Quick links: help overview · quick reference · user manual toc · reference manual toc
develop.txt          Nvim


                            NVIM REFERENCE MANUAL


Development of Nvim					development dev

This reference describes design constraints and guidelines, for developing
Nvim applications or Nvim itself.
Architecture and internal concepts are covered in src/nvim/README.md

Nvim is free and open source.  Everybody is encouraged to contribute.
    https://github.com/neovim/neovim/blob/master/CONTRIBUTING.md

                                      Type gO to see the table of contents.

==============================================================================
Design goals						design-goals

Most important things come first (roughly).  Some items conflict; this is
intentional.  A balance must be found.


NVIM IS... IMPROVED					design-improved

The Neo bits of Nvim should make it a better Vim, without becoming a
completely different editor.
- In matters of taste, prefer Vim/Unix tradition. If there is no relevant
  Vim/Unix tradition, consider the "common case".
- There is no limit to the features that can be added.  Select new features
  based on (1) what users ask for, (2) how much effort it takes to implement
  and (3) someone actually implementing it.
- Backwards compatibility is a feature.  The RPC API in particular should
  never break.


NVIM IS... WELL DOCUMENTED				design-documented

- A feature that isn't documented is a useless feature.  A patch for a new
  feature must include the documentation.
- Documentation should be comprehensive and understandable.  Use examples.
- Don't make the text unnecessarily long.  Less documentation means that an
  item is easier to find.


NVIM IS... FAST AND SMALL				design-speed-size

Keep Nvim small and fast. This directly affects versatility and usability.
- Computers are becoming faster and bigger each year.  Vim can grow too, but
  no faster than computers are growing.  Keep Vim usable on older systems.
- Many users start Vim from a shell very often.  Startup time must be short.
- Commands must work efficiently.  The time they consume must be as small as
  possible.  Useful commands may take longer.
- Don't forget that some people use Vim over a slow connection.  Minimize the
  communication overhead.
- Vim is a component among other components.  Don't turn it into a massive
  application, but have it work well together with other programs
  ("composability").


NVIM IS... MAINTAINABLE					design-maintain

- The source code should not become a mess.  It should be reliable code.
- Use comments in a useful way!  Quoting the function name and argument names
  is NOT useful.  Do explain what they are for.
- Porting to another platform should be made easy, without having to change
  too much platform-independent code.
- Use the object-oriented spirit: Put data and code together.  Minimize the
  knowledge spread to other parts of the code.


NVIM IS... NOT						design-not

Nvim is not an operating system; instead it should be composed with other
tools or hosted as a component. Marvim once said: "Unlike Emacs, Nvim does not
include the kitchen sink... but it's good for plumbing."


==============================================================================
Developer guidelines				        dev-guidelines


PROVIDERS						dev-provider

A primary goal of Nvim is to allow extension of the editor without special
knowledge in the core.  Some core functions are delegated to "providers"
implemented as external scripts.

Examples:

1. In the Vim source code, clipboard logic accounts for more than 1k lines of
   C source code (ui.c), to perform two tasks that are now accomplished with
   shell commands such as xclip or pbcopy/pbpaste.

2. Python scripting support: Vim has three files dedicated to embedding the
   Python interpreter: if_python.c, if_python3.c and if_py_both.h. Together
   these files sum about 9.5k lines of C source code. In contrast, Nvim Python
   scripting is performed by an external host process implemented in ~2k lines
   of Python.

The provider framework invokes VimL from C.  It is composed of two functions
in eval.c:

- eval_call_provider(name, method, arguments, discard): calls
  provider#{name}#Call with the method and arguments. If discard is true, any
  value returned by the provider will be discarded and empty value will be
  returned.
- eval_has_provider(name): Checks the g:loaded_{name}_provider variable
  which must be set to 2 by the provider script to indicate that it is
  "enabled and working". Called by has() to check if features are available.

