Ensure racket-repl hidden buffer uses racket-mode; fixes #713

racket-repl visits racket-repl-command-file (without visibly selecting
the buffer) and does racket--repl-run. Unless the major-mode is
racket-mode or racket-hash-lang-mode, the run will complain with an
error message.

Typically this won't happen because visiting a .rkt file will, in
general, automatically set the buffer's major-mode to racket-mode due
to us setting auto-mode-alist by default. Or maybe the user changes
auto-mode-alist to use racket-hash-lang-mode.

But a user's configuration could override this, intentionally or not,
possibly with surprising results. There are various mechanisms for
choosing the mode:

  https://www.gnu.org/software/emacs/manual/html_node/emacs/Choosing-Modes.html

A user probably will want to figure out and change their configuration
to set a major-mode consistently when opening .rkt files generally.

Regardless/meanwhile, we can at least avoid the racket-repl error
message by forcing the racket-repl-command-file buffer to use
racket-mode. (Even if a user prefers racket-hash-lang-mode for
editing, it shouldn't matter if we use racket-mode here.)

Author: greghendershott

racket-repl.el

@@ -505,6 +505,9 @@ even when the module language doesn't provide any binding for
 (declare-function racket-repl-buffer-name-unique "racket-repl-buffer-name" ())
 (autoload        'racket-repl-buffer-name-unique "racket-repl-buffer-name")
 
+(declare-function racket-mode "racket-mode" ())
+(autoload        'racket-mode "racket-mode")
+
 ;;;###autoload
 (defun racket-repl (&optional noselect)
   "Show a Racket REPL buffer in some window.
@@ -532,6 +535,7 @@ require other modules, or whatever."
   ;; Visit the file without selecting it, and run it.
   (let ((racket-repl-buffer-name-function #'racket-repl-buffer-name-unique))
     (with-current-buffer (find-file-noselect racket-repl-command-file)
+      (racket-mode) ;ensure: see #713
       (racket--repl-run
        (list racket-repl-command-file)
        nil