CC Mode: Prevent "const" inside an identifier being recognized as the keyword

This fixes bug #45560.

* lisp/progmodes/cc-engine.el (c-forward-declarator)
(c-forward-decl-or-cast-1): Amend certain regexp match numbers on account of
the change below.  Surround some looking-at calls with save-match-data.

* lisp/progmodes/cc-langs.el (c-type-decl-prefix-keywords-key): New lang
const.
(c-type-decl-prefix-key): Reformulate to match operators and keywords
separately, using the new lang const (above).

2 files changed, 41 insertions, 29 deletions

diff --git a/lisp/progmodes/cc-engine.el b/lisp/progmodes/cc-engine.el
index 3fce7dbafae..484624b8664 100644
--- a/lisp/progmodes/cc-engine.el
+++ b/lisp/progmodes/cc-engine.el
@@ -9021,14 +9021,15 @@ point unchanged and return nil."
                     (c-forward-noise-clause))
                    ((and (looking-at c-type-decl-prefix-key)
                          (if (and (c-major-mode-is 'c++-mode)
-                                  (match-beginning 3))
+                                  (match-beginning 4)) ; Was 3 - 2021-01-01
                              ;; If the third submatch matches in C++ then
                              ;; we're looking at an identifier that's a
                              ;; prefix only if it specifies a member pointer.
                              (progn
                                (setq id-start (point))
                                (c-forward-name)
-                               (if (looking-at "\\(::\\)")
+                               (if (save-match-data
+                                     (looking-at "\\(::\\)"))
                                    ;; We only check for a trailing "::" and
                                    ;; let the "*" that should follow be
                                    ;; matched in the next round.
@@ -9038,13 +9039,15 @@ point unchanged and return nil."
                                  (setq got-identifier t)
                                  nil))
                            t))
-                    (if (looking-at c-type-decl-operator-prefix-key)
+                    (if (save-match-data
+                          (looking-at c-type-decl-operator-prefix-key))
                         (setq decorated t))
                     (if (eq (char-after) ?\()
                         (progn
                           (setq paren-depth (1+ paren-depth))
                           (forward-char))
-                      (goto-char (match-end 1)))
+                      (goto-char (or (match-end 1)
+                                     (match-end 2))))
                     (c-forward-syntactic-ws)
                     t)))
 
@@ -9721,14 +9724,15 @@ This function might do hidden buffer changes."
               (setq after-paren-pos (point))))
         (while (and (looking-at c-type-decl-prefix-key)
                     (if (and (c-major-mode-is 'c++-mode)
-                             (match-beginning 3))
-                        ;; If the third submatch matches in C++ then
+                             (match-beginning 4))
+                        ;; If the fourth submatch matches in C++ then
                         ;; we're looking at an identifier that's a
                         ;; prefix only if it specifies a member pointer.
                         (when (progn (setq pos (point))
                                      (setq got-identifier (c-forward-name)))
                           (setq name-start pos)
-                          (if (looking-at "\\(::\\)")
+                          (if (save-match-data
+                                (looking-at "\\(::\\)"))
                               ;; We only check for a trailing "::" and
                               ;; let the "*" that should follow be
                               ;; matched in the next round.
@@ -9749,7 +9753,8 @@ This function might do hidden buffer changes."
             (when (save-match-data
                     (looking-at c-type-decl-operator-prefix-key))
               (setq got-function-name-prefix t))
-            (goto-char (match-end 1)))
+            (goto-char (or (match-end 1)
+                           (match-end 2))))
           (c-forward-syntactic-ws)))
 
       (setq got-parens (> paren-depth 0))
diff --git a/lisp/progmodes/cc-langs.el b/lisp/progmodes/cc-langs.el
index f4dcbcda962..07479389c62 100644
--- a/lisp/progmodes/cc-langs.el
+++ b/lisp/progmodes/cc-langs.el
@@ -3433,41 +3433,47 @@ possible for good performance."
   t (c-make-bare-char-alt (c-lang-const c-block-prefix-disallowed-chars) t))
 (c-lang-defvar c-block-prefix-charset (c-lang-const c-block-prefix-charset))
 
-(c-lang-defconst c-type-decl-prefix-key
-  "Regexp matching any declarator operator that might precede the
-identifier in a declaration, e.g. the \"*\" in \"char *argv\".  This
-regexp should match \"(\" if parentheses are valid in declarators.
-The end of the first submatch is taken as the end of the operator.
-Identifier syntax is in effect when this is matched (see
-`c-identifier-syntax-table')."
+(c-lang-defconst c-type-decl-prefix-keywords-key
+  ;; Regexp matching any keyword operator that might precede the identifier in
+  ;; a declaration, e.g. "const" or nil.  It doesn't test there is no "_"
+  ;; following the keyword.
   t (if (or (c-lang-const c-type-modifier-kwds) (c-lang-const c-modifier-kwds))
-        (concat
+        (concat
          (regexp-opt (c--delete-duplicates
                       (append (c-lang-const c-type-modifier-kwds)
                               (c-lang-const c-modifier-kwds))
                       :test 'string-equal)
                      t)
-         "\\>")
-      ;; Default to a regexp that never matches.
-      regexp-unmatchable)
+         "\\>")))
+
+(c-lang-defconst c-type-decl-prefix-key
+  "Regexp matching any declarator operator that might precede the
+identifier in a declaration, e.g. the \"*\" in \"char *argv\".  This
+regexp should match \"(\" if parentheses are valid in declarators.
+The operator found is either the first submatch (if it is not a
+keyword) or the second submatch (if it is)."
+  t (if (c-lang-const c-type-decl-prefix-keywords-key)
+        (concat "\\(\\`a\\`\\)\\|"      ; 1 - will never match.
+                (c-lang-const c-type-decl-prefix-keywords-key) ; 2
+                "\\([^_]\\|$\\)")                              ; 3
+      "\\`a\\`") ;; Default to a regexp that never matches.
   ;; Check that there's no "=" afterwards to avoid matching tokens
   ;; like "*=".
-  (c objc) (concat "\\("
+  (c objc) (concat "\\("                ; 1
                    "[*(]"
-                   "\\|"
-                   (c-lang-const c-type-decl-prefix-key)
-                   "\\)"
-                   "\\([^=]\\|$\\)")
-  c++  (concat "\\("
+                   "\\)\\|"
+                   (c-lang-const c-type-decl-prefix-keywords-key) ; 2
+                   "\\([^=_]\\|$\\)")   ; 3
+  c++  (concat "\\("                    ; 1
                "&&"
                "\\|"
                "\\.\\.\\."
                "\\|"
                "[*(&~]"
+               "\\)\\|\\("                                    ; 2
+               (c-lang-const c-type-decl-prefix-keywords-key) ; 3
                "\\|"
-               (c-lang-const c-type-decl-prefix-key)
-               "\\|"
-               (concat "\\("   ; 3
+               (concat "\\("   ; 4
                        ;; If this matches there's special treatment in
                        ;; `c-font-lock-declarators' and
                        ;; `c-font-lock-declarations' that check for a
@@ -3475,8 +3481,9 @@ Identifier syntax is in effect when this is matched (see
                        (c-lang-const c-identifier-start)
                        "\\)")
                "\\)"
-               "\\([^=]\\|$\\)")
+               "\\([^=_]\\|$\\)")       ; 5
   pike "\\(\\*\\)\\([^=]\\|$\\)")
+
 (c-lang-defvar c-type-decl-prefix-key (c-lang-const c-type-decl-prefix-key)
   'dont-doc)