Re: C file recoginzed as image file

[Kim F. Storm]

Stefan Monnier <address@hidden> writes:

>>> The reason I decided to detect images by their contents
>>> rather than by their file names is that it seems more correct
>>> as a way of recognizing them.
>
>>     Why does it seem that way to you?
>
>> The whole point of a magic number is to recognize the file type
>> from its contents, regardless of file name.
>
> But they're heuristics as well.  A text file may start with the title
> "GIF89a file format".
>
> Basically, I think that determining the major mode for a given file should
> neither give precedence to auto-mode-alist nor magic-mode-alist.  Instead it
> should consider both.  Each one can associate a file with a set of possible
> major modes (typically the set will be singleton) or say "don't know"
> (which would be basically the set of all major modes).
>
> E.g. auto-mode-alist would give "don't know" for a file named "/b/c/foo" but
> would give the set { perl-mode, prolog-mode } for a file named
> "/b/c/foo.pl".  Then magic-mode-alist would give other sets of modes (based
> on things like the #! interpreter name, the -*- ... -*- cookie, etc...).
> If the intersection of the two sets is a singleton, then use that
> major-mode, otherwise query the user to decide whether to believe the file
> name or the contents.  After all, an inconsistently named file is generally
> a sign that there's something wrong, so it's good to prompt the user
> about it.

This is definitely the best proposal I've seen so far for solving this.

-- 
Kim F. Storm <address@hidden> http://www.cua.dk