How to activate AUCTeX support for beamer without preamble?

Question

Usually, AUCTeX activates beamer-specific settings (e.g. syntax highlighting) depending on \documentclass. In my LaTeX templates, however, I have separated the preamble from the rest of the document using \input{beamer-preamble}.

Here's an MWE:

\input{beamer-preamble}  % `beamer-preamble.tex` only contains `\documentclass{beamer}`
\begin{document}

\title{Some title}

\begin{frame}
\frametitle{Some frame title}
\end{frame}

\end{document}

In this example, the argument of \frametitle should be highlighted similarly to the argument of \title.

How can I tell AUCTeX to still apply the beamer-specific settings?

Answer 1

First of all, I suggest you create a proper class file beamer-preamble.cls like this:

\NeedsTeXFormat{LaTeX2e} 
\ProvidesClass{beamer-preamble}
  [2017/04/26 v0.1 My Beamer Preamble]
\LoadClass[<beamer-options>]{beamer}

Next, you want to have an AUCTeX style file for beamer-preamble.cls. Doing M-x TeX-auto-generate RET in one way. But I recommend writing your own style file. Something like this should suffice:

(TeX-add-style-hook
 "beamer-preamble"
 (lambda ()
   (TeX-run-style-hooks "beamer"))
 LaTeX-dialect)

Customize TeX-style-private to a directory of your choice and save the code above as beamer-preamble.el there. Add this to your init file,

(setq TeX-parse-self t)

restart Emacs and open your .tex file.