Improve error reporting of builtin fn parser.

Author: thealmarty

plutus-core/plutus-core/src/PlutusCore/Error.hs

@@ -38,8 +38,10 @@ import PlutusCore.Pretty
 import Control.Lens hiding (use)
 import Control.Monad.Error.Lens
 import Control.Monad.Except
+import Data.Map (Map)
 import Data.Text qualified as T
 import ErrorCode
+import PlutusCore.Default (DefaultFun)
 import Prettyprinter (hardline, indent, squotes, (<+>))
 import Text.Megaparsec as M
 import Universe (Closed (Everywhere), GEq, GShow)
@@ -54,7 +56,7 @@ throwingEither r e = case e of
 data ParserError
     = UnknownBuiltinType T.Text SourcePos
     | BuiltinTypeNotAStar T.Text SourcePos
-    | UnknownBuiltinFunction T.Text SourcePos
+    | UnknownBuiltinFunction T.Text SourcePos (Map T.Text DefaultFun)
     | InvalidBuiltinConstant T.Text T.Text SourcePos
     deriving stock (Eq, Ord, Generic)
     deriving anyclass (NFData)
@@ -117,7 +119,7 @@ instance Pretty SourcePos where
 instance Pretty ParserError where
     pretty (UnknownBuiltinType s loc)       = "Unknown built-in type" <+> squotes (pretty s) <+> "at" <+> pretty loc
     pretty (BuiltinTypeNotAStar ty loc)     = "Expected a type of kind star (to later parse a constant), but got:" <+> squotes (pretty ty) <+> "at" <+> pretty loc
-    pretty (UnknownBuiltinFunction s loc)   = "Unknown built-in function" <+> squotes (pretty s) <+> "at" <+> pretty loc
+    pretty (UnknownBuiltinFunction s loc lBuiltin)   = "Unknown built-in function" <+> squotes (pretty s) <+> "at" <+> pretty loc <+> ". Parsable functions are " <+> pretty (show lBuiltin)
     pretty (InvalidBuiltinConstant c s loc) = "Invalid constant" <+> squotes (pretty c) <+> "of type" <+> squotes (pretty s) <+> "at" <+> pretty loc
 
 instance ShowErrorComponent ParserError where

plutus-core/plutus-core/src/PlutusCore/Parser/Builtin.hs

@@ -7,32 +7,34 @@ module PlutusCore.Parser.Builtin where
 import Data.Text qualified as T
 import Data.Text.Internal.Read (hexDigitToInt)
 import PlutusPrelude (Word8)
-import Text.Megaparsec (MonadParsec (takeWhileP), choice, many, manyTill)
+import Text.Megaparsec (MonadParsec (takeWhileP), choice, customFailure, getSourcePos, many, manyTill)
 import Text.Megaparsec.Char (char, hexDigitChar)
 import Text.Megaparsec.Char.Lexer qualified as Lex hiding (hexadecimal)
 
 import Data.ByteString (pack)
 import Data.Map (Map, empty, insert, lookup)
 import PlutusCore.Default
+import PlutusCore.Error
 import PlutusCore.Parser.ParserCommon (Parser, isIdentifierChar, lexeme, symbol, whitespace)
 import PlutusCore.Parser.Type (defaultUniType)
 import PlutusCore.Pretty (display)
 import Prelude hiding (lookup)
 
-mkCachedBuiltin :: [DefaultFun] -> Map T.Text DefaultFun -> Map T.Text DefaultFun
-mkCachedBuiltin (hdFns:tlFns) builtinMap =
-    mkCachedBuiltin tlFns (insert (display hdFns) hdFns builtinMap)
-mkCachedBuiltin [] builtinMap = builtinMap
-
 cachedBuiltin :: Map T.Text DefaultFun
-cachedBuiltin = mkCachedBuiltin [minBound .. maxBound] empty
+cachedBuiltin
+  = foldl
+      (\ currMap fn -> insert (display fn) fn currMap)
+      empty
+      [minBound .. maxBound]
 
 -- | Parser for builtin functions. Atm the parser can only parse `DefaultFun`.
 builtinFunction :: Parser DefaultFun
 builtinFunction = lexeme $ do
-    txt <- takeWhileP (Just "identifier") isIdentifierChar
+    txt <- takeWhileP (Just "builtin function identifier") isIdentifierChar
     case lookup txt cachedBuiltin of
-        Nothing      -> error $ "Not a builtin" <> show cachedBuiltin <> show txt
+        Nothing      -> do
+            pos <- getSourcePos
+            customFailure $ UnknownBuiltinFunction txt pos cachedBuiltin
         Just builtin -> pure builtin
 
 signedInteger :: Parser Integer