Avoid errors in forms-mode when default major mode is text

* lisp/forms.el (forms-mode): Bind
change-major-mode-with-file-name to nil when calling
set-visited-file-name.  (Bug#22982)

1 files changed, 8 insertions, 1 deletions

diff --git a/lisp/forms.el b/lisp/forms.el
index c141188788b..c0b48fd3b63 100644
--- a/lisp/forms.el
+++ b/lisp/forms.el
@@ -589,7 +589,14 @@ Commands:                        Equivalent keys in read-only mode:
         (make-local-variable 'forms--dynamic-text)
 
         ;; Prevent accidental overwrite of the control file and auto-save.
-        (set-visited-file-name nil)
+        ;; We bind change-major-mode-with-file-name to nil to prevent
+        ;; set-visited-file-name from calling set-auto-mode, which
+        ;; might kill all local variables and set forms-file nil,
+        ;; which will then barf in find-file-noselect below.  This can
+        ;; hapen when the user sets the default major mode that is
+        ;; different from the Fundamental mode.
+        (let (change-major-mode-with-file-name)
+          (set-visited-file-name nil))
 
         ;; Prepare this buffer for further processing.
         (setq buffer-read-only nil)