#+TITLE: LSP layer

#+TAGS: layer|tool

* Table of Contents                     :TOC_5_gh:noexport:
- [[#description][Description]]
  - [[#features][Features:]]
- [[#configuration][Configuration]]
  - [[#variables][Variables]]
  - [[#navigation-mode][Navigation mode]]
- [[#key-bindings][Key bindings]]
  - [[#key-binding-prefixes][Key binding prefixes]]
  - [[#core-key-bindings][Core key bindings]]
  - [[#language-specific-key-binding-extensions][Language-specific key binding extensions]]
    - [[#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~]]
- [[#diagnostics][Diagnostics]]
- [[#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-describe-session= 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
- Consistent core key bindings in LSP modes

* 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 only xref OR lsp-ui-peek navigation functions                                                             |
| =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)                                            |
| =lsp-prefer-flymake=            | nil     | When non-nil, use flymake. When nil, and =lsp-ui-flycheck= is available, use flycheck. When :none, use neither flymake nor flycheck. |

** 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.

* Key bindings
A number of lsp features useful for all/most modes have been bound to the lsp minor mode, meaning they'll be
available in all language layers based on the lsp layer.

** Key binding prefixes
The key bindings are grouped under the following prefixes:

| 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 F~ | folder      | Add/remove folders from workspace                                          |
| ~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.)    |

Some navigation key bindings (i.e. ~SPC m g~ / ~SPC m G~) use an additional level of grouping:

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

** Core key bindings
The lsp minor mode bindings are:

| binding     | function                                                                       |
|-------------+--------------------------------------------------------------------------------|
| ~SPC m = b~ | format buffer (lsp)                                                            |
| ~SPC m = r~ | format region (lsp)                                                            |
|-------------+--------------------------------------------------------------------------------|
| ~SPC m g t~ | goto type-definition (lsp)                                                     |
| ~SPC m g k~ | goto viewport word (avy) (See Note 1)                                          |
| ~SPC m g K~ | goto viewport symbol (avy) (See Note 1)                                        |
| ~SPC m g e~ | browse flycheck errors (lsp-treemacs)                                          |
| ~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 symbol in project (helm-lsp)                                              |
| ~SPC m g S~ | find symbol in all projects (helm-lsp)                                         |
| ~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 2)                                 |
| ~SPC m G n~ | goto next (lsp-ui-peek stack - see Note 2)                                     |
| ~SPC m G E~ | browse flycheck errors (lsp-ui)                                                |
|-------------+--------------------------------------------------------------------------------|
| ~SPC m h h~ | describe thing at point                                                        |
|-------------+--------------------------------------------------------------------------------|
| ~SPC m b s~ | lsp-shutdown-workspace                                                         |
| ~SPC m b r~ | lsp-restart-workspace                                                          |
| ~SPC m b a~ | execute code action                                                            |
| ~SPC m b d~ | lsp-describe-session                                                           |
|-------------+--------------------------------------------------------------------------------|
| ~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                                          |
| ~SPC m T l~ | toggle lenses                                                                  |
|-------------+--------------------------------------------------------------------------------|
| ~SPC m F r~ | Remove workspace folder                                                        |
| ~SPC m F a~ | Add workspace folder                                                           |
| ~SPC m F s~ | Switch workspace folder                                                        |

Note 1: Your language server may not distinguish between the word and symbol variants of this binding.
Note 2: There is a window local jump list dedicated to cross references.

** Language-specific key binding extensions
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.

* Diagnostics
If some features do not work as expected, here is a common check list.
- =M-x lsp-describe-session= 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

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