Added cquery and ccls backend support to c-c++ layer

<<Amendment 1 01/09/2018>>
Incorporated initial feedback from multiple sources (PR discussion)

<<Amendment 2 04/09/2018>>
Incorporated feedback from MaskRay.
Fixed projectile post-config hooks.
Added `c-c++-adopt-subprojects' layer option.

<<Amendment 3 07/09/18>>
Corrected cache section in README to describe new cache defaults introduced by
Amendment 2.

<<Amendment 4 13/09/18>>
Corrected config var names in readme.
Rebased on current develop branch tip.

<<Amendment 5 14/09/18>>
Minor adaptations for compatibility with upstream ccls changes.

<<Amendment 6 21/09/18>>
Bindings updated for consistency with lsp layer lsp-navigation config variable.

<<Amendment 7 1/11/18>>
Rebased

<<Amendment 8 06/11/18>>
Incorporated readme correction from svenihoney.

<<Amendment 9 06/11/18>>
Updated c-c++/refresh-index wrapper for ccls function renamed upstream.
Moved 2 bindings from 'l' to 'b' to reflect updated lsp-layer mnemonic

layers/+lang/c-c++/README.org

@@ -8,15 +8,28 @@
 - [[#install][Install]]
   - [[#layer][Layer]]
   - [[#default-mode-for-header-files][Default mode for header files]]
+  - [[#backends][Backends]]
+    - [[#rtags][RTags]]
+      - [[#external-dependencies][External dependencies]]
+      - [[#configuration][Configuration]]
+    - [[#cquery--ccls-lsp-backends][cquery / ccls (lsp backends)]]
+      - [[#features-1][Features:]]
+      - [[#external-dependencies-1][External dependencies]]
+      - [[#configuration-1][Configuration]]
+      - [[#completion][Completion]]
   - [[#clang-configuration][Clang Configuration]]
     - [[#clang-format][clang-format]]
     - [[#company-clang-and-flycheck][Company-clang and flycheck]]
-  - [[#rtags-configuration][RTags configuration]]
   - [[#enable-google-set-c-style][Enable google-set-c-style]]
   - [[#newlines][Newlines]]
+  - [[#projectile-sub-project-adoption][Projectile sub-project adoption]]
 - [[#key-bindings][Key Bindings]]
   - [[#formatting-clang-format][Formatting (clang-format)]]
-  - [[#rtags][RTags]]
+  - [[#rtags-1][RTags]]
+  - [[#cquery--ccls][cquery / ccls]]
+    - [[#goto][goto]]
+    - [[#helphierarchy][help/hierarchy]]
+    - [[#backend-language-server][backend (language server)]]
 
 * Description
 This layer adds configuration for C/C++ language.
@@ -37,6 +50,7 @@ This layer adds configuration for C/C++ language.
   company-ycmd (when =ycmd= layer is included).
 - Support for [[https://github.com/realgud/realgud][realgud]] debugger.
 - Support for [[https://github.com/Andersbakken/rtags][rtags]].
+- Support for [[https://github.com/cquery-project/cquery][cquery]] or [[https://github.com/MaskRay/ccls][ccls]] as an lsp backend.
 
 * Install
 ** Layer
@@ -59,6 +73,116 @@ by setting the variable =c-c++-default-mode-for-headers= to =c++-mode=.
 variable at the root of your project. More info on directory local variables
 can be found in the [[http://www.gnu.org/software/emacs/manual/html_node/elisp/Directory-Local-Variables.html][dir-locals]].
 
