Add support for tracing

Cargo.toml

@@ -32,6 +32,7 @@ byteorder = "1.4.3"
 thiserror = "2.0.11"
 once_cell = "1.18.0"
 itertools = "0.14.0"
+tracing = "0.1"
 
 # Use halo2curves ASM on x86_64 by default; disable ASM on non-x86_64
 [target.'cfg(target_arch = "x86_64")'.dependencies]

README.md

@@ -63,6 +63,37 @@ To run an example:
 cargo run --release --example minroot
 ```
 
+## Logging
+
+This library uses the [`tracing`](https://docs.rs/tracing) crate for structured, leveled logging. It emits tracing events and spans but **does not install a subscriber** — the application decides how (and whether) to consume output. When no subscriber is registered, all tracing macros are no-ops with near-zero overhead.
+
+To see log output, install a `tracing-subscriber` in your application:
+
+```rust
+use tracing_subscriber::EnvFilter;
+
+tracing_subscriber::fmt()
+    .with_env_filter(EnvFilter::from_default_env())
+    .init();
+```
+
+Then control verbosity with the `RUST_LOG` environment variable:
+
+```bash
+RUST_LOG=info cargo test --release ...    # setup complete, compression complete
+RUST_LOG=debug cargo test --release ...   # per-step prove_step, base case, verification
+```
+
+**Tracing levels used:**
+
+| Level   | What it covers |
+|---------|----------------|
+| `info`  | Setup complete, CompressedSNARK generated, constraint counts |
+| `debug` | Per-step prove_step, base case init, verification passed |
+| `warn`  | Validation failures (unused currently — reserved for downstream) |
+
+Applications that depend on this library automatically see these spans nested under their own tracing subscriber with zero integration work.
+
 ## References
 The following paper, which appeared at CRYPTO 2022, provides details of the Nova proof system and a proof of security:
 

src/frontend/gadgets/num.rs

@@ -33,7 +33,7 @@ impl<Scalar: PrimeField> AllocatedNum<Scalar> {
   ///
   /// This is useful when a variable is known to hold a valid field element
   /// due to constraints added separately, enabling zero-cost reinterpretation
-  /// (e.g., wrapping an [`AllocatedBit`](super::boolean::AllocatedBit)'s variable as a number).
+  /// (e.g., wrapping an [`AllocatedBit`]'s variable as a number).
   pub fn from_parts(variable: Variable, value: Option<Scalar>) -> Self {
     AllocatedNum { value, variable }
   }

src/neutron/mod.rs

@@ -21,6 +21,7 @@ use ff::Field;
 use once_cell::sync::OnceCell;
 use rand_core::OsRng;
 use serde::{Deserialize, Serialize};
+use tracing::{debug, info, instrument};
 
 mod circuit;
 pub mod nifs;
@@ -107,6 +108,7 @@ where
   /// let pp = PublicParams::setup(&circuit, ck_hint1, ck_hint2)?;
   /// Ok(())
   /// ```
+  #[instrument(skip_all, name = "neutron::PublicParams::setup")]
   pub fn setup(
     c: &C,
     ck_hint1: &CommitmentKeyHint<E1>,
@@ -131,6 +133,7 @@ where
     // Generate the commitment key
     let ck = R1CSShape::commitment_key(&[&r1cs_shape], &[ck_hint1])?;
 
+    let num_cons = r1cs_shape.num_cons;
     let structure = Structure::new(&r1cs_shape);
 
     let pp = PublicParams {
@@ -148,6 +151,8 @@ where
     // call pp.digest() so the digest is computed here rather than in RecursiveSNARK methods
     let _ = pp.digest();
 
+    info!(num_cons = %num_cons, "setup complete");
+
     Ok(pp)
   }
 
@@ -166,6 +171,7 @@ where
   /// * `ck_hint2`: A `CommitmentKeyHint` for the secondary circuit (unused but kept for API consistency).
   /// * `ptau_dir`: Path to the directory containing pruned ptau files.
