[Bug 2139113] [NEW] APT::Architecture-Variants "amd64v3" disables implicit native architecture (amd64) on minimal installs

[Shashank Taliwal]

Public bug reported:

Package: apt
Version: 3.1.6ubuntu2 (and dpkg 1.22.21ubuntu3.1)
Distro: Ubuntu Questing (25.04) / Docker Image

Description:
When following the official instructions to enable x86-64-v3 support by creating `/etc/apt/apt.conf.d/99-arch-variants` with content `APT::Architecture-Variants "amd64v3";`, APT behaves incorrectly on minimal installations (Docker).

Instead of treating 'amd64v3' as an overlay/variant of the native
'amd64' architecture, APT drops the implicit 'amd64' architecture
entirely.

Steps to Reproduce:
1. docker run --rm --platform linux/amd64 -it ubuntu:rolling bash
2. echo 'APT::Architecture-Variants "amd64v3";' > /etc/apt/apt.conf.d/99arch-variants
3. rm -rf /var/lib/apt/lists/*
4. apt update
5. ls -1 /var/lib/apt/lists/ | grep binary-amd64_Packages

Expected Result:
The 'binary-amd64' list files should exist (Base architecture).

Actual Result:
Only 'binary-amd64v3' list files exist. The system loses access to all packages not explicitly indexed in the v3 overlay.

** Affects: dpkg (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/2139113

Title:
  APT::Architecture-Variants "amd64v3" disables implicit native
  architecture (amd64) on minimal installs

Status in dpkg package in Ubuntu:
  New

Bug description:
  Package: apt
  Version: 3.1.6ubuntu2 (and dpkg 1.22.21ubuntu3.1)
  Distro: Ubuntu Questing (25.04) / Docker Image

  Description:
  When following the official instructions to enable x86-64-v3 support by creating `/etc/apt/apt.conf.d/99-arch-variants` with content `APT::Architecture-Variants "amd64v3";`, APT behaves incorrectly on minimal installations (Docker).

  Instead of treating 'amd64v3' as an overlay/variant of the native
  'amd64' architecture, APT drops the implicit 'amd64' architecture
  entirely.

  Steps to Reproduce:
  1. docker run --rm --platform linux/amd64 -it ubuntu:rolling bash
  2. echo 'APT::Architecture-Variants "amd64v3";' > /etc/apt/apt.conf.d/99arch-variants
  3. rm -rf /var/lib/apt/lists/*
  4. apt update
  5. ls -1 /var/lib/apt/lists/ | grep binary-amd64_Packages

  Expected Result:
  The 'binary-amd64' list files should exist (Base architecture).

  Actual Result:
  Only 'binary-amd64v3' list files exist. The system loses access to all packages not explicitly indexed in the v3 overlay.

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