+** Backends
+This layer supports the selection of one of 3 available backends for code navigation etc via the =c-c++-backend= configuration variable.
+
+*** RTags
+RTags is a well established clang-based source code indexing tool.
+
+**** External dependencies
+Install the RTags server via [[https://formulae.brew.sh/formula/rtags][homebrew]], the [[https://aur.archlinux.org/packages/rtags/][aur]] or from source according to the instructions [[https://github.com/Andersbakken/rtags][here]].
+N.B. RTags is not supported on Windows at the time of writing, although there is an [[https://github.com/Andersbakken/rtags/issues/770][open issue with some recent activity]] on github.
+
+**** Configuration
+To enable support for =rtags=, set the layer variable
+=c-c++-enable-rtags-support= to =t= in your dotfile.
+
+#+BEGIN_SRC emacs-lisp
+  (setq-default dotspacemacs-configuration-layers
+                '((c-c++ :variables c-c++-backend 'rtags)))
+#+END_SRC
+
+This will also enable =company-rtags= to be used as a backend for
+auto-completion (when =auto-completion= layer is included).
+To prevent this, while retaining the rest of Rtags functionality,
+set the variable =c-c++-rtags-completion= to =nil=:
+
+#+BEGIN_SRC emacs-lisp
+  (setq-default dotspacemacs-configuration-layers
+                '((c-c++ :variables
+                         c-c++-backend 'rtags
+                         c-c++-enable-rtags-completion nil)))
+#+END_SRC
+
+*** cquery / ccls (lsp backends)
+[[https://github.com/cquery-project/cquery][cquery]] and [[https://github.com/MaskRay/ccls][ccls]] are alternative implementations of the language server protocol based on libclang. They claim to be more efficient
+than existing tools at indexing large code bases.
+
+**** Features:
+- Cross references (definitions, references, base/derived classes/methods, type instances, ...)
+- Diagnostics
+- Completion with =company-lsp=
+- Semantic highlighting
+- See more on [[https://github.com/cquery-project/cquery/wiki/Emacs]]
+- Cross-platform - functional on Windows, Linux and OSX.
+
+**** External dependencies
+Install one (or both) of the following:
+
+***** cquery server
+Install the =cquery= server. [[https://github.com/cquery-project/cquery/wiki/Getting-started][Instructions]].
+
+***** ccls server
+Install the =ccls= server. [[https://github.com/MaskRay/ccls/wiki/Getting-started][Instructions]].
+
+**** Configuration
+***** Basic
+Select either =cquery= or =ccls= as the =c-c++= layer backend by adding the following to your dotfile:
+
+#+BEGIN_SRC emacs-lisp
+  (setq-default dotspacemacs-configuration-layers
+                '((c-c++ :variables c-c++-backend 'lsp-cquery))) ;or 'lsp-ccls
+#+END_SRC
+
+N.B. The [[../../+tools/lsp/README.org][LSP layer]] will be loaded automatically if either backend is selected.
+
+***** Setting path to backend executable
+The basic configuration above should work if the cquery/ccls executable folder is present in your path. If not, you can set the path explicitly.
+
+#+BEGIN_SRC emacs-lisp
+  (setq-default dotspacemacs-configuration-layers
+                '((c-c++ :variables
+                         c-c++-backend 'lsp-cquery
+                         c-c++-lsp-executable "/path/to/bin/cquery/or/ccls")))
+#+END_SRC
+
+If you need to expand =~= in the path, you can use =file-truename= like
+
+#+BEGIN_SRC emacs-lisp
+  (setq-default dotspacemacs-configuration-layers
+                '((c-c++ :variables
+                         c-c++-backend 'lsp-cquery
+                         c-c++-lsp-executable (file-truename "~/bin/cquery/or/ccls"))))
+#+END_SRC
+
+***** Semantic highlighting
+Semantic highlighting is disabled by default. To enable, set the =c-c++-lsp-sem-highlight-method= variable to either ='font-lock= or ='overlay=.
+To enable the rainbow semantic highlighting colour theme, set =c-c++-lsp-sem-highlight-rainbow= to =t=.
+
+***** Additional configuration options
+Both lsp backends are configured to store their index cache in a subdirectory of =.emacs.d/cache=. This can be overridden by
+specifying an explicit =c-c++-lsp-cache-dir=. Setting this value to a relative path will cause the index cache to be placed in a
+subdirectory of your project root.
+
+There are other initialization options such as the number of indexer threads, cache serialization format.
+They have good default values. See [[file:./config.el][config.el]] and the backends' respective homepages for more info.
+- [[https://github.com/cquery-project/cquery/wiki/Emacs][Emacs section of =cquery= wiki]]
+- [[https://github.com/MaskRay/ccls/wiki/Emacs][Emacs section of =ccls= wiki]]
+
+***** Example dotspacemacs-configuration-layers entry
+#+BEGIN_SRC emacs-lisp
+  (setq-default dotspacemacs-configuration-layers
+                '((c-c++ :variables
+                         c-c++-adopt-subprojects t
+                         c-c++-backend 'lsp-ccls
+                         c-c++-lsp-executable (file-truename "~/dev/cpp/ccls/Release/ccls")
+                         c-c++-lsp-sem-highlight-rainbow t)))
+#+END_SRC
+
+**** Completion
+=company-lsp= provides completion functionality. Client-side cache and sorting have been disabled in favour of server,
+as recommended by =cquery=/=ccls= wikis.
+
 ** Clang Configuration
 To enable Clang support, set the layer variable =c-c++-enable-clang-support=
 to =t= in the dotfile:
@@ -68,6 +192,8 @@ to =t= in the dotfile:
                 '((c-c++ :variables c-c++-enable-clang-support t)))
 #+END_SRC
 
