[Buildroot] [PATCH v2] Don't build host-cmake if it is available on the build host

[Arnout Vandecappelle <arnout@mind.be>]

On 16-02-16 14:55, Samuel Martin wrote:
> Hi Luca, all,
> 
> On Fri, Feb 5, 2016 at 12:07 PM, Luca Ceresoli <luca@lucaceresoli.net> wrote:
[snip]
>> > Finally, we do skip adding the dependency on host-cmake for all cmake
>> > packages when $(BUILD_HOST_CMAKE) != YES.
> Sorry for not spotting this earlier, but:
> host-cmake has a dependency on host-pkgconf, which cmake (the host
> program) may use at runtime to find the dependencies when it is
> configuring a project.
> In the BR host tree, pkg-config is a wrapper with environment
> variables correctly preset to find stuff in the sysroot tree by
> default.
> 
> Here is a test case:
> 
> A is a cmake-package depending on B.
> B is a generic-package providing a *.pc file.
> CMake uses its FindPkgConfig module to detect B.
> 
> So, currently we got:
> - A depends on: B and host-cmake
> - host-cmake depends on host-pkgconf
> - When configuring A, host-cmake should use host-pkgconf to find B
> 
> With this patch, in the case cmake build is skipped, we get:
> - A depends on: B
> - When configuring A, cmake (from the host system) may use pkg-config
> (from the host system) to find B, but this pkg-config won't have the
> env. vars. correctly set to find B in the sysroot. In the best case,
> it won't find B, in the worst case it will try to link against B from
> the host system.
> 
> I'm not sure what it the best and clean way to handle this...
> Maybe $(BUILD_HOST_CMAKE) != YES should be use to noop the
> HOST_CMAKE_{CONFIGURE,BUILD,INSTALLL}_CMDS commands, but we keep the
> dependency on host-cmake, so we don't lose host-cmake's dependencies.
> 
> Any thought about this?

 The correct approach would be to add explicit dependencies on host-pkgconf for
packages that need it, just like we do for autotools packages.

 The difficulty is of course finding out which packages need host-pkgconf. It
seems it's not as simple as searching for FindPkgConfig in the CMakeLists.txt
files of each cmake package, because there are other modules that implicitly use
this. So we'd have to make a list of all those modules and check for all of
them. And then of course there are the packages that install new cmake modules
that use this, but which don't use FindPkgConfig (or even cmake) themselves...

 In 3d475ee0 you added the unconditional host-pkgconf dependency to work around
this problem. If we remove that dependency, the autobuilders should detect the
missing host-pkgconf dependencies even when host-cmake is used.

 Regards,
 Arnout

[snip]

-- 
Arnout Vandecappelle      arnout dot vandecappelle at essensium dot com
Senior Embedded Software Architect . . . . . . +32-478-010353 (mobile)
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