Re: FreeBSD GCC warnings

[Bruno Haible]

Hello Ralf,

> > Oops, that did not work. autoconf >= 2.60 supports multiline replacements
> > in AC_SUBST, but 'automake' and 'make' don't.
> 
> Well.  There is no mapping that will automatically make multiline values
> be correctly escaped for makefiles.  Maybe it is time to publish
> AM_SUBST_NOTMAKE which is like AC_SUBST

Of course! Currently, in projects which use automake, AC_SUBST with multiline
values will only work if all lines except possibly the first one start with
a '#'.

Additionally, I wanted to use the value in a Makefile command. But this
resulted in an error message from 'make', because the Makefile looked like
this:

stdlib.h: stdlib.in.h
        sed -e 's/@PRAGMA_SYSTEM_HEADER@/#if __GNUC__ >= 3
#pragma GCC system_header
#endif/g' < stdlib.in.h > stdlib.h

So, what would be useful here, is a way to escape AC_SUBST values so that
newlines and '#' characters are hidden from 'make' when the macro is used
in the command section of a 'make' rule.

IMO, this belongs in automake because
  - AC_SUBST values are frequently used in Makefile commands,
  - It's not not trivial to do this escaping in a way that would preserve
    whitespace (or the lack of whitespace) at the end of the value,
  - It's out of scope for autoconf to care about special kinds of files,
    like Makefiles.

Bruno