Add postfix if the field name matches keyword

Author: ccycle

src/Proto3/Suite/DotProto/Internal.hs

@@ -528,7 +528,16 @@ prefixedFieldName msgName fieldName = do
 
 prefixedFieldNameWithFlag :: MonadError CompileError m => IsPrefixed -> String -> String -> m String
 prefixedFieldNameWithFlag (IsPrefixed flag) msgName fieldName = do
-  if flag then prefixedFieldName msgName fieldName else return fieldName
+  if flag then prefixedFieldName msgName fieldName else return $ if fieldName `elem` keywords then fieldName ++ "_" else fieldName
+  where
+    -- copy from https://hackage.haskell.org/package/hscolour-1.20.3/docs/src/Language-Haskell-HsColour-Classify.html#keywords
+    -- and remove "forall", "qualified", "ccall", "as", "safe", "unsafe"
+    keywords =
+      ["case","class","data","default","deriving","do","else"
+      ,"if","import","in","infix","infixl","infixr","instance","let","module"
+      ,"newtype","of","then","type","where","_"
+      ,"foreign"
+      ]
 
 dpIdentUnqualName :: MonadError CompileError m => DotProtoIdentifier -> m String
 dpIdentUnqualName (Single name)       = pure name