Hi,

Whilst working on the Reproducible Builds effort [0], we noticed that
towncrier generates nondeterministic output and is the cause of some
unreproducible packages.

For example, here is src:python-rosettasciio:

│ │ │ ├── ./usr/share/doc/python-rosettasciio-doc/html/changes.html
│ │ │ │ @@ -443,16 +443,16 @@
│ │ │ │  <p>Changelog entries for the development version are available at
│ │ │ │  <a class="reference external" href="https://rosettasciio.readthedocs.io/en/latest/changes.html">https://rosettasciio.readthedocs.io/en/latest/changes.html</a></p>
│ │ │ │ -<section id="release-unreleased-2026-07-30">
│ │ │ │ -<h2> [UNRELEASED] (2026-07-30)<a class="headerlink" href="#release-unreleased-2026-07-30" title="Link to this heading">#</a></h2>
│ │ │ │ +<section id="release-unreleased-2027-09-02">
│ │ │ │ +<h2> [UNRELEASED] (2027-09-02)<a class="headerlink" href="#release-unreleased-2027-09-02" title="Link to this heading">#</a></h2>
│ │ │ │  <section id="bug-fixes">

A patch is attached to make these values seeded from SOURCE_DATE_EPOCH (if
available).

  [0] https://reproducible-builds.org/


Regards,

Control: retitle -1 towncrier: Use reproducible builds 'SOURCE_DATE_EPOCH' standard for build timestamp
Control: tags -1 + confirmed
Control: forwarded -1 https://github.com/twisted/towncrier/issues/746

Thank you. I have worked this into a set of changes that properly tests the
new behaviour, and created an upstream bug report pointing to the changes.

<URL: https://salsa.debian.org/bignose/towncrier/-/tree/wip/issue/746/reproducible-build-source-date-epoch>