Re: Static multiple target rules

[tom honermann]

On 3/3/2010 2:03 AM, Edward Welbourne wrote:
> Another possibility crossed my mind over-night, with which I haven't
> experimented, but that seems like it theoretically should work.
> Replace the touch-file with a phony rule:
>
>     yacc.ts: grammar.y
>         yacc -d -v $^
>
>     y.tab.h y.tab.c y.output .PHONY: yacc.ts
>
> Because it's phony, and we never create it, it'll never exist and make
> shouldn't care that no such file exists; because the three real
> targets depend on it, any need for any of them shall force it to be
> made (causing them to all exist); but if more than one of them needs
> made, an individual run of make shall only make the phony once yet
> still know that it's made it, so not need to run yacc again for the
> sake of the others that depend on it.
>
> But I may be confused about proper use of .PHONY - please experiment
> and report your results !
>
>         Eddy.
>   
You're a genius!  .PHONY didn't do the trick, but .INTERMEDIATE did:

   .INTERMEDIATE: yacc.ts

   all: y.tab.h y.tab.c y.output y.tab.o

   clean:
           rm -f y.tab.h y.tab.c y.output y.tab.o

   grammar.y:
           @touch $@

   yacc.ts: grammar.y
           @echo "Running yacc..."
           @sleep 1
           @touch y.tab.h y.tab.c y.output

   y.tab.h y.tab.c y.output: yacc.ts

   y.tab.o: y.tab.c y.tab.h
           @echo "Compiling y.tab.c..."
           @sleep 1
           @touch $@

The only problem I could find with this approach is that downstream 
targets might not get rebuilt as expected.  For example, run gmake once 
to build everything, then remove y.output and run gmake again.  Using 
make 3.81 on Linux, y.output is rebuilt which also rebuilds y.tab.c and 
y.tab.h, but y.tab.o is not rebuilt (as might be expected since y.tab.h 
and y.tab.c were regenerated).  This makes sense because gmake has no 
way of knowing that rebuilding y.output would also regenerate y.tab.h 
and y.tab.c.  A full solution for static multiple target rules would 
recognize that these files had been regenerated and would also rebuild 
y.tab.o.  But, I think this is good enough for my use cases.

Thanks Eddy!
Tom.