+N.B. do not set this option if either the =cquery= or =ccls= backend
+
 *** clang-format
 [[http://clang.llvm.org/docs/ClangFormat.html][clang-format]] allows reformatting either a selected region of code
 (=clang-format-region=) or a whole buffer (=clang-format-buffer=)
@@ -80,8 +206,8 @@ To enable automatic buffer formatting on save, set the variable
 =c-c++-enable-clang-format-on-save= to =t=:
 
 #+BEGIN_SRC emacs-lisp
-  (setq-default dotspacemacs-configuration-layers '(
+  (setq-default dotspacemacs-configuration-layers
-    (c-c++ :variables c-c++-enable-clang-format-on-save t)))
+                '((c-c++ :variables c-c++-enable-clang-format-on-save t)))
 #+END_SRC
 
 *** Company-clang and flycheck
@@ -93,25 +219,6 @@ Not only does this allow proper autocomplete on projects with extra includes and
 flags, but there is also support for flycheck so that it doesn’t complain about
 missing header files.
 
-** RTags configuration
-To enable support for =rtags=, set the layer variable
-=c-c++-enable-rtags-support= to =t= in your dotfile.
-
-#+BEGIN_SRC emacs-lisp
-  (setq-default dotspacemacs-configuration-layers
-    '((c-c++ :variables c-c++-enable-rtags-support t)))
-#+END_SRC
-
-This will also enable =company-rtags= to be used as a backend for
-auto-completion (when =auto-completion= layer is included).
-To prevent this, while retaining the rest of Rtags functionality,
-set the variable =c-c++-enable-rtags-support= to ='no-completion=:
-
-#+BEGIN_SRC emacs-lisp
-  (setq-default dotspacemacs-configuration-layers
-    '((c-c++ :variables c-c++-enable-rtags-support 'no-completion)))
-#+END_SRC
-
 ** Enable google-set-c-style
 If you have clang enabled with =clang-format= as described earlier in this page
 you may not have a lot of neeed for =google-set-c-style= if you are already
@@ -140,7 +247,6 @@ set that up like this:
   (c-c++ :variables
          c-c++-enable-google-style t
          c-c++-enable-google-newline t)
-#+END_SRC
 
 ** Newlines
 You can enable the =Auto-newline= minor mode that automatically adds newlines
@@ -151,6 +257,18 @@ after certain characters by setting the =c-c++-enable-auto-newline= variable.
          c-c++-enable-auto-newline t)
 #+END_SRC
 
+** Projectile sub-project adoption
+To prevent projectile from using subproject root when visiting files in a subproject,
+set =c-c++-adopt-subprojects= to =t=.
+
+#+BEGIN_SRC emacs-lisp
+  (c-c++ :variables
+         c-c++-adopt-subprojects t)
+#+END_SRC emacs-lisp
+
+This is based on a recommendation on the =cquery= and =ccls= wikis, but should be more
+generally applicable.
+
 * Key Bindings
 
 | Key Binding | Description                                                   |
@@ -160,7 +278,7 @@ after certain characters by setting the =c-c++-enable-auto-newline= variable.
 | ~SPC m g A~ | open matching file in another window                          |
 |             | (e.g. switch between .cpp and .h, requires a project to work) |
 | ~SPC m D~   | disaster: disassemble c/c++ code                              |
-| ~SPC m r~   | srefactor: refactor thing at point.                           |
+| ~SPC m r .~ | srefactor: refactor thing at point.                           |
 
 *Note:* [[https://github.com/tuhdo/semantic-refactor][semantic-refactor]] is only available for Emacs 24.4+.
 
