[#526] Add TxValidationMode data type

cardano-ledger/cardano-ledger.cabal

@@ -98,6 +98,7 @@ library
                        Cardano.Chain.UTxO.UTxOConfiguration
                        Cardano.Chain.UTxO.TxProof
                        Cardano.Chain.UTxO.TxWitness
+                       Cardano.Chain.UTxO.ValidationMode
 
                        Cardano.Chain.Update.ApplicationName
                        Cardano.Chain.Update.InstallerHash

cardano-ledger/src/Cardano/Chain/UTxO/ValidationMode.hs

@@ -0,0 +1,34 @@
+module Cardano.Chain.UTxO.ValidationMode
+  ( TxValidationMode (..)
+  , whenTxValidation
+  ) where
+
+import Cardano.Prelude
+
+--------------------------------------------------------------------------------
+-- TxValidationMode
+--------------------------------------------------------------------------------
+
+-- | Indicates what sort of transaction validation should be performed.
+data TxValidationMode
+  = TxValidation
+  -- ^ Perform all transaction validations.
+  | TxValidationNoCrypto
+  -- ^ Because we've already validated this tranaction against some ledger
+  -- state, we know that cryptographic validation has passed. However, we
+  -- should still perform all of the other non-cryptographic checks since
+  -- we're validating against a potentially dfferent ledger state.
+  | NoTxValidation
+  -- ^ No validations should be performed as we have already validated this
+  -- transaction against this very same ledger state.
+  deriving (Eq, Show)
+
+-- | Perform an action only when in the 'TxValidation' mode. Otherwise, do
+-- nothing.
+whenTxValidation
+  :: MonadError err m
+  => TxValidationMode
+  -> m ()
+  -> m ()
+whenTxValidation TxValidation action = action
+whenTxValidation _ _ = pure ()