Add untested attestation validation logic

beacon_chain/attestation_validation/src/enums.rs

@@ -0,0 +1,34 @@
+/// Reasons why an `AttestationRecord` can be invalid.
+pub enum Invalid {
+    AttestationTooRecent,
+    AttestationTooOld,
+    JustifiedSlotImpermissable,
+    JustifiedBlockNotInChain,
+    JustifiedBlockHashMismatch,
+    UnknownShard,
+    ShardBlockHashMismatch,
+    SignatureInvalid,
+}
+
+/// The outcome of validating the `AttestationRecord`.
+///
+/// Distinct from the `Error` enum as an `Outcome` indicates that validation executed sucessfully
+/// and determined the validity `AttestationRecord`.
+pub enum Outcome {
+    Valid,
+    Invalid(Invalid),
+}
+
+/// Errors that prevent this function from correctly validating the `AttestationRecord`.
+///
+/// Distinct from the `Outcome` enum as `Errors` indicate that validation encountered an unexpected
+/// condition and was unable to perform its duty.
+pub enum Error {
+    BlockHasNoParent,
+    BadValidatorIndex,
+    UnableToLookupBlockAtSlot,
+    OutOfBoundsBitfieldIndex,
+    PublicKeyCorrupt,
+    NoPublicKeyForValidator,
+    DBError(String),
+}