Why expression fails in init file, but works fine during session [duplicate]

Question

I want to understand why an expression of the form

(load-theme 'my-kewl-theme t)

fails¹ when run as the last expression in my init (~/.emacs) file, but works fine if I evaluate it as soon as soon as Emacs' startup is done.

How can I troubleshoot/debug this conundrum?

The only clue I have is that right before (load-theme 'my-kewl-theme t) is evaluated at the end of the loading of ~/.emacs, the variable custom-theme-load-path has the value

(custom-theme-load-directory t)

whereas after Emacs starts, it has the value

("/path/to/my-kewl-theme/" custom-theme-load-directory t)

I don't know what accounts for this difference. (This variable is not referred to at all by ~/.emacs, at least explicitly.) The variable custom-theme-load-directory has the value ~/.emacs.d throughout.

---

^{1error: Unable to find theme file for `my-kewl-theme`}

Answer 1

From the emacs manual regarding packages:

By default, Emacs also automatically loads all installed packages in subsequent Emacs sessions. This happens at startup, after processing the init file.

So if your theme relies on some package initialisation you can put your call in after-init-hook. For example

(add-hook 'after-init-hook 
   (lambda ()
     (load-theme 'my-kewl-theme t)))

Alternatively, enable the theme by customising custom-enabled-themes, instead of using load-theme in your init file.

Answer 2

I believe it is standard practice for themes installed as packages to add their own paths to custom-theme-load-path as an autoload. A call to package-initialize will execute all of your package autoloads (among other things), and if there isn't an explicit call in your init file, it is called implicitly at the end of initialization.

I recommend putting a (package-initialize) towards the beginning of your init file, right after you configure package.el itself (adding repositories, etc.) and before you do anything with any packages not built-in to Emacs itself.