Print debugging info if a pod does not verify (#141)

* Print debugging info if a pod does not verify

* Use logging for incorrect pods; add additional test

src/backends/plonky2/mock_main/mod.rs

@@ -1,5 +1,6 @@
 use anyhow::{anyhow, Result};
 use itertools::Itertools;
+use log::error;
 use plonky2::hash::poseidon::PoseidonHash;
 use plonky2::plonk::config::Hasher;
 use std::any::Any;
@@ -434,10 +435,22 @@ impl Pod for MockMainPod {
                 self.operations[i]
                     .deref(&self.statements[..input_statement_offset + i])
                     .unwrap()
-                    .check(&self.params, &s.clone().try_into().unwrap())
+                    .check_and_log(&self.params, &s.clone().try_into().unwrap())
             })
             .collect::<Result<Vec<_>>>()
             .unwrap();
+        if !ids_match {
+            error!("Verification failed: POD ID is incorrect.");
+        }
+        if !has_type_statement {
+            error!("Verification failed: POD does not have type statement.");
+        }
+        if !value_ofs_unique {
+            error!("Verification failed: Repeated ValueOf");
+        }
+        if !statement_check.iter().all(|b| *b) {
+            error!("Verification failed: Statement did not check.")
+        }
         ids_match && has_type_statement && value_ofs_unique & statement_check.into_iter().all(|b| b)
     }
     fn id(&self) -> PodId {

src/frontend/mod.rs

@@ -2,7 +2,9 @@
 //! with Pods.
 
 use anyhow::{anyhow, Error, Result};
+use env_logger;
 use itertools::Itertools;
+use log::error;
 use std::collections::HashMap;
 use std::convert::From;
 use std::{fmt, hash as h};
@@ -1152,4 +1154,87 @@ pub mod tests {
         println!("{}", builder);
         println!("{}", false_pod);
     }
+
+    #[test]
+    #[should_panic]
+    fn test_incorrect_pod() {
+        // try to insert the same key multiple times
+        // right now this is not caught when you build the pod,
+        // but it is caught on verify
+        env_logger::init();
+
+        let params = Params::default();
+        let mut builder = MainPodBuilder::new(&params);
+        builder.insert((
+            Statement(
+                Predicate::Native(NativePredicate::ValueOf),
+                vec![
+                    StatementArg::Key(AnchoredKey(Origin(PodClass::Main, SELF), "a".into())),
+                    StatementArg::Literal(Value::Int(3)),
+                ],
+            ),
+            Operation(OperationType::Native(NativeOperation::NewEntry), vec![]),
+        ));
+        builder.insert((
+            Statement(
+                Predicate::Native(NativePredicate::ValueOf),
+                vec![
+                    StatementArg::Key(AnchoredKey(Origin(PodClass::Main, SELF), "a".into())),
+                    StatementArg::Literal(Value::Int(28)),
+                ],
+            ),
+            Operation(OperationType::Native(NativeOperation::NewEntry), vec![]),
+        ));
+
+        let mut prover = MockProver {};
+        let pod = builder.prove(&mut prover, &params).unwrap();
+        pod.pod.verify();
+
+        // try to insert a statement that doesn't follow from the operation
+        // right now the mock prover catches this when it calls compile()
+        let params = Params::default();
+        let mut builder = MainPodBuilder::new(&params);
+        let self_a = AnchoredKey(Origin(PodClass::Main, SELF), "a".into());
+        let self_b = AnchoredKey(Origin(PodClass::Main, SELF), "b".into());
+        let value_of_a = Statement(
+            Predicate::Native(NativePredicate::ValueOf),
+            vec![
+                StatementArg::Key(AnchoredKey(Origin(PodClass::Main, SELF), "a".into())),
+                StatementArg::Literal(Value::Int(3)),
+            ],
+        );
+        let value_of_b = Statement(
+            Predicate::Native(NativePredicate::ValueOf),
+            vec![
+                StatementArg::Key(AnchoredKey(Origin(PodClass::Main, SELF), "b".into())),
+                StatementArg::Literal(Value::Int(27)),
+            ],
+        );
+
+        builder.insert((
+            value_of_a.clone(),
+            Operation(OperationType::Native(NativeOperation::NewEntry), vec![]),
+        ));
+        builder.insert((
+            value_of_b.clone(),
+            Operation(OperationType::Native(NativeOperation::NewEntry), vec![]),
+        ));
+        builder.insert((
+            Statement(
+                Predicate::Native(NativePredicate::Equal),
+                vec![StatementArg::Key(self_a), StatementArg::Key(self_b)],
+            ),
+            Operation(
+                OperationType::Native(NativeOperation::EqualFromEntries),
+                vec![
+                    OperationArg::Statement(value_of_a),
+                    OperationArg::Statement(value_of_b),
+                ],
+            ),
+        ));
+
+        let mut prover = MockProver {};
+        let pod = builder.prove(&mut prover, &params).unwrap();
+        pod.pod.verify();
+    }
 }

src/middleware/operation.rs

@@ -1,6 +1,7 @@
 use std::fmt;
 
 use anyhow::{anyhow, Result};
+use log::error;
 
 use super::{CustomPredicateRef, NativePredicate, Statement, StatementArg};
 use crate::middleware::{AnchoredKey, Params, Predicate, Value, SELF};
@@ -308,6 +309,15 @@ impl Operation {
             .map(|(pred, st_args)| Statement::from_args(pred, st_args));
         x.transpose()
     }
+    /// Checks the given operation against a statement, and prints information if the check does not pass
+    pub fn check_and_log(&self, params: &Params, output_statement: &Statement) -> Result<bool> {
+        let valid: bool = self.check(params, output_statement)?;
+        if !valid {
+            error!("Check failed on the following statement");
+            error!("{}", output_statement);
+        }
+        Ok(valid)
+    }
     /// Checks the given operation against a statement.
     pub fn check(&self, _params: &Params, output_statement: &Statement) -> Result<bool> {
         use Statement::*;