From 9787f42696b5c9e40bb7be4ac3f480c705ec055b Mon Sep 17 00:00:00 2001
From: Nikolaos Bezirgiannis <bezirg@users.noreply.github.com>
Date: Wed, 31 Aug 2022 17:21:14 +0200
Subject: [PATCH] Remove the "dead" error about builtin arity

---
 .../src/PlutusCore/Evaluation/Machine/Exception.hs         | 7 -------
 plutus-errors/src/Errors.hs                                | 7 +++++--
 2 files changed, 5 insertions(+), 9 deletions(-)

diff --git a/plutus-core/plutus-core/src/PlutusCore/Evaluation/Machine/Exception.hs b/plutus-core/plutus-core/src/PlutusCore/Evaluation/Machine/Exception.hs
index d70f18fa87d..b0f5073e6d9 100644
--- a/plutus-core/plutus-core/src/PlutusCore/Evaluation/Machine/Exception.hs
+++ b/plutus-core/plutus-core/src/PlutusCore/Evaluation/Machine/Exception.hs
@@ -75,10 +75,6 @@ data MachineError fun
       -- ^ A builtin expected a term argument, but something else was received
     | UnexpectedBuiltinTermArgumentMachineError
       -- ^ A builtin received a term argument when something else was expected
-    | EmptyBuiltinArityMachineError
-      -- ^ We've reached a state where a builtin instantiation or application is attempted
-      -- when the arity is zero. In the absence of nullary builtins, this should be impossible.
-      -- See the machine implementations for details.
     | UnknownBuiltin fun
     deriving stock (Show, Eq, Functor, Generic)
     deriving anyclass (NFData)
@@ -201,8 +197,6 @@ instance (HasPrettyDefaults config ~ 'True, Pretty fun) =>
         "A builtin expected a term argument, but something else was received"
     prettyBy _      UnexpectedBuiltinTermArgumentMachineError =
         "A builtin received a term argument when something else was expected"
-    prettyBy _      EmptyBuiltinArityMachineError =
-        "A builtin was applied to a term or type where no more arguments were expected"
     prettyBy _      (UnliftingMachineError unliftingError)  =
         pretty unliftingError
     prettyBy _      (UnknownBuiltin fun)                  =
@@ -240,7 +234,6 @@ instance HasErrorCode UnliftingError where
       errorCode        UnliftingErrorE {}        = ErrorCode 30
 
 instance HasErrorCode (MachineError err) where
-      errorCode        EmptyBuiltinArityMachineError {}             = ErrorCode 34
       errorCode        UnexpectedBuiltinTermArgumentMachineError {} = ErrorCode 33
       errorCode        BuiltinTermArgumentExpectedMachineError {}   = ErrorCode 32
       errorCode        OpenTermEvaluatedMachineError {}             = ErrorCode 27
diff --git a/plutus-errors/src/Errors.hs b/plutus-errors/src/Errors.hs
index 401c0430291..a35ae2b3d4c 100644
--- a/plutus-errors/src/Errors.hs
+++ b/plutus-errors/src/Errors.hs
@@ -22,10 +22,14 @@ See plutus-errors/README.md
 {-# WARNING ObsoleteErrors "These errors and their error codes *should* not be thrown by any plutus code anymore" #-}
 data ObsoleteErrors =
     ReservedErrorCode
+  | EmptyBuiltinArityMachineError
+  -- ^ an old error when we were checking arities of builtins during evaluation
+
     -- append here the obsolete errors
 
 instance HasErrorCode ObsoleteErrors where
-    errorCode ReservedErrorCode {} = ErrorCode 0
+    errorCode ReservedErrorCode {}             = ErrorCode 0
+    errorCode EmptyBuiltinArityMachineError {} = ErrorCode 34
     -- append here the corresponding obsolete error codes
 
 -- | All errors among the whole Plutus project. This includes both existing and obsolete errors.
@@ -61,7 +65,6 @@ allErrors =
    , 'PLC.UnliftingErrorE
    , 'PLC.BuiltinTermArgumentExpectedMachineError
    , 'PLC.UnexpectedBuiltinTermArgumentMachineError
-   , 'PLC.EmptyBuiltinArityMachineError
    , 'PLC.CekOutOfExError
    , 'PLC.CekEvaluationFailure
    , 'PLC.ParseErrorB