Re: [PATCH 4/4] Use AM_MISSING_PROG when making bison the default YACC here

[Bruno Haible]

Hi Andreas,

> * m4/bison.m4 (gl_BISON): We need to use AM_MISSING_PROG for making
> bison the default YACC or else packages cannot be built without bison.
>    # getdate.y works with bison only.
> -  : ${YACC='bison -y'}

Can you explain what is the problem with YACC='bison -y'? This variable
will not be used if a user unpacks and compiles a virgin tarball.

Using 'missing' makes the compilation less reliable in the case that
the user has fiddled with the .y file and does not have bison on his machine.
With YACC='bison -y', the compilation will abort, and the user will be
forced to fix the situation in a reasonable way.
With YACC='missing bison -y', the missing script will create dummy files
instead of running bison, which will lead to breakage later. The warning that
it emits at that moment is likely to be overlooked in a long compilation log.

Besides that, I object to the use of the AM_MISSING_PROG macro because it
is undocumented and can therefore be changed without notice.

Bruno