Create a toggle between block and line comments in CC Mode.

Also (unrelated change) initialize the modes' keymaps at each loading.

* lisp/progmodes/cc-cmds.el (c-update-modeline): amend for the new information
on the modeline.
(c-block-comment-flag): New variable.
(c-toggle-comment-style): New function.

* lisp/progmodes/cc-langs.el (c-block-comment-starter)
(c-line-comment-starter): Make them c-lang-defvars.
(c-block-comment-is-default): New c-lang-defvar.
(comment-start, comment-end): Make the default values dependent on
c-block-comment-is-default.

* lisp/progmodes/cc-mode.el (c-mode-base-map): Define C-c C-k in this map.
(c-basic-common-init): Initialize c-block-comment-flag.
(c-mode-map, c++-mode-map, objc-mode-map, java-mode-map, idl-mode-map)
(pike-mode-map, awk-mode-map): Make entries in these key maps each time the
mode is loaded rather than just once per Emacs session.

* doc/misc/cc-mode.texi (Comment Commands): Introduce the notion of comment
style.
(Minor Modes): Define comment style.  Describe how comment style influences
the information displayed on the modeline.  Document c-toggle-comment-style.
(FAQ): Add a question about toggling the comment style.

3 files changed, 79 insertions, 43 deletions

diff --git a/lisp/progmodes/cc-cmds.el b/lisp/progmodes/cc-cmds.el
index 9c0798e7529..6250725c179 100644
--- a/lisp/progmodes/cc-cmds.el
+++ b/lisp/progmodes/cc-cmds.el
@@ -252,7 +252,8 @@ With universal argument, inserts the analysis as a comment on that line."
 
 ;; Minor mode functions.
 (defun c-update-modeline ()
-  (let ((fmt (format "/%s%s%s%s"
+  (let ((fmt (format "/%s%s%s%s%s"
+                     (if c-block-comment-flag "*" "/")
                      (if c-electric-flag "l" "")
                      (if (and c-electric-flag c-auto-newline)
                          "a" "")
@@ -270,9 +271,6 @@ With universal argument, inserts the analysis as a comment on that line."
         (bare-mode-name (if (string-match "\\(^[^/]*\\)/" mode-name)
                             (match-string 1 mode-name)
                           mode-name)))
-;;     (setq c-submode-indicators
-;;        (if (> (length fmt) 1)
-;;            fmt))
     (setq mode-name
           (if (> (length fmt) 1)
               (concat bare-mode-name fmt)
@@ -362,6 +360,37 @@ left out."
     (electric-indent-local-mode (if c-electric-flag 1 0)))
   (c-keep-region-active))
 
+;; `c-block-comment-flag' gets initialized to the current mode's default in
+;; c-basic-common-init.
+(defvar c-block-comment-flag nil)
+(make-variable-buffer-local 'c-block-comment-flag)
+
+(defun c-toggle-comment-style (&optional arg)
+  "Toggle the comment style between block and line comments.
+Optional numeric ARG, if supplied, switches to block comment
+style when positive, to line comment style when negative, and
+just toggles it when zero or left out.
+
+This action does nothing when the mode only has one comment style."
+  (interactive "P")
+  (setq c-block-comment-flag
+        (cond
+         ((and c-line-comment-starter c-block-comment-starter)
+          (c-calculate-state arg c-block-comment-flag))
+         (c-line-comment-starter nil)
+         (t t)))
+  (setq comment-start
+        (concat (if c-block-comment-flag
+                    c-block-comment-starter
+                  c-line-comment-starter)
+                " "))
+  (setq comment-end
+        (if c-block-comment-flag
+            (concat " " c-block-comment-ender)
+          ""))
+  (c-update-modeline)
+  (c-keep-region-active))
+
 
 ;; Electric keys
 
diff --git a/lisp/progmodes/cc-langs.el b/lisp/progmodes/cc-langs.el
index 84d4eab75af..a9d5ac34ad4 100644
--- a/lisp/progmodes/cc-langs.el
+++ b/lisp/progmodes/cc-langs.el
@@ -1449,6 +1449,7 @@ comment style.  Other stuff like the syntax table must also be set up
 properly."
   t    "/*"
   awk  nil)
+(c-lang-defvar c-block-comment-starter (c-lang-const c-block-comment-starter))
 
 (c-lang-defconst c-block-comment-ender
   "String that ends block comments, or nil if such don't exist.
@@ -1458,6 +1459,7 @@ comment style.  Other stuff like the syntax table must also be set up
 properly."
   t    "*/"
   awk  nil)
+(c-lang-defvar c-block-comment-ender (c-lang-const c-block-comment-ender))
 
 (c-lang-defconst c-block-comment-ender-regexp
   ;; Regexp which matches the end of a block comment (if such exists in the
@@ -1515,27 +1517,30 @@ properly."
 (c-lang-defvar c-doc-comment-start-regexp
   (c-lang-const c-doc-comment-start-regexp))
 
