Add new variable dotspacemacs-import-env-vars-shell-file-name

Used to fetch the environment variables. This allows to keep shell-file-name
untouched.

core/core-dotspacemacs.el

@@ -62,6 +62,13 @@ or `spacemacs'.")
 from your default shell on startup. This is enabled by default for macOS users
 and X11 users.")
 
+(defvar dotspacemacs-import-env-vars-shell-file-name nil
+  "If nil then use the default shell is used to fetch the environment variables.
+Set this variable to a different shell executable path to import the environment
+variables from this shell. Note that `file-shell-name' is preserved and always
+points to the default shell. For instance to use your fish shell environment
+variables set this variable to `/usr/local/bin/fish'.")
+
 (defvar dotspacemacs-enable-emacs-pdumper nil
   "If non-nil then enable support for the portable dumper. You'll need
 to compile Emacs 27 from source following the instructions in file

core/templates/.spacemacs.template

@@ -162,6 +162,15 @@ It should only modify the values of Spacemacs settings."
                                                 (or (eq system-type 'darwin)
                                                     (eq window-system 'x)))
 
+   ;; If nil then use the default shell is used to fetch the environment
+   ;; variables. Set this variable to a different shell executable path to
+   ;; import the environment variables from this shell. Note that
+   ;; `file-shell-name' is preserved and always points to the default shell. For
+   ;; instance to use your fish shell environment variables set this variable to
+   ;; `/usr/local/bin/fish'.
+   ;; (default nil)
+   dotspacemacs-import-env-vars-shell-file-name nil
+
    ;; Specify the startup banner. Default value is `official', it displays
    ;; the official spacemacs logo. An integer value is the index of text
    ;; banner, `random' chooses a random text banner in `core/banners'

doc/DOCUMENTATION.org

@@ -1733,12 +1733,13 @@ build of Emacs.
 At anytime you can import the environment variables by calling the function
 =spacemacs/loadenv=.
 
-You can define a different shell than the default shell by setting the variable
-=shell-file-name= in the =dotspacemacs/user-init= function of your dotfile.
+You can define a different shell than the default shell to look for environment
+variables by setting the variable =dotspacemacs-import-env-vars-shell-file-name=
+in your dotfile. Note that =shell-file-name= is not modified by this value.
 
 #+BEGIN_EXAMPLE emacs-lisp
-(defun dotspacemacs/user-init ()
-  (setq shell-file-name "/usr/local/bin/fish"))
+(defun dotspacemacs/init ()
+  (setq dotspacemacs-import-env-vars-shell-file-name "/usr/local/bin/fish"))
 #+END_EXAMPLE
 
 * Commands

layers/+distributions/spacemacs-bootstrap/funcs.el

@@ -18,8 +18,13 @@
   (require 'async nil t)
   (async-start
    `(lambda ()
-     ,(async-inject-variables "\\`shell-file-name\\'")
-     (split-string (shell-command-to-string "env") "\n"))
+      ,(async-inject-variables
+        "\\`dotspacemacs-import-env-vars-shell-file-name\\'")
+      (if dotspacemacs-import-env-vars-shell-file-name
+          (let ((shell-file-name
+                 dotspacemacs-import-env-vars-shell-file-name))
+            (split-string (shell-command-to-string "env") "\n"))
+        (split-string (shell-command-to-string "env") "\n")))
    (lambda (envvars)
      (spacemacs-buffer/message "Imported environment variables:")
      (dolist (env envvars)
@@ -29,8 +34,14 @@
                   (v (cadr var)))
              (spacemacs-buffer/message "  - %s=%s" k v)
              (if (string-equal "PATH" k)
-                 (setq exec-path (split-string v path-separator))
-               (setenv k v))))))))
+                 (let ((paths (split-string v path-separator)))
+                   (dolist (p paths)
+                     (add-to-list 'exec-path p)))
+               (setenv k v)))))
+     ;; be sure we keep the default shell in this Emacs session
+     ;; this is to prevent potential issues with packages which could
+     ;; expect a default shell
+     (setenv "SHELL" shell-file-name))))