[Geany-Devel] My non-C plugin roadmap

[Thomas Martitz]

Hello,

I was asked to share a bit about my roadmap regarding plugins. I'll try 
to give you a better idea with this post.

My ultimate goal is to implement a clean and maintainable way to support 
non-C plugins, preferably using existing widely used techniques. I 
concluded that libpeas[1] in conjunction with gobject-introspection can 
provide the base for this. Since Geany is not at all prepared for this I 
have several infrastructure which I do want to get merged into Geany. 
When Geany core is sufficiently setup for this, the non-C plugin 
enablement can happen outside the core, as a plugin, to stabilize there.

So, here's the set of infrastructure changes for the core. Please let me 
stress that all of this will happen in backward-compatible manner, no 
existing plugins break as part of this.

- linkage-cleanup (PR#429) - This changes the way plugins access Geany 
API functions. Instead of exporting a pointer to a struct of structs of 
API function pointers, now the APIs are exported directly. This work 
also includes an effort to stop exporting all function (we do this 
currently as a workaround to allow gtkbuilder to work), so *only* API 
function are exported and plugins cannot call internal function anymore. 
This change is also required to allow gobject-introspection to find 
geany functions at runtime (through g_module_symbol()) in the future.
- new API functions for registering keybindings (PR#376). The current 
API functions do not allow context information to be stored and passed 
to the key handler function. This makes it very hard for non-C plugins 
to use these function. So what's  needed are key handlers that get the 
necessary context information. This allows interprepted language plugins 
to register keybindings.
- A new plugin loader mechanism (a thread about this is already running 
on the devel list): Similarly to the keybindings, the plugin_* functions 
implemented by plugins do not carry any context information, making it 
hard for non-C plugins to implement them properly. Therefore a new 
loader mechaism is needed so that the context information can be passed. 
The loader works such that an API function is called to register a 
function pointer table. This is crucial to possibly support plugins that 
register other plugins (so called pluxies) which is simply not possible 
with the current mechaism. The current loader is kept for backwards 
compatibility (but will not receive new features).
- New API functions to allow plugins to act as proxy plugins (pluxies). 
These pluxies can then implement whatever is needed to execute code in 
the in the actual plugin, like invoking an interpreter or firing up a 
java vm. The pluxies call the new loader's API function on behalf of the 
actual plugin. The API function to implement the pluxies is a simple 
geany_register_pluxy() that, much like the normal plugin loader, that 
pluxies use to pass a function pointer table which implements the 
necessary hooks (probe(), load() and unload())

Once this is in place in the core, my roadmap contains the following 
items, which are implemented (at least initially) in a plugin, so no 
further changes to the cure should be necessary.
- Modify geanypy to use the new pluxy APIs. This will finally enable 
geanypy to show the python plugins in the normal PM dialog and support 
keybindings
- Create a new pluxy that supports libpeas-based plugins (codename: 
peasy). Peasy will use libpeas to load plugins and their metadata.
- Part of the peasy work is also work on creating vala and 
gobject-introspection bindings for Geany's API functions, so that we can 
support python, javascript and lua out of the box.

This is my roadmap so far. It changed quite a bit since I started this 
non-C-plugins effort a year ago, but I hope it will be good for 
everyone. Please share your opinions on this or ask questions.

Best regards.