New :env setting for pulling shell envvars into MacOS sessions

:env lets you specify what environment variables exec-path-from-shell
should pull in from your shell environment at startup. As such, these
need to be defined at startup. :env is useless post-init.

May address #433

core/core-os.el

@@ -36,6 +36,9 @@
               ;; environment, so envvars will be wrong. That includes the PATH
               ;; Emacs picks up. `exec-path-from-shell' fixes this.
               (when (require 'exec-path-from-shell nil t)
+                (def-setting! :env (&rest vars)
+                  "Ensure VARs are grabbed from your shell environment."
+                  `(nconc exec-path-from-shell-variables (list ,@vars)))
                 (setq exec-path-from-shell-check-startup-files nil
                       exec-path-from-shell-arguments (delete "-i" exec-path-from-shell-arguments))
                 (defvaralias 'exec-path-from-shell-debug 'doom-debug-mode)

modules/lang/go/config.el

@@ -1,5 +1,7 @@
 ;;; lang/go/config.el -*- lexical-binding: t; -*-
 
+(set! :env "GOPATH" "GOROOT")
+
 (def-package! go-mode
   :mode "\\.go$"
   :interpreter "go"

modules/lang/python/config.el

@@ -1,5 +1,7 @@
 ;;; lang/python/config.el -*- lexical-binding: t; -*-
 
+(set! :env "PYTHONPATH" "PYENV_ROOT")
+
 (defvar +python-pyenv-root nil
   "The path to pyenv's root directory. This is automatically set when `python'
 is loaded.")