condense the `(process-*)` functions in the qp namespace into a single...

condense the `(process-*)` functions in the qp namespace into a single function definition and unify the call stack so that we simply apply all of our qp middleware functions regardless of the query.  this simplifies the understanding of the qp code path and reduces a bit of redundant code.

the one requirement that comes out of this is that our qp middleware now needs to add some conditional code so that it only applies itself on queries that it's meant to work against.

src/metabase/driver/query_processor.clj

@@ -38,6 +38,12 @@
 ;; |                                     QP INTERNAL IMPLEMENTATION                                     |
 ;; +----------------------------------------------------------------------------------------------------+
 
+(defn structured-query?
+  "Predicate function which returns `true` if the given query represents a structured style query, `false` otherwise."
+  [query]
+  (= :query (keyword (:type query))))
+
+
 (defn- wrap-catch-exceptions [qp]
   (fn [query]
     (try (qp query)
@@ -55,7 +61,9 @@
 
 (defn- pre-expand [qp]
   (fn [query]
-    (qp (resolve/resolve (expand/expand query)))))
+    (if (structured-query? query)
+      (qp (resolve/resolve (expand/expand query)))
+      (qp query))))
 
 
 (defn- post-add-row-count-and-status
@@ -208,6 +216,16 @@
     (qp query)))
 
 
+(defn- wrap-guard-multiple-calls
+  "Throw an exception if a QP function accidentally calls (QP QUERY) more than once."
+  [qp]
+  (let [called? (atom false)]
+    (fn [query]
+      (assert (not @called?) "(QP QUERY) IS BEING CALLED MORE THAN ONCE!")
+      (reset! called? true)
+      (qp query))))
+
+
 ;; +------------------------------------------------------------------------------------------------------------------------+
 ;; |                                                     QUERY PROCESSOR                                                    |
 ;; +------------------------------------------------------------------------------------------------------------------------+
@@ -239,16 +257,12 @@
 ;;
 ;; Pre-processing then happens in order from bottom-to-top; i.e. POST-ANNOTATE gets to modify the results, then LIMIT, then CUMULATIVE-SUM, etc.
 
-(defn- wrap-guard-multiple-calls
-  "Throw an exception if a QP function accidentally calls (QP QUERY) more than once."
-  [qp]
-  (let [called? (atom false)]
-    (fn [query]
-      (assert (not @called?) "(QP QUERY) IS BEING CALLED MORE THAN ONCE!")
-      (reset! called? true)
-      (qp query))))
 
-(defn- process-structured [{:keys [driver], :as query}]
+(defn process
+  "Process a QUERY and return the results."
+  [driver query]
+  (when-not *disable-qp-logging*
+    (log/debug (u/format-color 'blue "\nQUERY: 😎\n%s" (u/pprint-to-str query))))
   (let [driver-process-query      (:process-query driver)
         driver-wrap-process-query (or (:process-query-in-context driver)
                                       (fn [qp] qp))]
@@ -263,26 +277,5 @@
           annotate/post-annotate
           pre-log-query
           wrap-guard-multiple-calls
-          driver-process-query) query)))
-
-(defn- process-native [{:keys [driver], :as query}]
-  (let [driver-process-query      (:process-query driver)
-        driver-wrap-process-query (or (:process-query-in-context driver)
-                                      (fn [qp] qp))]
-    ((<<- wrap-catch-exceptions
-          driver-wrap-process-query
-          post-add-row-count-and-status
-          limit
-          wrap-guard-multiple-calls
-          driver-process-query) query)))
-
-(defn process
-  "Process a QUERY and return the results."
-  [driver query]
-  (when-not *disable-qp-logging*
-    (log/debug (u/format-color 'blue "\nQUERY: 😎\n%s" (u/pprint-to-str query))))
-  ((case (keyword (:type query))
-     :native process-native
-     :query  process-structured)
-   (assoc query
-          :driver driver)))
+          driver-process-query) (assoc query
+                                       :driver driver))))