From 663545d8829395f5f0e77ceff3dd2673c58a4eb7 Mon Sep 17 00:00:00 2001
From: Jonathan Wang <jonathanpwang@users.noreply.github.com>
Date: Mon, 22 May 2023 19:54:11 -0700
Subject: [PATCH] fix: add better error messages/docs for catching empty inputs

---
 snark-verifier-sdk/src/halo2/aggregation.rs | 4 ++++
 snark-verifier/src/loader/evm/loader.rs     | 2 +-
 snark-verifier/src/loader/halo2/loader.rs   | 1 +
 snark-verifier/src/loader/native.rs         | 2 +-
 4 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/snark-verifier-sdk/src/halo2/aggregation.rs b/snark-verifier-sdk/src/halo2/aggregation.rs
index f361b876..b5dc148d 100644
--- a/snark-verifier-sdk/src/halo2/aggregation.rs
+++ b/snark-verifier-sdk/src/halo2/aggregation.rs
@@ -57,6 +57,9 @@ pub type Halo2Loader<'chip> = loader::halo2::Halo2Loader<G1Affine, BaseFieldEccC
 /// Returns the assigned instances of previous snarks and the new final pair that needs to be verified in a pairing check.
 /// For each previous snark, we concatenate all instances into a single vector. We return a vector of vectors,
 /// one vector per snark, for convenience.
+///
+/// # Assumptions
+/// * `snarks` is not empty
 pub fn aggregate<'a, AS>(
     svk: &Svk,
     loader: &Rc<Halo2Loader<'a>>,
@@ -76,6 +79,7 @@ where
             VerifyingKey = KzgAsVerifyingKey,
         >,
 {
+    assert!(!snarks.is_empty(), "trying to aggregate 0 snarks");
     let assign_instances = |instances: &[Vec<Fr>]| {
         instances
             .iter()
diff --git a/snark-verifier/src/loader/evm/loader.rs b/snark-verifier/src/loader/evm/loader.rs
index f6bf17b2..98ca5ca4 100644
--- a/snark-verifier/src/loader/evm/loader.rs
+++ b/snark-verifier/src/loader/evm/loader.rs
@@ -663,7 +663,7 @@ where
                 _ => ec_point.loader.ec_point_scalar_mul(ec_point, scalar),
             })
             .reduce(|acc, ec_point| acc.loader.ec_point_add(&acc, &ec_point))
-            .unwrap()
+            .expect("pairs should not be empty")
     }
 }
 
diff --git a/snark-verifier/src/loader/halo2/loader.rs b/snark-verifier/src/loader/halo2/loader.rs
index 9a8410d6..31be9841 100644
--- a/snark-verifier/src/loader/halo2/loader.rs
+++ b/snark-verifier/src/loader/halo2/loader.rs
@@ -536,6 +536,7 @@ impl<C: CurveAffine, EccChip: EccInstructions<C>> EcPointLoader<C> for Rc<Halo2L
     fn multi_scalar_multiplication(
         pairs: &[(&<Self as ScalarLoader<C::Scalar>>::LoadedScalar, &EcPoint<C, EccChip>)],
     ) -> EcPoint<C, EccChip> {
+        assert!(!pairs.is_empty(), "multi_scalar_multiplication: pairs is empty");
         let loader = &pairs[0].0.loader;
 
         let (constant, fixed_base, variable_base_non_scaled, variable_base_scaled) =
diff --git a/snark-verifier/src/loader/native.rs b/snark-verifier/src/loader/native.rs
index 96e7239a..783aaa89 100644
--- a/snark-verifier/src/loader/native.rs
+++ b/snark-verifier/src/loader/native.rs
@@ -66,7 +66,7 @@ impl<C: CurveAffine> EcPointLoader<C> for NativeLoader {
             .cloned()
             .map(|(scalar, base)| *base * scalar)
             .reduce(|acc, value| acc + value)
-            .unwrap()
+            .expect("pairs should not be empty")
             .to_affine()
     }
 }