c-c++ layer : Added doxygen support and keybindings via gendoxy

<<Amendment 1>> Corrected two  whitespace issues as per lebensterben's
comments.

CHANGELOG.develop

@@ -1560,12 +1560,14 @@ Other:
   - Fixed the =c-c++-default-mode-for-headers= should not affect the default
     behavior that opening a .h file will turn C or C++ mode depending on
     language used in Emacs > 26.1+ (thanks to Lin Sun)
+  - Added =Doxygen= doc comment generation using =gendoxy= (thanks to Cormac Cannon)
 - Key bindings:
   - ~SPC m = =~ clang-format current region or buffer (thanks to Dela Anthonio)
   - ~SPC m = f~ clang-format current function (thanks to Dela Anthonio)
   - Declare =mg= prefix as =goto= (thanks to Dela Anthonio)
   - Support =rtags=, available under ~SPC m g~ prefix
     (thanks to Alexander Dalshov and Sylvain Benner)
+  - =Doxygen=/=gendoxy= keybindings under ~SPC m i~ prefix
 - Fixes:
   - Fixed a typo by moving one closing parenthesis :-) (thanks to Richard Kim)
   - Fixed clang format on save (thanks to Dela Anthonio and Silver Chan)

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

@@ -37,6 +37,7 @@
   - [[#enable-google-set-c-style][Enable google-set-c-style]]
   - [[#newlines][Newlines]]
   - [[#projectile-sub-project-adoption][Projectile sub-project adoption]]
+  - [[#source-code-documentation-using-doxygen][Source code documentation using Doxygen]]
 - [[#key-bindings][Key bindings]]
   - [[#lsp-1][LSP]]
     - [[#ccls][ccls]]
@@ -46,6 +47,7 @@
       - [[#gotomember][goto/member]]
     - [[#debugger][debugger]]
   - [[#rtags-1][RTags]]
+  - [[#doxygen][Doxygen]]
   - [[#additional-key-bindings][Additional key bindings]]
     - [[#disassemble][Disassemble]]
     - [[#formatting-clang-format][Formatting (clang-format)]]
@@ -65,7 +67,8 @@ This layer adds configuration for C/C++ language.
 - Auto-completion via company (=auto-completion= layer required)
 - Support code reformatting with [[http://clang.llvm.org/docs/ClangFormat.html][clang-format]].
 - Support for disassembly of code with [[https://github.com/jart/disaster][disaster]].
-- =sematic= layer integration:
+- [[https://www.doxygen.nl][Doxygen]] code documentation comment generation (using [[https://github.com/mp81ss/gendoxy][gendoxy]]).
+- =semantic= layer integration:
   - Function or variable definition at the bottom
   - Current function cursor is at the top. See [[https://github.com/tuhdo/semantic-stickyfunc-enhance][stickyfunc-demos]] for
     demos in some programming languages.
@@ -323,7 +326,7 @@ may want =google-c-style= enabled and added to your common hooks.
 To get =google-c-style= actually install itself into your C/C++ common hooks,
 you need to have =c-c++-enable-google-style= defined to true when you load the
 C-C++ lang in Spacemacs. In your =~/.spacemacs= file, a possible way that this
-would look is that in your list of =dostpacemacs-configuration-layers= you have
+would look is that in your list of =dotspacemacs-configuration-layers= you have
 an entry like
 
 #+BEGIN_SRC emacs-lisp
@@ -358,6 +361,9 @@ set =c-c++-adopt-subprojects= to =t=.
 This is based on a recommendation on the =ccls= wikis, but should be more
 generally applicable.
 
+** Source code documentation using Doxygen
+The =gendoxy= package allows automatic generation of structured code documentation comments suitable for post-processing using [[https://www.doxygen.nl][Doxygen]]. Key bindings have been provided to insert a file header comment, to document a definition (function, struct, enum etc.) or a group. See the [[https://github.com/mp81ss/gendoxy][gendoxy documentation]] for further information.
+
 * Key bindings
 ** LSP
 The default key bindings for the LSP implementations are defined and documented in
@@ -491,6 +497,19 @@ A ~[ccls]~ suffix indicates that the binding is for the indicated backend only.
 | ~SPC m g X~ | fix fixit at point              |
 | ~SPC m g Y~ | cycle overlays on screen        |
 
+** Doxygen
+
+| Key binding | Description                                                         |
+|-------------+---------------------------------------------------------------------|
+| ~SPC m i h~ | document this file (i.e. insert header comment)                    |
+| ~SPC m i d~ | document declaration at point (function, struct etc.)               |
+| ~SPC m i D~ | document declaration at point (header only, omit e.g. enum members) |
+| ~SPC m i g~ | document group of declarations at point                             |
+| ~SPC m i G~ | document group of declarations at point (header only)               |
+| ~SPC m i s~ | document start of declaration group                                 |
+| ~SPC m i e~ | document end of declaration group                                   |
+
+
 ** Additional key bindings
 *** Disassemble
 

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

@@ -58,8 +58,27 @@
     ;; ycmd
     (company-ycmd :requires company)
     (flycheck-ycmd :requires flycheck)
+    (gendoxy :location (recipe
+                        :fetcher github
+                        :repo "cormacc/gendoxy"
+                        :branch "provides"))
     ycmd))
 
+(defun c-c++/init-gendoxy ()
+  "Initialise gendoxy (doxygen package)"
+  (use-package gendoxy
+    :defer t
+    :init (dolist (mode c-c++-modes)
+              (spacemacs/declare-prefix-for-mode mode "mi" "insert")
+              (spacemacs/set-leader-keys-for-major-mode mode
+                "ih" 'gendoxy-header
+                "id" 'gendoxy-tag
+                "iD" 'gendoxy-tag-header
+                "ig" 'gendoxy-group
+                "iG" 'gendoxy-group-header
+                "is" 'gendoxy-group-start
+                "ie" 'gendoxy-group-end))))
+
 (defun c-c++/init-cc-mode ()
   (use-package cc-mode
     :defer t
@@ -126,6 +145,7 @@
 
       (spacemacs/declare-prefix-for-mode 'c++-mode
         "mr" "refactor")
+
       (spacemacs/set-leader-keys-for-major-mode 'c++-mode
         "ri" #'spacemacs/c-c++-organize-includes))))