Add name field to Layouter::assign_region

src/circuit.rs

@@ -146,12 +146,13 @@ pub trait Layouter<C: Chip> {
     /// closure, the `Layouter` is allowed to optimise as it sees fit.
     ///
     /// ```ignore
-    /// fn assign_region(&mut self, |region| {
+    /// fn assign_region(&mut self, || "region name", |region| {
     ///     region.assign_advice(self.config.a, offset, || { Some(value)});
     /// });
     /// ```
-    fn assign_region(
+    fn assign_region<A, N, NR>(&mut self, name: N, assignment: A) -> Result<(), Error>
-        &mut self,
+    where
-        assignment: impl FnMut(Region<'_, C>) -> Result<(), Error>,
+        A: FnMut(Region<'_, C>) -> Result<(), Error>,
-    ) -> Result<(), Error>;
+        N: Fn() -> NR,
+        NR: Into<String>;
 }

src/circuit/layouter.rs

@@ -104,10 +104,12 @@ impl<'a, C: Chip, CS: Assignment<C::Field> + 'a> Layouter<C> for SingleChip<'a,
         &self.config
     }
 
-    fn assign_region(
+    fn assign_region<A, N, NR>(&mut self, name: N, mut assignment: A) -> Result<(), Error>
-        &mut self,
+    where
-        mut assignment: impl FnMut(Region<'_, C>) -> Result<(), Error>,
+        A: FnMut(Region<'_, C>) -> Result<(), Error>,
-    ) -> Result<(), Error> {
+        N: Fn() -> NR,
+        NR: Into<String>,
+    {
         let region_index = self.regions.len();
 
         // Get shape of the region.
@@ -130,11 +132,13 @@ impl<'a, C: Chip, CS: Assignment<C::Field> + 'a> Layouter<C> for SingleChip<'a,
             self.columns.insert(column, region_start + shape.row_count);
         }
 
+        self.cs.enter_region(name);
         let mut region = SingleChipRegion::new(self, region_index);
         {
             let region: &mut dyn RegionLayouter<C> = &mut region;
             assignment(region.into())?;
         }
+        self.cs.exit_region();
 
         Ok(())
     }

src/dev.rs

@@ -147,6 +147,15 @@ pub struct MockProver<F: Group> {
 }
 
 impl<F: Field + Group> Assignment<F> for MockProver<F> {
+    fn enter_region<NR, N>(&mut self, _: N)
+    where
+        NR: Into<String>,
+        N: FnOnce() -> NR,
+    {
+    }
+
+    fn exit_region(&mut self) {}
+
     fn assign_advice<V, A, AR>(
         &mut self,
         _: A,

src/plonk/circuit.rs

@@ -126,6 +126,27 @@ impl TryFrom<Column<Any>> for Column<Aux> {
 /// This trait allows a [`Circuit`] to direct some backend to assign a witness
 /// for a constraint system.
 pub trait Assignment<F: Field> {
+    /// Creates a new region and enters into it.
+    ///
+    /// Panics if we are currently in a region (if `exit_region` was not called).
+    ///
+    /// Not intended for downstream consumption; use [`Layouter::assign_region`] instead.
+    ///
+    /// [`Layouter::assign_region`]: crate::circuit::Layouter#method.assign_region
+    fn enter_region<NR, N>(&mut self, name_fn: N)
+    where
+        NR: Into<String>,
+        N: FnOnce() -> NR;
+
+    /// Exits the current region.
+    ///
+    /// Panics if we are not currently in a region (if `enter_region` was not called).
+    ///
+    /// Not intended for downstream consumption; use [`Layouter::assign_region`] instead.
+    ///
+    /// [`Layouter::assign_region`]: crate::circuit::Layouter#method.assign_region
+    fn exit_region(&mut self);
+
     /// Assign an advice column value (witness)
     fn assign_advice<V, A, AR>(
         &mut self,

src/plonk/keygen.rs

@@ -64,6 +64,18 @@ struct Assembly<F: Field> {
 }
 
 impl<F: Field> Assignment<F> for Assembly<F> {
+    fn enter_region<NR, N>(&mut self, _: N)
+    where
+        NR: Into<String>,
+        N: FnOnce() -> NR,
+    {
+        // Do nothing; we don't care about regions in this context.
+    }
+
+    fn exit_region(&mut self) {
+        // Do nothing; we don't care about regions in this context.
+    }
+
     fn assign_advice<V, A, AR>(
         &mut self,
         _: A,

src/plonk/prover.rs

@@ -100,6 +100,18 @@ pub fn create_proof<C: CurveAffine, T: TranscriptWrite<C>, ConcreteCircuit: Circ
             }
 
             impl<F: Field> Assignment<F> for WitnessCollection<F> {
+                fn enter_region<NR, N>(&mut self, _: N)
+                where
+                    NR: Into<String>,
+                    N: FnOnce() -> NR,
+                {
+                    // Do nothing; we don't care about regions in this context.
+                }
+
+                fn exit_region(&mut self) {
+                    // Do nothing; we don't care about regions in this context.
+                }
+
                 fn assign_advice<V, A, AR>(
                     &mut self,
                     _: A,