Zen modules dependency aliases

[KGOH]

After #27 will be implemented there will be increasing chance of namespace collisions.

Problem example:

• package1: defines namespaces A, B. A depends on B here

  A.edn
  {ns A
   import #{B}
   sym {:zen/tags #{B/tag}}}

• package2 defines namespaces B and C. C depends on B here

  C.edn
  {ns A
   import #{B}
   sym {:zen/tags #{B/tag}}}

• I'm interested in package1.A/sym namespace and in package2.C/sym
• I import both packages as my dependency.
• Namespaces collision by the name B will break one of these packages

Possible solutions:

• suggest user to copy and patch names in the lib with name clash manually
• add local custom package prefixes. When specifying a dependency could/should specify also a prefix which will prepend ALL of the symbols in this dependency

Urgency: low
This may be important architecture decision, i.e. we may want to decide to force all deps to have local alias

[KGOH]

Naive prefix solution:

;; our package 1 specifies deps like this
[[steve "url1"]
 [johny.r "url2"]
 [stan "url3"]]

;; deps in the "url2" repo
[[stan.r "url1"]]


;; our package after dependency download
zen-modules/
    steve/
       some-ns.edn: {ns some-ns sym1 {}} ;; prefix all symbols with `steve on ns read 
    stan
       some-ns.edn: {ns some-ns sym3 {}} ;; prefix all symbols with `stan on ns read
    johny/
     r/
      some-ns.edn: {ns some-ns sym2 {} ;; prefix all symbols with `johny.r on ns read
                    import {stan.some-ns}}
      stan/
        some-ns.edn {ns some-ns sym1 {}}  ;; prefix all symbols with `johny.r.stan on ns read
zrc/
    main.edn: {ns main
               import #{steve.some-ns johny.r.some-ns}

               symbol
               {...
                steve.some-ns/rsym
                johny.r.some-ns/vsym}}

This specific soultion makes the same package occur multiple times, but this can be fixed by not so naive implementation, for example we can store package under a uid and maintain aliases to uid relation in a package-lock file, then substitute local alias during a namespace read in zen

[KGOH]

We should do analysis why other systems like Clojure don't do prefixes. My guess is stat code is a dynamic entity and can not be definitely statically analyzed, but zen-lang is fully static and we can find & check all symbols used in a project which enables us to do prefixes like this

We also need to find what are the drawbacks of prefixes (I couldn't find any)

[KGOH]

(require '[clojure.walk])


(defn prefix [x]
  (symbol (str "johny."
               (when-let [nsps (namespace x)]
                 (str nsps "/"))
               (name x))))


(-> '{ns foo
      import #{bar baz}
      sym {:zen/tags #{zen/schema}
           :type zen/map
           :foo bar/b
           :keys {:a {:type zen/string}}}}
    (->> (clojure.walk/postwalk
           (fn [x]
             (if (and (qualified-symbol? x)
                      (not (= "zen" (namespace x))))
               (prefix x)
               x))))
    (update 'ns prefix)
    (update 'import #(into #{} (map prefix) %)))