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Announcing type-handling

Hi there,

Package maintainers reading this might like to know a flexible method for
extending system/cpu-specific package relationships in dpkg has been added
to the debian archive in unstable.

The package is called type-handling. Packages that need to check for
DEB_*_GNU_SYSTEM and/or DEB_*_GNU_CPU in their package relation fields
(e.g, Build-Depends, Depends..) can use the virtual Provides generated
dynamicaly in this package instead of the standard DEB_*_ARCH hardcoded in

type-handling acts as a frontend to dpkg-architecture, which allows for
checking of cpu and system separately. This is mostly advantageous for
supporting the non-Linux-based ports. Refer to dpkg-architecture's
documentation for details.

Here are some examples on how you can use type-handling to improve portability
of your packages:

CPU detection example

Package foo requires bar to build, but only when foo is being built for i386
cpus. foo's debian/control reads:

  Build-Depends: bar [i386]

But the [i386] above implies Linux, so if you want to support all kernels in
Debian you'd have to maintain a continously growing list:

  Build-Depends: bar [i386 hurd-i386 ...]

Here's how you would do it with type-handling:

  Build-Depends: bar | not+i386

That's all of it. type-handling provides a virtual package for the target
cpu, system and type, but also a list of all cpus, systems, and types that
do _not_ match the target preceded by the "not+" prefix. [1]

[1] This feature only on type-handling >= 0.1.0, currently in incoming.

System detection example

This one is mostly analogous to the previous example, so I'll be brief.
Package gdb build-depends on mig which is only needed when building on

  Build-Depends: mig [hurd-i386]

Everytime Debian GNU/Hurd is ported to a new CPU, we'll have to add it
to the list:

  Build-Depends: mig [hurd-i386 fubar-i386 ...]

Instead, you could just use type-handling:

  Build-Depends: mig | not+gnu

Whereas not+gnu is a virtual package provided by type-handling on all systems
but GNU/Hurd, on any architecture.

Robert Millan

"[..] but the delight and pride of Aule is in the deed of making, and in the
thing made, and neither in possession nor in his own mastery; wherefore he
gives and hoards not, and is free from care, passing ever on to some new work."

 -- J.R.R.T., Ainulindale (Silmarillion)

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