prm-mode.el : a mode for deal.II parameter files

Overview

I wrote this mode to scratch a long-time itch: there is no nice support for syntax highlighting or navigation in deal.II parameter files available for emacs. This small mode supports:

• Navigation between subsections with M-p and M-n
• Syntax highlighting
• automatic indentation (standard, not with electric-mode)

This mode is officially in beta, and may have wrong behavior in corner cases. It seems to work correctly for a couple of sample files (i.e., some of the large parameter files in ASPECT) but there are surely still bugs lurking somewhere in it. I have only tested it with emacs 24.5: I am not doing anything fancy so it should work with older versions (but I cannot guarantee it).

How to set it up

Standard stuff for emacs: add this to your init file:

(require 'prm-mode "~/path-to-prm-mode/prm-mode.el" nil)
(add-to-list 'auto-mode-alist '("/*.\.prm$" . prm-mode))

package.el support is on the TODO list.

The customization support is present but not well documented. If you look through the source you should see:

;; user configurable variables
(defvar prm-continuation-line-extra-indentation
  4
  "Amount of extra indentation to give continuation lines.")

(defvar prm-subsection-indentation-level
  2
  "Amount of indentation to use in subsections.")

(defvar prm-permit-subsection-cycling
  t
  "Whether or not to cycle through the buffer when searching for
  subsections.")

which are the three current customization options.

Relevant work

This mode is partly inspired by @davydden's syntax highlighting mode for Atom available here. We can't let the new editor on the block to have all the fun :)

How to help

I would greatly appreciate assistance with this mode. I think the indentation code is probably fine the way it is; using smie would probably make most of it simpler but I suspect handling backslashes correctly would be much harder. The syntax highlighting could probably be written better. If your workflow would benefit from new functions (tree-like navigation like in org-mode, snippets, etc), then please let me know.

Additionally, if you can make a weird enough parameter file that this mode highlights, indents, or navigates it incorrectly, please send it my way.

I have written some simple tests (and these did catch two new bugs) with ERT that cover basic indentation and navigation occurrences. I am not sure how to write tests for syntax highlighting; no matter what I try buffers created with with-temp-buffer do not ever do syntax highlighting. I would be very appreciative if someone could instruct me on how to make such a test.

Bugs that will probably not be fixed

comment handling

Since prm-mode is derived from prog-mode (the generic major programming mode for emacs), prm-mode treats comments differently from the parser in ParameterHandler. For example, prm-mode highlights backslashed comments as

   set foo = bar # proper comment
   set baz = \# some escaped comment

but, if I understand it correctly, ParameterHandler does not bother with backslashes in front of # and will just remove #some escaped comment from the line before setting the value of baz.

One could argue that this is a bug in ParameterHandler, but if no one over the last fifteen years has needed to get a # into a string, then it is probably not worth worrying over.

Syntax highlighting in continuations

Most emacs modes do this 'incorrectly'; if a line starts with a keyword, then that keyword will be highlighted, regardless of whether or not the last line ended in a \. Similarly, as far as my experiments can tell, emacs can only highlight constructions on a single line, so multi-line (with continuation) section headings are improperly highlighted.

A screenshot

This is what prm-mode looks like in emacs, with a slight variation on the comida theme: <img src="./screenshots/comida-prm-mode.png" width="500">