In defsystem, move user-provided protocol implementations after the generic ones

[MatthewDarling]

This allows the user to provide their own versions of start, stop, or status for systems. For my use case, I have code that depends on the system being initialized, so I want to provide a custom status method that checks specific things.

This behaviour seems to be allowed by vanilla defrecord - here's an example, with my version of Leaven installed locally:

user> (defprotocol Speak
        (say [this]))
Speak
user> (defrecord NewThing [attr]
        Speak
        (say [this] "woo")
        Speak
        (say [this] "boo"))
user.NewThing
user> (say (->NewThing 5))
"boo"
user=> (use 'com.palletops.leaven)
nil
user=> (defsystem TestingOut [config connection]
         {:depends {:connection [:config]}}
         com.palletops.leaven.protocols/Queryable
         (status [component] (if connection :started :stopped)))
user.TestingOut
user=> (status (map->TestingOut {:config :true}))
:stopped
user=> (status (map->TestingOut {:config :true :connection {:fake true}}))
:started

I realize that I could just make a plain record and implement the Leaven protocols myself, but I would like to rely on the other nice default behaviours of defsystem :)

[hugoduncan]

Merged, thanks!

[MatthewDarling]

Thanks! Unfortunately, I've found a minor wrinkle: this doesn't play nicely with namespace aliases.

user> (ns testing-leaven
        (:require [com.palletops.leaven.protocols :as leaven-p]
                  [com.palletops.leaven :refer [start stop status] :as leaven]))
;; => nil
testing-leaven> (leaven/defsystem TestingOut [config connection]
                  {:depends {:connection [:config]}}
                  leaven-p/Queryable
                  (status [component] (if connection :started :stopped)))
CompilerException java.lang.ClassFormatError: Duplicate method name&signature in class file testing_leaven/TestingOut, compiling:(/private/var/folders/gq/tjlj76ps59j81386jkt40jsm0000gn/T/form-init7169748078051573163.clj:1:1) 
testing-leaven> (leaven/defsystem TestingOut [config connection]
                  {:depends {:connection [:config]}}
                  com.palletops.leaven.protocols/Queryable
                  (status [component] (if connection :started :stopped)))
;; => testing_leaven.TestingOut

I really don't know why there would be different behaviour between the two.

Does it make sense to revert these changes for now?