[Buildroot] [PATCH] autotools: add with/without and enable/disable helpers

[Mike Frysinger <vapier@gentoo.org>]

On Friday, November 19, 2010 02:55:18 Thomas Petazzoni wrote:
> On Thu, 18 Nov 2010 23:33:57 -0500 Mike Frysinger wrote:
> > +# $(call _USE_CONF,enable,disable,LIB_FFMPEG,video,blah) ->
> > --enable-video=blah if LIB_FFMPEG +# $(call
> > _USE_CONF,with,without,LIB_FFMPEG,video)        -> --with-video if
> > LIB_FFMPEG +_USE_CONF = $(shell \
> > +	opt="$(5)"; test "$${opt:+set}" = "set" && opt="=$${opt}"; \
> > +	test "$(BR2_$(3))" = "y" \
> > +		&& echo "--$(1)-$(4)$${opt}" \
> > +		|| echo "--$(2)-$(4)")
> 
> However, I'm worried that this will start a shell process when
> evaluating *each* USE_ENABLE/USE_WITH call, and this will slow down the
> start up of Buildroot.

not really.  this is the whole point of make's lazy evaluation.  so unless 
somewhere the code is wrongly using ":=", these shouldnt be executed unless 
the configure script in question is actually run.  a simple test on my side 
says that it is working as i expect -- lazily.

> It'd be nicer if we could use a pure Makefile implementation. What
> about a simpler :
> 
> USE_WITH = $(if $(BR2_$(1)),--with-$(2),--without-$(2))
> USE_ENABLE = $(if $(BR2_$(1),--enable-$(2),--disable-$(2)))

this isnt functionally equivalent ... there is no support for the optional 
[=val] with the flag

> However, their usage might be a little limited: often when the option
> is enabled, we need to add a dependency to the package as well.

this is due to poor design on the behalf of buildroot.  it really needs to 
adopt more Kconfig style and do stuff like:
foo-y =
foo-$(BR2_xxx) += libpng

and again, please retain cc in replies
-mike
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