its at least worthwhile for supporting that build system if someone picks "GDExtension C++ only".

[Lazy-Rabbit-2001]

This looks wonderful as I've been annoying with handling the preparation of making GDExtension manually for days.
However, I think there could be an option to decide if godot-cpp is global or not, as some devs may use the same godot-cpp to avoid repeated compilations on this folder because of their parallel development on multiple GDExtensions.
For example, according to current status of pr, a dev may produce two GDExtensions like this:

addons

exm_a

src

godot_cpp

exm_b

src

godot_cpp

See? There are two godot_cpp-s in seperate projects, but the dev may hope to use only one for these two GDExtensions, like this:

addons

_bin

godot_cpp

exm_a

src

...

exm_b

src

...

As the direct placement of folder godot_cpp may bring ambiguity and vagueness to devs, it's better to place it in a single common folder named _bin or something else clear that resonates with the devs.

[aaronfranke]

@Naros The big question I have is what would this feature look like? Should cmake be included as one of the supported options out of the box? Should it be plugable? If so how? I guess plugins should add more options to the dropdown menu, so we would have "GDExtension C++ only (scons)" and "GDExtension C++ only (cmake)"? Or is it worth refactoring this menu to have a more generalized "GDExtension" option and a second dropdown for "C++ SCons", "C++ CMake", etc?

@Lazy-Rabbit-2001 I agree, but there are some technical challenges when trying to make the plugins share godot-cpp. When I try to do this, and both call into the same SConstruct, it is unable to compile from the top-level SConstruct:

scons: warning: Two different environments were specified for target gen/src/variant/utility_functions.cpp,
        but they appear to have the same action: scons_generate_bindings(target, source, env)
File "/Users/aaronfranke/workspace/projects/gdextension-test/addons/godot-cpp/tools/godotcpp.py", line 463, in _godot_cpp

scons: *** Two environments with different actions were specified for the same target: src/godot.macos.template_debug.universal.o

I would need some help from the build system gurus to make this work.

[dsnopek]

Thanks for taking this on! It looks really cool :-)

I did a quick test of the PR, and the "Compile on" checkbox didn't seem to work for me. It detected scons and git, but it encountered an error when trying to run it:

scons: Reading SConscript files ...
Auto-detected 32 CPU cores available for build parallelism. Using 31 cores by default. You can override it with the -j argument.
Building for architecture x86_64 on platform linux
KeyError: 'arch_suffix':
  File "/home/dsnopek/Sync/Projects/games/gdext-creation-test/SConstruct", line 4:
    SConscript("addons/zap/SConstruct")
  File "/usr/lib/python3/dist-packages/SCons/Script/SConscript.py", line 661:
    return method(*args, **kw)
  File "/usr/lib/python3/dist-packages/SCons/Script/SConscript.py", line 598:
    return _SConscript(self.fs, *files, **subst_kw)
  File "/usr/lib/python3/dist-packages/SCons/Script/SConscript.py", line 287:
    exec(compile(scriptdata, scriptname, 'exec'), call_stack[-1].globals)
  File "/home/dsnopek/Sync/Projects/games/gdext-creation-test/addons/zap/SConstruct", line 35:
    env["arch_suffix"],
  File "/usr/lib/python3/dist-packages/SCons/Environment.py", line 405:
    return self._dict[key]

If I change the SConstruct to remove the env["arch_suffix"] part, then it builds fine when running scons manually. After that, the ExampleNode class appears and I can add it to my scene!

It looks like this creates a plugin.cfg file, which leads to an entry on the "Plugins" tab in "Project Settings". However, GDExtensions aren't plugins in this sense, and enabling/disabling the created plugin there will actually have no effect. We do plan to eventually add the ability to enable/disable GDExtensions in "Project Settings", but work hasn't started on that yet.

However, GDExtensions are quite different from plugins in many ways. It may make sense for GDExtensions to have their own tab distinct from "Plugins"? And, if so, then the UI here should probably be disentangled from the "Create New Plugin" form and process.

Anyway, this is a great start!

[Naros]

The big question I have is what would this feature look like? Should cmake be included as one of the supported options out of the box? Should it be plugable? If so how? I guess plugins should add more options to the dropdown menu, so we would have "GDExtension C++ only (scons)" and "GDExtension C++ only (cmake)"? Or is it worth refactoring this menu to have a more generalized "GDExtension" option and a second dropdown for "C++ SCons", "C++ CMake", etc?

So first, I think David is right, we should completely separate GDExtension from GDScript plug-ins here, 💯 . An independent UI has several benefits:

• Avoids confusing GDScript plug-in creators with C++ / GDExtension noise.
• Allows creating a screen tailored for GDExtension and its toolings.

On the GDExtension create dialog, I could imagine this being a bit similar to Project Settings with a tree on the left, and a panel on the right where we display context-specific options based on the choice on the left. The left panel tree might look like this:

- General 
- Build, Execution, and Deployment
  - Toolchains
    - Custom compiler
  - CMake
  - Meson
  - Scons
  - ...
- Plugins
  - ... 

