Re: "Text is read-only"... except it isn't... or shouldn't be

[ken <gebser@mousecar.com>]

On 05/15/2013 01:17 AM Kevin Rodgers wrote:
> On 5/14/13 2:39 PM, ken wrote:
>> On 05/14/2013 09:39 AM Eli Zaretskii wrote:
>>>> Date: Tue, 14 May 2013 08:22:00 -0400
>>>> From: ken <gebser@mousecar.com>
>>>> CC: Eli Zaretskii <eliz@gnu.org>, help-gnu-emacs@gnu.org
>>>>
>>>> [...] overly simplistic strategy for determining a file type merely
>>>> by looking at the filename extension, especially when this can be
>>>> more suitably and accurately and intelligently accomplished by
>>>> determining a file's magic number as the Linux "file" utility does.
>>>
>>> Emacs does look at the magic signature, see magic-mode-alist.
>>>
>>
>> They why didn't it see that my file was (obviously) a text file and
>> not an image
>> file?
>
> 1. Because the default value of magic-mode-alist is nil.

If you mean this functionality was turned off in this version I recently 
installed, then, yes, that agrees with what I said earlier in this 
thread: emacs no longer determines a file's magic upon visiting a file. 
  The more comprehensive fix, then, would be to set magic-mode-alist to 
t, yes?  If so, what elisp statement(s) do you think would best 
accomplish that?


>
> 2. Because the default value of auto-mode-alist matches the ".gif"
> extension.

The documentation suggests that magic-mode-alist, if turned on, will 
override auto-mode-alist.


>
> 3. Because it is not obvious what the signature is for a text file --
> perhaps
>     something like "\\`[[:print:]\t\f\r\n]", which is so general that it
> would
>     prevent most of the existing automatic method from working.

Yes, the damned humans with their writing so random and the different 
languages characters and syntaxes and punctuation etc. make such 
evaluation nigh impossible.  Probably for this reason, magic mode adopts 
a different strategy.  The linux "file" utility, referred to earlier in 
this thread, probably does this also, as it makes fairly reliable 
evaluations of files' contents.