   #[cfg(feature = "io")]
+  #[instrument(skip_all, name = "neutron::PublicParams::setup_with_ptau_dir")]
   pub fn setup_with_ptau_dir(
     c: &C,
     ck_hint1: &CommitmentKeyHint<E1>,
@@ -194,6 +200,7 @@ where
     // Load the commitment key from ptau directory
     let ck = R1CSShape::commitment_key_from_ptau_dir(&[&r1cs_shape], &[ck_hint1], ptau_dir)?;
 
+    let num_cons = r1cs_shape.num_cons;
     let structure = Structure::new(&r1cs_shape);
 
     let pp = PublicParams {
@@ -211,6 +218,8 @@ where
     // call pp.digest() so the digest is computed here rather than in RecursiveSNARK methods
     let _ = pp.digest();
 
+    info!(num_cons = %num_cons, "setup complete");
+
     Ok(pp)
   }
 
@@ -256,6 +265,7 @@ where
   C: StepCircuit<E1::Scalar>,
 {
   /// Create new instance of recursive SNARK
+  #[instrument(skip_all, name = "neutron::RecursiveSNARK::new")]
   pub fn new(pp: &PublicParams<E1, E2, C>, c: &C, z0: &[E1::Scalar]) -> Result<Self, NovaError> {
     if z0.len() != pp.F_arity {
       return Err(NovaError::InvalidInitialInputLength);
@@ -291,6 +301,8 @@ where
       .map(|v| v.get_value().ok_or(SynthesisError::AssignmentMissing))
       .collect::<Result<Vec<<E1 as Engine>::Scalar>, _>>()?;
 
+    debug!("base case initialized");
+
     Ok(Self {
       z0: z0.to_vec(),
       r_W: FoldedWitness::default(&pp.structure),
@@ -305,6 +317,7 @@ where
   }
 
   /// Updates the provided `RecursiveSNARK` by executing a step of the incremental computation
+  #[instrument(skip_all, name = "neutron::RecursiveSNARK::prove_step", fields(step = self.i))]
   pub fn prove_step(&mut self, pp: &PublicParams<E1, E2, C>, c: &C) -> Result<(), NovaError> {
     // first step was already done in the constructor
     if self.i == 0 {
@@ -363,10 +376,13 @@ where
     self.l_u = l_u;
     self.l_w = l_w;
 
+    debug!(step = self.i, "step complete");
+
     Ok(())
   }
 
   /// Verify the correctness of the `RecursiveSNARK`
+  #[instrument(skip_all, name = "neutron::RecursiveSNARK::verify", fields(num_steps))]
   pub fn verify(
     &self,
     pp: &PublicParams<E1, E2, C>,
@@ -428,6 +444,8 @@ where
     res_r?;
     res_l?;
 
+    debug!("verification passed");
+
     Ok(self.zi.clone())
   }
 

src/neutron/nifs.rs

@@ -13,6 +13,7 @@ use ff::Field;
 use rand_core::OsRng;
 use rayon::prelude::*;
 use serde::{Deserialize, Serialize};
+use tracing::instrument;
 
 /// An NIFS message from NeutronNova's folding scheme
 #[allow(clippy::upper_case_acronyms)]
@@ -197,6 +198,7 @@ impl<E: Engine> NIFS<E> {
   /// In particular, it requires that `U1` and `U2` are such that the hash of `U1` is stored in the public IO of `U2`.
   /// In this particular setting, this means that if `U2` is absorbed in the RO, it implicitly absorbs `U1` as well.
   /// So the code below avoids absorbing `U1` in the RO.
+  #[instrument(skip_all, name = "neutron::NIFS::prove")]
   pub fn prove(
     ck: &CommitmentKey<E>,
     ro_consts: &RO2Constants<E>,
@@ -294,6 +296,7 @@ impl<E: Engine> NIFS<E> {
   /// with the guarantee that the folded instance `U`
   /// if and only if `U1` and `U2` are satisfiable.
