mu/closed-schema (and other m/schema-walker uses) produce extra wrappers for reference schemas

[opqdonut]

The result of mu/closed-schema needs one more m/deref to get to the concrete schema. The same happens with a trivial m/schema-walker use.

Demonstration:

user=> (require '[malli.core :as m])
nil
user=> (require '[malli.util :as mu])
nil
user=> (def s1 (m/schema [:schema {:registry {"Foo" :int}} "Foo"]))
#'user/s1
user=> (def s2 (mu/closed-schema s1))
#'user/s2
user=> (m/form s1)
[:schema {:registry {"Foo" :int}} "Foo"]
user=> (m/form s2)
[:schema {:registry {"Foo" :int}} "Foo"]
user=> (-> s1 m/deref m/deref)
:int
user=> (-> s2 m/deref m/deref)
"Foo"
user=> (-> s2 m/deref m/deref m/deref)     ;; one more deref needed!
:int
user=> (defn noop-walk [schema] (m/walk schema (m/schema-walker identity)))
#'user/noop-walk
user=> (def s3 (noop-walk s1))
#'user/s3
user=> (-> s3 m/deref m/deref)
"Foo"
user=> (-> s3 m/deref m/deref m/deref)     ;; one more deref needed!
:int

The root cause is the -walk implementation for -schema-schema:

            (-walk [this walker path options]
              (when (-accept walker this path options)
                (if (or (not id) ((-boolean-fn (::walk-schema-refs options false)) id))
                  (-outer walker this path (-inner-indexed walker path children options) options)
                  (-outer walker this path [id] options))))

This combined with m/schema-walker causes (m/-set-children schema [id]), which overrides the child from :int to "Foo". Luckily this doesn't cause a loop in later schema walking, just the need for one more deref.

[opqdonut]

I tried to set ::walk-schema-refs for m/closed-schema (in #883), but it had some really funky consequences:

user> (def closed (mu/closed-schema [:schema {:registry {"Foo" [:map [:a :int]]}} "Foo"]))
#'user/closed
user> (m/form closed)
[:schema {:registry {"Foo" [:map [:a :int]]}} "Foo"]
user> (-> closed m/deref m/deref m/form)
[:map {:closed true} [:a :int]]

Even though the schema prints out as "Foo", it's not equal to the "Foo" in the registry any more.