@@ -204,3 +322,37 @@ after certain characters by setting the =c-c++-enable-auto-newline= variable.
 | ~SPC m g V~ | print enum value at point       |
 | ~SPC m g X~ | fix fixit at point              |
 | ~SPC m g Y~ | cycle overlays on screen        |
+
+** cquery / ccls
+The keybindings listed below are in addition to the default keybindings defined by the [[file:../../+tools/lsp/README.org][LSP layer]].
+
+*** goto
+
+| Key Binding | Description               |
+|-------------+---------------------------|
+| ~SPC m g &~ | find references (address) |
+| ~SPC m g R~ | find references (read)    |
+| ~SPC m g W~ | find references (write)   |
+| ~SPC m g c~ | find callers              |
+| ~SPC m g C~ | find callees             |
+| ~SPC m g v~ | vars                      |
+
+*** help/hierarchy
+
+| Key Binding | Description                 |
+|-------------+-----------------------------|
+| ~SPC m h b~ | base class(es)              |
+| ~SPC m h d~ | derived class(es)           |
+| ~SPC m h c~ | call hierarchy              |
+| ~SPC m h C~ | call hierarchy (inv)        |
+| ~SPC m h i~ | inheritance hierarchy       |
+| ~SPC m h I~ | inheritance hierarchy (inv) |
+| ~SPC m h m~ | member hierarchy            |
+| ~SPC m h M~ | member hierarchy (inv)      |
+
+*** backend (language server)
+
+| Key Binding | Description                              |
+|-------------+------------------------------------------|
+| ~SPC m b f~ | refresh index (e.g. after branch change) |
+| ~SPC m b p~ | preprocess file                          |

layers/+lang/c-c++/config.el

@@ -17,6 +17,13 @@
 (defconst c-c++-mode-hooks '(c-mode-hook c++-mode-hook)
   "Primary hooks of the `c-c++' layer.")
 
+(defconst c-c++-lsp-backends '(lsp-cquery lsp-ccls)
+  "Language Server Protocol (LSP) backends supported by the `c-c++' layer.")
+
+(defvar c-c++-backend nil
+  "If `lsp-cquery' or `lsp-ccls' then selects language server protocol backend (cquery or ccls).
+  If `rtags' then enables rtags support")
+
 (defvar c-c++-enable-auto-newline nil
   "If non nil then enables the `Auto-newline' minor mode.")
 
@@ -31,9 +38,8 @@
   "If non-nil `google-make-newline-indent' will be added as as
   `c-mode-common-hook'.")
 
-(defvar c-c++-enable-rtags-support nil
+(defvar c-c++-enable-rtags-completion t
-  "If non nil Rtags related packages and configuration are enabled.
+  "If `nil', RTags completion is disabled when the RTags backend is enabled.")
-  If `no-completion', enable all but completion.")
 
 (defvar c-c++-enable-clang-format-on-save nil
   "If non-nil, automatically format code with ClangFormat on
@@ -44,3 +50,36 @@
 
 (defvar c-c++-default-mode-for-headers 'c-mode
   "Default mode to open header files. Can be `c-mode' or `c++-mode'.")
+
+(defvar c-c++-adopt-subprojects nil
+  "When non-nil, projectile will remember project root when visiting files in subprojects")
+
+;; c-c++-lsp-backend variables
+(defvar c-c++-lsp-cache-dir nil
+  "Cache directory. Absolute and relative paths supported.")
+
+(defvar c-c++-lsp-executable nil
+  "Path to cquery/ccls executable (default value assumes it's in the path)")
+
+(defvar c-c++-lsp-project-whitelist nil
+  "A list of project directory patterns for which lsp-c-c++ should be
+initialized. This overrides `c-c++-lsp-project-blacklist'.")
+
+(defvar c-c++-lsp-project-blacklist nil
+  "A list of project root patterns for which lsp-c-c++ shouldn't be
+initialized. `c-c++-lsp-project-whitelist' is checked first, then this,
+if no pattern matches the project root, lsp-c-c++ will be initialized.")
+
+(defvar c-c++-lsp-sem-highlight-method nil
+  "Set to 'font-lock or 'overlay to enable semantic highlighting")
+
+(defvar c-c++-lsp-sem-highlight-rainbow nil
+  "When non-nil, use rainbow semantic highlighting")
+
+;; I've left cquery/ccls -extra-init-params separate for now, as one has defaults while the other doesn't
+;; Just to facilitate switching between the two easily
+(defvar c-c++-lsp-extra-init-params '(:cacheFormat "msgpack")
+  "Extra initialisation parameters to pass to the backend. See
+https://github.com/cquery-project/cquery/blob/master/src/config.h or
+https://github.com/MaskRay/ccls/blob/master/src/config.h
+for details.")

