#neovim

###Introduction

Vim is a powerful text editor with a big, increasing community. Even though it is more than 20 years old, people still extend and improve it, mostly using vimscript or one of the supported scripting languages.

###Problem

Over its 20 years of life, vim has accumulated about 300k lines of scary C89 code that very few people understand or have the guts to mess with.

Another issue, is that as the only person responsible for maintaing vim's big codebase, Bram Moolenaar has to be extra-careful before accepting patches, because once merged, the new code will be his responsibility.

These problems make it pretty hard to have new features and bug fixes merged into the core. Vim just cant keep up with the development speed of its plugin echosystem.

###Solution

Neovim is a vim fork that seeks to aggressively refactor vim in order to achieve the following goals:

• Simplify maintenance to improve the speed that bug fixes and features get merged.
• Split the responsibility between multiple developers.
• Enable the implementation of new/modern user interfaces without any modifications to the core source.
• Improve the extensibility power with a new plugin architecture based on external processes. Plugins will be written in any programming language without any explicit support from the editor. This can be saw as a better implementation of the job control patch

Those goals should be achieved with little impact on vim's editing model or vimscript in general. Most vimscript plugins should continue to work normally.

The following topics summarizes the major changes that will be performed:

• Legacy support and compile-time features
• Platform-specific code
• New plugin architecture
• New GUI architecture
• Split into many repositories

Legacy support and compile-time features

Vim has a significant amount of code dedicated to supporting legacy systems and compilers. All that code increases the maintainance burden and will be removed.

Most optional features will no longer be optional, with the exception of some broken and useless fetures(eg: netbeans integration, sun workshop) which will be removed permanently. Vi emulation will also be removed(probably leave the 'set nocompatible' command as a no-op).

These changes wont affect most users. Those that only have a C89 compiler installed or develop on legacy systems such as Amiga, BeOS or MSDOS have two choices:

• Upgrade their software.
• Continue using vim

Platform-specific code

Most of the platform-specific code will be removed and libuv will be used to handle system differences. libuv has support for most unixes and windows, so the vast majority of vim's community will be supported.

New plugin architecture

All code supporting embedded scripting language interpreters will be replaced by a new plugin system that will support extensions written in any programming language.

Compatibility layers will be provided for easily porting vim plugins written in some of the currently supported scripting languages such as python or ruby.

This is how the new plugin system will work:

• Plugins are long-running programs/jobs that communicate with vim through stdin/stdout using msgpack-rpc or json-rpc.
• Vim will discover and run these programs at startup, keeping two-way communication channels with each plugin.
• Plugins will be able to listen to events and send commands to vim asynchronously.

Here's a sample plugin session using json-rpc (jsonrpc version omitted):

plugin -> vim: {"id": 1, "method": "listenEvent", "params": {"eventName": "keyPressed"}}
vim -> plugin: {"id": 1, "result": true}
vim -> plugin: {"method": "event", "params": {"name": "keyPressed", "eventArgs": {"keys": ["C"]}}}
vim -> plugin: {"method": "event", "params": {"name": "keyPressed", "eventArgs": {"keys": ["Ctrl", "Space"]}}}
plugin -> vim: {"id": 2, "method": "showPopup", "params": {"size": {"width": 10, "height": 2} "position": {"column": 2, "line": 3}, "items": ["Completion1", "Completion2"]}}
plugin -> vim: {"id": 2, "result": true}}

That shows the conversation between vim and an hypotetical completion plugin that popups completions when the user presses Ctrl+Space. The above scheme gives neovim near limitless extensibility and also improves stability as plugins will be automatically sandboxed from the main executable.

This system can also easily emulate scripting languages interfaces to vim. A plugin could, for example, emulate the current python interface by discovering python scripts in vim's runtime dir and exposing a 'vim' module with an API matching the current one. Calls to the API would simply be translated to json-rpc messages sent to vim.

New GUI architecture

Another contributing factor to vim's huge codebase is the explicit support for dozens of widget toolkits for GUI interfaces. Like the legacy code support, gui handling code will be removed from neovim's core.

Neovim will handle GUIs similarly to how it will handle plugins:

• GUIs are separate programs, possibly written in different programming languages.
• Neovim will use its own stdin/stdout to receive input and send updates, again using json-rpc or msgpack-rpc.

The difference between plugins and GUIs is that plugins will be started by neovim, where GUIs will start neovim(or perhaps attach to a running session). Here's a sample diagram of the process tree:

GUI program
  |
  ---> Neovim
         |
         ---> Plugin 1
         |
         ---> Plugin 2
         |
         ---> Plugin 3

Sample:

gui -> vim: {"id": 1, "method": "initClient", "params": {"size": {"rows": 20, "columns": 25}}}
vim -> gui: {"id": 1, "result": {"clientId": 1}}
vim -> gui: {"method": "redraw", "params": {"clientId": 1, "lines": {"5": "   Welcome to neovim!   "}}}
gui -> vim: {"id": 2, "method": "keyPress", "params": {"keys": ["H", "e", "l", "l", "o"]}}
vim -> gui: {"method": "redraw", "params": {"clientId": 1, "lines": {"1": "Hello                   ", "5": "                        "}}}

This new GUI architecture creates many interesting possibilities:

• Modern GUIs written in high-level programming languages that integrate better with the operating system. We can have GUIs written using C#/WPF on Windows or Ruby/Cocoa on Mac.
• Plugins will be able emit custom events that may be handled directly by GUIs. This will enable the implementaton of advanced features such as sublime's minimap.
• A multiplexing daemon could could keep neovim instances running in a headless server, while multiple remote GUIs could attach/detach to share editing sessions.
• Neovim can be easily embedded into other programs.

Split into many repositories

Neovim's code will be split across many repositories in the neovim organization. There will be separate repositories for GUIs, plugins, runtime files(official vimscript) and distributions. This will let neovim will receive improvements much faster as the patches wont have to pass through the approval of a single person.

###Status

Here's a list of things that have been done so far:

• Source tree was cleaned up, leaving only files necessary for compilation/testing of the core.
• Source files were processed with unifdef to remove tons of FEAT_* macros
• Files were processed with uncrustify to normalize source code formatting.
• The autotools build system was replaced by cmake

###Dependencies

For Ubuntu 12.04:

sudo apt-get install build-essential cmake libncurses5-dev

TODO: release the Dockerfile which has this in it

TODO: Arch instructions

TODO: OSX instructions

###Building

To generate the Makefiles:

make cmake

To build and run the tests:

make test