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
@@ -52,22 +66,134 @@ by setting the variable =c-c++-default-mode-for-headers= to =c++-mode=.
 
 #+BEGIN_SRC emacs-lisp
   (setq-default dotspacemacs-configuration-layers
-    '((c-c++ :variables c-c++-default-mode-for-headers 'c++-mode)))
+                '((c-c++ :variables c-c++-default-mode-for-headers 'c++-mode)))
 #+END_SRC
 
 *Note:* To set the variable for a given project, create a directory local
 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:
 
 #+BEGIN_SRC emacs-lisp
   (setq-default dotspacemacs-configuration-layers
-    '((c-c++ :variables c-c++-enable-clang-support t)))
+                '((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=)
@@ -81,7 +207,7 @@ To enable automatic buffer formatting on save, set the variable
 
 #+BEGIN_SRC emacs-lisp
   (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
-  "If non nil Rtags related packages and configuration are enabled.
-  If `no-completion', enable all but completion.")
+(defvar c-c++-enable-rtags-completion t
+  "If `nil', RTags completion is disabled when the RTags backend is enabled.")
 
 (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.")