Improve combine to not return lazy sequences

The `combine` function attempts to add new values to a collection by
merging them. However, for lists and a vectors, a lazy sequence is
returned rather than a list or a vector.

For lists, `(apply list (concat ...` is used instead of `(into ...` in
order to preserve element order for backwards compatibility, as `into`
would put the new elements at the head of the list.

For vectors, `into` is used, as new elements are added to the tail.

The implementation for sets is simplified.

CHANGES.markdown

@@ -6,6 +6,7 @@
   version which blocked updating some dependencies
 * Update clojure versions in the build matrix.
 * Allow `defresource` to have a docstring (#305)
+* Improve `liberator.util/combine` to not return lazy sequences (#304)
 
 ## Bugs fixed
 

src/liberator/util.clj

@@ -76,9 +76,9 @@
   (cond
    (-> newval meta :replace) newval
    (and (map? curr) (map? newval)) (merge-with combine curr newval)
-   (and (list? curr) (coll? newval)) (concat curr newval)
-   (and (vector? curr) (coll? newval)) (concat curr newval)
-   (and (set? curr) (coll? newval)) (set (concat curr newval))
+   (and (list? curr) (coll? newval)) (apply list (concat curr newval))
+   (and (vector? curr) (coll? newval)) (into curr newval)
+   (and (set? curr) (coll? newval)) (into curr newval)
    :otherwise newval))
 
 (defn is-protocol-exception?

test/test_util.clj

@@ -5,9 +5,13 @@
 (facts "combine function"
   (facts "simple combinations"
     (fact "merges map" (combine {:a 1} {:b 2}) => {:a 1 :b 2})
+    (fact "returns a map" (combine {:a 1} {:b 2}) => map?)
     (fact "concats list" (combine '(1 2) [3 4]) => '(1 2 3 4))
+    (fact "returns a list" (combine '(1 2) [3 4]) => list?)
     (fact "concats vector" (combine [1 2] '(3 4)) => [1 2 3 4])
+    (fact "returns a vector" (combine [1 2] '(3 4)) => vector?)
     (fact "concats set" (combine #{1 2} [3 4]) => #{1 2 3 4})
+    (fact "returns a set" (combine #{1 2} [3 4]) => set?)
     (facts "replaces other types"
       (fact (combine 123 456) => 456)
       (fact (combine "abc" 123) => 123)