The General tab allows you to define basic data about the extension, its name, a custom entry point name, the base path for where the compiled binaries should be copied, i.e. res:\\addons\<addon-name>\bin being the default. Additionally, this is where the user can define the minimum compatibility, hot-reload, etc.

Under the Build tab, we'd have sections for each supported build system that would be output for the user. These tabs could include specific options that can be customized for that specific build system. For example, here's what I could imagine being the case for CMAKE:

The Plugins section is really some future scope I would say, but could be where the build files get customized, additional classes added, or some other customizations are done that can be tailored to an organization's needs.

---

And circling back to Limbo's idea of a shared godot-cpp, this got me thinking about whether the C++ code should really reside in the project folder itself or would it make sense to reside in something like user://, with top-level paths like:

• user://godot-cpp (shared godot-cpp)
• user://gdextension/<extension-name>

I'm just not sure I like the idea of embedding the C++ code into the Godot project, but I'm not 100% sold either way. But now I do question if some of these settings belong configurable in the Project Settings and not in the "Create Extension" dialog 🤔

[HeadClot]

Bit of a question about this Draft PR will this trigger a compile after the GDExtention is created or do will we have to do that manually?

[aaronfranke]

@HeadClot It attempts a compile for you, but this may fail if Git, SCons, or a C++ compiler/linker/etc are missing.

[HeadClot]

@HeadClot It attempts a compile for you, but this may fail if Git, SCons, or a C++ compiler/linker/etc are missing.

Got it thank you for the info :)

[dsnopek]

Decide how we want this to work for non-C++ languages (currently the code is not designed to be plugable).

I think it probably makes sense to make this pluggable via an editor plugin, similar to the EditorExtensionSourceCodePlugin proposed in godotengine/godot-proposals#9806 (or even just being additional methods on that same plugin - keeping everything related to managing GDExtension source together makes sense).

Also, it could make sense to include the C++ support in a godotcpp module? That way, we can disable the module on certain platforms (for example, web) or folks could make custom builds of Godot that don't include this additional integration with C++ (if, for example, they wanted an editor build that focused on a different GDExtension language).

[aaronfranke]

I overhauled the entire UI frontend of this PR. Instead of using the same dialog as GDScript plugins, now there is an entirely separate tab with 2 dialogs for creating and editing GDExtensions.

I have updated the OP, please read that for a summary of how the workflow looks like. In addition to what's in the OP, here is a short description of what the classes are:

• ProjectSettingsGDExtension: Lists GDExtensions as a tab in Project Settings. Allows opening the dialogs.
• GDExtensionCreateDialog: Dialog for creating new GDExtensions. Uses classes that extend GDExtensionCreatorBase to do the heavy lifting. Which one the dialog uses depends on which is selected in the dropdown.
• GDExtensionConfigDialog: Dialog for configuring/editing GDExtensions.
• GDExtensionCreatorBase: Base class for GDExtension creator classes, the classes which are able to take in a few parameters and generate a GDExtension for some language. In the future when we expose the ability for users to add custom classes for new languages or build systems, they would extend this class.
• CppSconsGDExtensionCreator: Extends GDExtensionCreatorBase, used for generating C++ with SCons extensions. This is the only class that knows about C++ and SCons, the other classes are language-agnostic.

If I change the SConstruct to remove the env["arch_suffix"] part, then it builds fine when running scons manually.

This should be fixed now. It will now add arch_suffix if it's missing.

It looks like this creates a plugin.cfg file, which leads to an entry on the "Plugins" tab in "Project Settings".

This is gone now.

And circling back to Limbo's idea of a shared godot-cpp, this got me thinking about whether the C++ code should really reside in the project folder itself or would it make sense to reside in

The create dialog now allows specifying any path. You can use res://gdextension/my_extension if you want, or even use a top-level folder using res://my_extension.

[KoBeWi]

• This reintroduces Project Settings window too small when using different language #91009, except it also happens in English now. We might need to re-think the dialog, because it's getting too many tabs.

EDIT:
The solution might be adding a new tab called Addons, which would have sub-tabs Plugins and GDExtension (similar to how Localization has sub-tabs.

• When creating extension and typing a name, there is a noticeable delay between each letter (at least in debug build), likely caused by field updating. There could be some debouncing applied here.

godot.windows.editor.dev.x86_64_WmCRfH6YBH.mp4

EDIT:
The dialog also checks for git and scons, which might be another thing slowing it down. This should be cached, e.g. when opening the dialog.

• While performing initial compilation the editor is completely unresponsive. The compilation should run in an independent process, to not stall the editor. You could display indeterminate progress bar, or if you are ambitious, you can show compilation progress and output in real time, using the new execute_with_pipe() method.

