Re: shared-mime-info: distinguish x-octave and x-matlab files

[Mike Miller]

Hey, I think this is an interesting project and appreciate you taking it
on with the freedesktop folks.

On Wed, Jan 28, 2015 at 13:01:34 +0000, Carnë Draug wrote:
> Hi
> 
> currently, shared-mime-info [1] treats x-octave as an alias of x-matlab.
> It does this despite using "##" as magic to identify the file as Matlab.
> The most obvious problem of this is with text editors picking Matlab as
> syntax highlight for Octave code.  My take on the two mime types, is that
> having the file written in Octave does not matter, what matters where it
> can run.  This means that a file written in Octave that is Matlab compatible
> deserves a x-matlab mime.

Agree so far.

> I submitted them a patch that splits them into two types and added magic
> to recognize a shebang line for an octave interpreter [2].  In addition,
> it also replaces the common "##" magic with "#" for Octave and "%" for
> Matlab.  However this last got rejected since this seems to be too small
> of magic for their new standards.  Can anyone suggest new magic that
> would help in distinguish between code that is meant to be Octave only
> and Matlab compatible?

I honestly don't know if this is possible. As much as I'd also like to
see an Octave MIME type stand on its own, I don't know how it can be
automatically detected like this in a small way that would be acceptable
to the freedesktop mime database (I assume they don't want to be parsing
full files extensively just to derive the MIME type). I tried thinking
of some strings that could be used, but strings that may distinguish
Octave files are really just conventions that we use. As we like to say,
the Matlab language is a subset of the Octave language. So a Matlab .m
file is also an Octave .m file. The only thing that makes an Octave .m
file not a Matlab .m file are specific coding styles, syntaxes, and
function calls used.

Put another way, it's like trying to differentiate between a C++98 .cc
file and a C++11 .cc file. There are any number of things you could try
to match on to detect whether it's a C++11 file.

There are any number of things you could search for in an Octave .m file
("## -*- texinfo -*-", "%!test", or "print_usage") but the lack of any
of them does not mean it's not an Octave .m file. If I take a Matlab .m
file and add a broadcasting operation, or double-quoted strings, that
makes it an Octave .m file.

> Another thing I would suggest is to start adding a shebang line to our
> Octave files.  This has two advantages, 1) make it easier for such
> applications to recognize the file as Octave source, and 2) raise awareness
> that it is possible to actually write an Octave program (I think this is a
> really nice feature of Octave that it is not given enough attention).

I don't think this is a good idea. Some tools may interpret the presence
of a shebang line as an executable script, whether the file is
executable or not (thinking of systems like Windows where there is no
execute bit), some Linux packaging tools may parse shebang lines and
handle the files differently, etc.

As much as I'd like this to go somewhere, I think it is probably best
handled as more extensive checks in each editor or IDE where possible,
or as a user preference where it needs to be.

-- 
mike