### Bug Description Subordinate charms use the base of the principal charm. Therefore, subordinate charms such as MySQL Router need to support multiple bases, since we can't enforce the principal charm to use a particular base. Currently MySQL Router supports 20.04 and 22.04 and plans to support 24.04. However, with the new `base` and `platforms` syntax in charmcraft 3, it is not possible to build a subordinate charm on 20.04, 22.04, and 24.04 with a single charmcraft.yaml and git branch Additional context: I believe @jnsgruk and @sergiusens were/are discussing this. Created an issue to track officially per @taurus-forever's request ### To Reproduce 1. Create charmcraft.yaml with ```yaml bases: - name: ubuntu channel: "20.04" architectures: [amd64] - name: ubuntu channel: "22.04" architectures: [amd64] - name: ubuntu channel: "22.04" architectures: [arm64] - name: ubuntu channel: "24.04" architectures: [amd64] - name: ubuntu channel: "24.04" architectures: [arm64] ``` 2. charmcraft pack ### Environment Ubuntu 22.04 ### charmcraft.yaml ```shell # Copyright 2022 Canonical Ltd. # See LICENSE file for licensing details. type: charm bases: # Whenever "bases" is changed: # - Update tests/conftest.py::pytest_configure() # - Update .github/workflow/ci.yaml integration-test matrix - name: ubuntu channel: "20.04" architectures: [amd64] - name: ubuntu channel: "22.04" architectures: [amd64] - name: ubuntu channel: "22.04" architectures: [arm64] - name: ubuntu channel: "24.04" architectures: [amd64] - name: ubuntu channel: "24.04" architectures: [arm64] parts: charm: override-pull: | craftctl default if [[ ! -f requirements.txt ]] then echo 'ERROR: Use "tox run -e build-dev" instead of calling "charmcraft pack" directly' >&2 exit 1 fi # TODO: enable after https://github.com/canonical/charmcraft/issues/1456 fixed charm-strict-dependencies: false charm-entrypoint: src/machine_charm.py prime: - charm_version - workload_version build-packages: - libffi-dev - libssl-dev - pkg-config - rustc - cargo ``` ### Relevant log output ```shell Bad charmcraft.yaml content: - base requires 'platforms' definition: {'name': 'ubuntu', 'channel': '24.04', 'architectures': ['amd64']} (in field 'bases[3]') - base requires 'platforms' definition: {'name': 'ubuntu', 'channel': '24.04', 'architectures': ['arm64']} (in field 'bases[4]') ```