[Emergency fix] spacemacs//mark-repl-as-useful

This function is making asynchronous commands fail because it tries to
add string literal to spacemacs-useful-buffers-regexp while add-to-list
only works when first argument is a symbol and the second is an
element. Otherwise, it throws this error and stop all async commands to
do any further work at this point:

if: Wrong type argument: symbolp

This commit fixes the following issues:

- Don't add spacemacs//mark-repl-as-useful to
  buffer-list-update-hook. We only need this function to switch to next
  or previous buffer. So, better check when and only when those commands
  are actually used.

- As a result, we remove the function since it's unneeded anymore.

- Do the checking in of comint-mode in spacemacs-useful-buffer-p
  function. Better do it in one place than scatter the logic in a hook
  and this function.

- Change useless-buffer-p to accept an actual buffer object and check
  for buffer name inside.

doc/HOWTOs.md

@@ -64,9 +64,3 @@ Examples:
 (push "\\*Messages\\*" spacemacs-useful-buffers-regexp)
 ```
 
-Most repl buffers are marked useful by default. This behavior can be disabled
-with the following code:
-
-```elisp
-(remove-hook 'after-change-major-mode-hook 'spacemacs//mark-repl-as-useful)
-```

spacemacs/config.el

@@ -78,8 +78,7 @@
 (defvar spacemacs-useful-buffers-regexp '("\\*\\(scratch\\|terminal\.\+\\|ansi-term\\|eshell\\)\\*")
   "Regexp used to define buffers that are useful despite matching
 `spacemacs-useless-buffers-regexp'.")
-;; Automatically make comint buffers useful-buffers
-(add-hook 'buffer-list-update-hook 'spacemacs//mark-repl-as-useful)
+
 ;; activate winner mode use to undo and redo windows layout
 (winner-mode t)
 ;; no beep pleeeeeease ! (and no visual blinking too please)

spacemacs/funcs.el

@@ -345,29 +345,28 @@ argument takes the kindows rotate backwards."
   (interactive "p")
   (rotate-windows (* -1 count)))
 
-(defun spacemacs//mark-repl-as-useful ()
-  "Marks all buffers derived from `comint-mode' as useful."
-  (if (eq (get (buffer-local-value 'major-mode (current-buffer)) 'derived-mode-parent)
-          'comint-mode)
-      (add-to-list (format "*\\%s\\*" (replace-regexp-in-string "*" "" (buffer-name)))
-                   spacemacs-useful-buffers-regexp)))
-
-(defun spacemacs/useless-buffer-p (buffer-name)
+(defun spacemacs/useless-buffer-p (buffer)
   "Determines if a buffer is useful."
-  (cond ((cl-loop for regexp in spacemacs-useful-buffers-regexp do
-                  (if (string-match regexp buffer-name)
-                      (return t))) nil)
-        ((cl-loop for regexp in spacemacs-useless-buffers-regexp do
-                  (if (string-match regexp buffer-name)
-                      (return t))) t)
-        (t nil)))
+  (let ((buf-paren-major-mode (get (with-current-buffer buffer
+                                     major-mode)
+                                   'derived-mode-parent))
+        (buf-name (buffer-name buffer)))
+    ;; first find if useful buffer exists, if so returns nil and don't check for
+    ;; useless buffers. If no useful buffer is found, check for useless buffers.
+    (unless (cl-loop for regexp in spacemacs-useful-buffers-regexp do
+                     (when (or (eq buf-paren-major-mode 'comint-mode)
+                               (string-match regexp buf-name))
+                       (return t)))
+      (cl-loop for regexp in spacemacs-useless-buffers-regexp do
+               (when (string-match regexp buf-name)
+                 (return t))))))
 
 (defun spacemacs/next-useful-buffer ()
   "Switch to the next buffer and avoid special buffers."
   (interactive)
   (let ((start-buffer (current-buffer)))
     (next-buffer)
-    (while (and (spacemacs/useless-buffer-p (buffer-name (current-buffer)))
+    (while (and (spacemacs/useless-buffer-p (current-buffer))
                 (not (eq (current-buffer) start-buffer)))
       (next-buffer))))
 
@@ -376,7 +375,7 @@ argument takes the kindows rotate backwards."
   (interactive)
   (let ((start-buffer (current-buffer)))
     (previous-buffer)
-    (while (and (spacemacs/useless-buffer-p (buffer-name (current-buffer)))
+    (while (and (spacemacs/useless-buffer-p (current-buffer))
                 (not (eq (current-buffer) start-buffer)))
       (previous-buffer))))