[Buildroot] [PATCH 02/10] core: add waf-package infra

[Yann E. MORIN]

Thomas, All,

On 2016-11-17 00:02 +0100, Thomas Petazzoni spake thusly:
> On Sun, 30 Oct 2016 17:02:13 +0100, Yann E. MORIN wrote:
> > This new waf-package infrastructure simplifies writing waf-based
> > packages. It can be used by our six current such packages, plus a
> > later-incoming one by Romain.
> > 
> > Signed-off-by: "Yann E. MORIN" <yann.morin.1998 at free.fr>
> > Cc: Romain Naour <romain.naour at openwide.fr>
> 
> I am generally happy with the whole series, I just have a few comments
> on this specific patch, which are mainly questions. We discussed them
> on IRC, but I'd like to raise the questions here as well, in case
> people have some opinions.

My answers below...

> If nobody gives some feedback, then I'm going to apply the series.

:-)

> > +# If the package does not have its own waf, use our own.
> > +ifeq ($$($(2)_BUNDLED_WAF),NO)
> 
> Where is the default value of this variable defined? It seems it's not
> defined anywhere, while it should be set to "YES".

We don't really need to set a default, because we're not testing the
default. We're only testing if it was set by the package.

> However, what I dislike a bit is the slightly "negative" logic of this
> variable. By default, we assume packages have their bundled version of
> waf, so this variable is by default assumed to be set to "YES" (even
> though in fact it's empty).
> 
> Only packages that do *NOT* have a bundled version of waf can set
> <pkg>_BUNDLED_WAF = NO, to tell the infrastructure to add a dependency
> on host-waf.
> 
> To me it feels a bit weird to:
> 
>  1. Have a boolean that defaults to YES and that can be overridden to
>     NO. I generally expects the opposite.
> 
>  2. Have a boolean that when set to "NO" actually asks the
>     infrastructure to do more things. I generally expects the opposite.
> 
> So, ideally, I'd like to invert this variable, but I can't really find
> a good name for it.
> 
> I propose <pkg>_NEEDS_WAF on IRC, but I'm not convinced because all
> packages need waf, either bundled or external.
> <pkg>_NEEDS_EXTERNAL_WAF ?

That last one is OK for me.

> Anyone has some other proposal ?
> 
> > +# Dependency on host-python is done by host-waf
> > +$(2)_DEPENDENCIES += host-waf
> > +$(2)_WAF = $(HOST_DIR)/usr/bin/waf
> > +else
> > +# We need host-python to run the package's waf
> > +$(2)_DEPENDENCIES += host-python
> > +$(2)_WAF = ./waf
> > +endif
> 
> Here another point where I'm hesitating. host-waf doesn't really need
> to build-depend on host-python. It's *running* host-waf that requires
> host-python. So I'm wondering if we shouldn't:
> 
>  1. Remove the host-python dependency from host-waf
> 
>  2. In the first case above (no bundled waf), add to the package a
>     dependency on host-waf *and* host-python.
> 
> On IRC, you suggested that packages that depend on host-waf should not
> have to know host-python is needed to run it, which is fair point.

Yes, I followed the same as we do with AUTORECONF: we automatically add
host-automake, host-autoconf, host-libtool and, if needed, host-gettext.
Packages need not add them as they are dependencies of their build
systems (autotools), not their own dependencies. The only exceptions
being packages that do need libtool for themselves (for libltdl).

Same goes for host-python: it is a dependency of the build system, not
of the package, so it should go in the infra.

> So I'm opening the question to others.
> 
> > +ifndef $(2)_MAKE
> > + ifdef $(3)_MAKE
> > +  $(2)_MAKE = $$($(3)_MAKE)
> > + else
> > +  $(2)_MAKE ?= $$(MAKE)
> > + endif
> > +endif
> 
> Is $(2)_MAKE used anywhere in this infrastructure?

Not used. I initially added it because I did contemplate converting
samba4 as well, but it does not make sense to have such support for a
single package, so I backed off. I just forgot to remove this hunk.

> Thomas
> -- 
> Thomas Petazzoni, CTO, Free Electrons
> Embedded Linux and Kernel engineering
> http://free-electrons.com

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