layers/+lang/c-c++/funcs.el

@@ -9,6 +9,9 @@
 ;;
 ;;; License: GPLv3
 
+(require 'cl-lib)
+(require 'subr-x)
+
 (defun spacemacs//c-toggle-auto-newline ()
   "Toggle auto-newline."
   (c-toggle-auto-newline 1))
@@ -157,9 +160,9 @@ and the arguments for flyckeck-clang based on a project-specific text file."
            rtags-last-request-not-indexed)
       (gtags-find-tag)))
 
-(defun spacemacs/c-c++-tags-find-references-at-point (&optional prefix)
+(defun spacemacs/c-c++-tags-find-refs-at-point (&optional prefix)
   (interactive "P")
-  (if (and (not (rtags-find-references-at-point prefix))
+  (if (and (not (rtags-find-refs-at-point prefix))
            rtags-last-request-not-indexed)
       (gtags-find-rtag)))
 
@@ -182,3 +185,169 @@ and the arguments for flyckeck-clang based on a project-specific text file."
   (interactive)
   (call-interactively (if (spacemacs/c-c++-use-rtags t)
                           'rtags-imenu 'idomenu)))
+
+
+;; lsp
+(defun spacemacs//c-c++-lsp-enabled ()
+  "Return true if one or other of the lsp backends is enabled"
+  (member c-c++-backend c-c++-lsp-backends))
+
+;; -- BEGIN helper functions for common configuration of cquery and ccls backends
+(defun spacemacs//c-c++-lsp-backend ()
+  "Return a string representation of the LSP backend specified by the `c-c++-backend' configuration variable, without the `lsp-' prefix."
+  (ecase c-c++-backend
+    ('lsp-ccls "ccls")
+    ('lsp-cquery "cquery")))
+
+(defun spacemacs//c-c++-lsp-string (prefix suffix)
+  (concat prefix (spacemacs//c-c++-lsp-backend) suffix))
+
+(defun spacemacs//c-c++-lsp-symbol (prefix suffix)
+  "Return a symbol for the LSP backend specified by the `c-c++-backend' configuration variable."
+  (intern (spacemacs//c-c++-lsp-string prefix suffix)))
+
+(defun spacemacs//c-c++-lsp-call-function (prefix suffix &rest args)
+  (apply (spacemacs//c-c++-lsp-symbol prefix suffix) args))
+
+(defun spacemacs//c-c++-lsp-funcall-interactively (prefix suffix &rest args)
+  (funcall-interactively (spacemacs//c-c++-lsp-symbol prefix suffix) args))
+
+(defun spacemacs//c-c++-lsp-funcall-interactively-no-args (prefix suffix)
+  (funcall-interactively (spacemacs//c-c++-lsp-symbol prefix suffix)))
+
+(defun spacemacs//c-c++-lsp-set-symbol (prefix suffix value)
+  (set (spacemacs//c-c++-lsp-symbol prefix suffix) (symbol-value value)))
+
+(defun spacemacs//c-c++-lsp-set-config (param prefix suffix)
+  (when (symbol-value param) (spacemacs//c-c++-lsp-set-symbol prefix suffix param)))
+
+(defun spacemacs//c-c++-lsp-apply-config (suffix)
+  (spacemacs//c-c++-lsp-set-config (intern (concat "c-c++-lsp-" suffix)) nil (concat "-" suffix)))
+;; -- END helper functions for common configuration of cquery and ccls backends
+
+
+(defun spacemacs//c-c++-lsp-enable ()
+  "Enable the LSP backend specified by the `c-c++-backend' configuration variable."
+    (progn (condition-case nil
+             (spacemacs//c-c++-lsp-call-function "lsp-" "-enable")
+             (user-error nil))))
+
+(defun spacemacs//c-c++-lsp-config ()
+  "Configure the LSP backend specified by the `c-c++-backend' configuration variable."
+    (progn
+      (spacemacs//c-c++-lsp-setup-company)
+      (spacemacs//c-c++-lsp-define-extensions)
+      (spacemacs//c-c++-lsp-wrap-functions)
+      (setq-default flycheck-disabled-checkers '(c/c++-clang c/c++-gcc))
+
+      (if (eq c-c++-lsp-cache-dir nil)
+        (progn
+          (setq c-c++-lsp-cache-dir (file-truename(concat "~/.emacs.d/.cache/" (symbol-name c-c++-backend))))
+          (message (concat "c-c++: No c-c++-lsp-cache-dir specified: defaulting to " c-c++-lsp-cache-dir))))
+
+      (dolist (param '("executable" "extra-init-params" "cache-dir" "project-whitelist" "project-blacklist" "sem-highlight-method"))
+        (spacemacs//c-c++-lsp-apply-config param))
+
+      (when c-c++-lsp-sem-highlight-rainbow
+        (unless c-c++-lsp-sem-highlight-method
+          (progn
+            (setq c-c++-lsp-sem-highlight-method 'font-lock)
+            (message "c-c++: No semantic highlight method specified. Defaulting to `font-lock'.")))
+        (ecase c-c++-backend
+          ('lsp-cquery (cquery-use-default-rainbow-sem-highlight))
+          ('lsp-ccls (ccls-use-default-rainbow-sem-highlight))))
+
+      (dolist (mode c-c++-modes)
+        (spacemacs/lsp-bind-keys-for-mode mode)
+        (spacemacs//c-c++-lsp-bind-keys-for-mode mode))
+
