Add support for explain clause

https://www.postgresql.org/docs/current/sql-explain.html

Author: govindkrjoshi

src/honeysql_postgres/format.cljc

@@ -31,7 +31,8 @@
 
 (def ^:private postgres-clause-priorities
   "Determines the order that clauses will be placed within generated SQL"
-  (merge {:with 30
+  (merge {:explain 20
+          :with 30
           :with-recursive 40
           :except 45
           :except-all 45
@@ -297,3 +298,33 @@
        (-> extension-name
            util/get-first
            sqlf/to-sql)))
+
+(defmethod format-clause :explain [[_ [params]] _]
+  (if (empty? params)
+    "EXPLAIN"
+    (let [params-string-map
+          {:costs "COSTS"
+           :settings "SETTINGS"
+           :buffers "BUFFERS"
+           :wal "WAL"
+           :timing "TIMING"
+           :summary "SUMMARY"}
+
+          format-string-map
+          {:text "TEXT"
+           :xml "XML"
+           :json "JSON"
+           :yaml "YAML"}
+
+          ->param-string
+          (fn [[k v]]
+            (case k
+              :analyze "ANALYZE"
+              :verbose "VERBOSE"
+              :format (sqlf/paren-wrap (str "FORMAT" " " (format-string-map v)))
+              (when-let [param-name (params-string-map k)]
+                (sqlf/paren-wrap
+                 (sqlf/space-join [param-name (if (true? v) "TRUE" "FALSE")])))))]
+
+      (sqlf/space-join ["EXPLAIN"
+                        (sqlf/space-join (map ->param-string params))]))))

src/honeysql_postgres/helpers.cljc

@@ -83,3 +83,6 @@
 
 (defhelper drop-extension [m extension-name]
   (assoc m :drop-extension (sqlh/collify extension-name)))
+
+(defhelper explain [m args]
+  (assoc m :explain args))

test/honeysql_postgres/postgres_test.cljc

@@ -18,6 +18,7 @@
               drop-column
               drop-extension
               drop-table
+              explain
               filter
               insert-into-as
               on-conflict
@@ -354,6 +355,7 @@
              (within-group [(sql/call :percentile_disc (hsql-types/array [0.25 0.5 0.75])) (order-by :s.i) :alias])
              (from (sql/raw "generate_series(1,10) AS s(i)"))
              (sql/format)))))
+
 (deftest create-extension-test
   (testing "create extension"
     (is (= ["CREATE EXTENSION \"uuid-ossp\""]
@@ -372,3 +374,55 @@
            (-> (drop-extension :uuid-ossp)
                (sql/format :allow-dashed-names? true
                            :quoting :ansi))))))
+
+(deftest explain-test
+  (let [query (-> (select :*)
+                  (from :products))]
+    (testing "EXPLAIN without any arguments"
+      (is (= ["EXPLAIN SELECT * FROM products"]
+             (-> query (explain) (sql/format)))))
+    (testing "Explain with analyze"
+      (is (= ["EXPLAIN ANALYZE SELECT * FROM products"]
+             (-> query (explain {:analyze true}) (sql/format)))))
+    (testing "Explain with analyze verbose"
+      (is (= ["EXPLAIN ANALYZE VERBOSE SELECT * FROM products"]
+             (-> query (explain {:analyze true :verbose true}) (sql/format)))))
+    (testing "Explain with costs"
+      (is (= ["EXPLAIN (COSTS TRUE) SELECT * FROM products"]
+             (-> query (explain {:costs true}) (sql/format))))
+      (is (= ["EXPLAIN (COSTS FALSE) SELECT * FROM products"]
+             (-> query (explain {:costs false}) (sql/format)))))
+    (testing "Explain with settings"
+      (is (= ["EXPLAIN (SETTINGS TRUE) SELECT * FROM products"]
+             (-> query (explain {:settings true}) (sql/format))))
+      (is (= ["EXPLAIN (SETTINGS FALSE) SELECT * FROM products"]
+             (-> query (explain {:settings false}) (sql/format)))))
+    (testing "Explain with buffers"
+      (is (= ["EXPLAIN (BUFFERS TRUE) SELECT * FROM products"]
+             (-> query (explain {:buffers true}) (sql/format))))
+      (is (= ["EXPLAIN (BUFFERS FALSE) SELECT * FROM products"]
+             (-> query (explain {:buffers false}) (sql/format)))))
+    (testing "Explain with wal"
+      (is (= ["EXPLAIN (WAL TRUE) SELECT * FROM products"]
+             (-> query (explain {:wal true}) (sql/format))))
+      (is (= ["EXPLAIN (WAL FALSE) SELECT * FROM products"]
+             (-> query (explain {:wal false}) (sql/format)))))
+    (testing "Explain with timing"
+      (is (= ["EXPLAIN (TIMING TRUE) SELECT * FROM products"]
+             (-> query (explain {:timing true}) (sql/format))))
+      (is (= ["EXPLAIN (TIMING FALSE) SELECT * FROM products"]
+             (-> query (explain {:timing false}) (sql/format)))))
+    (testing "Explain with summary"
+      (is (= ["EXPLAIN (SUMMARY TRUE) SELECT * FROM products"]
+             (-> query (explain {:summary true}) (sql/format))))
+      (is (= ["EXPLAIN (SUMMARY FALSE) SELECT * FROM products"]
+             (-> query (explain {:summary false}) (sql/format)))))
+    (testing "Explain with format"
+      (is (= ["EXPLAIN (FORMAT TEXT) SELECT * FROM products"]
+             (-> query (explain {:format :text}) (sql/format))))
+      (is (= ["EXPLAIN (FORMAT XML) SELECT * FROM products"]
+             (-> query (explain {:format :xml}) (sql/format))))
+      (is (= ["EXPLAIN (FORMAT JSON) SELECT * FROM products"]
+             (-> query (explain {:format :json}) (sql/format))))
+      (is (= ["EXPLAIN (FORMAT YAML) SELECT * FROM products"]
+             (-> query (explain {:format :yaml}) (sql/format)))))))