Misc code for using emacsclient with nix-shell

nix-shell-env.el

(defun nix-shell-c-system-header-paths ()
  "Extract header search paths from the NIX_CFLAGS_COMPILE env variable"
  (cl-labels ((every-other (li &optional pick)
                           (when li
                             (if pick
                                 (cons (car li) (every-other (cdr li)))
                               (every-other (cdr li) (not pick))))
                           ))
    (let* ((cflags (getenv "NIX_CFLAGS_COMPILE")))
      (every-other (split-string cflags)))))

(defun nix-shell-add-company-c-headers (&optional paths)
  (setq company-c-headers-path-system
        (append company-c-headers-path-system
                (or paths (nix-shell-c-system-header-paths)))))

(defun nix-shell-add-c-headers-paths ()
  (let ((paths (nix-shell-c-system-header-paths)))
    (nix-shell-set-company-c-headers paths)

    ;; Why the fuck doesn't ffap-c know about semantic-dependency-system-include-path?
    (setq ffap-c-path
          (append ffap-c-path paths))

    (dolist (path paths)
      (semantic-add-system-include path major-mode))))


(defun nix-shell--split-env-var-str (varstr)
  "Split VARSTR - a 'VAR=VALUE' string"
  (let ((i (find ?= varstr)))
    (cons (substring varstr 0 i)
          (substring varstr (+ i 1))))
  )

;; See https://github.com/travisbhartwell/nix-emacs/blob/master/nix-sandbox.el
;; for useful helper functions and a candidate for a future home
(defun nix-shell-load-env (nix-file)
  "Loads the environment defined by NIX-FILE. Runs nix-shell to get the
environment and makes process-environment buffer local"
  (interactive "fnix-file")
  (let ((environment
         (with-temp-buffer
           (let* ((nix-file-shell-safe (shell-quote-argument nix-file))
                  (command (format "nix-shell %s --command 'printenv -0' 2>/dev/null"
                                   nix-file-shell-safe))
                  (status (call-process-shell-command command nil t)))
             (when (> status 0)
               (message "'nix-shell %s' failed with %d" nix-file-shell-safe status)
               (return nil))
             (split-string (buffer-string) "\0")))))

    (when environment
      (set (make-local-variable 'process-environment)
           environment))
    ))

;; (split-string  (shell-command-to-string "printenv -0") "\0" t)