Re: What should /\08/ match and do?

Abigail wrote:
> On Fri, Jun 04, 2010 at 07:45:36AM -0600, karl williamson wrote:
>> Abigail wrote:
>>
>> OK.  What about '\0a'  It doesn't warn currently.  It is analogous to  
>> \08 but has a non-octal hex digit instead of a non-octal decimal digit.  
>> Should it warn?
> 
> 
> IMO, no. It doesn't now, and it's too easy to generate false warnings.
> I also think it's very less likely to make a hexadecimal-instead-of-octal
> error, then a digital-instead-of-octal error. After all, for most people
> digital is what they've learned early in life. As Nick said, warning on
> \08 makes sense, as it may happen because someone added 1 to \07, forgetting
> about the octal issue. 
> 
> Heck, we don't even warn (and we shouldn't start now, I may add) on /\xabc/.
> 
> 
> Abigail
> 

OK.  I think we have agreement.  I'll recap to give people another 
chance to disagree, but first, am I overlooking something if I change 
the docs to say that using 3 digits always for \OOO causes the 
ambiguities to completely go away, including concatenation of strings to 
form larger patterns, as long as there are fewer than 64 (= \100) 
capture groups?

So here's what I'm planning:

Existing Behavior Changes
   [\8\9] will mean [89] instead of [89\000].  	
   The current wrong warning "Illegal octal digit
   ignored" will change to "Unrecognized escape"

   \400 and above in one context now generates a
   deprecated message and is taken modulo \400.
   It wil will now mean \x{100} and above, with
   no warning.  This matches behavior in all other
   places except -0 on the command line.

   \o{...} will now generate an octal constant
   instead of the literal o{...} and the
   "Unrecognized escape" warning on the 'o'

   \o not followed by a { will now be a syntax
   error instead of "Unrecognized escape" warning
   on the 'o'

Additional warning message changes
   \08 \009 will generate a new message instead of
   the existing wrong "Illegal octal digit ignored".
   I'm thinking: "Too few digits in octal character
   constant; assuming you meant '\\%04d'".

Documentation will be updated, including saying that -0400 and above on 
the command line means the same as -0777 currently does.