Let display-warning work during bootstrap

* lisp/emacs-lisp/warnings.el (display-warning): Only call
`special-mode' and `newline' if they are `fbound'.

1 files changed, 7 insertions, 3 deletions

diff --git a/lisp/emacs-lisp/warnings.el b/lisp/emacs-lisp/warnings.el
index 665733181cb..c4d97ceab03 100644
--- a/lisp/emacs-lisp/warnings.el
+++ b/lisp/emacs-lisp/warnings.el
@@ -241,11 +241,15 @@ See also `warning-series', `warning-prefix-function' and
                (old (get-buffer buffer-name))
                (buffer (or old (get-buffer-create buffer-name)))
                (level-info (assq level warning-levels))
+               ;; `newline' may be unbound during bootstrap.
+               (newline (if (fboundp 'newline) #'newline
+                          (lambda () (insert "\n"))))
                start end)
           (with-current-buffer buffer
             ;; If we created the buffer, disable undo.
             (unless old
-              (special-mode)
+              (when (fboundp 'special-mode) ; Undefined during bootstrap.
+                (special-mode))
               (setq buffer-read-only t)
               (setq buffer-undo-list t))
             (goto-char (point-max))
@@ -256,7 +260,7 @@ See also `warning-series', `warning-prefix-function' and
                         (funcall warning-series)))))
             (let ((inhibit-read-only t))
               (unless (bolp)
-                (newline))
+                (funcall newline))
               (setq start (point))
               (if warning-prefix-function
                   (setq level-info (funcall warning-prefix-function
@@ -264,7 +268,7 @@ See also `warning-series', `warning-prefix-function' and
               (insert (format (nth 1 level-info)
                               (format warning-type-format typename))
                       message)
-              (newline)
+              (funcall newline)
               (when (and warning-fill-prefix (not (string-match "\n" message)))
                 (let ((fill-prefix warning-fill-prefix)
                       (fill-column 78))