fix: disable modulo for fields (#3009)

compiler/noirc_frontend/src/ast/expression.rs

@@ -273,6 +273,10 @@ impl BinaryOpKind {
     pub fn is_bit_shift(&self) -> bool {
         matches!(self, BinaryOpKind::ShiftRight | BinaryOpKind::ShiftLeft)
     }
+
+    pub fn is_modulo(&self) -> bool {
+        matches!(self, BinaryOpKind::Modulo)
+    }
 }
 
 #[derive(PartialEq, PartialOrd, Eq, Ord, Hash, Debug, Copy, Clone)]

compiler/noirc_frontend/src/hir/type_check/errors.rs

@@ -78,6 +78,8 @@ pub enum TypeCheckError {
     IntegerTypeMismatch { typ: Type, span: Span },
     #[error("Cannot use an integer and a Field in a binary operation, try converting the Field into an integer first")]
     IntegerAndFieldBinaryOperation { span: Span },
+    #[error("Cannot do modulo on Fields, try casting to an integer first")]
+    FieldModulo { span: Span },
     #[error("Fields cannot be compared, try casting to an integer first")]
     FieldComparison { span: Span },
     #[error("The number of bits to use for this bitwise operation is ambiguous. Either the operand's type or return type should be specified")]
@@ -195,7 +197,8 @@ impl From<TypeCheckError> for Diagnostic {
             | TypeCheckError::FieldComparison { span, .. }
             | TypeCheckError::AmbiguousBitWidth { span, .. }
             | TypeCheckError::IntegerAndFieldBinaryOperation { span }
-            | TypeCheckError::OverflowingAssignment { span, .. } => {
+            | TypeCheckError::OverflowingAssignment { span, .. }
+            | TypeCheckError::FieldModulo { span } => {
                 Diagnostic::simple_error(error.to_string(), String::new(), span)
             }
             TypeCheckError::PublicReturnType { typ, span } => Diagnostic::simple_error(

compiler/noirc_frontend/src/hir/type_check/expr.rs

@@ -11,7 +11,7 @@ use crate::{
         types::Type,
     },
     node_interner::{DefinitionKind, ExprId, FuncId, TraitMethodId},
-    Signedness, TypeBinding, TypeVariableKind, UnaryOp,
+    BinaryOpKind, Signedness, TypeBinding, TypeVariableKind, UnaryOp,
 };
 
 use super::{errors::TypeCheckError, TypeChecker};
@@ -974,16 +974,20 @@ impl<'interner> TypeChecker<'interner> {
                 if let TypeBinding::Bound(binding) = &*int.borrow() {
                     return self.infix_operand_type_rules(binding, op, other, span);
                 }
-
-                if op.is_bitwise() && (other.is_bindable() || other.is_field()) {
+                if (op.is_modulo() || op.is_bitwise()) && (other.is_bindable() || other.is_field())
+                {
                     let other = other.follow_bindings();
                     let kind = op.kind;
                     // This will be an error if these types later resolve to a Field, or stay
                     // polymorphic as the bit size will be unknown. Delay this error until the function
                     // finishes resolving so we can still allow cases like `let x: u8 = 1 << 2;`.
                     self.push_delayed_type_check(Box::new(move || {
                         if other.is_field() {
-                            Err(TypeCheckError::InvalidBitwiseOperationOnField { span })
+                            if kind == BinaryOpKind::Modulo {
+                                Err(TypeCheckError::FieldModulo { span })
+                            } else {
+                                Err(TypeCheckError::InvalidBitwiseOperationOnField { span })
+                            }
                         } else if other.is_bindable() {
                             Err(TypeCheckError::AmbiguousBitWidth { span })
                         } else if kind.is_bit_shift() && other.is_signed() {
@@ -1054,6 +1058,9 @@ impl<'interner> TypeChecker<'interner> {
                 if op.is_bitwise() {
                     return Err(TypeCheckError::InvalidBitwiseOperationOnField { span });
                 }
+                if op.is_modulo() {
+                    return Err(TypeCheckError::FieldModulo { span });
+                }
                 Ok(FieldElement)
             }
 

compiler/noirc_frontend/src/hir_def/expr.rs

@@ -68,6 +68,10 @@ impl HirBinaryOp {
     pub fn is_bit_shift(&self) -> bool {
         self.kind.is_bit_shift()
     }
+
+    pub fn is_modulo(&self) -> bool {
+        self.kind.is_modulo()
+    }
 }
 
 #[derive(Debug, Clone)]

tooling/nargo_cli/tests/compile_failure/field_modulo/Nargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "field_modulo"
+type = "bin"
+authors = [""]
+compiler_version = "0.9.0"
+
+[dependencies]

tooling/nargo_cli/tests/compile_failure/field_modulo/src/main.nr

@@ -0,0 +1,4 @@
+
+fn main(x: Field) -> pub Field {
+    x % 2
+}

tooling/nargo_cli/tests/execution_success/arithmetic_binary_operations/src/main.nr

@@ -4,8 +4,7 @@
 // Binary addition, multiplication, division, constant modulo
 // x = 3, y = 4, z = 5
 fn main(x : Field, y : Field, z : Field) -> pub Field {
-    //constant modulo
-    assert(x % 2 == 1);
+    //cast
     assert(y as u1 == 0);
 
     let a = x + x; // 3 + 3 = 6