+(c-lang-defconst c-block-comment-is-default
+  "Non-nil when the default comment style is block comment."
+  ;; Note to maintainers of derived modes: You are responsible for ensuring
+  ;; the pertinent `c-block-comment-{starter,ender}' or
+  ;; `c-line-comment-{starter,ender}' are non-nil.
+  t nil
+  c t)
+(c-lang-defvar c-block-comment-is-default
+  (c-lang-const c-block-comment-is-default))
+
 (c-lang-defconst comment-start
   "String that starts comments inserted with M-; etc.
 `comment-start' is initialized from this."
-  ;; Default: Prefer line comments to block comments, and pad with a space.
-  t (concat (or (c-lang-const c-line-comment-starter)
-                (c-lang-const c-block-comment-starter))
-            " ")
-  ;; In C we still default to the block comment style since line
-  ;; comments aren't entirely portable.
-  c "/* ")
+  t (concat
+     (if (c-lang-const c-block-comment-is-default)
+         (c-lang-const c-block-comment-starter)
+       (c-lang-const c-line-comment-starter))
+     " "))
 (c-lang-setvar comment-start (c-lang-const comment-start))
 
 (c-lang-defconst comment-end
   "String that ends comments inserted with M-; etc.
 `comment-end' is initialized from this."
-  ;; Default: Use block comment style if comment-start uses block
-  ;; comments, and pad with a space in that case.
-  t (if (string-match (concat "\\`\\("
-                              (c-lang-const c-block-comment-start-regexp)
-                              "\\)")
-                      (c-lang-const comment-start))
+  t (if (c-lang-const c-block-comment-is-default)
         (concat " " (c-lang-const c-block-comment-ender))
       ""))
 (c-lang-setvar comment-end (c-lang-const comment-end))
diff --git a/lisp/progmodes/cc-mode.el b/lisp/progmodes/cc-mode.el
index 20c63d4dbe2..a501ebba256 100644
--- a/lisp/progmodes/cc-mode.el
+++ b/lisp/progmodes/cc-mode.el
@@ -398,7 +398,7 @@ control).  See \"cc-mode.el\" for more info."
   ;;(define-key c-mode-base-map "\C-c\C-v"  'c-version)
   ;; (define-key c-mode-base-map "\C-c\C-y"  'c-toggle-hungry-state)  Commented out by ACM, 2005-11-22.
   (define-key c-mode-base-map "\C-c\C-w" 'c-subword-mode)
-  )
+  (define-key c-mode-base-map "\C-c\C-k" 'c-toggle-comment-style))
 
 ;; We don't require the outline package, but we configure it a bit anyway.
 (cc-bytecomp-defvar outline-level)
@@ -547,7 +547,7 @@ that requires a literal mode spec at compile time."
         (setq yank-handled-properties (remq yank-cat-handler
                                             yank-handled-properties)))))
 
-  ;; For the benefit of adaptive file, which otherwise mis-fills.
+  ;; For the benefit of adaptive fill, which otherwise mis-fills.
   (setq fill-paragraph-handle-comment nil)
 
   ;; Install `c-fill-paragraph' on `fill-paragraph-function' so that a
@@ -623,6 +623,8 @@ that requires a literal mode spec at compile time."
 
   ;; setup the comment indent variable in a Emacs version portable way
   (set (make-local-variable 'comment-indent-function) 'c-comment-indent)
+  ;; What sort of comments are default for M-;?
+  (setq c-block-comment-flag c-block-comment-is-default)
 
   ;; In Emacs 24.4 onwards, prevent Emacs's built in electric indentation from
   ;; messing up CC Mode's, and set `c-electric-flag' if `electric-indent-mode'
@@ -1621,10 +1623,10 @@ This function is called from `c-common-init', once per mode initialization."
 
 (defvar c-mode-map
   (let ((map (c-make-inherited-keymap)))
-    ;; Add bindings which are only useful for C.
-    (define-key map "\C-c\C-e"  'c-macro-expand)
     map)
   "Keymap used in c-mode buffers.")
+;; Add bindings which are only useful for C.
+(define-key c-mode-map "\C-c\C-e"  'c-macro-expand)
 
 
 (easy-menu-define c-c-menu c-mode-map "C Mode Commands"
@@ -1737,13 +1739,13 @@ the code is C or C++ and based on that chooses whether to enable
 
 (defvar c++-mode-map
   (let ((map (c-make-inherited-keymap)))
-    ;; Add bindings which are only useful for C++.
-    (define-key map "\C-c\C-e" 'c-macro-expand)
-    (define-key map "\C-c:"    'c-scope-operator)
-    (define-key map "<"        'c-electric-lt-gt)
-    (define-key map ">"        'c-electric-lt-gt)
     map)
   "Keymap used in c++-mode buffers.")
+;; Add bindings which are only useful for C++.
+(define-key c++-mode-map "\C-c\C-e" 'c-macro-expand)
+(define-key c++-mode-map "\C-c:"    'c-scope-operator)
+(define-key c++-mode-map "<"        'c-electric-lt-gt)
+(define-key c++-mode-map ">"        'c-electric-lt-gt)
 
