[Buildroot] [PATCH] package/ninja: add dependency to host-cmake for host-ninja

[Thomas Petazzoni <thomas.petazzoni@bootlin.com>]

On Fri, 6 Mar 2020 15:06:49 +0200
Eugen Hristev <eugen.hristev@microchip.com> wrote:

> If we change the minimum CMAKE version in external,
> buildroot will try to build host-cmake , but, host-cmake
> is not built yet at the time of ninja build.
> So, we need to add a dependency to host-cmake in host-ninja.
> Otherwise, host-ninja will try to use the host-cmake but
> 'file not found' error.
> 
> Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>

I don't understand what problem you are facing.

ninja.mk calls host-cmake-package, which already has:

$(2)_DEPENDENCIES += $(BR2_CMAKE_HOST_DEPENDENCY)

So it already adds a dependency on host-cmake if there is no available
CMake on the system, or its version is not appropriate.

> I am unsure about this patch, but this fixes the issue for me.
> If we change the minimum CMAKE version in our external tree, we hit this
> issue: the fact that the host-cmake is not yet built when it's needed.
> How can we fix that ?
> This patch makes host-cmake being built at the moment when ninja needs it.

See above: this is already taken care of by the host-cmake-package
infrastructure.

> It can happen that some other package may need it before, but I cannot know,
> if it's not enabled in our config.
> 
> Actually, this all started from the fact that BR2_CMAKE_VERSION_MIN is hardcoded
> in mk file in the support/dependencies.
> How can this be hardcoded, when we can build buildroot with an external that
> needs a newer CMAKE ?

Buildroot indeed only takes care of setting BR2_CMAKE_VERSION_MIN
according to the minimum version needed by all Buildroot packages. We
cannot know which version is used in a BR2_EXTERNAL.

> So, to fix this I added in the external.mk:
> 
> 
> BR2_CMAKE_VERSION_MIN = 3.13
> 
> BR2_CMAKE_CANDIDATES ?= cmake cmake3
> BR2_CMAKE ?= $(call suitable-host-package,cmake,\
>        $(BR2_CMAKE_VERSION_MIN) $(BR2_CMAKE_CANDIDATES))
> ifeq ($(BR2_CMAKE),)
> BR2_CMAKE = $(HOST_DIR)/bin/cmake
> BR2_CMAKE_HOST_DEPENDENCY = host-cmake
> endif
> 
> 
> But now ninja fails because host-cmake does not exist yet. Not built yet.
> So with this patch , all is fixed, but is this the right way, and can we
> do it better from just the external ? To force the host-cmake to build
> and ALL packets needing cmake to start using it.

Your patch is indeed not the right way. I guess the issue is that the
BR2_CMAKE_HOST_DEPENDENCY gets set too late, after ninja.mk has been
expanded or something like that.

Perhaps we should have a way for each package to declare its minimum
CMake version, and use that instead of a global value ?

Or tweak what we have today, by making it possible to override this
minimum version from an external tree.

Thomas
-- 
Thomas Petazzoni, CTO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com