var-transforms do not provide a mechanism for mutating dissimilar inputs to the same variable

[OddBloke]

opa-envoy uses a versioning scheme of <upstream version>-envoy<local revision> but <local revision> is omitted for the first release. So, for example, the last two versions currently are 1.1.0-envoy-1 and 1.0.0-envoy. These aren't valid APK versions (per https://github.com/wolfi-dev/wolfictl/blob/b168a068d4ea555968116a7577964310adf8ec33/pkg/versions/validate.go#L8-L23) so we need to mutate these to strings that are: respectively, 1.1.0-r1 (that's not an epoch!) and 1.0.0.

The version-transform logic correctly mutates from the upstream version to the versions we want, but we then need to mutate back from the APK version to the upstream naming schema, to checkout the appropriate tag. Due to the absence of the -0 on the upstream versioning in the "first release" case, there isn't a single regex match/replace that can do the job. ^(\d+\.\d+\.\d+)$ -> $1-envoy handles the first version case, and ^(.+)-r(\d+)$ -> $1-envoy-$2 handles the subsequent versions case. This maps simply enough into melange configuration:

var-transforms:
  - from: ${{package.version}}
    # 1.0.0 -> 1.0.0-envoy
    match: ^(\d+\.\d+\.\d+)$
    replace: $1-envoy
    to: mangled-package-version
  - from: ${{package.version}}
    # 1.0.0-r2 -> 1.0.0-envoy-2
    match: ^(.+)-r(\d+)$
    replace: $1-envoy-$2
    to: mangled-package-version

However, this configuration doesn't work: melange applies var-transforms in order, overwriting any previous values, meaning that this configuration will only handle the 1.1.0-r1 case. If the stanzas were reversed, the configuration would only handle the 1.0.0 case.

Ideally, it would be possible to specify that a transform should be applied if and only if its match regex actually matches the from input. If there was, e.g., a must-match: true option we could apply here, then only the actually applicable stanza's output would be used for mangled-package-version, solving the problem.

[OddBloke]

(As it happens, I did manage to craft a single ugly regex which handles this case halfway through writing this issue (^([0-9]+.[0-9]+.[0-9]+)((-)r(\d+))?$ -> $1-envoy$3$4) but (a) this may not always be possible, and (b) this regex is inscrutable, the multi-stanza version is much more maintainable.)