+      (evil-set-initial-state '(spacemacs//c-c++-lsp-symbol nil "-tree-mode") 'emacs)
+      ;;evil-record-macro keybinding clobbers q in cquery-tree-mode-map for some reason?
+      (evil-make-overriding-map (symbol-value (spacemacs//c-c++-lsp-symbol nil "-tree-mode-map")))))
+
+(defun spacemacs//c-c++-lsp-setup-company ()
+  "Setup LSP backend auto-completion."
+    (progn
+      (spacemacs|add-company-backends :backends company-lsp :modes c-mode-common)
+      ;;Disable client-side cache and sorting, as server does a better job
+      (setq company-transformers nil company-lsp-async t company-lsp-cache-candidates nil)))
+
+(defun spacemacs//c-c++-lsp-wrap-functions ()
+  "Wrap navigation functions for the LSP backend specified by the `c-c++-backend' configuration variable."
+  (defun c-c++/call-hierarchy () (interactive) (spacemacs//c-c++-lsp-funcall-interactively nil "-call-hierarchy" nil))
+  (defun c-c++/call-hierarchy-inv () (interactive) (spacemacs//c-c++-lsp-funcall-interactively nil "-call-hierarchy" t))
+  (defun c-c++/inheritance-hierarchy () (interactive) (spacemacs//c-c++-lsp-funcall-interactively nil "-inheritance-hierarchy"))
+  (defun c-c++/inheritance-hierarchy-inv () (interactive) (spacemacs//c-c++-lsp-funcall-interactively nil "-inheritance-hierarchy" t))
+  (defun c-c++/member-hierarchy () (interactive) (spacemacs//c-c++-lsp-funcall-interactively-no-args nil "-member-hierarchy"))
+  (defun c-c++/preprocess-file () (interactive) (spacemacs//c-c++-lsp-funcall-interactively nil "-preprocess-file"))
+  (defun c-c++/refresh-index () (interactive) ()
+    (ecase c-c++-backend
+      ('lsp-cquery (cquery-freshen-index))
+      ('lsp-ccls (ccls-reload)))))
+
+(defun spacemacs//c-c++-lsp-bind-keys-for-mode (mode)
+  "Bind LSP backend functions for the specified mode."
+  (spacemacs/set-leader-keys-for-major-mode mode
+    ;; backend
+    "bf" #'c-c++/refresh-index
+    "bp" #'c-c++/preprocess-file
+    ;; goto
+    "gf" 'find-file-at-point
+    "gF" 'ffap-other-window
+    ;; hierarchy
+    "ghc" #'c-c++/call-hierarchy
+    "ghC" #'c-c++/call-hierarchy-inv
+    "ghi" #'c-c++/inheritance-hierarchy
+    "ghI" #'c-c++/inheritance-hierarchy-inv
+    ;; members
+    "gmh" #'c-c++/member-hierarchy)
+
+  (spacemacs/lsp-bind-extensions-for-mode mode "c-c++"
+    "&" 'refs-address
+    "R" 'refs-read
+    "W" 'refs-write
+    "c" 'callers
+    "C" 'callees
+    "v" 'vars
+    "hb" 'base) ;;Replace this with lsp-goto-implementation in lsp-layer?
+
+  (when (eq c-c++-backend 'lsp-ccls)
+    (spacemacs/set-leader-keys-for-major-mode mode
+      "bR" 'ccls-reload)
+    (spacemacs/lsp-bind-extensions-for-mode mode "c-c++"
+      "mc" 'member-classes
+      "mf" 'member-functions
+      "mv" 'member-vars)))
+
+(defun spacemacs//c-c++-lsp-define-extensions ()
+  "Wrap some backend-specific extensions using the find functions provided by lsp-mode and lsp-ui"
+  (spacemacs//c-c++-lsp-call-function "spacemacs//c-c++-lsp-define-" "-extensions")
+
+  (spacemacs/lsp-define-extensions "c-c++" 'vars
+    (spacemacs//c-c++-lsp-string "$" "/vars"))
+
+  (spacemacs/lsp-define-extensions "c-c++" 'refs-address
+    "textDocument/references"
+    '(plist-put (lsp--text-document-position-params) :context '(:role 128)))
+
+  (spacemacs/lsp-define-extensions "c-c++" 'refs-read
+    "textDocument/references"
+    '(plist-put (lsp--text-document-position-params) :context '(:role 8)))
+
+  (spacemacs/lsp-define-extensions "c-c++" 'refs-write
+    "textDocument/references"
+    '(plist-put (lsp--text-document-position-params) :context '(:role 16))))
+
+(defun spacemacs//c-c++-lsp-define-cquery-extensions ()
+  (spacemacs/lsp-define-extensions "c-c++" 'callers "$cquery/callers")
+  (spacemacs/lsp-define-extensions "c-c++" 'callees "$cquery/callers" '(:callee t))
+  (spacemacs/lsp-define-extensions "c-c++" 'base "$cquery/base"))
+
+(defun spacemacs//c-c++-lsp-define-ccls-extensions ()
+  (spacemacs/lsp-define-extensions "c-c++" 'callers "$ccls/call")
+  (spacemacs/lsp-define-extensions "c-c++" 'callees "$ccls/call" '(:callee t))
+  (spacemacs/lsp-define-extensions "c-c++" 'base "$ccls/inheritance" '(:levels 3))
+  ;;ccls features without a cquery analogue...
+  (spacemacs/lsp-define-extensions "c-c++" 'member-classes "$ccls/member" `(:kind 2))
+  (spacemacs/lsp-define-extensions "c-c++" 'member-functions "$ccls/member" `(:kind 3))
+  (spacemacs/lsp-define-extensions "c-c++" 'member-vars "$ccls/member" `(:kind 0)))