   #[cfg(test)]
+  #[instrument(skip_all, name = "neutron::NIFS::verify")]
   pub fn verify(
     &self,
     ro_consts: &RO2Constants<E>,

src/nova/mod.rs

@@ -28,6 +28,7 @@ use ff::Field;
 use once_cell::sync::OnceCell;
 use rand_core::OsRng;
 use serde::{Deserialize, Serialize};
+use tracing::{debug, info, instrument};
 
 mod circuit;
 pub mod nifs;
@@ -122,6 +123,7 @@ where
   /// Ok(())
   /// # }
   /// ```
+  #[instrument(skip_all, name = "nova::PublicParams::setup")]
   pub fn setup(
     c: &C,
     ck_hint1: &CommitmentKeyHint<E1>,
@@ -159,6 +161,8 @@ where
       return Err(NovaError::InvalidStepCircuitIO);
     }
 
+    let num_cons = r1cs_shape_primary.num_cons;
+
     let pp = PublicParams {
       F_arity,
 
@@ -181,6 +185,8 @@ where
     // call pp.digest() so the digest is computed here rather than in RecursiveSNARK methods
     let _ = pp.digest();
 
+    info!(num_cons = %num_cons, "setup complete");
+
     Ok(pp)
   }
 
@@ -219,6 +225,7 @@ where
   /// )?;
   /// ```
   #[cfg(feature = "io")]
+  #[instrument(skip_all, name = "nova::PublicParams::setup_with_ptau_dir")]
   pub fn setup_with_ptau_dir(
     c: &C,
     ck_hint1: &CommitmentKeyHint<E1>,
@@ -264,6 +271,8 @@ where
       return Err(NovaError::InvalidStepCircuitIO);
     }
 
+    let num_cons = r1cs_shape_primary.num_cons;
+
     let pp = PublicParams {
       F_arity,
 
@@ -286,6 +295,8 @@ where
     // call pp.digest() so the digest is computed here rather than in RecursiveSNARK methods
     let _ = pp.digest();
 
+    info!(num_cons = %num_cons, "setup complete");
+
     Ok(pp)
   }
 
@@ -351,6 +362,7 @@ where
   C: StepCircuit<E1::Scalar>,
 {
   /// Create new instance of recursive SNARK
+  #[instrument(skip_all, name = "nova::RecursiveSNARK::new")]
   pub fn new(pp: &PublicParams<E1, E2, C>, c: &C, z0: &[E1::Scalar]) -> Result<Self, NovaError> {
     if z0.len() != pp.F_arity {
       return Err(NovaError::InvalidInitialInputLength);
@@ -430,6 +442,8 @@ where
       .map(|v| v.get_value().ok_or(SynthesisError::AssignmentMissing))
       .collect::<Result<Vec<<E1 as Engine>::Scalar>, _>>()?;
 
+    debug!("base case initialized");
+
     Ok(Self {
       z0: z0.to_vec(),
 
@@ -453,6 +467,7 @@ where
   }
 
   /// Updates the provided `RecursiveSNARK` by executing a step of the incremental computation
+  #[instrument(skip_all, name = "nova::RecursiveSNARK::prove_step", fields(step = self.i))]
   pub fn prove_step(&mut self, pp: &PublicParams<E1, E2, C>, c: &C) -> Result<(), NovaError> {
     // first step was already done in the constructor
     if self.i == 0 {
@@ -560,10 +575,13 @@ where
     self.ri_primary = r_next_primary;
     self.ri_secondary = r_next_secondary;
 
+    debug!(step = self.i, "step complete");
+
     Ok(())
   }
 
   /// Verify the correctness of the `RecursiveSNARK`
+  #[instrument(skip_all, name = "nova::RecursiveSNARK::verify", fields(num_steps))]
   pub fn verify(
     &self,
     pp: &PublicParams<E1, E2, C>,
@@ -661,6 +679,8 @@ where
     res_r_secondary?;
     res_l_secondary?;
 
