fix!: Make for loops a statement (noir-lang#2975)

compiler/noirc_frontend/src/ast/expression.rs

@@ -22,7 +22,6 @@ pub enum ExpressionKind {
     MemberAccess(Box<MemberAccessExpression>),
     Cast(Box<CastExpression>),
     Infix(Box<InfixExpression>),
-    For(Box<ForExpression>),
     If(Box<IfExpression>),
     Variable(Path),
     Tuple(Vec<Expression>),
@@ -181,14 +180,6 @@ impl Expression {
     }
 }
 
-#[derive(Debug, PartialEq, Eq, Clone)]
-pub struct ForExpression {
-    pub identifier: Ident,
-    pub start_range: Expression,
-    pub end_range: Expression,
-    pub block: Expression,
-}
-
 pub type BinaryOp = Spanned<BinaryOpKind>;
 
 #[derive(PartialEq, PartialOrd, Eq, Ord, Hash, Debug, Copy, Clone)]
@@ -469,7 +460,6 @@ impl Display for ExpressionKind {
             MethodCall(call) => call.fmt(f),
             Cast(cast) => cast.fmt(f),
             Infix(infix) => infix.fmt(f),
-            For(for_loop) => for_loop.fmt(f),
             If(if_expr) => if_expr.fmt(f),
             Variable(path) => path.fmt(f),
             Constructor(constructor) => constructor.fmt(f),
@@ -603,16 +593,6 @@ impl Display for BinaryOpKind {
     }
 }
 
-impl Display for ForExpression {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        write!(
-            f,
-            "for {} in {} .. {} {}",
-            self.identifier, self.start_range, self.end_range, self.block
-        )
-    }
-}
-
 impl Display for IfExpression {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         write!(f, "if {} {}", self.condition, self.consequence)?;

compiler/noirc_frontend/src/ast/statement.rs

@@ -23,6 +23,7 @@ pub enum Statement {
     Constrain(ConstrainStatement),
     Expression(Expression),
     Assign(AssignStatement),
+    For(ForLoopStatement),
     // This is an expression with a trailing semi-colon
     Semi(Expression),
     // This statement is the result of a recovered parse error.
@@ -65,13 +66,13 @@ impl Statement {
                 }
                 self
             }
+            // A semicolon on a for loop is optional and does nothing
+            Statement::For(_) => self,
 
             Statement::Expression(expr) => {
                 match (&expr.kind, semi, last_statement_in_block) {
                     // Semicolons are optional for these expressions
-                    (ExpressionKind::Block(_), semi, _)
-                    | (ExpressionKind::For(_), semi, _)
-                    | (ExpressionKind::If(_), semi, _) => {
+                    (ExpressionKind::Block(_), semi, _) | (ExpressionKind::If(_), semi, _) => {
                         if semi.is_some() {
                             Statement::Semi(expr)
                         } else {
@@ -459,13 +460,22 @@ impl LValue {
     }
 }
 
+#[derive(Debug, PartialEq, Eq, Clone)]
+pub struct ForLoopStatement {
+    pub identifier: Ident,
+    pub start_range: Expression,
+    pub end_range: Expression,
+    pub block: Expression,
+}
+
 impl Display for Statement {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         match self {
             Statement::Let(let_statement) => let_statement.fmt(f),
             Statement::Constrain(constrain) => constrain.fmt(f),
             Statement::Expression(expression) => expression.fmt(f),
             Statement::Assign(assign) => assign.fmt(f),
+            Statement::For(for_loop) => for_loop.fmt(f),
             Statement::Semi(semi) => write!(f, "{semi};"),
             Statement::Error => write!(f, "Error"),
         }
@@ -544,3 +554,13 @@ impl Display for Pattern {
         }
     }
 }
+
+impl Display for ForLoopStatement {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(
+            f,
+            "for {} in {} .. {} {}",
+            self.identifier, self.start_range, self.end_range, self.block
+        )
+    }
+}

