#+TITLE: LSP layer

* Table of Contents                     :TOC_4_gh:noexport:
- [[#description][Description]]
  - [[#features][Features:]]
- [[#configuration][Configuration]]
  - [[#derived-layers][Derived layers]]
    - [[#spacemacslsp-bind-keys-for-mode-mode][=spacemacs/lsp-bind-keys-for-mode mode=]]
      - [[#declared-prefixes][Declared prefixes]]
      - [[#default-key-bindings][Default key bindings]]
  - [[#variables][Variables]]
  - [[#diagnostics][Diagnostics]]
- [[#future-additionsimprovements][Future additions/improvements]]
  - [[#make-spacemacslsp-bind-keys-for-mode-bind-conditionally][Make =spacemacs/lsp-bind-keys-for-mode= bind conditionally]]
- [[#references][References]]

* Description
This layer adds support for basic language server protocol packages speaking
[[https://microsoft.github.io/language-server-protocol/specification][language server protocol]].

Different language servers may support the language server protocol to varying degrees
and they may also provide extensions; check the language server’s website for
details.
=M-x lsp-capabilities= in a LSP buffer to list capabilities of the server.

** Features:
- Cross references (definitions, references, document symbol, workspace symbol
  search and others)
- Workspace-wide symbol rename
- Symbol highlighting
- Flycheck
- Completion with =company-lsp=
- Signature help with eldoc
- Symbol documentation in a child frame (=lsp-ui-doc=)
- Navigation using imenu

* Configuration
The LSP ecosystem is based on two packages: [[https://github.com/emacs-lsp/lsp-mode][lsp-mode]] and [[https://github.com/emacs-lsp/lsp-ui][lsp-ui]].
Please check out their documentation.

If you add =lsp-*-enable= to major mode hooks for auto initialization of
language clients, customize =lsp-project-whitelist= =lsp-project-blacklist= to
disable projects you don’t want to enable LSP.

** Derived layers
A number of elisp functions have been added to facilitate development of derived layers.

*** =spacemacs/lsp-bind-keys-for-mode mode=
This function binds keys to a number of lsp features useful for all/most modes for the given major mode.
It also declares some relevant keyboard shortcut prefixes.

**** Declared prefixes
The following prefixes have been declared:

| prefix | name           | functional area                                                            |
|--------+----------------+----------------------------------------------------------------------------|
| ~m =~  | format         | Source formatting                                                          |
| ~m g~  | goto           | Source navigation                                                          |
| ~m h~  | help/hierarchy | Help and functions related to hierarchy (class relationships etc.)         |
| ~m l~  | lsp/backend    | Catchall. Restart LSP backend, other implementation-specific functionality |
| ~m r~  | refactor       | What it says on the tin                                                    |
| ~m T~  | toggle         | Toggle LSP backend features (documentation / symbol info overlays etc.)    |

**** Default key bindings
The default bindings are listed below. Derived language server layers should extend this list.

| binding | function                                        |
|---------+-------------------------------------------------|
| ~m = b~ | format buffer (lsp)                             |
|---------+-------------------------------------------------|
| ~m g i~ | goto implementation (lsp)                       |
| ~m g t~ | goto type-definition (lsp)                      |
| ~m g k~ | goto viewport symbol (avy)                      |
| ~m g m~ | browse file symbols (lsp-ui-imenu)              |
| ~m g d~ | find definitions (lsp-ui-peek)                  |
| ~m g l~ | find implementations (lsp-ui-peek)              |
| ~m g r~ | find references (lsp-ui-peek)                   |
| ~m g s~ | find-workspace-symbol (lsp-ui-peek)             |
| ~m g p~ | jump prev (lsp-ui-peek stack - see Note 1)      |
| ~m g n~ | jump next (lsp-ui-peek stack - see Note 1)      |
| ~m g f~ | jump to flycheck error                          |
|---------+-------------------------------------------------|
| ~m h h~ | describe thing at point                         |
|---------+-------------------------------------------------|
| ~m l r~ | lsp-restart-workspace                           |
| ~m l a~ | execute code action                             |
|---------+-------------------------------------------------|
| ~m r r~ | rename                                          |
|---------+-------------------------------------------------|
| ~m T d~ | toggle documentation overlay                    |
| ~m T F~ | toggle documentation overlay function signature |
| ~m T s~ | toggle symbol info overlay                      |
| ~m T S~ | toggle symbol info overlay symbol name          |
| ~m T I~ | toggle symbol info overlay duplicates           |

Note 1: There is a window local jump list dedicated to cross references

** Variables
A number of configuration variables have been exposed via the LSP layer =config.el=.
Sensible defaults have been provided, however they may all be overridden in your .spacemacs, or dynamically using the bindings added
under the derived mode t prefix by =(spacemacs/lsp-bind-keys-for-mode mode)=

| Variable name                   | Default | Description                                                                               |
|---------------------------------+---------+-------------------------------------------------------------------------------------------|
| =lsp-ui-remap-xref-keybindings= | nil     | When non-nil, xref key bindings remapped to lsp-ui-peek-find-{definition,references}      |
| =lsp-ui-doc-enable=             | t       | When non-nil, the documentation overlay is displayed                                      |
| =lsp-ui-doc-include-signature=  | nil     | When nil, signature omitted from lsp-ui-doc overlay (this is usually redundant)           |
| =lsp-ui-sideline-enable=        | t       | When non-nil, the symbol information overlay is displayed                                 |
| =lsp-ui-sideline-show-symbol=   | nil     | When non-nil, the symbol information overlay includes symbol name (redundant for c-modes) |

** Diagnostics
If some features do not work as expected, here is a common check list.
- =M-x lsp-capabilities= If the LSP workspace is initialized correctly
- =M-: xref-backend-functions= should be =(lsp--xref-backend)= for cross
  references
- =M-: completion-at-point-functions= should be =(lsp-completion-at-point)= for
  completion

* Future additions/improvements
** Make =spacemacs/lsp-bind-keys-for-mode= bind conditionally
i.e. only bind keys if the language server supports the capability (queried using =lsp-capabilities=).
=lsp-capabilities= uses current buffer to determine the language server, so this would probably entail adding the bindings dynamically in
a mode hook.

* References
- [[https://github.com/emacs-lsp/lsp-mode][lsp-mode repo]]
- [[https://github.com/emacs-lsp/lsp-ui][lsp-ui repo]]