AT_DATA and AS_ECHO_N (was: Re: Warn about character literals not of length one.)

[Joel E. Denny]

I've added bug-autoconf for this part of the discussion.

On Thu, 23 Jul 2009, Eric Blake wrote:

> Joel E. Denny <jdenny <at> clemson.edu> writes:

> > In the new test group, I wish I could check the case where a character 
> > literal ends at eof without a newline.  However, the documentation for 
> > AT_DATA demands that the file contents end with an "end of line", so I'm 
> > not sure what to do.  I might write the Autoconf people later if no one 
> > around here already knows how to work around this limitation.
> 
> That's an inherent limitation of AT_DATA (since it is implemented using a 
> shell 
> here-doc); the only way around it is to manually use printf or $ECHO_N to 
> concatenate data to the end of the desired file.

Thanks.  In the Autoconf manual's section on portability, the entry for 
echo implies that printf is not as portable as AS_ECHO* constructs:

  New applications which are not aiming at portability should use
  `printf' instead of `echo'.  M4sh provides the `AS_ECHO' and
  `AS_ECHO_N' macros, which choose between `echo -n' on
  implementations where that works, `printf' if it is available, or
  other creative tricks in order to work around the above problems.

Shouldn't the entry for printf mention this portability shortcoming of 
printf as well?

Also, I find the first sentence above confusing.  Why is printf 
recommended if not for portability?

> I've been meaning to add a new macro to autotest to allow more flexibility in 
> generating files (no trailing newline, and/or allowing shell expansions) but 
> it 
> will not be in time for autoconf 2.64.  Feel free to ping the autoconf list, 
> so 
> that I'll have a reminder email.

Is it necessary to have a new macro for omitting the trailing newline?  
Couldn't AT_DATA detect whether a trailing newline is present in the 
expansion and then work whatever magic is necessary to print the last line 
correctly?

I'll try to remember to ping again later.