Add bounds check to Assignment::query_instance impls.

src/dev.rs

@@ -297,6 +297,10 @@ impl<F: Field + Group> Assignment<F> for MockProver<F> {
     }
 
     fn query_instance(&self, column: Column<Instance>, row: usize) -> Result<Option<F>, Error> {
+        if !self.usable_rows.contains(&row) {
+            return Err(Error::BoundsFailure);
+        }
+
         self.instance
             .get(column.index())
             .and_then(|column| column.get(row))

src/dev/graph/layout.rs

@@ -308,8 +308,6 @@ impl<F: Field> Assignment<F> for Layout {
         self.assign_fixed(annotation, selector.0, row, || Ok(F::one()))
     }
 
-    /// Query the value of the cell of an instance column at a particular
-    /// absolute row, if known.
     fn query_instance(&self, _: Column<Instance>, _: usize) -> Result<Option<F>, Error> {
         Ok(None)
     }

src/plonk/keygen.rs

@@ -83,7 +83,11 @@ impl<F: Field> Assignment<F> for Assembly<F> {
         self.assign_fixed(annotation, selector.0, row, || Ok(F::one()))
     }
 
-    fn query_instance(&self, _: Column<Instance>, _: usize) -> Result<Option<F>, Error> {
+    fn query_instance(&self, _: Column<Instance>, row: usize) -> Result<Option<F>, Error> {
+        if !self.usable_rows.contains(&row) {
+            return Err(Error::BoundsFailure);
+        }
+
         // There is no instance in this context.
         Ok(None)
     }

src/plonk/prover.rs

@@ -166,6 +166,10 @@ pub fn create_proof<
                     column: Column<Instance>,
                     row: usize,
                 ) -> Result<Option<F>, Error> {
+                    if !self.usable_rows.contains(&row) {
+                        return Err(Error::BoundsFailure);
+                    }
+
                     self.instances
                         .get(column.index())
                         .and_then(|column| column.get(row))