layers/+lang/c-c++/layers.el

@@ -0,0 +1,14 @@
+;;; layers.el --- C/C++ Layer declarations File for Spacemacs
+;;
+;; Copyright (c) 2012-2018 Sylvain Benner & Contributors
+;;
+;; Author: Sylvain Benner <sylvain.benner@gmail.com>
+;; URL: https://github.com/syl20bnr/spacemacs
+;;
+;; This file is not part of GNU Emacs.
+;;
+;;; License: GPLv3
+
+(when (and (boundp 'c-c++-backend)
+           (member c-c++-backend '(lsp-cquery lsp-ccls)))
+  (configuration-layer/declare-layer 'lsp))

layers/+lang/c-c++/packages.el

@@ -36,7 +36,11 @@
      stickyfunc-enhance
      xcscope
      ycmd
-    ))
+     ;;lsp-backend
+     (cquery :requires lsp-mode)
+     (ccls :requires lsp-mode)
+     projectile))
+
 
 (defun c-c++/init-cc-mode ()
   (use-package cc-mode
@@ -60,7 +64,7 @@
 
 (defun c-c++/init-clang-format ()
   (use-package clang-format
-    :if c-c++-enable-clang-support
+    :if (or c-c++-enable-clang-support (spacemacs//c-c++-lsp-enabled))
     :init
     (progn
       (when c-c++-enable-clang-format-on-save
@@ -75,10 +79,15 @@
   (when (configuration-layer/package-used-p 'cmake-mode)
     (spacemacs|add-company-backends :backends company-cmake :modes cmake-mode))
   (when c-c++-enable-clang-support
-    (spacemacs|add-company-backends :backends company-clang
+    (if (spacemacs//c-c++-lsp-enabled)
-      :modes c-mode-common)
+      (display-warning :error "`c-c++-enable-clang-support' ignored when using lsp backend")
+      (progn
+        (spacemacs|add-company-backends :backends company-clang :modes c-mode-common)
+        (when c-c++-enable-c++11
+          (setq company-clang-arguments '("-std=c++11")))
         (setq company-clang-prefix-guesser 'spacemacs/company-more-than-prefix-guesser)
-    (spacemacs/add-to-hooks 'spacemacs/c-c++-load-clang-args c-c++-mode-hooks)))
+        (spacemacs/add-to-hooks 'spacemacs/c-c++-load-clang-args c-c++-mode-hooks)
+        ()))))
 
