Early exit in error callback from Wasm (#9)

* Early exit in error callback from Wasm

This avoids Wasm execution hanging due to problems such as wrong public
input.

Mimics circom_runtime behaviour with less detailed debug information.

See https://github.com/iden3/circom_runtime/blob/master/js/witness_calculator.js#L52-L64

Adds test for wrong public input. Without early exit, the test stalls.
With it, the Circom build step fails as expected.

* chore: clean up error handling

* ci: add caching

Co-authored-by: Georgios Konstantopoulos <me@gakonst.com>

tests/groth16.rs

@@ -37,3 +37,24 @@ fn groth16_proof() -> Result<()> {
 
     Ok(())
 }
+
+#[test]
+fn groth16_proof_wrong_input() {
+    let cfg = CircomConfig::<Bn254>::new(
+        "./test-vectors/mycircuit.wasm",
+        "./test-vectors/mycircuit.r1cs",
+    )
+    .unwrap();
+    let mut builder = CircomBuilder::new(cfg);
+    builder.push_input("a", 3);
+    // This isn't a public input to the circuit, should faild
+    builder.push_input("foo", 11);
+
+    // create an empty instance for setting it up
+    let circom = builder.setup();
+
+    let mut rng = thread_rng();
+    let _params = generate_random_parameters::<Bn254, _, _>(circom, &mut rng).unwrap();
+
+    builder.build().unwrap_err();
+}