Add function to access anchor data from GovAction and fix typo

cardano-api/internal/Cardano/Api/Certificate.hs

@@ -743,7 +743,7 @@ instance Error AnchorDataFromCertificateError where
   prettyError (InvalidPoolMetadataHashError url hash) =
     "Invalid pool metadata hash for URL " <> fromString (show url) <> ": " <> fromString (show hash)
 
--- | Get anchor data hash from a certificate. A return value of `Nothing`
+-- | Get anchor data url and hash from a certificate. A return value of `Nothing`
 -- means that the certificate does not contain anchor data.
 getAnchorDataFromCertificate
   :: Certificate era

cardano-api/internal/Cardano/Api/Governance/Actions/ProposalProcedure.hs

@@ -230,3 +230,19 @@ createAnchor url anchorData =
     { anchorUrl = url
     , anchorDataHash = hashAnchorData $ Ledger.AnchorData anchorData
     }
+
+-- | Get anchor data url and hash from a governance action. A return value of `Nothing`
+-- means that the governance action does not contain anchor data.
+getAnchorDataFromGovernanceAction
+  :: EraCrypto (ShelleyLedgerEra era) ~ StandardCrypto
+  => Gov.GovAction (ShelleyLedgerEra era)
+  -> Maybe (Ledger.Anchor StandardCrypto)
+getAnchorDataFromGovernanceAction govAction =
+  case govAction of
+    Gov.ParameterChange{} -> Nothing
+    Gov.HardForkInitiation _ _ -> Nothing
+    Gov.TreasuryWithdrawals _ _ -> Nothing
+    Gov.NoConfidence _ -> Nothing
+    Gov.UpdateCommittee{} -> Nothing
+    Gov.NewConstitution _ constitution -> Just $ Ledger.constitutionAnchor constitution
+    Gov.InfoAction -> Nothing

cardano-api/src/Cardano/Api.hs

@@ -999,6 +999,9 @@ module Cardano.Api
   , DRepMetadataReference
   , hashDRepMetadata
 
+    -- ** Governance actions
+  , getAnchorDataFromGovernanceAction
+
     -- ** Governance related certificates
   , AnchorDataHash (..)
   , AnchorUrl (..)