Make `next-error' output fewer messages about locus

* lisp/simple.el (next-error-verbosity): New user variable.
(next-error, next-error-internal): Use it to control only outputting
locus message if locus changed.

etc/NEWS

@@ -303,6 +303,10 @@ and directory-local variables.
 'with-connection-local-profiles'.  No argument 'profiles' needed any
 longer.
 
+---
+** next-error-verbosity controls when `next-error' outputs a message
+   about the error locus.
+
 
 * Editing Changes in Emacs 27.1
 

lisp/simple.el

@@ -110,6 +110,15 @@ If non-nil, the value is passed directly to `recenter'."
   :type 'hook
   :group 'next-error)
 
+(defcustom next-error-verbosity nil
+  "If nil, `next-error' always outputs the current error buffer.
+If non-nil, the message is output only when the error buffer
+changes."
+  :group 'next-error
+  :type 'boolean
+  :safe #'booleanp
+  :version "27.1")
+
 (defvar next-error-highlight-timer nil)
 
 (defvar next-error-overlay-arrow-position nil)
@@ -312,21 +321,27 @@ To control which errors are matched, customize the variable
       ;; We know here that next-error-function is a valid symbol we can funcall
       (with-current-buffer buffer
         (funcall next-error-function (prefix-numeric-value arg) reset)
-        (next-error-found buffer (current-buffer))
-        (message "%s locus from %s"
-                 (cond (reset                             "First")
-                       ((eq (prefix-numeric-value arg) 0) "Current")
-                       ((< (prefix-numeric-value arg) 0)  "Previous")
-                       (t                                 "Next"))
-                 next-error-last-buffer)))))
+        (let ((prev next-error-last-buffer))
+          (next-error-found buffer (current-buffer))
+          (when (or (not next-error-verbosity)
+                    (not (eq prev next-error-last-buffer)))
+            (message "%s locus from %s"
+                     (cond (reset                             "First")
+                           ((eq (prefix-numeric-value arg) 0) "Current")
+                           ((< (prefix-numeric-value arg) 0)  "Previous")
+                           (t                                 "Next"))
+                     next-error-last-buffer)))))))
 
 (defun next-error-internal ()
   "Visit the source code corresponding to the `next-error' message at point."
   (let ((buffer (current-buffer)))
     ;; We know here that next-error-function is a valid symbol we can funcall
     (funcall next-error-function 0 nil)
-    (next-error-found buffer (current-buffer))
-    (message "Current locus from %s" next-error-last-buffer)))
+    (let ((prev next-error-last-buffer))
+      (next-error-found buffer (current-buffer))
+      (when (or (not next-error-verbosity)
+                (not (eq prev next-error-last-buffer)))
+        (message "Current locus from %s" next-error-last-buffer)))))
 
 (defun next-error-found (&optional from-buffer to-buffer)
   "Function to call when the next locus is found and displayed.