Pretify multi-line string arguments as block strings

Fixes #10.

tests/Language/GraphQL/AST/EncoderSpec.hs

@@ -1,23 +1,46 @@
 {-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE QuasiQuotes #-}
 module Language.GraphQL.AST.EncoderSpec
     ( spec
     ) where
 
-import Language.GraphQL.AST (Value(..))
+import Language.GraphQL.AST
 import Language.GraphQL.AST.Encoder
-import Test.Hspec ( Spec
-                  , describe
-                  , it
-                  , shouldBe
-                  )
+import Test.Hspec (Spec, context, describe, it, shouldBe)
+import Text.RawString.QQ (r)
 
 spec :: Spec
-spec = describe "value" $ do
-    it "escapes \\" $
-        value minified (String "\\") `shouldBe` "\"\\\\\""
-    it "escapes quotes" $
-        value minified (String "\"") `shouldBe` "\"\\\"\""
-    it "escapes backspace" $
-        value minified (String "a\bc") `shouldBe` "\"a\\bc\""
-    it "escapes Unicode" $
-        value minified (String "\0") `shouldBe` "\"\\u0000\""
+spec = do
+    describe "value" $ do
+        context "minified" $ do
+            it "escapes \\" $
+                value minified (String "\\") `shouldBe` "\"\\\\\""
+            it "escapes quotes" $
+                value minified (String "\"") `shouldBe` "\"\\\"\""
+            it "escapes backspace" $
+                value minified (String "a\bc") `shouldBe` "\"a\\bc\""
+            it "escapes Unicode" $
+                value minified (String "\0") `shouldBe` "\"\\u0000\""
+
+        context "pretty" $ do
+            it "uses strings for short string values" $
+                value pretty (String "Short text") `shouldBe` "\"Short text\""
+            it "uses block strings for text with new lines" $
+                value pretty (String "Line 1\nLine 2")
+                    `shouldBe` "\"\"\"\n  Line 1\n  Line 2\n\"\"\""
+            it "escapes \\ in short strings" $
+                value pretty (String "\\") `shouldBe` "\"\\\\\""
+
+    describe "definition" $
+        it "indents block strings in arguments" $
+            let arguments = [Argument "message" (String "line1\nline2")]
+                field = Field Nothing "field" arguments [] []
+                set = OperationSelectionSet $ pure $ SelectionField field
+                operation = DefinitionOperation set
+             in definition pretty operation `shouldBe` [r|{
+  field(message: """
+    line1
+    line2
+  """)
+}
+|]