Bug#847805: reprotest: document/support simple reproducibility test with sbuild

[Sean Whitton]

Hello,

On Sun, Dec 11, 2016 at 03:12:57PM -0700, Sean Whitton wrote:
> I have sbuild properly set up on my machine, and I want to use it to
> test package reproducibility.  Something like this, where PWD is an
> unpacked source package:
> 
> 1) sbuild
> 2) record .deb checksums from .changes file
> 3) sbuild
> 4) compare .deb checksums in new .changes file
> 5) run diffoscope if the checksums differ

Thanks to #debian-reproducible, this is mostly what I wanted:

    reprotest auto . -- schroot unstable-amd64-sbuild

This doesn't actually invoke sbuild, but it does perform the builds
inside the schroot I already have set up, and compare the results.

This is useful, but it would also be good if reprotest could invoke
sbuild(1) itself.  That is because sbuild has lots of useful options.

For example, suppose that foo depends on dh_bar, and I am hacking on
dh_bar in the hope of making foo reproducible.  Then I want to build foo
against my local version of dh_bar.  With sbuild, I can do this using
--extra-package and --add-depends.  reprotest with a pure schroot
backend can't do that kind of thing, so far as I can tell.

With regard to documentation, for users like me who are used to just
invoking `sbuild`, I'd like to suggesting add this third example to the
top of /usr/share/doc/reprotest/README.md.gz:

    # Where PWD is an unpacked source package, construct a .dsc and
    # build it in a schroot.  This is equivalent to invoking `sbuild`
    # twice, and comparing the results
    reprotest auto . -- schroot unstable-amd64-sbuild

-- 
Sean Whitton
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