Re: getting warmer error messages

[Philip Guenther]

On 12/28/06, Martin Dorey <address@hidden> wrote:
...
> > there are usually many possible pattern rules
> > which it MIGHT match, if it could build the
> > prerequisites
>
> An example might help persuade - % is often make-able from %.c - so any list of 
> potentially missing prerequisites would have to include %.c.  I'm tempted to 
> suggest that I might sometimes find the list of missing prerequisites useful 
> when debugging but perhaps it would be so explosively large that it wouldn't be 
> useful even as an option.  I do OK with make -p anyway.

The trick, of course, is that the list of missing prerequisities can
be quite large.  For the first Makefile in the OP's message, the list
of possible prerequisites is:

RCS/x.aa
RCS/x.aa,v
RCS/x.bb
RCS/x.bb,v
SCCS/s.x.aa
SCCS/s.x.bb
s.x.aa
s.x.bb
x.aa,v
x.bb
x.bb,v

...plus 107** possible prerequistes for the Makefile itself!  Don't
laugh: the problem may very well be that the Makefile is out of date.
If the target doesn't have a suffix, the list of possible
prerequisites is much larger.  Listing them all is not actually likely
to be that useful, IMHO.


Philip Guenther


** Perhaps GNU make should include a pattern rule to prevent the
non-terminal pattern rules from applying to the Makefile itself.  For
example, if you add the following line to your Makefile:
   %akefile:
then there are only five prerequisites for the Makefile itself, from
the RCS and SCCS rules.