Test json rpc arguments

In particular, check buggy behavior around embedded quoted JSON
and Postgres versions, compare

https://www.postgresql.org/message-id/D6921B37-BD8E-4664-8D5F-DB3525765DCD%40vllmrt.net

This adds version-bounded tests for the handling of quoted JSON,
and a pending test that documents the assumption that Postgres >=10
intends to parse quoted JSON as a string (similar to how jsonb works
now).

test/Feature/RpcSpec.hs

@@ -6,12 +6,13 @@ import Network.Wai      (Application)
 import Network.Wai.Test (SResponse (simpleBody, simpleStatus))
 
 import Network.HTTP.Types
-import Test.Hspec
+import Test.Hspec          hiding (pendingWith)
 import Test.Hspec.Wai
 import Test.Hspec.Wai.JSON
 import Text.Heredoc
 
-import PostgREST.Types (PgVersion, pgVersion95)
+import PostgREST.Types (PgVersion, pgVersion100, pgVersion95,
+                        pgVersion96)
 import Protolude       hiding (get)
 import SpecHelper
 
@@ -230,6 +231,63 @@ spec actualPgVersion =
           [json|null|]
           { matchHeaders = [matchContentTypeJson] }
 
+    context "proc argument types" $ do
+      it "accepts a variety of arguments" $
+        post "/rpc/varied_arguments"
+            [json| {
+              "double": 3.1,
+              "varchar": "hello",
+              "boolean": true,
+              "date": "20190101",
+              "money": 0,
+              "enum": "foo",
+              "integer": 43,
+              "json": {"some key": "some value"},
+              "jsonb": {"another key": [1, 2, "3"]}
+            } |]
+          `shouldRespondWith`
+            [json|"Hi"|]
+            { matchHeaders = [matchContentTypeJson] }
+
+      it "parses embedded JSON arguments as JSON" $
+        post "/rpc/json_argument"
+            [json| { "arg": { "key": 3 } } |]
+          `shouldRespondWith`
+            [json|"object"|]
+            { matchHeaders = [matchContentTypeJson] }
+
+      when (actualPgVersion <= pgVersion96) $
+        it "parses quoted JSON arguments as JSON (Postgres <= 9.6)" $
+          post "/rpc/json_argument"
+              [json| { "arg": "{ \"key\": 3 }" } |]
+            `shouldRespondWith`
+              [json|"object"|]
+              { matchHeaders = [matchContentTypeJson] }
+
+      when (actualPgVersion >= pgVersion100) $ do
+        it "parses quoted JSON arguments as JSON string (Postgres >= 10)" $ do
+          -- Postgres bug report:
+          -- https://www.postgresql.org/message-id/D6921B37-BD8E-4664-8D5F-DB3525765DCD%40vllmrt.net
+          -- * json_to_record fails (see following test)
+          -- * jsonb_to_record parses the embedded quoted JSON to a JSON string,
+          --   so that's probably the expected behavior for Postgres >= 10
+          pendingWith "Postgres >= 10 fails to parse quoted embedded JSON"
+          post "/rpc/json_argument"
+              [json| { "arg": "{ \"key\": 3 }" } |]
+            `shouldRespondWith`
+              [json|"string"|]
+              { matchHeaders = [matchContentTypeJson] }
+
+        it "fails to parse quoted JSON arguments (Postgres >= 10)" $
+          -- Confirming buggy Postgres behavior (see previous test)
+          post "/rpc/json_argument"
+              [json| { "arg": "{ \"key\": 3 }" } |]
+            `shouldRespondWith`
+              [json|{"hint":null,"details":"Token \"key\" is invalid.","code":"22P02","message":"invalid input syntax for type json"}|]
+              { matchStatus  = 400
+              , matchHeaders = [matchContentTypeJson]
+              }
+
     context "improper input" $ do
       it "rejects unknown content type even if payload is good" $ do
         request methodPost "/rpc/sayhello"

test/Feature/StructureSpec.hs

@@ -426,6 +426,14 @@ spec = do
                   "integer": {
                     "format": "integer",
                     "type": "integer"
+                  },
+                  "json": {
+                    "format": "json",
+                    "type": "string"
+                  },
+                  "jsonb": {
+                    "format": "jsonb",
+                    "type": "string"
                   }
                 },
                 "type": "object",