compiler/noirc_frontend/src/hir/resolution/resolver.rs

@@ -13,9 +13,9 @@
 // XXX: Resolver does not check for unused functions
 use crate::hir_def::expr::{
     HirArrayLiteral, HirBinaryOp, HirBlockExpression, HirCallExpression, HirCapturedVar,
-    HirCastExpression, HirConstructorExpression, HirExpression, HirForExpression, HirIdent,
-    HirIfExpression, HirIndexExpression, HirInfixExpression, HirLambda, HirLiteral,
-    HirMemberAccess, HirMethodCallExpression, HirPrefixExpression,
+    HirCastExpression, HirConstructorExpression, HirExpression, HirIdent, HirIfExpression,
+    HirIndexExpression, HirInfixExpression, HirLambda, HirLiteral, HirMemberAccess,
+    HirMethodCallExpression, HirPrefixExpression,
 };
 
 use crate::hir_def::traits::{Trait, TraitConstraint};
@@ -26,7 +26,7 @@ use std::rc::Rc;
 
 use crate::graph::CrateId;
 use crate::hir::def_map::{LocalModuleId, ModuleDefId, TryFromModuleDefId, MAIN_FUNCTION};
-use crate::hir_def::stmt::{HirAssignStatement, HirLValue, HirPattern};
+use crate::hir_def::stmt::{HirAssignStatement, HirForStatement, HirLValue, HirPattern};
 use crate::node_interner::{
     DefinitionId, DefinitionKind, ExprId, FuncId, NodeInterner, StmtId, StructId, TraitId,
 };
@@ -957,6 +957,25 @@ impl<'a> Resolver<'a> {
                 let stmt = HirAssignStatement { lvalue: identifier, expression };
                 HirStatement::Assign(stmt)
             }
+            Statement::For(for_loop) => {
+                let start_range = self.resolve_expression(for_loop.start_range);
+                let end_range = self.resolve_expression(for_loop.end_range);
+                let (identifier, block) = (for_loop.identifier, for_loop.block);
+
+                // TODO: For loop variables are currently mutable by default since we haven't
+                //       yet implemented syntax for them to be optionally mutable.
+                let (identifier, block) = self.in_new_scope(|this| {
+                    let decl = this.add_variable_decl(
+                        identifier,
+                        false,
+                        true,
+                        DefinitionKind::Local(None),
+                    );
+                    (decl, this.resolve_expression(block))
+                });
+
+                HirStatement::For(HirForStatement { start_range, end_range, block, identifier })
+            }
             Statement::Error => HirStatement::Error,
         }
     }
@@ -1169,30 +1188,6 @@ impl<'a> Resolver<'a> {
                 lhs: self.resolve_expression(cast_expr.lhs),
                 r#type: self.resolve_type(cast_expr.r#type),
             }),
-            ExpressionKind::For(for_expr) => {
-                let start_range = self.resolve_expression(for_expr.start_range);
-                let end_range = self.resolve_expression(for_expr.end_range);
-                let (identifier, block) = (for_expr.identifier, for_expr.block);
-
-                // TODO: For loop variables are currently mutable by default since we haven't
-                //       yet implemented syntax for them to be optionally mutable.
-                let (identifier, block_id) = self.in_new_scope(|this| {
-                    let decl = this.add_variable_decl(
-                        identifier,
-                        false,
-                        true,
-                        DefinitionKind::Local(None),
-                    );
-                    (decl, this.resolve_expression(block))
-                });
-
-                HirExpression::For(HirForExpression {
-                    start_range,
-                    end_range,
-                    block: block_id,
-                    identifier,
-                })
-            }
             ExpressionKind::If(if_expr) => HirExpression::If(HirIfExpression {
                 condition: self.resolve_expression(if_expr.condition),
                 consequence: self.resolve_expression(if_expr.consequence),
@@ -1738,7 +1733,7 @@ mod test {
             let (hir_func, _, _) = resolver.resolve_function(func, id);
 
             // Iterate over function statements and apply filtering function
-            parse_statement_blocks(
+            find_lambda_captures(
                 hir_func.block(&interner).statements(),
                 &interner,
                 &mut all_captures,
@@ -1747,33 +1742,23 @@ mod test {
         all_captures
     }
 
