feat(test): Fuzz poseidon hases against an external library (#6273)

# Description

## Problem\*

Related to #6141 

## Summary\*

Testing `std::hash::poseidon::bn254::hash_[1-12]` against
https://github.com/Lightprotocol/light-poseidon/tree/v0.2.0

The library doesn't support inputs wider than 12 (doesn't have the
parameters for it), so the Noir function `hash_[13-16]` are not covered.

## Additional Context



## Documentation\*

Check one:
- [x] No documentation needed.
- [ ] Documentation included in this PR.
- [ ] **[For Experimental Features]** Documentation to be submitted in a
separate PR.

# PR Checklist\*

- [x] I have tested the changes locally.
- [ ] I have formatted the changes with [Prettier](https://prettier.io/)
and/or `cargo fmt` on default settings.

deny.toml

@@ -7,7 +7,7 @@ yanked = "warn"
 
 ignore = [
     "RUSTSEC-2020-0168", # mach unmaintained
-    "RUSTSEC-2020-0016"  # net2 unmaintained
+    "RUSTSEC-2020-0016", # net2 unmaintained
 ]
 
 # This section is considered when running `cargo deny check bans`.
@@ -58,7 +58,7 @@ allow = [
     # bitmaps 2.1.0, im 15.1.0
     "MPL-2.0",
     # Boost Software License
-    "BSL-1.0"
+    "BSL-1.0",
 ]
 
 # Allow 1 or more licenses on a per-crate basis, so that particular licenses
@@ -101,7 +101,4 @@ unknown-git = "deny"
 #
 # crates.io rejects git dependencies so anything depending on these is unpublishable and you'll ruin my day
 # when I find out.
-allow-git = [
-    "https://github.com/jfecher/chumsky",
-    "https://github.com/noir-lang/clap-markdown",
-]
+allow-git = ["https://github.com/noir-lang/clap-markdown"]

tooling/nargo_cli/Cargo.toml

@@ -71,6 +71,7 @@ tracing-appender = "0.2.3"
 tokio-util = { version = "0.7.8", features = ["compat"] }
 
 [dev-dependencies]
+ark-bn254.workspace = true
 tempfile.workspace = true
 dirs.workspace = true
 assert_cmd = "2.0.8"
@@ -85,6 +86,7 @@ sha2.workspace = true
 sha3.workspace = true
 iai = "0.1.1"
 test-binary = "3.0.2"
+light-poseidon = "0.2.0"
 
 
 [[bench]]

tooling/nargo_cli/tests/stdlib-props.rs

@@ -259,23 +259,17 @@ fn fuzz_sha512_equivalence() {
 fn fuzz_poseidon2_equivalence() {
     use bn254_blackbox_solver::poseidon_hash;
 
-    for max_len in [0, 1, 3, 4, 511, 512] {
+    // Test empty, small, then around the RATE value, then bigger inputs.
+    for max_len in [0, 1, 3, 4, 100] {
         let source = format!(
             "fn main(input: [Field; {max_len}], message_size: u32) -> pub Field {{
                 std::hash::poseidon2::Poseidon2::hash(input, message_size)
             }}"
         );
 
         let strategy = (0..=max_len)
-            .prop_flat_map(|len: usize| {
-                // Generate Field elements from random 32 byte vectors.
-                let field = prop::collection::vec(any::<u8>(), 32)
-                    .prop_map(|bytes| FieldElement::from_be_bytes_reduce(&bytes));
-
-                prop::collection::vec(field, len)
-            })
+            .prop_flat_map(field_vec_strategy)
             .prop_map(move |mut msg| {
-                // The output hash is a single field element.
                 let output = poseidon_hash(&msg, msg.len() < max_len).expect("failed to hash");
 
                 // The input has to be padded to the maximum length.
@@ -296,8 +290,49 @@ fn fuzz_poseidon2_equivalence() {
     }
 }
 
+#[test]
+fn fuzz_poseidon_equivalence() {
+    use light_poseidon::{Poseidon, PoseidonHasher};
+
+    let poseidon_hash = |inputs: &[FieldElement]| {
+        let mut poseidon = Poseidon::<ark_bn254::Fr>::new_circom(inputs.len()).unwrap();
+        let frs: Vec<ark_bn254::Fr> = inputs.iter().map(|f| f.into_repr()).collect::<Vec<_>>();
+        let hash = poseidon.hash(&frs).expect("failed to hash");
+        FieldElement::from_repr(hash)
+    };
+
+    // Noir has hashes up to length 16, but the reference library won't work with more than 12.
+    for len in 1..light_poseidon::MAX_X5_LEN {
+        let source = format!(
+            "fn main(input: [Field; {len}]) -> pub Field {{
+                std::hash::poseidon::bn254::hash_{len}(input)
+            }}"
+        );
+
+        let strategy = field_vec_strategy(len)
+            .prop_map(move |msg| {
+                let output = poseidon_hash(&msg);
+                let inputs = vec![("input", InputValue::Vec(vecmap(msg, InputValue::Field)))];
+
+                SnippetInputOutput::new(inputs, InputValue::Field(output))
+                    .with_description(format!("len = {len}"))
+            })
+            .boxed();
+
+        run_snippet_proptest(source.clone(), false, strategy);
+    }
+}
+
 fn bytes_input(bytes: &[u8]) -> InputValue {
     InputValue::Vec(
         bytes.iter().map(|b| InputValue::Field(FieldElement::from(*b as u32))).collect(),
     )
 }
+
+fn field_vec_strategy(len: usize) -> impl Strategy<Value = Vec<FieldElement>> {
+    // Generate Field elements from random 32 byte vectors.
+    let field = prop::collection::vec(any::<u8>(), 32)
+        .prop_map(|bytes| FieldElement::from_be_bytes_reduce(&bytes));
+
+    prop::collection::vec(field, len)
+}