From b054393dd1b9146522d8aeb21cb9b1ad52210a33 Mon Sep 17 00:00:00 2001
From: Alan Mackenzie <acm@muc.de>
Date: Fri, 11 Sep 2020 14:18:43 +0000
Subject: [PATCH] CC Mode: Fix minor bugs in the string handling functions

These sometimes gave rise to the tail of a buffer being "stringed out".

* lixp/progmodes/cc-defs.el (c-will-be-unescaped): New macro.

* lisp/progmodes/cc-mode.el (c-before-change-check-unbalanced-strings)
(c-after-change-mark-abnormal-strings): Fix bugs in the handling of string
fence syntax-table text properties.
---
 lisp/progmodes/cc-defs.el |  9 +++++++++
 lisp/progmodes/cc-mode.el | 25 ++++++++++++++++---------
 2 files changed, 25 insertions(+), 9 deletions(-)

diff --git a/lisp/progmodes/cc-defs.el b/lisp/progmodes/cc-defs.el
index 9a3d7adf61d..77e263f1aad 100644
--- a/lisp/progmodes/cc-defs.el
+++ b/lisp/progmodes/cc-defs.el
@@ -434,6 +434,15 @@ to it is returned.  This function does not modify the point or the mark."
 	 (setq count (+ count (skip-chars-backward "\\\\"))))
        (not (zerop (logand count 1))))))
 
+(defmacro c-will-be-unescaped (beg end)
+  ;; Would the character after END be unescaped after the removal of (BEG END)?
+  ;; This is regardless of its current status.  It is assumed that (>= POS END).
+  `(save-excursion
+    (let (count)
+      (goto-char ,beg)
+      (setq count (skip-chars-backward "\\\\"))
+      (zerop (logand count 1)))))
+
 (defvar c-use-extents)
 
 (defmacro c-next-single-property-change (position prop &optional object limit)
diff --git a/lisp/progmodes/cc-mode.el b/lisp/progmodes/cc-mode.el
index 2ffbde99aa4..73275cfa621 100644
--- a/lisp/progmodes/cc-mode.el
+++ b/lisp/progmodes/cc-mode.el
@@ -1478,9 +1478,11 @@ Note that the style variables are always made local to the buffer."
 		 (c-will-be-escaped end beg end))
 	    (c-remove-string-fences end)
 	    (goto-char (1+ end)))
-	   ;; Are we unescaping a newline by inserting stuff between \ and \n?
-	   ((and (eq end beg)
-		 (c-is-escaped end))
+	   ;; Are we unescaping a newline ...
+	   ((and
+	     (c-is-escaped end)
+	     (or (eq beg end) ; .... by inserting stuff between \ and \n?
+	      	 (c-will-be-unescaped beg end))) ;  ... by removing an odd number of \s?
 	    (goto-char (1+ end))) ; To after the NL which is being unescaped.
 	   (t
 	    (goto-char end)))
@@ -1518,10 +1520,11 @@ Note that the style variables are always made local to the buffer."
 		 (not (c-characterp c-multiline-string-start-char))))
       (when (and (eq end-literal-type 'string)
 		 (not (eq (char-before (cdr end-limits)) ?\())
-		 (memq (char-after (car end-limits)) c-string-delims)
-		 (equal (c-get-char-property (car end-limits) 'syntax-table)
-			'(15)))
-	(c-remove-string-fences (car end-limits))
+		 (memq (char-after (car end-limits)) c-string-delims))
+	(setq c-new-END (max c-new-END (cdr end-limits)))
+	(when (equal (c-get-char-property (car end-limits) 'syntax-table)
+		     '(15))
+	  (c-remove-string-fences (car end-limits)))
 	(setq c-new-END (max c-new-END (cdr end-limits))))
 
       (when (and (eq beg-literal-type 'string)
@@ -1594,8 +1597,12 @@ Note that the style variables are always made local to the buffer."
 		   ; insertion/deletion of string delimiters.
 	  (max
 	   (progn
-	     (goto-char (min (1+ end)	; 1+, in case a NL has become escaped.
-			     (point-max)))
+	     (goto-char
+	      (if (and (memq (char-after end) '(?\n ?\r))
+		       (c-is-escaped end))
+		  (min (1+ end)	; 1+, if we're inside an escaped NL.
+		       (point-max))
+		end))
 	     (re-search-forward "\\(?:\\\\\\(?:.\\|\n\\)\\|[^\\\n\r]\\)*"
 				nil t)
 	     (point))
-- 
2.39.2