* lisp/progmodes/cc-{defs,engine,langs,vars}.el: Comment the use of "a\\`"

lisp/progmodes/cc-defs.el

@@ -81,7 +81,7 @@
   (progn
     (require 'font-lock)
     (let (font-lock-keywords)
-      (font-lock-compile-keywords '("a\\`"))
+      (font-lock-compile-keywords '("a\\`")) ; doesn't match anything.
       font-lock-keywords))))
 
 
@@ -1775,7 +1775,7 @@ when it's needed.  The default is the current language taken from
 	      (t
 	       re)))
 
-    ;; Produce a regexp that matches nothing.
+    ;; Produce a regexp that doesn't match anything.
     (if adorn
 	"\\(a\\`\\)"
       "a\\`")))

lisp/progmodes/cc-engine.el

@@ -870,7 +870,7 @@ comment at the start of cc-engine.el for more info."
 	stack
 	;; Regexp which matches "for", "if", etc.
 	(cond-key (or c-opt-block-stmt-key
-		      "a\\`"))	; Matches nothing.
+		      "a\\`"))	; Doesn't match anything.
 	;; Return value.
 	(ret 'same)
 	;; Positions of the last three sexps or bounds we've stopped at.
@@ -8522,7 +8522,7 @@ comment at the start of cc-engine.el for more info."
       ;; Skip over type decl prefix operators.  (Note similar code in
       ;; `c-forward-declarator'.)
       (if (and c-recognize-typeless-decls
-	       (equal c-type-decl-prefix-key "a\\`"))
+	       (equal c-type-decl-prefix-key "a\\`")) ; Regexp which doesn't match
 	  (when (eq (char-after) ?\()
 	    (progn
 	      (setq paren-depth (1+ paren-depth))
@@ -10154,7 +10154,7 @@ comment at the start of cc-engine.el for more info."
 	      ;; legal because it's part of a "compound keyword" like
 	      ;; "enum class".	Of course, if c-after-brace-list-key
 	      ;; is nil, we can skip the test.
-	      (or (equal c-after-brace-list-key "a\\`")
+	      (or (equal c-after-brace-list-key "a\\`") ; Regexp which doesn't match
 		  (save-match-data
 		    (save-excursion
 		      (not

lisp/progmodes/cc-langs.el

@@ -1280,7 +1280,7 @@ operators."
 	   (c--set-difference (c-lang-const c-assignment-operators)
 			      '("=")
 			      :test 'string-equal)))
-      "a\\`"))
+      "a\\`"))				; Doesn't match anything.
 (c-lang-defvar c-assignment-op-regexp
   (c-lang-const c-assignment-op-regexp))
 
@@ -1503,7 +1503,7 @@ properly."
   ;; language)
   t (if (c-lang-const c-block-comment-ender)
 	(regexp-quote (c-lang-const c-block-comment-ender))
-      "a\\`"))
+      "a\\`"))				; Doesn't match anything.
 (c-lang-defvar c-block-comment-ender-regexp
 	       (c-lang-const c-block-comment-ender-regexp))
 
@@ -1522,7 +1522,7 @@ properly."
   ;; language)
   t (if (c-lang-const c-block-comment-starter)
 	(regexp-quote (c-lang-const c-block-comment-starter))
-      "a\\`"))
+      "a\\`"))				; Doesn't match anything.
 (c-lang-defvar c-block-comment-start-regexp
   (c-lang-const c-block-comment-start-regexp))
 
@@ -1531,7 +1531,7 @@ properly."
   ;; language; it does in all 7 CC Mode languages).
   t (if (c-lang-const c-line-comment-starter)
 	(regexp-quote (c-lang-const c-line-comment-starter))
-      "a\\`"))
+      "a\\`"))				; Doesn't match anything.
 (c-lang-defvar c-line-comment-start-regexp
 	       (c-lang-const c-line-comment-start-regexp))
 
@@ -1546,7 +1546,7 @@ properly."
 
