Re: Dynamic top-level targets

[Philip Guenther]

On Wed, Jun 11, 2008 at 12:03 AM, Timothy Reilly <address@hidden> wrote:
> I've got a program that I'd like to compile with varying sets of options.
> All of these options are completely independent, and the actual dependencies
> of the targets are the same- they differ only in options passed to the
> commands.  My idea was to have each set of flags be a pattern match rule and
> an explicit rule.  The pattern match rule would match the option-set to the
> suffix, strip the suffix, and depend on the prefix, which would repeat the
> process until only a single option-set remained, which would match the
> explicit rule.  Here's the relevant portion of the makefile :
>
> debug: CXXFLAGS := $(CXXFLAGS) -Wall -g
> debug: all
>
> benchmark: CXXFLAGS := $(CXXFLAGS) -DBENCHMARK
> benchmark: all
...
> %_debug: CXXFLAGS := $(CXXFLAGS) -Wall -g
> %_debug: %
>
> %_benchmark: CXXFLAGS := $(CXXFLAGS) -DBENCHMARK
> %_benchmark: %
...
> The idea was to be able to do something as such:
>
> make vector_debug_openmp_benchmark
>
> and have CXXFLAGS expand to all of the relevant flags.
>
> The pattern match rules do not do what I'd like them to do, and I do not
> understand why.  Is what I'm trying to do feasible/possible?

Yes, it's feasible.  Indeed, you're very, very close.
1) a pattern rule without commands does not _define_ a pattern rule, but rather
    _cancels_ it.  So, if you want a pattern rule that does nothing,
give it an empty
    command by appending a semicolon:
       %_debug: % ;

2) when make finds a target-specific variable assignment (= or :=, but not +=),
    it ignores any assignments for that variable that were previously in effect.
    That's true even if the new one is a simple assignment (:=) that references
    the variable in the new value!  If you want multiple target-specific changes
    to apply, you can only use append (+=)

So, combining those:

$ cat Makefile
var := base
all: var += all
all:
        @echo ${var}

%_foo: % ;
%_foo: var += foo

%_bar: % ;
%_bar: var += bar
$ make all_bar_foo
base foo bar all
$


Philip Guenther