Add a conversion from ProofError to R1CSError.

In the long term, I think that it would be better to combine R1CSError with
ProofError, if we can do that without breaking stability.  If not, we should
refactor the TranscriptProtocol so that it returns a TranscriptError type that
can be converted into either a ProofError or an R1CSError.

Author: hdevalence

src/errors.rs

@@ -91,6 +91,8 @@ pub enum MPCError {
 }
 
 /// Represents an error during the proving or verifying of a constraint system.
+///
+/// XXX: should this be separate from a `ProofError`?
 #[cfg(feature = "yoloproofs")]
 #[derive(Fail, Clone, Debug, Eq, PartialEq)]
 pub enum R1CSError {
@@ -118,3 +120,15 @@ pub enum R1CSError {
         description: String,
     },
 }
+
+#[cfg(feature = "yoloproofs")]
+impl From<ProofError> for R1CSError {
+    fn from(e: ProofError) -> R1CSError {
+        match e {
+            ProofError::InvalidGeneratorsLength => R1CSError::InvalidGeneratorsLength,
+            ProofError::FormatError => R1CSError::FormatError,
+            ProofError::VerificationError => R1CSError::VerificationError,
+            _ => panic!("unexpected error type in conversion"),
+        }
+    }
+}