#+TITLE: LSP layer

* Table of Contents                     :TOC_4_gh:noexport:
- [[#description][Description]]
  - [[#features][Features:]]
- [[#configuration][Configuration]]
  - [[#variables][Variables]]
  - [[#navigation-mode][Navigation mode]]
    - [[#extended-navigation-functions-for-derived-layers][Extended navigation functions for derived layers]]
      - [[#spacemacslsp-define-extensions-layer-name-kind-request-optional-extra-parameters][~spacemacs/lsp-define-extensions layer-name kind request &optional extra-parameters~]]
      - [[#spacemacslsp-bind-extensions-for-mode][~spacemacs/lsp-bind-extensions-for-mode~]]
  - [[#core-keybindings-for-derived-layers][Core keybindings for derived layers]]
    - [[#declared-prefixes][Declared prefixes]]
      - [[#navigation-prefixes][Navigation prefixes]]
    - [[#default-keybindings][Default keybindings]]
  - [[#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.

** 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-navigation=                | `both'  | `simple' or `peek' to bind xref OR lsp-ui-peek navigation functions                       |
| =lsp-ui-remap-xref-keybindings= | nil     | When non-nil, xref keybindings 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) |

** Navigation mode
The ~lsp-navigation~ variable defined in =config.el= allows you to define a preference for lightweight or pretty
(using =lsp-ui-peek=) source navigation styles. By default, the lightweight functions are bound under ~SPC m g~
and the =lsp-ui-peek= variants under ~SPC m G~. Setting ~lsp-navigation~ to either  ~'simple~ or ~'peek~ eliminates
the bindings under ~SPC m G~ and creates bindings under ~SPC m g~ according to the specified preference.

*** Extended navigation functions for derived layers
Some LSP server implementations provide extensions to the protocol, which can be leveraged using ~lsp-find-custom~
or ~lsp-ui-peek-find-custom~. A number of additional functions have been provided to facilitate wrapping these extensions
in a manner consistent with the ~lsp-navigation~ setting.

**** ~spacemacs/lsp-define-extensions layer-name kind request &optional extra-parameters~
Use this to define an extension to the lsp find functions. An example from the c-c++ layer:

#+BEGIN_SRC elisp
  (spacemacs/lsp-define-extensions "c-c++" 'refs-address
                                   "textDocument/references"
                                   '(plist-put (lsp--text-document-position-params) :context '(:role 128)))
#+END_SRC

This defines the following interactive functions:
- ~c-c++/find-refs-address~
- ~c-c++/peek-refs-address~

**** ~spacemacs/lsp-bind-extensions-for-mode~
Use this to bind one or more extensions under ~SPC m g~ and/or ~SPC m G~, as dictated by the value of ~lsp-navigation~.
Using another example from the c-c++ layer:

#+BEGIN_SRC elisp
  (spacemacs/lsp-bind-extensions-for-mode mode "c-c++"
                                          "&" 'refs-address
                                          "R" 'refs-read
                                          "W" 'refs-write
                                          "c" 'callers
                                          "C" 'callees
                                          "v" 'vars)
#+END_SRC

With ~lsp-navigation~ set to ~'both~ (the default), this is equivalent to:

#+BEGIN_SRC elisp
  (spacemacs/set-leader-keys-for-major-mode mode
    "g&" 'c-c++/find-refs-address
    "gR" 'c-c++/find-refs-read
    "gW" 'c-c++/find-refs-write
    "gc" 'c-c++/find-callers
    "gC" 'c-c++/find-callees
    "gv" 'c-c++/find-vars
    "G&" 'c-c++/peek-refs-address
    "GR" 'c-c++/peek-refs-read
    "GW" 'c-c++/peek-refs-write
    "Gc" 'c-c++/peek-callers
    "GC" 'c-c++/peek-callees
    "Gv" 'c-c++/peek-vars)
#+END_SRC
whereas with ~lsp-navigation~ set to ~'peek~, this is equivalent to:

#+BEGIN_SRC elisp
  (spacemacs/set-leader-keys-for-major-mode mode
    "g&" 'c-c++/peek-refs-address
    "gR" 'c-c++/peek-refs-read
    "gW" 'c-c++/peek-refs-write
    "gc" 'c-c++/peek-callers
    "gC" 'c-c++/peek-callees
    "gv" 'c-c++/peek-vars)
#+END_SRC

etc.