+    debug!("verification passed");
+
     Ok(self.zi.clone())
   }
 
@@ -759,6 +779,7 @@ where
   S2: RelaxedR1CSSNARKTrait<E2>,
 {
   /// Creates prover and verifier keys for `CompressedSNARK`
+  #[instrument(skip_all, name = "nova::CompressedSNARK::setup")]
   pub fn setup(
     pp: &PublicParams<E1, E2, C>,
   ) -> Result<(ProverKey<E1, E2, C, S1, S2>, VerifierKey<E1, E2, C, S1, S2>), NovaError> {
@@ -783,10 +804,13 @@ where
       _p: Default::default(),
     };
 
+    info!("CompressedSNARK setup complete");
+
     Ok((pk, vk))
   }
 
   /// Create a new `CompressedSNARK` (provides zero-knowledge)
+  #[instrument(skip_all, name = "nova::CompressedSNARK::prove")]
   pub fn prove(
     pp: &PublicParams<E1, E2, C>,
     pk: &ProverKey<E1, E2, C, S1, S2>,
@@ -877,6 +901,8 @@ where
       },
     );
 
+    info!("CompressedSNARK proof generated");
+
     Ok(Self {
       r_U_secondary: recursive_snark.r_U_secondary.clone(),
       ri_secondary: recursive_snark.ri_secondary,
@@ -906,6 +932,7 @@ where
   }
 
   /// Verify the correctness of the `CompressedSNARK` (provides zero-knowledge)
+  #[instrument(skip_all, name = "nova::CompressedSNARK::verify", fields(num_steps))]
   pub fn verify(
     &self,
     vk: &VerifierKey<E1, E2, C, S1, S2>,
@@ -1021,6 +1048,8 @@ where
     res_primary?;
     res_secondary?;
 
+    debug!("CompressedSNARK verification passed");
+
     Ok(self.zn.clone())
   }
 }

src/nova/nifs.rs

@@ -11,6 +11,7 @@ use crate::{
 use ff::Field;
 use rand_core::OsRng;
 use serde::{Deserialize, Serialize};
+use tracing::instrument;
 
 /// An NIFS message from Nova's folding scheme
 #[allow(clippy::upper_case_acronyms)]
@@ -33,6 +34,7 @@ impl<E: Engine> NIFS<E> {
   /// In particular, it requires that `U1` and `U2` are such that the hash of `U1` is stored in the public IO of `U2`.
   /// In this particular setting, this means that if `U2` is absorbed in the RO, it implicitly absorbs `U1` as well.
   /// So the code below avoids absorbing `U1` in the RO.
+  #[instrument(skip_all, name = "nova::NIFS::prove")]
   pub fn prove(
     ck: &CommitmentKey<E>,
     ro_consts: &ROConstants<E>,
@@ -77,6 +79,7 @@ impl<E: Engine> NIFS<E> {
   /// and outputs a folded instance `U` with the same shape,
   /// with the guarantee that the folded instance `U`
   /// if and only if `U1` and `U2` are satisfiable.
+  #[instrument(skip_all, name = "nova::NIFS::verify")]
   pub fn verify(
     &self,
     ro_consts: &ROConstants<E>,
@@ -117,6 +120,7 @@ pub struct NIFSRelaxed<E: Engine> {
 
 impl<E: Engine> NIFSRelaxed<E> {
   /// Same as `prove`, but takes two Relaxed R1CS Instance/Witness pairs
+  #[instrument(skip_all, name = "nova::NIFSRelaxed::prove")]
   pub fn prove(
     ck: &CommitmentKey<E>,
     ro_consts: &ROConstants<E>,
@@ -167,6 +171,7 @@ impl<E: Engine> NIFSRelaxed<E> {
   }
 
   /// Same as `verify`, but takes two Relaxed R1CS Instance/Witness pairs
+  #[instrument(skip_all, name = "nova::NIFSRelaxed::verify")]
   pub fn verify(
     &self,
     ro_consts: &ROConstants<E>,