Replace ambrevar/prefer-eshell by helm-ff-preferred-shell-mode.

.emacs.d/lisp/init-eshell.el

@@ -215,8 +215,7 @@ This should be faster then `seq-uniq'."
 ;; (add-hook 'eshell-mode-hook 'ambrevar/fix-local-epa-file-encrypt-to)
 
 ;;; Spawning
-(defvar ambrevar/prefer-eshell nil
-  "If non-nil, default to Eshell instead of M-x shell.")
+(require 'init-shell); For `helm-ff-preferred-shell-mode'.
 (when (require 'patch-helm nil 'noerror)
   (helm-defswitcher
    "Eshell"
@@ -226,12 +225,12 @@ This should be faster then `seq-uniq'."
         (derived-mode-p 'eshell-mode)
         (derived-mode-p 'shell-mode))))
    (lambda (&optional name)
-     (if ambrevar/prefer-eshell
+     (if (eq helm-ff-preferred-shell-mode 'eshell-mode)
          (eshell 'new)
        (shell (generate-new-buffer (generate-new-buffer-name "*shell*"))))
      (when name
        (rename-buffer (format "*%sshell<%s>*"
-                              (if ambrevar/prefer-eshell "e" "")
+                              (if (eq helm-ff-preferred-shell-mode 'eshell-mode) "e" "")
                               name)
                       'unique)))
    nil

.emacs.d/lisp/init-guix.el

@@ -190,7 +190,7 @@ If MANIFEST is nil, it is queried from the manifests found in `ambrevar/guix-man
 
 (defun %ambrevar/guix-install-manifest (&optional manifests channel)
   "Install list of (NAME MANIFEST-FILE) using CHANNEL."
-  (require 'init-eshell)                ; For `ambrevar/prefer-eshell'.
+  (require 'init-shell)                ; For `helm-ff-preferred-shell-mode'.
   (let* ((guix (if channel
                    (let ((dest (expand-file-name
                                 ;; TODO: What name should we use with multiple manifests?
@@ -207,7 +207,7 @@ If MANIFEST is nil, it is queried from the manifests found in `ambrevar/guix-man
         (make-directory (expand-file-name manifest-name
                                           ambrevar/guix-extra-profiles)
                         'parents)))
-    (funcall (if ambrevar/prefer-eshell
+    (funcall (if (eq helm-ff-preferred-shell-mode 'eshell-mode)
                  'ambrevar/run-in-eshell
                'ambrevar/run-in-shell)
              (mapconcat #'identity
@@ -282,10 +282,11 @@ With a prefix argument, query for a channel specification file."
 
 System is queried from those found in `ambrevar/guix-system-directory'. "
   (interactive)
+  (require 'init-shell) ; For `helm-ff-preferred-shell-mode'.
   (let* ((system-pair (ambrevar/guix-query-system system))
          (system-name (first system-pair))
          (system (second system-pair)))
-    (funcall (if ambrevar/prefer-eshell
+    (funcall (if (eq helm-ff-preferred-shell-mode 'eshell-mode)
                  'ambrevar/run-in-eshell
                'ambrevar/run-in-shell)
              (string-join