With the advanced grammar, only the last - to clause is respected

[simondeziel]

Bug Description

In the LXD snap, we have some parts that are meant to be supported on some arches only. For example, we don't want to ship QEMU for armhf nor riscv64. As such, the qemu part is constructed to avoid installing the build-packages and the stage-packages when building for armhf/riscv64:

  qemu:
    build-packages:
      - to armhf:
        - cmake      # placeholder pkg (actually used by lxd part) to avoid installing build-packages on unsupported arches
      - to riscv64:
        - cmake      # placeholder pkg (actually used by lxd part) to avoid installing build-packages on unsupported arches
      - else:
        - bison
        - ...
        - librbd-dev
    stage-packages:
      - to armhf:
        - acl      # placeholder pkg (actually used by lxd part) to avoid installing stage-packages on unsupported arches
      - to riscv64:
        - acl      # placeholder pkg (actually used by lxd part) to avoid installing stage-packages on unsupported arches
      - else:
        - genisoimage
        - ...
        - qemu-system-data # This is needed due to --disable-install-blobs.
  ...

However, only the last - to $ARCH: clause seems to be respected as on armhf, the builds on LP builders always fail complaining that librbd-dev is not available. librbd-dev is indeed not available for armhf which is the whole reason why we try to exclude it with the - to/- else clauses.

The exclusion works for the - to riscv64: as neither librbd-dev nor qemu-system-data are found in the riscv64 build logs.

important: Inverting the - to armhf: and - to riscv64: made the armhf build work as it then stops trying to pull librbd-dev

To Reproduce

snapcraft remote-build --platform amd64,armhf,riscv64 on a cloned repo from https://github.com/canonical/lxd-pkg-snap

Environment

$ snap list snapcraft
Name       Version  Rev    Tracking       Publisher   Notes
snapcraft  8.6.1    13459  latest/stable  canonical✓  classic

snapcraft.yaml

https://github.com/canonical/lxd-pkg-snap/blob/f3327146996d52e66f8726a88766021f678e2575/snapcraft.yaml

Relevant log output

Running pull phase...
Initialising lifecycle
Installing build-packages
Cannot find package listed in 'build-packages': librbd-dev

Additional context

No response