checkdoc.el (checkdoc-file): New function

* lisp/emacs-lisp/checkdoc.el (checkdoc-error): When
  `checkdoc-diagnostic-buffer' is set to "*warn*", print the warning
  to the standard output.

(bug#20754)

etc/NEWS

@@ -84,6 +84,10 @@ command line when `initial-buffer-choice' is non-nil.
 
 * Changes in Emacs 25.1
 
+** New function `checkdoc-file' checks for style errors.
+It's meant for use together with `compile':
+emacs -batch --eval "(checkdoc-file \"subr.el\")"
+
 ** New command `comment-line' bound to `C-x C-;'.
 
 ** New function `custom-prompt-customize-unsaved-options' checks for

lisp/emacs-lisp/checkdoc.el

@@ -870,6 +870,13 @@ otherwise stop after the first error."
 	(if take-notes (checkdoc-show-diagnostics))
 	(message "Checking buffer for style...Done."))))
 
+;;;###autoload
+(defun checkdoc-file (file)
+  "Check FILE for document, comment, error style, and rogue spaces."
+  (with-current-buffer (find-file-noselect file)
+    (let ((checkdoc-diagnostic-buffer "*warn*"))
+      (checkdoc-current-buffer t))))
+
 ;;;###autoload
 (defun checkdoc-start (&optional take-notes)
   "Start scanning the current buffer for documentation string style errors.
@@ -2614,13 +2621,13 @@ function called to create the messages."
                     (int-to-string
                      (count-lines (point-min) (or point (point-min))))
                     ": " msg)))
+    (if (string= checkdoc-diagnostic-buffer "*warn*")
+        (warn (apply #'concat text))
       (with-current-buffer (get-buffer checkdoc-diagnostic-buffer)
           (let ((inhibit-read-only t)
                 (pt (point-max)))
             (goto-char pt)
-        (apply #'insert text)
-        (when noninteractive
-          (warn (buffer-substring pt (point-max))))))))
+            (apply #'insert text))))))
 
 (defun checkdoc-show-diagnostics ()
   "Display the checkdoc diagnostic buffer in a temporary window."