Don't use record notation for single-field datacons in tactics (#1456)

* Don't use record notation for single-field datacons

* Comment as to why this new check is here

Author: isovector

plugins/hls-tactics-plugin/src/Ide/Plugin/Tactic/CodeGen/Utils.hs

@@ -21,7 +21,8 @@ mkCon dcon (fmap unLoc -> args)
   | dataConIsInfix dcon
   , (lhs : rhs : args') <- args =
       noLoc $ foldl' (@@) (op lhs (coerceName dcon_name) rhs) args'
-  | Just fields <- getRecordFields dcon =
+  | Just fields <- getRecordFields dcon
+  , length fields >= 2 =  --  record notation is unnatural on single field ctors
       noLoc $ recordConE (coerceName dcon_name) $ do
         (arg, (field, _)) <- zip args fields
         pure (coerceName field, arg)

plugins/hls-tactics-plugin/test/GoldenSpec.hs

@@ -151,6 +151,7 @@ spec = do
     autoTest "GoldenArbitrary.hs" 25 13
     autoTest "FmapBoth.hs"        2 12
     autoTest "RecordCon.hs"       7  8
+    autoTest "NewtypeRecord.hs"   6  8
     autoTest "FmapJoin.hs"        2 14
     autoTest "Fgmap.hs"           2 9
     autoTest "FmapJoinInLet.hs"   4 19

plugins/hls-tactics-plugin/test/golden/NewtypeRecord.hs

@@ -0,0 +1,7 @@
+newtype MyRecord a = Record
+    { field1 :: a
+    }
+
+blah :: (a -> Int) -> a -> MyRecord a
+blah = _
+

plugins/hls-tactics-plugin/test/golden/NewtypeRecord.hs.expected

@@ -0,0 +1,7 @@
+newtype MyRecord a = Record
+    { field1 :: a
+    }
+
+blah :: (a -> Int) -> a -> MyRecord a
+blah _ = Record
+