Using clojure.spec for api migrations?

[Jeroen van Dijk]

Hi, 

I'm playing with the idea of using clojure.spec to make an API backwards compatible by using conform and unform to transform data from the old version format to a new format version. Below is an example of this in code:

Say we have API change that involves changing the name of a nested key:

(do

  ;; Old api

  (s/def :api.v0.input.nested/label keyword?)

  (s/def :api.v0.input/nested (s/keys :req-un [:api.v0.input.nested/label]))

  (s/def :api.v0/input (s/keys :req-un [:api.v0.input/nested]))

  ;; New api

  (s/def :api.v1.input.nested/key keyword?)

  (s/def :api.v1.input/nested (s/keys :req-un [:api.v1.input.nested/key]))

  (s/def :api.v1/input (s/keys :req-un [:api.v1.input/nested]))

  

  ;; Migration specs

  (s/def :api.v0-v1.migration.input/nested (s/conformer (fn [_] (throw (ex-info "Don't use as conformer" {})))

                                                        (fn [x] (clojure.set/rename-keys x {:label :key}))))

  (s/def :api.v0-v1.migration/input (s/conformer (fn [x]

                                                   (s/conform :api.v1/input x))

                                                 (fn [x]

                                                   (s/unform (s/keys :req-un [:api.v0-v1.migration.input/nested]) x))))

  

  ;; Changes {:nested {:label :hi}} to {:nested {:key :hi}}

  (s/unform :api.v0-v1.migration/input {:nested {:label :hi}}))

So this kind of works, but I wonder whether there is an easier way or if I'm thinking about this the wrong way. I was hoping there would be something like with-unformer (like with-gen) that allows me to change the unforming action for a specific key without having to copy most of the old spec.

Any suggestions or advise is appreciated.

Thanks,

Jeroen

[Jeroen van Dijk]

Oh I meant `clojure.spec/gen` instead of `clojure.spec/with-gen`. `clojure.spec/gen` has an overrides option. I (think I) need something like this to cleanly change the unforming action in a nested spec.

Jeroen