Why does a theme change cause reloading - YASnippet

Question

The problem:

Before installing YASnippet changing themes was instantaneous, now it YASnippet reloads itself in someway making changes take a few seconds.

Is this functionality necessary? Can I turn it off?

Is there some way around it?

Context:

I have this as part of my evil mode config:

;; Evil Mode Switcher
(defun toggle-evil-mode ()
  (interactive)
  (if (not evil-mode)
      (progn
        (evil-mode 1)
        (enable-theme 'ample))
    (progn
      (evil-mode 0)
      (enable-theme 'ample-flat))))

(global-set-key (kbd "<C-escape>") 'toggle-evil-mode)

It allows me to switch in and out of evil mode with C-escape.

While doing though it toggles to a darker theme, this makes it easier to recognise whether I am in it or not.

It used to work well, but now that I have YASnippet installed it takes too long.

Updated: Stack trace

Here is a slightly truncated stacktrace, by using debug-on-entry. From this it appears that yas is adding custom items to the theme, do they need to be updated though?

Debugger entered--entering a function:
* yas-reload-all()
  yas--global-mode-reload-with-jit-maybe()
  run-hooks(yas-global-mode-hook yas-global-mode-on-hook)
  yas-global-mode(1)
  custom-set-minor-mode(yas-global-mode t)
  custom-theme-recalc-variable(yas-global-mode)
  enable-theme(user)
  enable-theme(ample)
  toggle-evil-mode()
  call-interactively(toggle-evil-mode nil nil)
  command-execute(toggle-evil-mode)

Answer 1

It looks like yas-global-mode became part of your user theme (perhaps because you set it via the customize interface? (the docstring of custom-set-variables says "These settings are registered as theme `user'.")).

A possible workaround could be to let-bind yas-global-mode-hook in toggle-evil-mode:

;; Evil Mode Switcher
(defun toggle-evil-mode ()
  (interactive)
  (let ((yas-global-mode-hook nil)) ; don't reload snippets
    (if (not evil-mode)
        (progn
          (evil-mode 1)
          (enable-theme 'ample))
      (progn
        (evil-mode 0)
        (enable-theme 'ample-flat)))))

Another possibility might be to remove yas-global-mode from your custom settings, and just call (yas-global-mode +1) in your init file directly.