### What needs to get done Validate that architectures only contain alphanumeric characters and recommend using brackets for multiple architectures. ```yaml archictectures: - build-on: amd64 build-for: bad, value ``` ```shell > snapcraft Error: Architecture 'bad, value' must only contain alphanumeric characters. Use brackets to list multiple architectures: '[arch1, arch2]'. For more information, check out: https://snapcraft.io/docs/architectures ``` This validation can be done during yaml validation and should be similar for the core20 and core22 implementations. This issue is referenced in the documentation and should be updated when completed. (both [readthedocs](https://canonical-snapcraft.readthedocs-hosted.com/en/latest/explanation/index.html) and snapcraft.io/docs) #### Breaking changes This can break previously working core20 snap builds. However the snap themselves are useless; `snap install "my-snap_1.0_amd64, arm64.snap"` always fails. ### Why it needs to get done Consider the following snapcraft.yaml: ```yaml base: core20 architectures: - build-on: amd64 run-on: amd64, arm64 # problematic: this is a scalar, not a list ``` This scenario happens during iterative development. A user starts with a single scalar architecture `amd64` and later adds another architecture without adding brackets. So `amd64, arm64` is still treated as a scalar. The correct syntax is a yaml list: `[amd64, arm64]`. In core20, this is allowed. It would produce a snap named `my-snap_1.0_amd64, arm64.snap`. In core22, this is not allowed but the error could be improved. It may not be obvious that the square brackets are missing. source: https://bugs.launchpad.net/snapcraft/+bug/2009520