For example, the Python provider is implemented by the
"autoload/provider/python.vim" script, which sets g:loaded_python_provider
to 2 only if a valid external Python host is found.  Then has("python")
reflects whether Python support is working.

							provider-reload
Sometimes a GUI or other application may want to force a provider to
"reload".  To reload a provider, undefine its "loaded" flag, then use
:runtime to reload it: 

    :unlet g:loaded_clipboard_provider
    :runtime autoload/provider/clipboard.vim


DOCUMENTATION						dev-doc

- "Just say it". Avoid mushy, colloquial phrasing in all documentation
  (docstrings, user manual, website materials, newsletters, …). Don't mince
  words. Personality and flavor, used sparingly, are welcome--but in general,
  optimize for the reader's time and energy: be "precise yet concise".
    - See https://developers.google.com/style/tone
    - Prefer the active voice: "Foo does X", not "X is done by Foo".
- Start function docstrings with present tense ("Gets"), not imperative
  ("Get"). This tends to reduce ambiguity and improve clarity. 
    GOOD:
    /// Gets a highlight definition.
    BAD:
    /// Get a highlight definition.
- Avoid starting docstrings with "The" or "A" unless needed to avoid
  ambiguity. This is a visual aid and reduces noise. 
    GOOD:
    /// @param dirname Path fragment before `pend`
    BAD:
    /// @param dirname The path fragment before `pend`
- Vim differences:
    - Do not prefix help tags with "nvim-". Use vim_diff.txt to catalog
      differences from Vim; no other distinction is necessary.
    - If a Vim feature is removed, delete its help section and move its tag to
      vim_diff.txt.
- Mention deprecated features in deprecated.txt and delete their old doc.
- Use consistent language.
    - "terminal" in a help tag always means "the embedded terminal emulator",
      not "the user host terminal".
    - Use "tui-" to prefix help tags related to the host terminal, and "TUI"
      in prose if possible.

Documentation format 

For Nvim-owned docs, use the following strict subset of "vimdoc" to ensure
the help doc renders nicely in other formats (such as HTML:
https://neovim.io/doc/user ).

Strict "vimdoc" subset:

- Use lists (like this!) prefixed with "-" or "•", for adjacent lines that you
  don't want to auto-wrap. Lists are always rendered with "flow" layout
  (soft-wrapped) instead of preformatted (hard-wrapped) layout common in
  legacy :help docs.
  - Limitation: currently the parser https://github.com/neovim/tree-sitter-vimdoc
    does not understand numbered listitems, so use a bullet symbol (- or •)
    before numbered items, e.g. "• 1." instead of "1.".
- Separate blocks (paragraphs) of content by a blank line.
- Do not use indentation in random places—that prevents the page from using
  "flow" layout. If you need a preformatted section, put it in
  a help-codeblock starting with ">".

C docstrings 

Nvim API documentation lives in the source code, as docstrings (Doxygen
comments) on the function definitions.  The api :help is generated
from the docstrings defined in src/nvim/api/*.c.

Docstring format:
- Lines start with ///
- Special tokens start with @ followed by the token name:
  @note, @param, @returns
- Limited markdown is supported.
  - List-items start with - (useful to nest or "indent")
- Use <pre> for code samples.
  Code samples can be annotated as vim or lua

Example: the help for nvim_open_win() is generated from a docstring defined
in src/nvim/api/win_config.c like this: 

    /// Opens a new window.
    /// ...
    ///
    /// Example (Lua): window-relative float
    /// <pre>lua
    ///     vim.api.nvim_open_win(0, false,
    ///       {relative='win', row=3, col=3, width=12, height=3})
    /// </pre>
    ///
    /// @param buffer Buffer to display
    /// @param enter  Enter the window
    /// @param config Map defining the window configuration. Keys:
    ///   - relative: Sets the window layout, relative to:
    ///      - "editor" The global editor grid.
    ///      - "win"    Window given by the `win` field.
    ///      - "cursor" Cursor position in current window.
    /// ...
    /// @param[out] err Error details, if any
    ///
    /// @return Window handle, or 0 on error


Lua docstrings 
							dev-lua-doc
Lua documentation lives in the source code, as docstrings on the function
definitions.  The lua-vim :help is generated from the docstrings.

Docstring format:
- Lines in the main description start with ---
- Special tokens start with ---@ followed by the token name:
  ---@see, ---@param, ---@returns
- Limited markdown is supported.
  - List-items start with - (useful to nest or "indent")
- Use <pre> for code samples.
  Code samples can be annotated as vim or lua

Example: the help for vim.paste() is generated from a docstring decorating
vim.paste in runtime/lua/vim/_editor.lua like this: 

    --- Paste handler, invoked by |nvim_paste()| when a conforming UI
    --- (such as the |TUI|) pastes text into the editor.
    ---
    --- Example: To remove ANSI color codes when pasting:
    --- <pre>lua
    --- vim.paste = (function()
    ---   local overridden = vim.paste
    ---   ...
    --- end)()
    --- </pre>
    ---
    ---@see |paste|
    ---
    ---@param lines  ...
    ---@param phase  ...
    ---@returns false if client should cancel the paste.


