Add test cases exercising Error::NotEnoughColumnsForConstants

src/circuit/floor_planner/single_pass.rs

@@ -305,3 +305,58 @@ impl<'r, 'a, F: Field, CS: Assignment<F> + 'a> RegionLayouter<F>
         Ok(())
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use pasta_curves::vesta;
+
+    use super::SimpleFloorPlanner;
+    use crate::{
+        dev::MockProver,
+        plonk::{Advice, Circuit, Column, Error},
+    };
+
+    #[test]
+    fn not_enough_columns_for_constants() {
+        struct MyCircuit {}
+
+        impl Circuit<vesta::Scalar> for MyCircuit {
+            type Config = Column<Advice>;
+            type FloorPlanner = SimpleFloorPlanner;
+
+            fn without_witnesses(&self) -> Self {
+                MyCircuit {}
+            }
+
+            fn configure(meta: &mut crate::plonk::ConstraintSystem<vesta::Scalar>) -> Self::Config {
+                meta.advice_column()
+            }
+
+            fn synthesize(
+                &self,
+                config: Self::Config,
+                mut layouter: impl crate::circuit::Layouter<vesta::Scalar>,
+            ) -> Result<(), crate::plonk::Error> {
+                layouter.assign_region(
+                    || "assign constant",
+                    |mut region| {
+                        region.assign_advice_from_constant(
+                            || "one",
+                            config,
+                            0,
+                            vesta::Scalar::one(),
+                        )
+                    },
+                )?;
+
+                Ok(())
+            }
+        }
+
+        let circuit = MyCircuit {};
+        assert_eq!(
+            MockProver::run(3, &circuit, vec![]).unwrap_err(),
+            Error::NotEnoughColumnsForConstants,
+        );
+    }
+}

src/circuit/floor_planner/v1.rs

@@ -414,3 +414,57 @@ impl<'r, 'a, F: Field, CS: Assignment<F> + 'a> RegionLayouter<F> for V1Region<'r
         Ok(())
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use pasta_curves::vesta;
+
+    use crate::{
+        dev::MockProver,
+        plonk::{Advice, Circuit, Column, Error},
+    };
+
+    #[test]
+    fn not_enough_columns_for_constants() {
+        struct MyCircuit {}
+
+        impl Circuit<vesta::Scalar> for MyCircuit {
+            type Config = Column<Advice>;
+            type FloorPlanner = super::V1;
+
+            fn without_witnesses(&self) -> Self {
+                MyCircuit {}
+            }
+
+            fn configure(meta: &mut crate::plonk::ConstraintSystem<vesta::Scalar>) -> Self::Config {
+                meta.advice_column()
+            }
+
+            fn synthesize(
+                &self,
+                config: Self::Config,
+                mut layouter: impl crate::circuit::Layouter<vesta::Scalar>,
+            ) -> Result<(), crate::plonk::Error> {
+                layouter.assign_region(
+                    || "assign constant",
+                    |mut region| {
+                        region.assign_advice_from_constant(
+                            || "one",
+                            config,
+                            0,
+                            vesta::Scalar::one(),
+                        )
+                    },
+                )?;
+
+                Ok(())
+            }
+        }
+
+        let circuit = MyCircuit {};
+        assert_eq!(
+            MockProver::run(3, &circuit, vec![]).unwrap_err(),
+            Error::NotEnoughColumnsForConstants,
+        );
+    }
+}

src/plonk.rs

@@ -134,7 +134,7 @@ pub struct ProvingKey<C: CurveAffine> {
 
 /// This is an error that could occur during proving or circuit synthesis.
 // TODO: these errors need to be cleaned up
-#[derive(Debug)]
+#[derive(Debug, PartialEq)]
 pub enum Error {
     /// This is an error that can occur during synthesis of the circuit, for
     /// example, when the witness is not present.