neovim/runtime/doc/remote_plugin.txt

*remote_plugin.txt*    For Nvim.					 {Nvim}


		 NVIM REFERENCE MANUAL    by Thiago de Arruda


Nvim support for remote plugins 		  *remote-plugin*

1. Introduction					|remote-plugin-intro|
2. Plugin hosts					|remote-plugin-hosts|
3. Example					|remote-plugin-example|
4. Plugin manifest				|remote-plugin-manifest|

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1. Introduction					    *remote-plugin-intro*

Extensibility is a primary goal of Nvim. Any programming language may be used
to extend nvim without changes to nvim itself. This is achieved with remote
plugins, coprocesses that have a direct communication channel (via
|msgpack-rpc|) with the Nvim process.

Even though these plugins are running in separate processes they can call, be
called, and receive events just as if the code was being executed in the main
process.

==============================================================================
2. Plugin hosts					    *remote-plugin-hosts*

While plugins can be implemented as arbitrary programs that communicate
directly with the high-level Nvim API and are called via |rpcrequest()| and
|rpcnotify()|, that is not the best approach available. Instead, developers
should first check if a plugin host implementation is available for their
chosen programming language.

Plugin hosts are programs that provide a high level environment for plugins,
taking care of most boilerplate involved in defining commands, autocmds, and
functions that are implemented over |msgpack-rpc| connections. Hosts are
loaded only when one of their registered plugins require it, keeping Nvim's
startup as fast as possible if many plugins/hosts are installed.

==============================================================================
3. Example					    *remote-plugin-example*

The best way to learn about remote plugins is with an example, so let's see
what a Python plugin looks like. This plugin exports a command, a function and
an autocmd. The plugin is called 'Limit', and all it does is limit the number
of requests made to it. Here's the plugin source code:
>
    import neovim

    @neovim.plugin
    class Limit(object):
        def __init__(self, vim):
            self.vim = vim
            self.calls = 0

        @neovim.command('Cmd', range='', nargs='*', sync=True)
        def command_handler(self, args, range):
            self._increment_calls()
            self.vim.current.line = (
                'Command: Called %d times, args: %s, range: %s' % (self.calls,
                                                                   args,
                                                                   range))

        @neovim.autocmd('BufEnter', pattern='*.py', eval='expand("<afile>")',
                        sync=True)
        def autocmd_handler(self, filename):
            self._increment_calls()
            self.vim.current.line = (
                'Autocmd: Called %s times, file: %s' % (self.calls, filename))

        @neovim.function('Func')
        def function_handler(self, args):
            self._increment_calls()
            self.vim.current.line = (
                'Function: Called %d times, args: %s' % (self.calls, args))

        def _increment_calls(self):
            if self.calls == 5:
                raise Exception('Too many calls!')
            self.calls += 1
<

As can be seen, the plugin is implemented using pure Python idioms (classes,
methods, and decorators), the translation between these language-specific
idioms to vimscript occurs while the plugin manifest is being generated (see
below).

Notice that the exported command and autocmd are defined with the "sync" flag,
which affects how Nvim calls the plugin: with "sync" the |rpcrequest()|
function is used, which will block Nvim until the handler function returns a
value. Without the "sync" flag, the call is made using a fire and forget
approach with |rpcnotify()| (return values or exceptions raised in the handler
function are ignored).

To test the above plugin, it must be saved in "rplugin/python" in a
'runtimepath' directory (~/.nvim/rplugin/python/limit.py for example). Then,
the remote plugin manifest must be generated with `:UpdateRemotePlugins`.

==============================================================================
4. Remote plugin manifest			    *remote-plugin-manifest*

Just installing remote plugins to "rplugin/{host}" isn't enough for them to be
automatically loaded when required. The `:UpdateRemotePlugins` command must be
executed every time a remote plugin is installed, updated, or deleted.

`:UpdateRemotePlugins` will generate the remote plugin manifest, a special
vimscript file containing declarations for all vimscript entities
(commands/autocommands/functions) defined by all remote plugins, with each
entity associated with the host and plugin path. The manifest can be seen as a
generated extension to the user's vimrc (it even has the vimrc filename
prepended).

The manifest declarations are nothing but calls to the remote#host#RegisterPlugin
function, which will take care of bootstrapping the host as soon as the
declared command, autocommand, or function is used for the first time.

The manifest generation step is necessary to keep Nvim's startup fast in
situations where a user has remote plugins with different hosts. For example,
say a user has three plugins, for Python, java and .NET hosts respectively. If
we were to load all three plugins at startup, then three language runtimes
would also be spawned which could take seconds!

With the manifest, each host will only be loaded when required. Continuing
with the example, say the java plugin is a semantic completion engine for java
source files. If it defines the autocommand "BufEnter *.java", then the java
host will only be spawned when files ending with ".java" are loaded.

If the explicit call to `:UpdateRemotePlugins` seems incovenient, try to see
it like this: It's a way to give IDE-like capabilities to nvim while still
keeping it fast and lightweight for general use. It can also be seen as
analogous to the |:helptags| facility.

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