• After compiling finishes, the new GDExtension does not appear in the list until you click the window. Seems like editor ends unfocused somehow and clicking it refreshes the list or something. (might need further testing)

• The layout for editing extension is awkward.
  
  You could add some text to the checkbox (e.g. On or Enabled) and align it to the right.

Despite these minor problems, the extension is created correctly and is usable out-of-the-box, which is very nice.

I only requested changes because of .framework features, but that can be solved later. I no longer think we need to resolve this to merge the PR.
Will likely approve it later when I have another look!

[akien-mga]

Just noting for clarity that we're entering release freeze for 4.5, so this feature won't make the cut and will be considered for the 4.6 dev cycle.

I support the proposals / goals from this PR but I had some doubts about the original implementation, which I believe have been at least partially addressed since my last review. But I haven't had time to do a deeper review yet.

Let's make a priority to get this fully re-assessed by relevant maintainers and hopefully merged early on in the 4.6 dev cycle, so we have enough time to polish the experience further until the 4.6 stable release.

[fire]

I wanted to mention that we can [as external download] bundle the zig compiler because surprisingly it's a complete C++ compiler and use it to compile c++ gdextensions.

[Calinou]

I've tried the latest revision of this PR (not rebased due to merge conflicts), and am getting this after creating the GDExtension on Linux:

ERROR: Attempt to get non-existent interface function: 'classdb_register_extension_class5'.
   at: get_interface_function (./core/extension/gdextension.cpp:711)
ERROR: Unable to load GDExtension interface function classdb_register_extension_class5()
   at: init (src/godot-cpp/src/godot.cpp:480)
ERROR: GDExtension initialization function 'test_library_init' returned an error.
   at: initialize (./core/extension/gdextension_library_loader.cpp:231)

Any ideas as to why I'm getting this? For context, I'm looking to create a simple GDExtension I can include in a test project for CI.

[fire]

https://github.com/aaronfranke/godot/blob/9759c44a95e3933940eab929dce6b520db14b3cd/.github/workflows/linux_builds.yml#L11 points to 4.4

[Calinou]

aaronfranke/godot@9759c44/.github/workflows/linux_builds.yml#L11 points to 4.4

I'm running the PR locally, compiling it from source (both the engine and the GDExtension I created). This means the version used in the workflow shouldn't impact things for me.

[aaronfranke]

@Calinou Rebasing was required because we need PR #108614 included because godot-cpp's master branch uses it.

[Calinou]

@Calinou Rebasing was required because we need PR #108614 included because godot-cpp's master branch uses it.

It works, thanks! This will save me a lot of time 🙂

I noticed the SConstruct generated by the PR fails ruff checks:

misc/test_project/addons/test_extension/SConstruct:5:7: F821 Undefined name `SConscript`
  |
3 | # This file is for building as a Godot GDExtension.
4 |
5 | env = SConscript("src/godot-cpp/SConstruct")
  |       ^^^^^^^^^^ F821
6 |
7 | # Add source files.
  |

misc/test_project/addons/test_extension/SConstruct:9:11: F821 Undefined name `Glob`
   |
 7 | # Add source files.
 8 | env.Append(CPPPATH=["src/"])
 9 | sources = Glob("src/*.cpp")
   |           ^^^^ F821
10 |
11 | env.Append(CPPDEFINES=["GDEXTENSION"])
   |

misc/test_project/addons/test_extension/SConstruct:24:16: F821 Undefined name `Glob`
   |
22 |     # If you don't want to compile editor stuff in templates, move these 2 lines to a separate "if" block.
23 |     env.Append(CPPPATH=["src/editor/"])
24 |     sources += Glob("src/editor/*.cpp")
   |                ^^^^ F821
25 |     # Add documentation XML files as a generated cpp file. Only works in Godot 4.3+.
26 |     doc_data = env.GodotCPPDocData("src/gen/doc_data.gen.cpp", source=Glob("doc_classes/*.xml"))
   |

misc/test_project/addons/test_extension/SConstruct:26:71: F821 Undefined name `Glob`
   |
24 |     sources += Glob("src/editor/*.cpp")
25 |     # Add documentation XML files as a generated cpp file. Only works in Godot 4.3+.
26 |     doc_data = env.GodotCPPDocData("src/gen/doc_data.gen.cpp", source=Glob("doc_classes/*.xml"))
   |                                                                       ^^^^ F821
27 |     sources.append(doc_data)
   |

misc/test_project/addons/test_extension/SConstruct:54:1: F821 Undefined name `Default`
   |
52 |     )
53 |
54 | Default(library)
   | ^^^^^^^ F821
   |

Found 6 errors (1 fixed, 5 remaining).

I suppose you need to import explicitly what you're using to make sure it passes CI (if your project uses the same ruff checks as the engine). I worked around this on #109146 with noqa comments in the meantime.

[fire]

Try adding:

#!/usr/bin/env python
from misc.utility.scons_hints import *

to the top.