[buildd-tools-devel] Bug#695287: sbuild: synthetic cross-build-dependencies for compilers

[Johannes Schauer]

Control: tag -1 + moreinfo

Hi,

On Thu, 6 Dec 2012 16:54:23 +0000 Colin Watson <cjwatson at ubuntu.com> wrote:
> (This is a bit of an RFC.  I think I understand the general shape of the
> problem, but I'd welcome comments on the design.)
> 
> One of the problems we have with cross-building packages is with
> alternative compilers and other cross-tools.  Generally speaking,
> cross-build chroots start with a reasonable set of cross-tools
> preinstalled, such as gcc-HOST and pkg-config-HOST.  If somebody
> build-depends on pkg-config, pkg-config-HOST is already installed so
> it's OK.  However, if somebody build-depends on, say, g++-4.6, then
> nothing knows how to install g++-4.6-HOST; or I can easily imagine that
> we might want a gobject-introspection-HOST in the future.  It does not
> seem correct to me to deal with these problems by adding more and more
> packages to the cross-build-essential set.
> 
> When I was writing my patch for #695203, it occurred to me that this
> offered an opportunity for sbuild to step in and synthesise
> build-dependencies in some situations.  A possible design would be as
> follows:
> 
>   When cross-building, if the package being built build-depends on A
>   (taking any [] into account), A is not Multi-Arch: foreign, and A-HOST
>   exists in the apt cache, then rewrite the build-dependency to
>   "A:native, A-HOST" (including any versioning present).
> 
> Wookey suggested that we might also want something for people who don't
> use sbuild; I think perhaps a similar algorithm in 'dpkg-checkbuilddeps
> -aHOST' would be useful and reasonable.  (CCing debian-dpkg.)  An
> alternative to the "exists in the apt cache" rule, which I can imagine
> being troublesome, might be to have a hardcoded list of relevant
> packages; this would change from time to time but hopefully not too
> often.  Or we could have a package control field for "there's a cross
> version of this".
> 
> Does this sound right to you?  I think I could probably figure out how
> to do this on top of my previous patch, but I'd like to make sure that we
> agree on the design first.

we now have crossbuild-essential-$hostarch packages which depend on the
respective essential crossbuild packages to compile for $hostarch. Sbuild also
already automatically adds an implicit dependency on
crossbuild-essential-$hostarch if $buildarch is unequal $hostarch.

Would you agree that this fixes this bug?

Thanks!

cheers, josch
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