LUA STDLIB DESIGN GUIDELINES				dev-lua

See also dev-naming.

- Keep the core Lua modules lua-stdlib simple. Avoid elaborate OOP or
  pseudo-OOP designs. Plugin authors just want functions to call, not a big,
  fancy inheritance hierarchy.
- Avoid requiring or returning special objects in the Nvim stdlib. Plain
  tables or values are easier to serialize, easier to construct from literals,
  easier to inspect and print, and inherently compatible with all Lua plugins.
  (This guideline doesn't apply to opaque, non-data objects like vim.cmd.)
- stdlib functions should follow these common patterns:
  - accept iterable instead of table
    - exception: in some cases iterable doesn't make sense, e.g. spair() sorts
      the input by definition, so there is no reason for it to accept an
      iterable, because the input needs to be "hydrated", it can't operate on
      a "stream".
  - return iterable instead of table
  - mimic the pairs() or ipairs() interface if the function is intended to be
    used in a "for" loop.


API DESIGN GUIDELINES					dev-api

See also dev-naming.

- When adding an API, check the following:
  - What precedents did you draw from? How does your solution compare to them?
  - Does your new API allow future expansion? How? Or why not?
  - Is the new API similar to existing APIs? Do we need to deprecate the old ones?
  - Did you cross-reference related concepts in the docs?
- Avoid "mutually exclusive" parameters--via constraints or limitations, if
  necessary. For example nvim_create_autocmd() has mutually exclusive
  "callback" and "command" args; but the "command" arg could be eliminated by
  simply not supporting Vimscript function names, and treating a string
  "callback" arg as an Ex command (which can call Vimscript functions). The
  "buffer" arg could also be eliminated by treating a number "pattern" as
  a buffer number.
- Avoid functions that depend on cursor position, current buffer, etc. Instead
  the function should take a position parameter, buffer parameter, etc.

NAMING GUIDELINES                                       dev-naming

Naming is exceedingly important: the name of a thing is the primary interface
for uses it, discusses it, searches for it, shares it... Consistent
naming in the stdlib, API, and UI helps both users and developers discover and
intuitively understand related concepts ("families"), and reduces cognitive
burden. Discoverability encourages code re-use and likewise avoids redundant,
overlapping mechanisms, which reduces code surface-area, and thereby minimizes
bugs...

Naming conventions 

In general, look for precedent when choosing a name, that is, look at existing
(non-deprecated) functions. In particular, see below...

							dev-name-common
Use existing common {verb} names (actions) if possible:
    - add:          Appends or inserts into a collection
    - attach:       Listens to something to get events from it (TODO: rename to "on"?)
    - call:         Calls a function
    - clear:        Clears state but does not destroy the container
    - create:       Creates a new (non-trivial) thing (TODO: rename to "def"?)
    - del:          Deletes a thing (or group of things)
    - detach:       Dispose attached listener (TODO: rename to "un"?)
    - eval:         Evaluates an expression
    - exec:         Executes code
    - fmt:          Formats
    - get:          Gets things (often by a query)
    - inspect:      Presents a high-level, often interactive, view
    - open:         Opens something (a buffer, window, …)
    - parse:        Parses something into a structured form
    - set:          Sets a thing (or group of things)
    - try_{verb}:   Best-effort operation, failure returns null or error obj

Do NOT use these deprecated verbs:
    - list:         Redundant with "get"
    - show:         Redundant with "print", "echo"
    - notify:       Redundant with "print", "echo"

Use consistent names for {noun} (nouns) in API functions: buffer is called
"buf" everywhere, not "buffer" in some places and "buf" in others.
    - buf:          Buffer
    - chan:         channel
    - cmd:          Command
    - cmdline:      Command-line UI or input
    - fn:           Function
    - hl:           Highlight
    - pos:          Position
    - proc:         System process
    - tabpage:      Tabpage
    - win:          Window

Do NOT use these deprecated nouns:
    - buffer
    - command
    - window

							dev-name-events
Use the "on_" prefix to name event-handling callbacks and also the interface for
"registering" such handlers (on_key). The dual nature is acceptable to avoid
a confused collection of naming conventions for these related concepts.