** Core keybindings for derived layers
The ~spacemacs/lsp-bind-keys-for-mode mode~ 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                                                            |
|-----------+-------------+----------------------------------------------------------------------------|
| ~SPC m =~ | format      | Source formatting                                                          |
| ~SPC m g~ | goto        | Source navigation                                                          |
| ~SPC m G~ | peek        | Source navigation (lsp-ui-peek overlay)                                    |
| ~SPC m h~ | help        | Help                                                                       |
| ~SPC m b~ | lsp/backend | Catchall. Restart LSP backend, other implementation-specific functionality |
| ~SPC m r~ | refactor    | What it says on the tin                                                    |
| ~SPC m T~ | toggle      | Toggle LSP backend features (documentation / symbol info overlays etc.)    |

**** Navigation prefixes
 The following prefixes have been declared under each of the navigation prefixes (i.e. ~SPC m g~ / ~SPC m G~)

| prefix          | name             | functional area                                          |
|-----------------+------------------+----------------------------------------------------------|
| ~SPC m <g/G> h~ | hierarchy        | Heirarchy (i.e. call/inheritance hierarchy etc. )        |
| ~SPC m <g/G> m~ | member hierarchy | Class/namespace members (functions, nested classes, vars |

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

| binding     | function                                                                     |
|-------------+------------------------------------------------------------------------------|
| ~SPC m = b~ | format buffer (lsp)                                                          |
|-------------+------------------------------------------------------------------------------|
| ~SPC m g t~ | goto type-definition (lsp)                                                   |
| ~SPC m g k~ | goto viewport symbol (avy)                                                   |
| ~SPC m g e~ | browse flycheck errors                                                       |
| ~SPC m g M~ | browse file symbols (lsp-ui-imenu)                                           |
|-------------+------------------------------------------------------------------------------|
| Note        | /Replaced by the lsp-ui-peek equivalents when ~lsp-navigation~ == 'peek/     |
| ~SPC m g i~ | find implementations (lsp)                                                   |
| ~SPC m g d~ | find definitions (xref/lsp)                                                  |
| ~SPC m g r~ | find references (xref/lsp)                                                   |
| ~SPC m g s~ | find-workspace-symbol (lsp-ui)                                               |
| ~SPC m g p~ | goto previous (xref-pop-marker-stack)                                        |
|-------------+------------------------------------------------------------------------------|
| Note        | /Omitted when ~lsp-navigation~ == 'peek or 'simple/                          |
|             | /Bound under ~SPC m g~ rather than ~SPC m G~ when ~lsp-navigation~ == 'peek/ |
| ~SPC m G i~ | find implementation (lsp-ui-peek)                                            |
| ~SPC m G d~ | find definitions (lsp-ui-peek)                                               |
| ~SPC m G r~ | find references (lsp-ui-peek)                                                |
| ~SPC m G s~ | find-workspace-symbol (lsp-ui-peek)                                          |
| ~SPC m G p~ | goto previous (lsp-ui-peek stack - see Note 1)                               |
| ~SPC m G n~ | goto next (lsp-ui-peek stack - see Note 1)                                   |
|-------------+------------------------------------------------------------------------------|
| ~SPC m h h~ | describe thing at point                                                      |
|-------------+------------------------------------------------------------------------------|
| ~SPC m b r~ | lsp-restart-workspace                                                        |
| ~SPC m b a~ | execute code action                                                          |
| ~SPC m b c~ | lsp-capabilities                                                             |
|-------------+------------------------------------------------------------------------------|
| ~SPC m r r~ | rename                                                                       |
|-------------+------------------------------------------------------------------------------|
| ~SPC m T d~ | toggle documentation overlay                                                 |
| ~SPC m T F~ | toggle documentation overlay function signature                              |
| ~SPC m T s~ | toggle symbol info overlay                                                   |
| ~SPC m T S~ | toggle symbol info overlay symbol name                                       |
| ~SPC m T I~ | toggle symbol info overlay duplicates                                        |

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

** 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]]