Getting Emacs fill-paragraph to play nice with javadoc-like comments

Question

I'm writing an Emacs major mode for an APL dialect I use at work. I've gotten basic font locking to work, and after setting comment-start and comment-start-skip, comment/uncomment region and fill paragraph also work.

However, comment blocks often contain javadoc style comments and i would like fill-paragraph to avoid glueing together lines starting with such commands.

If I have this (\ instead of javadoc @):

# This is a comment that is long and should be wrapped.
# \arg Description of argument
# \ret Description of return value

M-q gives me:

# This is a comment that is long and
# should be wrapped. \arg Description
# of argument \ret Description of
# return value

But I want:

# This is a comment that is long and
# should be wrapped.
# \arg Description of argument
# \ret Description of return value

I've tried setting up paragraph-start and paragraph-separate to appropriate values, but fill-paragraph still doesn't work inside a comment block. If I remove the comment markers, M-q works as I want to, so the regexp I use for paragraph-start seems to work.

Do I have to write a custom fill-paragraph for my major mode? cc-mode has one that handles cases like this, but it's really complex, I'd like to avoid it if possible.

Answer 1

There's other modes that have less complex functions used for fill-paragraph-function. Browsing through my install, it looks like the ones in ada-mode and make-mode are good examples.

Answer 2

What I do in these cases is open a blank line between the paragraph lines and the argument lines, then use M-q to wrap the paragraph lines, then kill the blank line between them. Not ideal, but it works and is easy enough to record in a macro if you need to repeat it.

Answer 3

The problem was that the paragraph-start regexp has to match the entire line to work, including the actual comment character. The following elisp works for the example I gave:

(setq paragraph-start "^\\s-*\\#\\s-*\\\\\\(arg\\|ret\\).*$")

Here a page that has an example regexp for php-mode that does this: http://barelyenough.org/blog/2006/10/nicer-phpdoc-comments/