add warning about improper use of repl :eval option

When users pass a string to the repl's `eval` option on the CLI this works fine:

    boot repl --eval "(println \"foo\")"

if they do the same in their build.boot or other Clojure code
the direct translation won't work:

    (repl :eval "(println \"foo\")")

The issue here is that the passed value is interpreted as edn and a string is a valid edn
value. This commit introduces a warning whenever the users passes a string to the :eval
option from Clojure code.

This issue probably affects other tasks making me think that there should be some kind
of `form` type for task options which are expected to be executable Clojure code.

CHANGES.md

@@ -33,6 +33,7 @@ and `technomancy` for the above explanation.
 - Environment variables BOOT_AS_ROOT, BOOT_WATCHERS_DISABLE und BOOT_COLOR accept `true` as a truthy value beside `1` and `yes` [#631][631]
 - Bump [pomegranate](https://github.com/cemerick/pomegranate) and [dynapath](https://github.com/tobias/dynapath) to `1.0.0`. [#612][612]
 - Digest `java.io.File` instead `String` path of jar at sift-action `:add-jar` method [#678][678]
+- Add warning about improper use of repl :eval option [#666][666]
 
 #### Fixed
 
@@ -52,10 +53,14 @@ and `technomancy` for the above explanation.
 [629]: https://github.com/boot-clj/boot/pull/629
 [654]: https://github.com/boot-clj/boot/issues/654
 [566]: https://github.com/boot-clj/boot/pull/566
+<<<<<<< HEAD
 [631]: https://github.com/boot-clj/boot/issues/631
 [612]: https://github.com/boot-clj/boot/pull/612
 [678]: https://github.com/boot-clj/boot/pull/678
 [679]: https://github.com/boot-clj/boot/pull/679
+=======
+[666]: https://github.com/boot-clj/boot/pull/666
+>>>>>>> add warning about improper use of repl :eval option
 
 ## 2.7.2
 

boot/core/src/boot/task/built_in.clj

@@ -473,6 +473,8 @@
    m middleware SYM [sym] "The REPL middleware vector."
    x handler SYM    sym   "The REPL handler (overrides middleware options)."]
 
+  (when (string? eval)
+    (util/warn "When passing :eval to the repl task in your build.boot, use a quoted form instead of a string\n"))
   (let [cpl-path (.getPath (core/tmp-dir!))
         srv-opts (->> [:bind :port :init-ns :middleware :handler :pod]
                       (select-keys *opts*))