Re: Static multiple target rules

[tom honermann]

On 3/29/2010 2:18 PM, tom honermann wrote: 
>    .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.
This isn't working as well as I had at first thought.  For example, 
updating grammar.y doesn't always result in y.tab.o getting rebuilt.  
This can be reproduced consistently in parallel make invocations:

   rtdc60007stdb:$ gmake clean
   rm -f y.tab.h y.tab.c y.output y.tab.o
   rtdc60007stdb:$ gmake
   Running yacc...
   Compiling y.tab.c...
   rtdc60007stdb:$ touch grammar.y
   rtdc60007stdb:$ gmake
   Running yacc...
   Compiling y.tab.c...
   rtdc60007stdb:$ gmake
   gmake: Nothing to be done for `all'.

   rtdc60007stdb:$ gmake clean
   rm -f y.tab.h y.tab.c y.output y.tab.o
   rtdc60007stdb:$ gmake -j
   Running yacc...
   Compiling y.tab.c...
   rtdc60007stdb:$ touch grammar.y
   rtdc60007stdb:$ gmake -j
   Running yacc...
   rtdc60007stdb:$ gmake -j
   Compiling y.tab.c...
   rtdc60007stdb:$ gmake -j
   gmake: Nothing to be done for `all'.

Note that the second run using '-j' required an extra 'gmake' invocation 
before everything was up to date.  Bummer.

Tom.