-    fn parse_statement_blocks(
+    fn find_lambda_captures(
         stmts: &[StmtId],
         interner: &NodeInterner,
         result: &mut Vec<Vec<String>>,
     ) {
-        let mut expr: HirExpression;
-
         for stmt_id in stmts.iter() {
             let hir_stmt = interner.statement(stmt_id);
-            match hir_stmt {
-                HirStatement::Expression(expr_id) => {
-                    expr = interner.expression(&expr_id);
-                }
-                HirStatement::Let(let_stmt) => {
-                    expr = interner.expression(&let_stmt.expression);
-                }
-                HirStatement::Assign(assign_stmt) => {
-                    expr = interner.expression(&assign_stmt.expression);
-                }
-                HirStatement::Constrain(constr_stmt) => {
-                    expr = interner.expression(&constr_stmt.0);
-                }
-                HirStatement::Semi(semi_expr) => {
-                    expr = interner.expression(&semi_expr);
-                }
+            let expr_id = match hir_stmt {
+                HirStatement::Expression(expr_id) => expr_id,
+                HirStatement::Let(let_stmt) => let_stmt.expression,
+                HirStatement::Assign(assign_stmt) => assign_stmt.expression,
+                HirStatement::Constrain(constr_stmt) => constr_stmt.0,
+                HirStatement::Semi(semi_expr) => semi_expr,
+                HirStatement::For(for_loop) => for_loop.block,
                 HirStatement::Error => panic!("Invalid HirStatement!"),
-            }
+            };
+            let expr = interner.expression(&expr_id);
             get_lambda_captures(expr, interner, result); // TODO: dyn filter function as parameter
         }
     }
@@ -1794,7 +1779,7 @@ mod test {
             // Check for other captures recursively within the lambda body
             let hir_body_expr = interner.expression(&lambda_expr.body);
             if let HirExpression::Block(block_expr) = hir_body_expr {
-                parse_statement_blocks(block_expr.statements(), interner, result);
+                find_lambda_captures(block_expr.statements(), interner, result);
             }
         }
     }

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

@@ -11,7 +11,7 @@ use crate::{
         types::Type,
     },
     node_interner::{DefinitionKind, ExprId, FuncId, TraitMethodId},
-    Shared, Signedness, TypeBinding, TypeVariableKind, UnaryOp,
+    Signedness, TypeBinding, TypeVariableKind, UnaryOp,
 };
 
 use super::{errors::TypeCheckError, TypeChecker};
@@ -194,40 +194,6 @@ impl<'interner> TypeChecker<'interner> {
                 let span = self.interner.expr_span(expr_id);
                 self.check_cast(lhs_type, cast_expr.r#type, span)
             }
-            HirExpression::For(for_expr) => {
-                let start_range_type = self.check_expression(&for_expr.start_range);
-                let end_range_type = self.check_expression(&for_expr.end_range);
-
-                let start_span = self.interner.expr_span(&for_expr.start_range);
-                let end_span = self.interner.expr_span(&for_expr.end_range);
-
-                // Check that start range and end range have the same types
-                let range_span = start_span.merge(end_span);
-                self.unify(&start_range_type, &end_range_type, || TypeCheckError::TypeMismatch {
-                    expected_typ: start_range_type.to_string(),
-                    expr_typ: end_range_type.to_string(),
-                    expr_span: range_span,
-                });
-
-                let fresh_id = self.interner.next_type_variable_id();
-                let type_variable = Shared::new(TypeBinding::Unbound(fresh_id));
-                let expected_type =
-                    Type::TypeVariable(type_variable, TypeVariableKind::IntegerOrField);
-
-                self.unify(&start_range_type, &expected_type, || {
-                    TypeCheckError::TypeCannotBeUsed {
-                        typ: start_range_type.clone(),
-                        place: "for loop",
-                        span: range_span,
-                    }
-                    .add_context("The range of a loop must be known at compile-time")
-                });
-
-                self.interner.push_definition_type(for_expr.identifier.id, start_range_type);
-
-                self.check_expression(&for_expr.block);
-                Type::Unit
-            }
             HirExpression::Block(block_expr) => {
                 let mut block_type = Type::Unit;
 

