(compile-reinitialize-errors): Rename first arg from ARGP to REPARSE.

Test only its nilness.
(compile-goto-error): Pass (consp ARGP) to compile-reinitialize-errors
instead of ARGP itself.
(next-error): Code broken out into two new functions; call them.
(compilation-next-error-locus): New function; bulk of code from next-error.
Silently skip errors whose source loci are markers in killed buffers.
(compilation-goto-locus): New function, final code from next-error.

lisp/progmodes/compile.el

@@ -633,13 +633,14 @@ Does NOT find the source line like \\[next-error]."
 
 ;; Parse any new errors in the compilation buffer,
 ;; or reparse from the beginning if the user has asked for that.
-(defun compile-reinitialize-errors (argp &optional limit-search find-at-least)
+(defun compile-reinitialize-errors (reparse
+				    &optional limit-search find-at-least)
   (save-excursion
     (set-buffer compilation-last-buffer)
     ;; If we are out of errors, or if user says "reparse",
     ;; discard the info we have, to force reparsing.
     (if (or (eq compilation-error-list t)
-	    (consp argp))
+	    reparse)
 	(compilation-forget-errors))
     (if (and compilation-error-list
 	     (or (not limit-search)
@@ -686,7 +687,7 @@ other kinds of prefix arguments are ignored."
   (or (compilation-buffer-p (current-buffer))
       (error "Not in a compilation buffer."))
   (setq compilation-last-buffer (current-buffer))
-  (compile-reinitialize-errors argp (point))
+  (compile-reinitialize-errors (consp argp) (point))
 
   ;; Move to bol; the marker for the error on this line will point there.
   (beginning-of-line)
@@ -763,29 +764,43 @@ See variables `compilation-parse-errors-function' and
 \`compilation-error-regexp-alist' for customization ideas."
   (interactive "P")
   (setq compilation-last-buffer (compilation-find-buffer))
-  (compile-reinitialize-errors argp nil
+  (compilation-goto-locus (compilation-next-error-locus
 			   ;; We want to pass a number here only if
 			   ;; we got a numeric prefix arg, not just C-u.
 			   (and (not (consp argp))
-				    (if (< (prefix-numeric-value argp) 1)
-					0
-				      (1- (prefix-numeric-value argp)))))
-  ;; Make ARGP nil if the prefix arg was just C-u,
-  ;; since that means to reparse the errors, which the
-  ;; compile-reinitialize-errors call just did.
-  ;; Now we are only interested in a numeric prefix arg.
-  (if (consp argp)
-      (setq argp nil))
+				(prefix-numeric-value argp))
+			   (consp argp))))
+;;;###autoload (define-key ctl-x-map "`" 'next-error)
+
+(defun compilation-next-error-locus (&optional move reparse)
+  "Visit next compilation error and return locus in corresponding source code.
+This operates on the output from the \\[compile] command.
+If all preparsed error messages have been processed,
+the error message buffer is checked for new ones.
+
+Returns a cons (ERROR . SOURCE) of two markers: ERROR is a marker at the
+location of the error message in the compilation buffer, and SOURCE is a
+marker at the location in the source code indicated by the error message.
+
+Optional first arg MOVE says how many error messages to move forwards (or
+backwards, if negative); default is 1.  Optional second arg REPARSE, if
+non-nil, says to reparse the error message buffer and reset to the first
+error (plus MOVE - 1).
+
+The current buffer should be the desired compilation output buffer."
+  (or move (setq move 1))
+  (compile-reinitialize-errors reparse nil (and (not reparse)
+						(if (< move 1) 0 (1- move))))
   (let (next-errors next-error)
     (save-excursion
       (set-buffer compilation-last-buffer)
       ;; compilation-error-list points to the "current" error.
       (setq next-errors 
-	    (if (> (prefix-numeric-value argp) 0)
-		(nthcdr (1- (prefix-numeric-value argp))
+	    (if (> move 0)
+		(nthcdr (1- move)
 			compilation-error-list)
 	      ;; Zero or negative arg; we need to move back in the list.
-	      (let ((n (1- (prefix-numeric-value argp)))
+	      (let ((n (1- move))
 		    (i 0)
 		    (e compilation-old-error-list))
 		;; See how many cdrs away the current error is from the start.
@@ -797,10 +812,9 @@ See variables `compilation-parse-errors-function' and
 		  (nthcdr (+ i n) compilation-old-error-list))))
 	    next-error (car next-errors))
       (while
-	  (progn
 	  (if (null next-error)
 	      (progn
-		  (if argp (if (> (prefix-numeric-value argp) 0)
+		(if move (if (> move 0)
 			     (error "Moved past last error")
 			   (error "Moved back past first error")))
 		(compilation-forget-errors)
@@ -878,9 +892,10 @@ See variables `compilation-parse-errors-function' and
 				     (setq last-line this)
 				     (setcdr (car errors) (point-marker))))
 			      (setq errors (cdr errors)))))))))
-		;; If we didn't get a marker for this error,
-		;; go on to the next one.
-		(not (markerp (cdr next-error))))))
+	      ;; If we didn't get a marker for this error, or this
+	      ;; marker's buffer was killed, go on to the next one.
+	      (or (not (markerp (cdr next-error)))
+		  (not (marker-buffer (cdr next-error))))))
 	(setq next-errors compilation-error-list
 	      next-error (car next-errors))))
 
@@ -890,7 +905,14 @@ See variables `compilation-parse-errors-function' and
 		(equal (cdr (car compilation-error-list)) (cdr next-error)))
       (setq compilation-error-list (cdr compilation-error-list)))
 
-    ;; We now have a marker for the position of the error.
+    ;; We now have a marker for the position of the error source code.
+    ;; NEXT-ERROR is a cons (ERROR . SOURCE) of two markers.
+    next-error))
+
+(defun compilation-goto-locus (next-error)
+  "Jump to an error locus returned by `compilation-next-error-locus'.
+Takes one argument, a cons (ERROR . SOURCE) of two markers.
+Selects a window with point at SOURCE, with another window displaying ERROR."
   (switch-to-buffer (marker-buffer (cdr next-error)))
   (goto-char (cdr next-error))
   ;; If narrowing got in the way of
@@ -904,10 +926,8 @@ See variables `compilation-parse-errors-function' and
   (let* ((pop-up-windows t)
 	 (w (display-buffer (marker-buffer (car next-error)))))
     (set-window-point w (car next-error))
-      (set-window-start w (car next-error)))))
-
-;;;###autoload (define-key ctl-x-map "`" 'next-error)
-
+    (set-window-start w (car next-error))))
+
 ;; Find a buffer for file FILENAME.
 ;; Search the directories in compilation-search-path.
 ;; A nil in compilation-search-path means to try the