🚀 go-pugleaf

Here are some thoughts I've been having about GNU make but could pertain
to makes all over the world.  I would be interested in what y'all would
have to say about them.

[For those of you unfamilar with GNU make, $(shell cmd args...)
expands to the output of the 'cmd args...' in the default shell.]

#0. What about changing the way variable expansion is done so that

 % : $(shell SCRIPT %)
	... rules ...

will substitute the expansion of % BEFORE expanding $(shell ...).
I realize that this may be undesirable in most cases and perhaps
impossible given the way GNU make implements variable expansion,
but I could see a use for it.

#1. I would like to specify when a target is out of date rather than
being restricted to make's default rules.  Has anyone thought of
enhancing make to allow for, say, variable expansion to determine if
a target is out of date?  For example, the syntax

  x : d1 d2 d3 &$(shell SCRIPT)

would tell make that target x is out of date if any of d1, d2, d3 is
older than x or if the expansion of $(shell SCRIPT) is non-blank.

But, since make doesn't have this feature...
	
#2. Suppose I have the following declaration in a make file:

  .PHONY: x
  x : $(shell SCRIPT)
	$(rules)

The idea is that the command SCRIPT will determine if x is up to date
and that its output will direct make to execute $(rules) or not.

What behavior should SCRIPT have in order to do this, or, as I suspect,
can't this problem be solved this way?

I have come up with a partial solution, namely:

  .PHONY: x all
  x :
	$(rules)
  all : $(shell SCRIPT)

where SCRIPT outputs all those targets which it finds out of date.
However, 'make x' will always execute $(rules) regardless of what SCRIPT
says.

Another solution I don't like is

  x :
	if SCRIPT; then $(rules) fi

because I would like the rules for a target to be executed only if
the target is determined to be out of date.  In particular, I would
like 'make -n x' to possibly return 'Nothing needs to be done for x.'

#3. Somewhere in the make texinfo doc it reads:

  ``A phony target should not be a dependency of a real target file;
    strange things can result from that.  As long as you don't do that,
    ... ''

Pray tell, what kind of strange things can happen?

--
Erik Rantapaa                              rantapaa@math.umn.edu