Earlier quoted context omitted.
Basically what infinity0 described in his sibling comments. I want to have a source package that can be used to build the binary package in a deterministic and reproducible way.
This post describes how to do that, via PPAs: https://is.gd/Eu55IG .
Also... look at that guide. Why is it so difficult and obtuse? Why do I have to run so many odd tools, including apparently modifying some file in /etc and running other stuff as root? In contrast, this was my first contribution to Nixpkgs: https://github.com/NixOS/nixpkgs/commit/0b8efd8724e59964bad0... Easily as reproducible as anything Debian, and apart from installing Nix it didn't require any funkyness in the build environment. I tested the definition by running 'nix-build . -A oclgrind' in my checkout of the Nixpkgs repository. I managed this after running NixOS for two days.
This is the same software that I also contributed to Homebrew: https://github.com/Homebrew/homebrew-core/commit/1268459f761... Again, a simple declarative-ish package description (written in Ruby, which is not my favourite, but it's better than the weird Makefile/shell amalgamations that are used by DPKG and RPM).
Both Nix and Homebrew have serious limitations compared to Debian (Homebrew in particular is aggressively limiting its scope to gain simplicity and in particularly doesn't care as much about reproducibility). But as a user, I must admit I have not missed what Debian provides that these do not. Whenever I tried to package stuff for Debian, I felt that I was paying a tax for unclear gain. It's a shame, because I like Debian for over a decade, and I am strongly sympathetic to the idea of the project in principle.