`:merge` with registries does not round-trip

[frenchy64]

If schemas with registries are merged with :merge, the dereferenced schema often cannot be round-tripped.

Notice the following schema is missing a ::z binding so is no longer well-formed.

(-> (m/deref
      [:merge
       [:map {:registry {::y int?}}
        [:y ::y]]
       [:map {:registry {::z boolean?}}
        [:z ::z]]]
      options)
    m/form)
=>
[:map {:registry {::y boolean?}}
 [:y ::y]
 [:z ::z]]

We might be able to fix this by merging the registries, but something else is needed if the registries both define the same names.

For example, here the schema for :y is being captured by the wrong scope, and becomes [:y boolean?] instead of [:y int?].

(-> (m/deref
      [:merge
       [:map {:registry {::y int?}}
        [:y ::y]]
       [:map {:registry {::y boolean?}}
        [:z ::y]]]
      options)
    m/form)
=>
[:map {:registry {::y boolean?}}
 [:y ::y]
 [:z ::y]]

[frenchy64]

This example doesn't work at all, and complains that ::y is not in scope.

[:merge
 [:map
  {::y boolean?}
  [:y ::y]]
 [:map]]

[ikitommi]

The latter example works right, got fixed at some point?

(-> (m/schema
     [:merge
      [:map {:registry {::z boolean?}}
       [:y ::z]]
      [:map {:registry {::z int?}}
       [:x ::z]]])
    (malli.edn/write-string)
    (malli.edn/read-string))
;[:merge
; [:map {:registry #:use{:z boolean?}} [:y :user/z]]
; [:map {:registry #:user{:z int?}} [:x :user/z]]]

and:

(-> (m/deref
     [:merge
      [:map {:registry {::z boolean?}}
       [:y ::z]]
      [:map {:registry {::z int?}}
       [:x ::z]]])
    (malli.edn/write-string)
    (malli.edn/read-string))
;[:map {:registry #:user{:z int?}} 
; [:y :user/z] 
; [:x :user/z]]

but this doesn't:

(-> (m/deref
     [:merge
      [:map {:registry {::z boolean?
                        ::y boolean?}}
       [:y ::z]
       [:z ::y]]
      [:map {:registry {::z int?}}
       [:x ::z]]])
    (malli.edn/write-string)
    (malli.edn/read-string))
; =throws=> :missing ::y

so, yes, the registries should be merged propertly.

my 1 cent:

1. we could have 2 registries, global and local -> schemas can assume that the global is always available and only carry the accumulated local registry with them. this should be pushed to schema forms so one can create schemas out of the forms