From 574b5e644eafdac7ea8b27a18eb46da45ed3ceed Mon Sep 17 00:00:00 2001
From: Jonathan Wang <31040440+jonathanpwang@users.noreply.github.com>
Date: Tue, 25 Jul 2023 18:44:12 -0600
Subject: [PATCH] fix: `RlpThreadBuilder` assign constraints when no RLC
 columns (#19)

---
 axiom-eth/src/rlp/builder.rs | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/axiom-eth/src/rlp/builder.rs b/axiom-eth/src/rlp/builder.rs
index 6a490192..cc14f000 100644
--- a/axiom-eth/src/rlp/builder.rs
+++ b/axiom-eth/src/rlp/builder.rs
@@ -174,22 +174,19 @@ impl<F: ScalarField> RlcThreadBuilder<F> {
         }: KeygenAssignments<F>,
     ) -> KeygenAssignments<F> {
         assert!(!self.witness_gen_only());
-        if rlc.basic_gates.is_empty() {
-            return KeygenAssignments { assigned_advices, assigned_constants, break_points };
-        }
         let use_unknown = self.use_unknown();
         let max_rows = gate.max_rows;
 
         // first we assign all RLC contexts, basically copying gate::builder::assign_all except that the length of the RLC vertical gate is 3 instead of 4 (which was length of basic gate)
         let mut gate_index = 0;
         let mut row_offset = 0;
-        let mut basic_gate = rlc.basic_gates[0];
+        let mut basic_gate = None;
         for ctx in self.threads_rlc.iter() {
             // TODO: if we have more similar vertical gates this should be refactored into a general function
             for (i, (&advice, &q)) in
                 ctx.advice.iter().zip(ctx.selector.iter().chain(iter::repeat(&false))).enumerate()
             {
-                let (mut column, mut q_rlc) = basic_gate;
+                let (mut column, mut q_rlc) = basic_gate.unwrap_or(rlc.basic_gates[gate_index]);
                 let value = if use_unknown { Value::unknown() } else { Value::known(advice) };
                 #[cfg(feature = "halo2-axiom")]
                 let cell = *region.assign_advice(column, row_offset, value).cell();
@@ -203,11 +200,11 @@ impl<F: ScalarField> RlcThreadBuilder<F> {
                     row_offset = 0;
                     gate_index += 1;
                     // when there is a break point, because we may have two gates that overlap at the current cell, we must copy the current cell to the next column for safety
-                    basic_gate = *rlc
+                    basic_gate = Some(*rlc
                         .basic_gates
                         .get(gate_index)
-                        .unwrap_or_else(|| panic!("NOT ENOUGH RLC ADVICE COLUMNS. Perhaps blinding factors were not taken into account. The max non-poisoned rows is {max_rows}"));
-                    (column, q_rlc) = basic_gate;
+                        .unwrap_or_else(|| panic!("NOT ENOUGH RLC ADVICE COLUMNS. Perhaps blinding factors were not taken into account. The max non-poisoned rows is {max_rows}")));
+                    (column, q_rlc) = basic_gate.unwrap();
 
                     #[cfg(feature = "halo2-axiom")]
                     {
@@ -232,7 +229,7 @@ impl<F: ScalarField> RlcThreadBuilder<F> {
         }
         // in order to constrain equalities and assign constants, we copy the RLC equality constraints into the gate builder (it doesn't matter which context the equalities are in), so `GateThreadBuilder::assign_all` can take care of it
         // the phase doesn't matter for equality constraints, so we use phase 0 since we're sure there's a main context there
-        let main_ctx = self.gate_builder.main(0);
+        let main_ctx = self.gate_builder.main(FIRST_PHASE);
         for ctx in self.threads_rlc.iter_mut() {
             main_ctx.advice_equality_constraints.append(&mut ctx.advice_equality_constraints);
             main_ctx.constant_equality_constraints.append(&mut ctx.constant_equality_constraints);