From 605cfb8b7a4ef8f73ddc8f2de5c086f3a7455971 Mon Sep 17 00:00:00 2001
From: Alan Mackenzie <acm@muc.de>
Date: Sat, 18 Oct 2014 10:02:59 +0000
Subject: [PATCH] Check that a "macro" found near point-min isn't a ##
 operator.  Fixes bug #18749. progmodes/cc-engine.el (c-macro-is-genuine-p):
 New function. (c-beginning-of-macro): Use the above new function.

---
 lisp/ChangeLog              |  7 +++++++
 lisp/progmodes/cc-engine.el | 21 ++++++++++++++++++++-
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index 0da7f2877e1..0e99febb366 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,10 @@
+2014-10-18  Alan Mackenzie  <acm@muc.de>
+
+	Check that a "macro" found near point-min isn't a ## operator.
+	Fixes bug #18749.
+	* progmodes/cc-engine.el (c-macro-is-genuine-p): New function.
+	(c-beginning-of-macro): Use the above new function.
+
 2014-10-18  Teodor Zlatanov  <tzz@lifelogs.com>
 
 	* net/gnutls.el (gnutls-negotiate): Don't use cl-mapcan; pass
diff --git a/lisp/progmodes/cc-engine.el b/lisp/progmodes/cc-engine.el
index 9a2531d1e99..ccc3f067571 100644
--- a/lisp/progmodes/cc-engine.el
+++ b/lisp/progmodes/cc-engine.el
@@ -249,6 +249,24 @@
     (setq c-macro-cache-start-pos beg
 	  c-macro-cache-syntactic nil))))
 
+(defun c-macro-is-genuine-p ()
+  ;; Check that the ostensible CPP construct at point is a real one.  In
+  ;; particular, if point is on the first line of a narrowed buffer, make sure
+  ;; that the "#" isn't, say, the second character of a "##" operator.  Return
+  ;; t when the macro is real, nil otherwise.
+  (let ((here (point)))
+    (beginning-of-line)
+    (prog1
+	(if (and (eq (point) (point-min))
+		 (/= (point) 1))
+	    (save-restriction
+	      (widen)
+	      (beginning-of-line)
+	      (and (looking-at c-anchored-cpp-prefix)
+		   (eq (match-beginning 1) here)))
+	  t)
+      (goto-char here))))
+
 (defun c-beginning-of-macro (&optional lim)
   "Go to the beginning of a preprocessor directive.
 Leave point at the beginning of the directive and return t if in one,
@@ -279,7 +297,8 @@ comment at the start of cc-engine.el for more info."
 	    (forward-line -1))
 	  (back-to-indentation)
 	  (if (and (<= (point) here)
-		   (looking-at c-opt-cpp-start))
+		   (looking-at c-opt-cpp-start)
+		   (c-macro-is-genuine-p))
 	      (progn
 		(setq c-macro-cache (cons (point) nil)
 		      c-macro-cache-start-pos here)
-- 
2.11.4.GIT