Bug#1102295: d/control must not change during build

Package: debian-policy
X-Debbugs-CC: [email protected], [email protected], [email protected], [email protected]

Dear Policy Editors,

it appears that currently there is no requirement for d/control to 
stay the same before and after a build. However, many things require 
this to be the case, and ftp-master also requires this in their 
reject-faq [1].

Below is a minimal patch, mostly as a discussion starter. I've 
ponderred if listing examples of things breaking would be good, but 
decided against it for the policy text.

This change suggestion started when Jochen et al discovered that the 
"pcp" package currently rewrites its d/control file, which causes 
rebuilds of the in-archive package to produce a different result. [2]


Thanks,
Chris


[1] https://ftp-master.debian.org/REJECT-FAQ.html "debian/control breakage #2"
[2] https://reproduce.debian.net/amd64/#pcp and https://bugs.debian.org/1102289

(CC'ed people I expect to be interested.)


diff --git i/policy/ch-controlfields.rst w/policy/ch-controlfields.rst
index 3151816..cffca22 100644
--- i/policy/ch-controlfields.rst
+++ w/policy/ch-controlfields.rst
@@ -98,7 +98,8 @@ Debian source package template control files -- ``debian/control``

  The ``debian/control`` file contains the most vital (and
  version-independent) information about the source package and about the
-binary packages it creates.
+binary packages it creates. The file must stay unchanged when building
+a package.

  The first stanza of the control file contains information about the
  source package in general. The subsequent stanzas each describe a