fix: Overflowing assignment will result in an error

crates/nargo_cli/tests/compile_failure/overflowing_assignment/Nargo.toml

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

crates/nargo_cli/tests/compile_failure/overflowing_assignment/src/main.nr

@@ -0,0 +1,5 @@
+fn main() {
+    let x:u8 = -1;
+    let y:u8 = 300;
+    assert(x!=y);
+}

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

@@ -1,3 +1,4 @@
+use acvm::FieldElement;
 use noirc_errors::CustomDiagnostic as Diagnostic;
 use noirc_errors::Span;
 use thiserror::Error;
@@ -29,6 +30,8 @@ pub enum Source {
 pub enum TypeCheckError {
     #[error("Operator {op:?} cannot be used in a {place:?}")]
     OpCannotBeUsed { op: HirBinaryOp, place: &'static str, span: Span },
+    #[error("The literal `{expr:?}` cannot fit into `{ty}` which has range `{range}`")]
+    OverflowingAssignment { expr: FieldElement, ty: Type, range: String, span: Span },
     #[error("Type {typ:?} cannot be used in a {place:?}")]
     TypeCannotBeUsed { typ: Type, place: &'static str, span: Span },
     #[error("Expected type {expected_typ:?} is not the same as {expr_typ:?}")]
@@ -170,7 +173,8 @@ impl From<TypeCheckError> for Diagnostic {
             | TypeCheckError::IntegerTypeMismatch { span, .. }
             | TypeCheckError::FieldComparison { span, .. }
             | TypeCheckError::AmbiguousBitWidth { span, .. }
-            | TypeCheckError::IntegerAndFieldBinaryOperation { span } => {
+            | TypeCheckError::IntegerAndFieldBinaryOperation { span }
+            | TypeCheckError::OverflowingAssignment { span, .. } => {
                 Diagnostic::simple_error(error.to_string(), String::new(), span)
             }
             TypeCheckError::PublicReturnType { typ, span } => Diagnostic::simple_error(

crates/noirc_frontend/src/hir/type_check/stmt.rs

@@ -1,6 +1,6 @@
 use noirc_errors::{Location, Span};
 
-use crate::hir_def::expr::HirIdent;
+use crate::hir_def::expr::{HirExpression, HirIdent, HirLiteral};
 use crate::hir_def::stmt::{
     HirAssignStatement, HirConstrainStatement, HirLValue, HirLetStatement, HirPattern, HirStatement,
 };
@@ -259,9 +259,39 @@ impl<'interner> TypeChecker<'interner> {
                     expr_span,
                 }
             });
+            if annotated_type.is_unsigned() {
+                self.lint_overflowing_uint(&rhs_expr, &annotated_type);
+            }
             annotated_type
         } else {
             expr_type
         }
     }
+
+    /// Check if an assignment is overflowing with respect to `annotated_type`
+    /// in a declaration statement where `annotated_type` is an unsigned integer
+    fn lint_overflowing_uint(&mut self, rhs_expr: &ExprId, annotated_type: &Type) {
+        let expr = self.interner.expression(rhs_expr);
+        let span = self.interner.expr_span(rhs_expr);
+        match expr {
+            HirExpression::Literal(HirLiteral::Integer(value)) => {
+                let v = value.to_u128();
+                if let Type::Integer(_, bit_count) = annotated_type {
+                    let max = 1 << bit_count;
+                    if v >= max {
+                        self.errors.push(TypeCheckError::OverflowingAssignment {
+                            expr: value,
+                            ty: annotated_type.clone(),
+                            range: format!("0..={}", max - 1),
+                            span,
+                        });
+                    };
+                };
+            }
+            HirExpression::Prefix(_) => self
+                .errors
+                .push(TypeCheckError::InvalidUnaryOp { kind: annotated_type.to_string(), span }),
+            _ => {}
+        }
+    }
 }

crates/noirc_frontend/src/hir_def/types.rs

@@ -447,6 +447,10 @@ impl Type {
         matches!(self.follow_bindings(), Type::Integer(Signedness::Signed, _))
     }
 
+    pub fn is_unsigned(&self) -> bool {
+        matches!(self.follow_bindings(), Type::Integer(Signedness::Unsigned, _))
+    }
+
     fn contains_numeric_typevar(&self, target_id: TypeVariableId) -> bool {
         // True if the given type is a NamedGeneric with the target_id
         let named_generic_id_matches_target = |typ: &Type| {