 (easy-menu-define c-c++-menu c++-mode-map "C++ Mode Commands"
                   (cons "C++" (c-lang-const c-mode-menu c++)))
@@ -1789,10 +1791,10 @@ Key bindings:
 
 (defvar objc-mode-map
   (let ((map (c-make-inherited-keymap)))
-    ;; Add bindings which are only useful for Objective-C.
-    (define-key map "\C-c\C-e" 'c-macro-expand)
     map)
   "Keymap used in objc-mode buffers.")
+;; Add bindings which are only useful for Objective-C.
+(define-key objc-mode-map "\C-c\C-e" 'c-macro-expand)
 
 (easy-menu-define c-objc-menu objc-mode-map "ObjC Mode Commands"
                   (cons "ObjC" (c-lang-const c-mode-menu objc)))
@@ -1842,9 +1844,9 @@ Key bindings:
 
 (defvar java-mode-map
   (let ((map (c-make-inherited-keymap)))
-    ;; Add bindings which are only useful for Java.
     map)
   "Keymap used in java-mode buffers.")
+;; Add bindings which are only useful for Java.
 
 ;; Regexp trying to describe the beginning of a Java top-level
 ;; definition.  This is not used by CC Mode, nor is it maintained
@@ -1895,9 +1897,9 @@ Key bindings:
 
 (defvar idl-mode-map
   (let ((map (c-make-inherited-keymap)))
-    ;; Add bindings which are only useful for IDL.
     map)
   "Keymap used in idl-mode buffers.")
+;; Add bindings which are only useful for IDL.
 
 (easy-menu-define c-idl-menu idl-mode-map "IDL Mode Commands"
                   (cons "IDL" (c-lang-const c-mode-menu idl)))
@@ -1942,10 +1944,10 @@ Key bindings:
 
 (defvar pike-mode-map
   (let ((map (c-make-inherited-keymap)))
-    ;; Additional bindings.
-    (define-key map "\C-c\C-e" 'c-macro-expand)
     map)
   "Keymap used in pike-mode buffers.")
+;; Additional bindings.
+(define-key pike-mode-map "\C-c\C-e" 'c-macro-expand)
 
 (easy-menu-define c-pike-menu pike-mode-map "Pike Mode Commands"
                   (cons "Pike" (c-lang-const c-mode-menu pike)))
@@ -1994,19 +1996,19 @@ Key bindings:
 
 (defvar awk-mode-map
   (let ((map (c-make-inherited-keymap)))
-    ;; Add bindings which are only useful for awk.
-    (define-key map "#" 'self-insert-command);Overrides electric parent binding.
-    (define-key map "/" 'self-insert-command);Overrides electric parent binding.
-    (define-key map "*" 'self-insert-command);Overrides electric parent binding.
-    (define-key map "\C-c\C-n" 'undefined) ; #if doesn't exist in awk.
-    (define-key map "\C-c\C-p" 'undefined)
-    (define-key map "\C-c\C-u" 'undefined)
-    (define-key map "\M-a" 'c-beginning-of-statement) ; 2003/10/7
-    (define-key map "\M-e" 'c-end-of-statement)       ; 2003/10/7
-    (define-key map "\C-\M-a" 'c-awk-beginning-of-defun)
-    (define-key map "\C-\M-e" 'c-awk-end-of-defun)
     map)
   "Keymap used in awk-mode buffers.")
+;; Add bindings which are only useful for awk.
+(define-key awk-mode-map "#" 'self-insert-command);Overrides electric parent binding.
+(define-key awk-mode-map "/" 'self-insert-command);Overrides electric parent binding.
+(define-key awk-mode-map "*" 'self-insert-command);Overrides electric parent binding.
+(define-key awk-mode-map "\C-c\C-n" 'undefined) ; #if doesn't exist in awk.
+(define-key awk-mode-map "\C-c\C-p" 'undefined)
+(define-key awk-mode-map "\C-c\C-u" 'undefined)
+(define-key awk-mode-map "\M-a" 'c-beginning-of-statement) ; 2003/10/7
+(define-key awk-mode-map "\M-e" 'c-end-of-statement)       ; 2003/10/7
+(define-key awk-mode-map "\C-\M-a" 'c-awk-beginning-of-defun)
+(define-key awk-mode-map "\C-\M-e" 'c-awk-end-of-defun)
 
 (easy-menu-define c-awk-menu awk-mode-map "AWK Mode Commands"
                   (cons "AWK" (c-lang-const c-mode-menu awk)))