df/load! properly handles components with a union query (#557)

df/load! was altering component queries and making them invalid when
they were a union query at the top level component. More info can be
found in issue#556.

This commit wraps the component query in a temporary top level root
query before eliding attributes provided by the without option, which is
what was causing the problem.

src/main/com/fulcrologic/fulcro/data_fetch.cljc

@@ -70,7 +70,12 @@
   "Remove items from a query when the query element where the (node-predicate key) returns true. Commonly used with
    a set as a predicate to elide specific well-known UI-only paths."
   [query node-predicate]
-  (-> query eql/query->ast (elide-ast-nodes node-predicate) eql/ast->query))
+  (-> query
+      (as-> <> [{::temp-root <>}])
+      eql/query->ast
+      (elide-ast-nodes node-predicate)
+      eql/ast->query
+      (get-in [0 ::temp-root])))
 
 (defn load-params*
   "Internal function to validate and process the parameters of `load` and `load-action`."

src/test/com/fulcrologic/fulcro/data_fetch_spec.cljc

@@ -30,12 +30,22 @@
    :ident         [:parent/by-id :x]
    :query         [:x :z {:child (comp/get-query InitTestChild)}]})
 
+(defsc UnionComponent [this props]
+  {:initial-state (fn [params] {:a/id 1 :a/name "Alice"})
+   :ident (fn [] (cond
+                   (:a/id props) [:a/id (:a/id props)]
+                   (:b/id props) [:b/id (:b/id props)]
+                   :else nil))
+   :query (fn [] {:a/id [:a/id :a/name]
+                  :b/id [:b/id :b/another-prop]})})
+
 (def app (app/fulcro-app))
 
 (specification "Load parameters"
   (let [
         query-with-params       (:query (df/load-params* app :prop Person {:params {:n 1}}))
-        ident-query-with-params (:query (df/load-params* app [:person/by-id 1] Person {:params {:n 1}}))]
+        ident-query-with-params (:query (df/load-params* app [:person/by-id 1] Person {:params {:n 1}}))
+        union-query (:query (df/load-params* app :prop UnionComponent {:without #{}}))]
     (assertions
       "Accepts nil for subquery and params"
       (:query (df/load-params* app [:person/by-id 1] nil {})) => [[:person/by-id 1]]
@@ -48,7 +58,9 @@
       (:target (df/load-params* app :prop Person {:target [:a :b]})) => [:a :b]
       "Constructs a JOIN query (with params on join and prop)"
       query-with-params => `[({:prop ~(comp/get-query Person)} {:n 1})]
-      ident-query-with-params => `[({[:person/by-id 1] ~(comp/get-query Person)} {:n 1})]))
+      ident-query-with-params => `[({[:person/by-id 1] ~(comp/get-query Person)} {:n 1})]
+      "Properly handles components with a union query"
+      union-query => [{:prop (comp/get-query UnionComponent)}]))
   (behavior "can focus the query"
     (assertions
       (:query (df/load-params* app [:item/by-id 1] Item {:focus [:name {:comments [:title]}]}))