[08/17] packages: add infrastructure for virtual packages

From: "Yann E. MORIN" <yann.morin.1998@free.fr>

The virtual-package infrastructure allows to easily define a
virtual package in a single line:

    $ package/some-virtual-package/some-virtual-package.mk:
    $(eval $(virtual-package))

And that's all. :-)

Thanks to Éric for his work on the manual, that prompted the
idea for this virtual-package infrastructure! ;-)

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Eric Le Bihan <eric.le.bihan.dev@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Thomas De Schampheleire <patrickdepinguin@gmail.com>
Cc: Mike Zick <minimod@morethan.org>
---
 package/Makefile.in    |  1 +
 package/pkg-virtual.mk | 65 ++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 66 insertions(+)
 create mode 100644 package/pkg-virtual.mk

"Yann E. MORIN" <yann.morin.1998@free.fr> schreef:
>From: "Yann E. MORIN" <yann.morin.1998@free.fr>
>
>The virtual-package infrastructure allows to easily define a
>virtual package in a single line:
>
>    $ package/some-virtual-package/some-virtual-package.mk:
>    $(eval $(virtual-package))
>
>And that's all. :-)
>
>Thanks to Éric for his work on the manual, that prompted the
>idea for this virtual-package infrastructure! ;-)
>
>Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
>Cc: Eric Le Bihan <eric.le.bihan.dev@free.fr>
>Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
>Cc: Thomas De Schampheleire <patrickdepinguin@gmail.com>
>Cc: Mike Zick <minimod@morethan.org>
>---
> package/Makefile.in    |  1 +
> package/pkg-virtual.mk | 65 ++++++++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 66 insertions(+)
> create mode 100644 package/pkg-virtual.mk
>
>diff --git a/package/Makefile.in b/package/Makefile.in
>index 454f614..c5cdf5a 100644
>--- a/package/Makefile.in
>+++ b/package/Makefile.in
>@@ -362,4 +362,5 @@ include package/pkg-cmake.mk
> include package/pkg-luarocks.mk
> include package/pkg-perl.mk
> include package/pkg-python.mk
>+include package/pkg-virtual.mk
> include package/pkg-generic.mk
>diff --git a/package/pkg-virtual.mk b/package/pkg-virtual.mk
>new file mode 100644
>index 0000000..3932302
>--- /dev/null
>+++ b/package/pkg-virtual.mk
>@@ -0,0 +1,65 @@
>+################################################################################
>+# Virtual package infrastructure
>+#
>+# This file implements an infrastructure that eases development of
>+# package .mk files for virtual packages. It should be used for all
>+# virtual packages.
>+#
>+# See the Buildroot documentation for details on the usage of this
>+# infrastructure
>+#
>+# In terms of implementation, this virtual infrastructure requires
>+# the .mk file to only call the 'virtual-package' macro.
>+#
>+################################################################################
>+
>+
>+################################################################################
>+# inner-virtual-package -- defines the dependency rules of the virtual
>+# package against its provider.
>+#
>+#  argument 1 is the lowercase package name
>+#  argument 2 is the uppercase package name, including an HOST_ prefix
>+#             for host packages
>+#  argument 3 is the uppercase package name, without the HOST_ prefix
>+#             for host packages
>+#  argument 4 is the type (target or host)
>+################################################################################
>+
>+# Note: putting this comment here rather than in the define block, otherwise
>+# make would try to expand the $(error ...) in the comment, which is not
>+# really what we want.
>+# We need to use second-expansion for the $(error ...) call, below,
>+# so it is not evaluated now, but as part of the generated make code.
>+
>+define inner-virtual-package
>+
>+# Ensure the virtual package has an implementation defined.
>+ifeq ($(BR2_PACKAGE_HAS_$(2)),y)
>+ifeq ($(call qstrip,$(BR2_PACKAGE_PROVIDES_$(2))),)
>+$$(error No implementation selected for virtual package $(1). Configuration error)
>+endif
>+endif
>+
>+# A virtual package does not have any source associated
>+$(2)_SOURCE =
>+
>+# This must be repeated from inner-generic-package, otherwise we get an empty
>+# _DEPENDENCIES
>+$(2)_DEPENDENCIES ?= $(filter-out $(1),$(patsubst host-host-%,host-%,$(addprefix host-,$($(3)_DEPENDENCIES))))
>+
>+# Add dependency against the provider
>+$(2)_DEPENDENCIES += $(call qstrip,$(BR2_PACKAGE_PROVIDES_$(2)))
>+
>+# Call the generic package infrastructure to generate the necessary
>+# make targets
>+$(call inner-generic-package,$(1),$(2),$(3),$(4))
>+
>+endef
>+
>+################################################################################
>+# virtual-package -- the target generator macro for virtual packages
>+################################################################################
>+
>+virtual-package = $(call inner-virtual-package,$(pkgname),$(call UPPERCASE,$(pkgname)),$(call UPPERCASE,$(pkgname)),target)
>+host-virtual-package = $(call inner-virtual-package,host-$(pkgname),$(call UPPERCASE,host-$(pkgname)),$(call UPPERCASE,$(pkgname)),host)

I haven't yet checked the details of your series, but what about using this series as an opportunity to set the VERSION of a virtual package to 'virtual' instead of the default 'undefined'? This will be visible both in output/build as in the log messages...

Best regards,
Thomas

Thomas DS, All,

On 2014-03-01 20:25 +0100, Thomas De Schampheleire spake thusly:
> "Yann E. MORIN" <yann.morin.1998@free.fr> schreef:
> >The virtual-package infrastructure allows to easily define a
> >virtual package in a single line:
[--SNIP--]
> I haven't yet checked the details of your series, but what about using
> this series as an opportunity to set the VERSION of a virtual package
> to 'virtual' instead of the default 'undefined'? This will be visible
> both in output/build as in the log messages...

OK, why not. I'll add that to the series.

Regards,
Yann E. MORIN.