 (defun c-c++/init-company-c-headers ()
   (use-package company-c-headers
@@ -89,8 +98,7 @@
 
 (defun c-c++/init-company-rtags ()
   (use-package company-rtags
-    :if (and c-c++-enable-rtags-support
+    :if (and (eq c-c++-backend 'rtags) c-c++-enable-rtags-completion)
-             (not (eq c-c++-enable-rtags-support 'no-completion)))
     :defer t
     :init
     (progn
@@ -125,7 +133,7 @@
 ;; TODO lazy load this package
 (defun c-c++/init-flycheck-rtags ()
   (use-package flycheck-rtags
-    :if c-c++-enable-rtags-support))
+    :if (eq c-c++-backend 'rtags)))
 
 (defun c-c++/post-init-ggtags ()
   (add-hook 'c-mode-local-vars-hook #'spacemacs/ggtags-mode-enable)
@@ -161,19 +169,19 @@
 ;; TODO lazy load this package
 (defun c-c++/init-helm-rtags ()
   (use-package helm-rtags
-    :if c-c++-enable-rtags-support
+    :if (eq c-c++-backend 'rtags)
     :init (setq rtags-display-result-backend 'helm)))
 
 ;; TODO lazy load this package
 (defun c-c++/init-ivy-rtags ()
   (use-package ivy-rtags
-    :if c-c++-enable-rtags-support
+    :if (eq c-c++-backend 'rtags)
     :init (setq rtags-display-result-backend 'ivy)))
 
 ;; TODO lazy load this package
 (defun c-c++/init-rtags ()
   (use-package rtags
-    :if c-c++-enable-rtags-support
+    :if (eq c-c++-backend 'rtags)
     :init
     (progn
       (setq rtags-autostart-diagnostics t)
@@ -227,7 +235,7 @@
 
 (defun c-c++/post-init-srefactor ()
   (dolist (mode c-c++-modes)
-    (spacemacs/set-leader-keys-for-major-mode mode "r" 'srefactor-refactor-at-point))
+    (spacemacs/set-leader-keys-for-major-mode mode "r." 'srefactor-refactor-at-point))
   (spacemacs/add-to-hooks 'spacemacs/load-srefactor c-c++-mode-hooks))
 
 (defun c-c++/post-init-stickyfunc-enhance ()
@@ -250,3 +258,46 @@
     :post-init
     (dolist (mode c-c++-modes)
       (spacemacs/set-leader-keys-for-major-mode mode "gi" 'cscope-index-files))))
+
+;; BEGIN LSP BACKEND PACKAGES
+
+;; See also https://github.com/cquery-project/cquery/wiki/Emacs
+(defun c-c++/init-cquery ()
+  (use-package cquery
+    :if (eq c-c++-backend 'lsp-cquery)
+    :defer t
+    :commands lsp-cquery-enable
+    :init
+    (add-hook 'c-mode-common-hook #'spacemacs//c-c++-lsp-enable)
+    :config
+    (spacemacs//c-c++-lsp-config)))
+
+;; See also https://github.com/MaskRay/ccls/wiki/Emacs
+(defun c-c++/init-ccls ()
+  (use-package ccls
+    :if (eq c-c++-backend 'lsp-ccls)
+    :defer t
+    :commands lsp-ccls-enable
+    :init
+    (add-hook 'c-mode-common-hook #'spacemacs//c-c++-lsp-enable)
+    :config
+    (spacemacs//c-c++-lsp-config)))
+
+;;Intentionally adding both cquery and ccls cache dirs to ignore list, to facilitate switching between
+;;two without multiple caches polluting projectile find file results
+(defun c-c++/pre-init-projectile ()
+  (spacemacs|use-package-add-hook projectile
+    :post-config
+    (progn
+      (add-to-list 'projectile-globally-ignored-directories ".cquery_cached_index")
+      (add-to-list 'projectile-globally-ignored-directories ".ccls-cache")
+      (when c-c++-lsp-cache-dir
+        (add-to-list 'projectile-globally-ignored-directories c-c++-lsp-cache-dir))
+      (when c-c++-adopt-subprojects
+        (setq projectile-project-root-files-top-down-recurring
+          (append '("compile_commands.json"
+                     ".cquery"
+                     ".ccls")
+            projectile-project-root-files-top-down-recurring))))))
+
+;; END LSP BACKEND PACKAGES