Introduce boot.task/deftask-edn, create tasks with pure data

[arichiardi]

This PR adds the deftask-edn facilities. It basically uses edn data to generate tasks.

A better explanation can be found in the docstring:

(defmacro deftask-edn
  "Create boot tasks based on an edn conf.

  The body of this macro will be evaluated and the expected result has
  to match the following example:

      {:env {:resource-paths #{\"resources\"}
             :source-paths #{\"src/web\" \"src/shared\"}
             :dependencies '[[org.clojure/clojure \"1.9.0-alpha14\"]
                             [adzerk/boot-cljs \"2.0.0-SNAPSHOT\" :scope \"test\"]
                             [org.clojure/clojurescript \"1.9.456\"  :scope \"test\"]
                             [reagent \"0.6.0\"]
                             ...]}
       :pipeline '(comp (pandeiro.boot-http/serve)
                        (watch)
                        (powerlaces.boot-cljs-devtools/cljs-devtools)
                        (powerlaces.boot-figreload/reload)
                        (adzerk.boot-cljs-repl/cljs-repl)
                        (adzerk.boot-cljs/cljs))
       :cljs {:source-map true
              :optimizations :advanced
              :compiler-options {:closure-defines {\"goog.DEBUG\" false}
                                 :verbose true}}
       :cljs-devtools {...}}

  As in any declarative approach, we need to establish some convention:

   - the `:env` key will be passed with no modification to `set-env!`
   - the `:props` key will need to contain a map of `string` keys to
     `string` values that will set Java System Properties
   - the keys that match a task name will provide options to that task
   - the `:pipeline` key will contain the `comp` typically used in
     `boot` tasks (order counts)
   - if a tasks has full namespace in `:pipeline`, the namespace will be
     required and the task resolved. If not, the task will be resolved in
     `boot.task.built-in` first and finally in `boot.user`"
  [sym & forms]
...

I welcome any feedback or rejection of this. It is basically taking the declarative/lein approach, which sometimes can be very convenient. Of course for me this should go in core so that the user has the choice 😄

[burn2delete]

Interesting, I am using a declarative approach for the env like this:
https://github.com/flyboarder/meta/blob/master/src/meta/boot.clj#L27-L34

[arichiardi]

@flyboarder It looks very similar!

So from Slack there are two votes for renaming it to boot.task/deftask-edn. Naming is hard 😄

[arichiardi]

Also, the :pipeline key could be converted to a vector, or even a map, so that it will be easier to replace tasks in the pipeline, by either using conj or assoc on it.

[SevereOverfl0w]

Should the :env key be using merge-env!? Occasionally I need to compose multiple tasks which modify env in multiple ways (or rather I have a base & then add dev to the env).

Props is awesome, this is the other thing I commonly do.

I'm a little confused by the :cljs and :cljs-devtools key, is this related to task-options!

[arichiardi]

Yes names are only attempts 😀 So those keys are identifying the task your want to declarativly set options for . So they must be task names.

…

-- Sent from my Android device with K-9 Mail. Please excuse my brevity.

[arichiardi]

Only once for every task call the set-env! is invoked.

[SevereOverfl0w]

If I have multiple tasks which add to the source-paths, does using set-env! cause them to clobber? (I thought it did, so I've been using merge-env!)

How does powerlaces.boot-cljs-devtools/cljs-devtools link to :cljs-devtools? Should it be using the full namespace (e.g. :powerlaces.boot-cljs-devtools/cljs-devtools) instead? Although I think this is kind of impractical. ::dev-tools/cljs-devtools makes the syntax a little more palatable though.

[SevereOverfl0w]

Actually, to use the full namespace, we could use symbols instead. This makes it nicer for :refer'd variables:

{`test {:foo :bah}}
;; => {adzerk.boot-test/test {:foo :bah}}

[arichiardi]

Yes we could, but I did not want to type it every time so the macro looks for task symbols in order at the moment: https://github.com/adzerk-oss/bootlaces/pull/16/files#diff-ce48b98546ca95cbc67c4ae8588d0bacR43

[arichiardi]

About set-env!, it works fine but I have noticed something...haven't had time to debug it but it looks like composing tasks will call set-env! multiple times and therefore make a mess as you are saying..