 (c-lang-defconst c-doc-comment-start-regexp
   "Regexp to match the start of documentation comments."
-  t    "a\\`"
+  t    "a\\`"	; Doesn't match anything.
   ;; From font-lock.el: `doxygen' uses /*! while others use /**.
   (c c++ objc) "/\\*[*!]"
   java "/\\*\\*"
@@ -3001,7 +3001,7 @@ Note that Java specific rules are currently applied to tell this from
   "Regexp matching a keyword that is followed by a colon, where
   the whole construct can precede a declaration.
   E.g. \"public:\" in C++."
-  t "a\\`"
+  t "a\\`"				; Doesn't match anything.
   c++ (c-make-keywords-re t (c-lang-const c-protection-kwds)))
 (c-lang-defvar c-decl-start-colon-kwd-re
   (c-lang-const c-decl-start-colon-kwd-re))
@@ -3379,7 +3379,7 @@ list."
 (c-lang-defconst c-pre-id-bracelist-key
   "A regexp matching tokens which, preceding an identifier, signify a bracelist.
 "
-  t "a\\`"
+  t "a\\`"				; Doesn't match anything.
   c++ "new\\([^[:alnum:]_$]\\|$\\)\\|&&?\\(\\S.\\|$\\)")
 (c-lang-defvar c-pre-id-bracelist-key (c-lang-const c-pre-id-bracelist-key))
 
@@ -3435,7 +3435,7 @@ the invalidity of the putative template construct."
 	 ;; before the '{' of the enum list, to avoid searching too far.
 	 "[^][{};/#=]*"
 	 "{")
-      "a\\`"))
+      "a\\`"))				; Doesn't match anything.
 (c-lang-defvar c-enum-clause-introduction-re
 	       (c-lang-const c-enum-clause-introduction-re))
 
@@ -3551,7 +3551,7 @@ i.e. before \":\".  Only used if `c-recognize-colon-labels' is set."
   "Regexp matching things that can't occur two symbols before a colon in
 a label construct.  This catches C++'s inheritance construct \"class foo
 : bar\".  Only used if `c-recognize-colon-labels' is set."
-  t "a\\`"				; matches nothing
+  t "a\\`"				; Doesn't match anything.
   c++ (c-make-keywords-re t '("class")))
 (c-lang-defvar c-nonlabel-token-2-key (c-lang-const c-nonlabel-token-2-key))
 

lisp/progmodes/cc-vars.el

@@ -1647,6 +1647,7 @@ white space either before or after the operator, but not both."
   :type 'boolean
   :group 'c)
 
+;; Initialize the next two to a regexp which never matches.
 (defvar c-noise-macro-with-parens-name-re "a\\`")
 (defvar c-noise-macro-name-re "a\\`")
 
@@ -1677,7 +1678,7 @@ These are recognized by CC Mode only in declarations."
   ;; Convert `c-noise-macro-names' and `c-noise-macro-with-parens-names' into
   ;; `c-noise-macro-name-re' and `c-noise-macro-with-parens-name-re'.
   (setq c-noise-macro-with-parens-name-re
-	(cond ((null c-noise-macro-with-parens-names) "a\\`")
+	(cond ((null c-noise-macro-with-parens-names) "a\\`") ; Never matches.
 	      ((consp c-noise-macro-with-parens-names)
 	       (concat (regexp-opt c-noise-macro-with-parens-names t)
 		       "\\([^[:alnum:]_$]\\|$\\)"))
@@ -1686,7 +1687,7 @@ These are recognized by CC Mode only in declarations."
 	      (t (error "c-make-noise-macro-regexps: \
 c-noise-macro-with-parens-names is invalid: %s" c-noise-macro-with-parens-names))))
   (setq c-noise-macro-name-re
-	(cond ((null c-noise-macro-names) "a\\`")
+	(cond ((null c-noise-macro-names) "a\\`") ; Never matches anything.
 	      ((consp c-noise-macro-names)
 	       (concat (regexp-opt c-noise-macro-names t)
 		       "\\([^[:alnum:]_$]\\|$\\)"))