Debugging Plugins and nvim-hs

[saep]

This issue should gather ideas on how to improve debugging. (Solutions are welcome, too!)

Currently we have:

• Saving a file in $XDG_CONFIG_HOME/nvim will trigger a rebuild and put compile time errors in the quickflix list
• If logging is enabled, the raw msgpack-rpc messages we receive are logged.

Those things are incredibly useful, but I think we can do better!

1. When I was implementing the registration of functions or filling the quickfixlist with compile errors from dyre, looking at the logged msgpack-rpc messages was insanely useful. I think this should be made more accessible and integrated. I imagine opening a window inside neovim that (pretty) prints all the msgpack-rpc communication after issueing a command (e.g. :DebugNvimhs).
2. Implementing new functions that interact with neovim, and hence require the Neovim transformer stack, should be possible from a REPL. I don't know if it's possible to run a ghci-like session inside such a transformer. Or something int he direction of https://github.com/chrisdone/ghci-reload-demo could be conveniently achieved.

[saep]

Idea for first debugging interface:

Start ghci with nvim-hs package and environment variable $NVIM_LISTEN_ADDRESS set to a valid neovim instance. Test functions with a debug function. It should connect to the socket at $NVIM_LISTEN_ADDRESS issue the commands and disconnect.

The following interface should be implemented.

debug :: NvimObject a => r -> st -> Neovim r st a -> IO ()

debug' :: NvimObject a => Neovim' a -> IO ()

A more sophisticated solution is very welcome. :-)

[saep]

Implemented some slightly different, yet more general and useful version of those 2 debug functions.

[saep]

The Debug module definitely needs documentation.

[saep]

Something in the spirit of the ghci-live-reload demo mentioned in the issue description does not seem to be possible in a convenient way at the moment. I cannot find a mechanism, that is not a hack, to find the channel identifier that the current thread is connected to. The (un)subscribe functions from the remote API magically insert it into the internal function's parameters and I might just try to create a pull request for it.

The hacky solution would entail writing a proxy program that simply broadcasts all msgpack-rpc communication from neovim to all connected clients and routes all communication from the clients to neovim.

[saep]

Oh, it seems like vim_get_api_info returns the channel id as its first element of the answer list.

[saep]

After reimplementing runPluginProvider with its finalizer argument, it was almost trivial to get the live-reload-demo adapted to nvim-hs. Although, we need some more utility functions for inspection of the internals, this issue is practiacally resolved. I'll create a 0.0.3 release without additional debug functions.

[saep]

With a good set of functions and a few hooks, we might actually be able to remove the logging code as we are able to poke at almost anything in a running instance.

[saep]

Once I have the ghcid-quickfix-filling plugin done, I'll record a small video on how I can debug that with the live-reload thingie in Neovim.Debug. Apart from adding more helper functions, the basis is done and this issue can be closed once that video is up and I haven't found any more issues while working on said plugin.