master 64850eaf989: Fix an infinite loop in c-beginning-of-defun-1

[Alan Mackenzie]

branch: master
commit 64850eaf989cdf3a69abc9b0c2fa37e098e7b0b9
Author: Alan Mackenzie <acm@muc.de>
Commit: Alan Mackenzie <acm@muc.de>

    Fix an infinite loop in c-beginning-of-defun-1
    
    This fixes bug#61436.
    
    The loop manifested itself in c-get-fallback-scan-pos as the
    position returned wasn't at a {, so the search back in
    c-beginning-of-defun-1 with a defun-prompt-regexp found the
    same BOL and moved forward to after the match, repeat.
    
    * lisp/progmodes/cc-defs.el (c-beginning-of-defun-1): Accept a
    position found by beginning-of-defun (which uses
    defun-prompt-regexp) only when the \\s( following it is a {.
    Repeat the backward search when this isn't the case.
---
 lisp/progmodes/cc-defs.el | 84 +++++++++++++++++++++++++----------------------
 1 file changed, 45 insertions(+), 39 deletions(-)

diff --git a/lisp/progmodes/cc-defs.el b/lisp/progmodes/cc-defs.el
index 8662e0cade6..e15ce54da7f 100644
--- a/lisp/progmodes/cc-defs.el
+++ b/lisp/progmodes/cc-defs.el
@@ -927,7 +927,8 @@ be after it."
      (when dest (goto-char dest) t)))
 
 (defmacro c-beginning-of-defun-1 ()
-  ;; Wrapper around beginning-of-defun.
+  ;; Wrapper around beginning-of-defun.  Note that the return value from this
+  ;; macro has no significance.
   ;;
   ;; NOTE: This function should contain the only explicit use of
   ;; beginning-of-defun in CC Mode.  Eventually something better than
@@ -940,44 +941,49 @@ be after it."
   ;; `c-parse-state'.
 
   `(progn
-     (if (and ,(fboundp 'buffer-syntactic-context-depth)
-             c-enable-xemacs-performance-kludge-p)
-        ,(when (fboundp 'buffer-syntactic-context-depth)
-           ;; XEmacs only.  This can improve the performance of
-           ;; c-parse-state to between 3 and 60 times faster when
-           ;; braces are hung.  It can also degrade performance by
-           ;; about as much when braces are not hung.
-           '(let (beginning-of-defun-function end-of-defun-function
-                                              pos)
-              (while (not pos)
-                (save-restriction
-                  (widen)
-                  (setq pos (c-safe-scan-lists
-                             (point) -1 (buffer-syntactic-context-depth))))
-                (cond
-                 ((bobp) (setq pos (point-min)))
-                 ((not pos)
-                  (let ((distance (skip-chars-backward "^{")))
-                    ;; unbalanced parenthesis, while invalid C code,
-                    ;; shouldn't cause an infloop!  See unbal.c
-                    (when (zerop distance)
-                      ;; Punt!
-                      (beginning-of-defun)
-                      (setq pos (point)))))
-                 ((= pos 0))
-                 ((not (eq (char-after pos) ?{))
-                  (goto-char pos)
-                  (setq pos nil))
-                 ))
-              (goto-char pos)))
-       ;; Emacs, which doesn't have buffer-syntactic-context-depth
-       (let (beginning-of-defun-function end-of-defun-function)
-        (beginning-of-defun)))
-     ;; if defun-prompt-regexp is non-nil, b-o-d won't leave us at the
-     ;; open brace.
-     (and defun-prompt-regexp
-         (looking-at defun-prompt-regexp)
-         (goto-char (match-end 0)))))
+     (while
+        (progn
+          (if (and ,(fboundp 'buffer-syntactic-context-depth)
+                   c-enable-xemacs-performance-kludge-p)
+              ,(when (fboundp 'buffer-syntactic-context-depth)
+                 ;; XEmacs only.  This can improve the performance of
+                 ;; c-parse-state to between 3 and 60 times faster when
+                 ;; braces are hung.  It can also degrade performance by
+                 ;; about as much when braces are not hung.
+                 '(let (beginning-of-defun-function end-of-defun-function
+                                                    pos)
+                    (while (not pos)
+                      (save-restriction
+                        (widen)
+                        (setq pos (c-safe-scan-lists
+                                   (point) -1 
(buffer-syntactic-context-depth))))
+                      (cond
+                       ((bobp) (setq pos (point-min)))
+                       ((not pos)
+                        (let ((distance (skip-chars-backward "^{")))
+                          ;; unbalanced parenthesis, while invalid C code,
+                          ;; shouldn't cause an infloop!  See unbal.c
+                          (when (zerop distance)
+                            ;; Punt!
+                            (beginning-of-defun)
+                            (setq pos (point)))))
+                       ((= pos 0))
+                       ((not (eq (char-after pos) ?{))
+                        (goto-char pos)
+                        (setq pos nil))
+                       ))
+                    (goto-char pos)))
+            ;; Emacs, which doesn't have buffer-syntactic-context-depth
+            (let (beginning-of-defun-function end-of-defun-function)
+              (beginning-of-defun)))
+          (and (not (bobp))
+               ;; if defun-prompt-regexp is non-nil, b-o-d won't leave us at
+               ;; the open brace.
+               defun-prompt-regexp
+               (looking-at (concat defun-prompt-regexp "\\s("))
+               (or (not (eq (char-before (match-end 0)) ?{))
+                   (progn (goto-char (1- (match-end 0)))
+                          nil)))))))
 
 
 
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