Editor events (autocommands) are historically named like: 
    {Noun}{Event}

Use this format to name API (RPC) events: 
    nvim_{noun}_{event-name}_event

Example: 
    nvim_buf_changedtick_event

							dev-name-api
Use this format to name new RPC API functions: 
    nvim_{noun}_{verb}_{arbitrary-qualifiers}

If the function acts on an object then {noun} is the name of that object
(e.g. "buf" or "win"). If the function operates in a "global" context then
{noun} is usually omitted (but consider "namespacing" your global operations
with a {noun} that groups functions under a common concept).

- Example: nvim_get_keymap('v') operates in a global context (first
  parameter is not a Buffer). The "get" verb indicates that it gets anything
  matching the given filter parameter. A "list" verb is unnecessary because
  nvim_get_keymap('') (empty filter) returns all items.
- Example: nvim_buf_del_mark acts on a Buffer object (the first parameter)
  and uses the "del" {verb}.


API-CLIENT						dev-api-client

							api-client
API clients wrap the Nvim API to provide idiomatic "SDKs" for their
respective platforms (see jargon). You can build a new API client for your
favorite platform or programming language.

List of API clients:
    https://github.com/neovim/neovim/wiki/Related-projects#api-clients

							pynvim
The Python client is the reference implementation for API clients.
    https://github.com/neovim/pynvim

Standard Features 

- API clients exist to hide msgpack-rpc details. The wrappers can be
  automatically generated by reading the api-metadata from Nvim. api-mapping
- Clients should call nvim_set_client_info() after connecting, so users and
  plugins can detect the client by handling the ChanInfo event. This avoids
  the need for special variables or other client hints.
- Clients should handle nvim_error_event notifications, which will be sent
  if an async request to nvim was rejected or caused an error.

Package Naming 

API client packages should NOT be named something ambiguous like "neovim" or
"python-client".  Use "nvim" as a prefix/suffix to some other identifier
following ecosystem conventions.

For example, Python packages tend to have "py" in the name, so "pynvim" is
a good name: it's idiomatic and unambiguous. If the package is named "neovim",
it confuses users, and complicates documentation and discussions.

Examples of API-client package names:
- GOOD: nvim-racket
- GOOD: pynvim
- BAD:  python-client
- BAD:  neovim

API client implementation guidelines 

- Separate the transport layer from the rest of the library. rpc-connecting
- Use a MessagePack library that implements at least version 5 of the
  MessagePack spec, which supports the BIN and EXT types used by Nvim.
- Use a single-threaded event loop library/pattern.
- Use a fiber/coroutine library for the language being used for implementing
  a client. These greatly simplify concurrency and allow the library to
  expose a blocking API on top of a non-blocking event loop without the
  complexity that comes with preemptive multitasking.
- Don't assume anything about the order of responses to RPC requests.
- Clients should expect requests, which must be handled immediately because
  Nvim is blocked while waiting for the client response.
- Clients should expect notifications, but these can be handled "ASAP" (rather
  than immediately) because they won't block Nvim.
- For C/C++ projects, consider libmpack instead of the msgpack.org library.
    https://github.com/libmpack/libmpack/
  libmpack is small (no dependencies, can inline into your C/C++ project) and
  efficient (no allocations). It also implements msgpack-RPC, the protocol
  required by Nvim.
    https://github.com/msgpack-rpc/msgpack-rpc


EXTERNAL UI						dev-ui

External UIs should be aware of the api-contract. In particular, future
versions of Nvim may add new items to existing events. The API is strongly
backwards-compatible, but clients must not break if new (optional) fields are
added to existing events.

Standard Features 

External UIs are expected to implement these common features:

- Call nvim_set_client_info() after connecting, so users and plugins can
  detect the UI by handling the ChanInfo event. This avoids the need for
  special variables and UI-specific config files (gvimrc, macvimrc, …).
- Cursor style (shape, color) should conform to the 'guicursor' properties
  delivered with the mode_info_set UI event.
- Send the ALT/META ("Option" on macOS) key as a <M- chord.
- Send the "super" key (Windows key, Apple key) as a <D- chord.
- Avoid mappings that conflict with the Nvim keymap-space; GUIs have many new
  chords (<C-,> <C-Enter> <C-S-x> <D-x>) and patterns ("shift shift") that do
  not potentially conflict with Nvim defaults, plugins, etc.
- Consider the "option_set" ui-global event as a hint for other GUI
  behaviors. Various UI-related options ('guifont', 'ambiwidth', …) are
  published in this event. See also "mouse_on", "mouse_off".


 vim:tw=78:ts=8:sw=4:et:ft=help:norl:


Quick links: help overview · quick reference · user manual toc · reference manual toc