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

@@ -325,11 +325,11 @@ mod test {
     fn basic_for_expr() {
         let src = r#"
             fn main(_x : Field) {
-                let _j = for _i in 0..10 {
+                for _i in 0..10 {
                     for _k in 0..100 {
 
                     }
-                };
+                }
             }
 
         "#;

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

@@ -3,10 +3,12 @@ use noirc_errors::{Location, Span};
 
 use crate::hir_def::expr::{HirExpression, HirIdent, HirLiteral};
 use crate::hir_def::stmt::{
-    HirAssignStatement, HirConstrainStatement, HirLValue, HirLetStatement, HirPattern, HirStatement,
+    HirAssignStatement, HirConstrainStatement, HirForStatement, HirLValue, HirLetStatement,
+    HirPattern, HirStatement,
 };
 use crate::hir_def::types::Type;
 use crate::node_interner::{DefinitionId, ExprId, StmtId};
+use crate::{Shared, TypeBinding, TypeVariableKind};
 
 use super::errors::{Source, TypeCheckError};
 use super::TypeChecker;
@@ -48,11 +50,45 @@ impl<'interner> TypeChecker<'interner> {
             HirStatement::Let(let_stmt) => self.check_let_stmt(let_stmt),
             HirStatement::Constrain(constrain_stmt) => self.check_constrain_stmt(constrain_stmt),
             HirStatement::Assign(assign_stmt) => self.check_assign_stmt(assign_stmt, stmt_id),
+            HirStatement::For(for_loop) => self.check_for_loop(for_loop),
             HirStatement::Error => (),
         }
         Type::Unit
     }
 
+    fn check_for_loop(&mut self, for_loop: HirForStatement) {
+        let start_range_type = self.check_expression(&for_loop.start_range);
+        let end_range_type = self.check_expression(&for_loop.end_range);
+
+        let start_span = self.interner.expr_span(&for_loop.start_range);
+        let end_span = self.interner.expr_span(&for_loop.end_range);
+
+        // Check that start range and end range have the same types
+        let range_span = start_span.merge(end_span);
+        self.unify(&start_range_type, &end_range_type, || TypeCheckError::TypeMismatch {
+            expected_typ: start_range_type.to_string(),
+            expr_typ: end_range_type.to_string(),
+            expr_span: range_span,
+        });
+
+        let fresh_id = self.interner.next_type_variable_id();
+        let type_variable = Shared::new(TypeBinding::Unbound(fresh_id));
+        let expected_type = Type::TypeVariable(type_variable, TypeVariableKind::IntegerOrField);
+
+        self.unify(&start_range_type, &expected_type, || {
+            TypeCheckError::TypeCannotBeUsed {
+                typ: start_range_type.clone(),
+                place: "for loop",
+                span: range_span,
+            }
+            .add_context("The range of a loop must be known at compile-time")
+        });
+
+        self.interner.push_definition_type(for_loop.identifier.id, start_range_type);
+
+        self.check_expression(&for_loop.block);
+    }
+
     /// Associate a given HirPattern with the given Type, and remember
     /// this association in the NodeInterner.
     pub(crate) fn bind_pattern(&mut self, pattern: &HirPattern, typ: Type) {

compiler/noirc_frontend/src/hir_def/expr.rs

@@ -26,7 +26,6 @@ pub enum HirExpression {
     Call(HirCallExpression),
     MethodCall(HirMethodCallExpression),
     Cast(HirCastExpression),
-    For(HirForExpression),
     If(HirIfExpression),
     Tuple(Vec<ExprId>),
     Lambda(HirLambda),
@@ -48,14 +47,6 @@ pub struct HirIdent {
     pub id: DefinitionId,
 }
 
-#[derive(Debug, Clone)]
-pub struct HirForExpression {
-    pub identifier: HirIdent,
-    pub start_range: ExprId,
-    pub end_range: ExprId,
-    pub block: ExprId,
-}
-
 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
 pub struct HirBinaryOp {
     pub kind: BinaryOpKind,