chore: convert BlockExpression into a standard struct (#4623)

# Description

## Problem\*

Resolves <!-- Link to GitHub Issue -->

## Summary\*

This PR splits out some more mundane changes from #4429.
`BlockExpression` is now a standard rather than tuple struct to make it
easier for us to add an `unsafe` property (and potentially `unchecked`
in future)

## Additional Context



## Documentation\*

Check one:
- [x] No documentation needed.
- [ ] Documentation included in this PR.
- [ ] **[Exceptional Case]** Documentation to be submitted in a separate
PR.

# PR Checklist\*

- [x] I have tested the changes locally.
- [x] I have formatted the changes with [Prettier](https://prettier.io/)
and/or `cargo fmt` on default settings.

---------

Co-authored-by: jfecher <jake@aztecprotocol.com>

aztec_macros/src/transforms/events.rs

@@ -47,10 +47,14 @@ pub fn generate_selector_impl(structure: &NoirStruct) -> TypeImpl {
     let mut from_signature_path = selector_path.clone();
     from_signature_path.segments.push(ident("from_signature"));
 
-    let selector_fun_body = BlockExpression(vec![make_statement(StatementKind::Expression(call(
-        variable_path(from_signature_path),
-        vec![expression(ExpressionKind::Literal(Literal::Str(SIGNATURE_PLACEHOLDER.to_string())))],
-    )))]);
+    let selector_fun_body = BlockExpression {
+        statements: vec![make_statement(StatementKind::Expression(call(
+            variable_path(from_signature_path),
+            vec![expression(ExpressionKind::Literal(Literal::Str(
+                SIGNATURE_PLACEHOLDER.to_string(),
+            )))],
+        )))],
+    };
 
     // Define `FunctionSelector` return type
     let return_type =

aztec_macros/src/transforms/functions.rs

@@ -39,29 +39,29 @@ pub fn transform_function(
     // Add check that msg sender equals this address and flag function as internal
     if is_internal {
         let is_internal_check = create_internal_check(func.name());
-        func.def.body.0.insert(0, is_internal_check);
+        func.def.body.statements.insert(0, is_internal_check);
     }
 
     // Add initialization check
     if insert_init_check {
         let init_check = create_init_check();
-        func.def.body.0.insert(0, init_check);
+        func.def.body.statements.insert(0, init_check);
     }
 
     // Add assertion for initialization arguments and sender
     if is_initializer {
-        func.def.body.0.insert(0, create_assert_initializer());
+        func.def.body.statements.insert(0, create_assert_initializer());
     }
 
     // Add access to the storage struct
     if storage_defined {
         let storage_def = abstract_storage(&ty.to_lowercase(), false);
-        func.def.body.0.insert(0, storage_def);
+        func.def.body.statements.insert(0, storage_def);
     }
 
     // Insert the context creation as the first action
     let create_context = create_context(&context_name, &func.def.parameters)?;
-    func.def.body.0.splice(0..0, (create_context).iter().cloned());
+    func.def.body.statements.splice(0..0, (create_context).iter().cloned());
 
     // Add the inputs to the params
     let input = create_inputs(&inputs_name);
@@ -71,20 +71,20 @@ pub fn transform_function(
     if let Some(return_values) = abstract_return_values(func) {
         // In case we are pushing return values to the context, we remove the statement that originated it
         // This avoids running duplicate code, since blocks like if/else can be value returning statements
-        func.def.body.0.pop();
+        func.def.body.statements.pop();
         // Add the new return statement
-        func.def.body.0.push(return_values);
+        func.def.body.statements.push(return_values);
     }
 
     // Before returning mark the contract as initialized
     if is_initializer {
         let mark_initialized = create_mark_as_initialized();
-        func.def.body.0.push(mark_initialized);
+        func.def.body.statements.push(mark_initialized);
     }
 
     // Push the finish method call to the end of the function
     let finish_def = create_context_finish();
-    func.def.body.0.push(finish_def);
+    func.def.body.statements.push(finish_def);
 
     let return_type = create_return_type(&return_type_name);
     func.def.return_type = return_type;
@@ -109,12 +109,12 @@ pub fn transform_vm_function(
     // Create access to storage
     if storage_defined {
         let storage = abstract_storage("public_vm", true);
-        func.def.body.0.insert(0, storage);
+        func.def.body.statements.insert(0, storage);
     }
 
     // Push Avm context creation to the beginning of the function
     let create_context = create_avm_context()?;
-    func.def.body.0.insert(0, create_context);
+    func.def.body.statements.insert(0, create_context);
 
     // We want the function to be seen as a public function
     func.def.is_unconstrained = true;
@@ -131,7 +131,7 @@ pub fn transform_vm_function(
 ///
 /// This will allow developers to access their contract' storage struct in unconstrained functions
 pub fn transform_unconstrained(func: &mut NoirFunction) {
-    func.def.body.0.insert(0, abstract_storage("Unconstrained", true));
+    func.def.body.statements.insert(0, abstract_storage("Unconstrained", true));
 }
 
 /// Helper function that returns what the private context would look like in the ast
@@ -393,7 +393,7 @@ fn create_avm_context() -> Result<Statement, AztecMacroError> {
 /// Any primitive type that can be cast will be casted to a field and pushed to the context.
 fn abstract_return_values(func: &NoirFunction) -> Option<Statement> {
     let current_return_type = func.return_type().typ;
-    let last_statement = func.def.body.0.last()?;
+    let last_statement = func.def.body.statements.last()?;
 
     // TODO: (length, type) => We can limit the size of the array returned to be limited by kernel size
     // Doesn't need done until we have settled on a kernel size
@@ -645,7 +645,8 @@ fn create_loop_over(var: Expression, loop_body: Vec<Statement>) -> Statement {
 
     // What will be looped over
     // - `hasher.add({ident}[i] as Field)`
-    let for_loop_block = expression(ExpressionKind::Block(BlockExpression(loop_body)));
+    let for_loop_block =
+        expression(ExpressionKind::Block(BlockExpression { statements: loop_body }));
 
     // `for i in 0..{ident}.len()`
     make_statement(StatementKind::For(ForLoopStatement {

aztec_macros/src/transforms/storage.rs

@@ -150,7 +150,7 @@ pub fn generate_storage_implementation(module: &mut SortedModule) -> Result<(),
                 true,
             )),
         )],
-        &BlockExpression(vec![storage_constructor_statement]),
+        &BlockExpression { statements: vec![storage_constructor_statement] },
         &[],
         &return_type(chained_path!("Self")),
     ));

compiler/noirc_frontend/src/ast/expression.rs

@@ -192,16 +192,18 @@ impl Expression {
         // with tuples without calling them. E.g. `if c { t } else { e }(a, b)` is interpreted
         // as a sequence of { if, tuple } rather than a function call. This behavior matches rust.
         let kind = if matches!(&lhs.kind, ExpressionKind::If(..)) {
-            ExpressionKind::Block(BlockExpression(vec![
-                Statement { kind: StatementKind::Expression(lhs), span },
-                Statement {
-                    kind: StatementKind::Expression(Expression::new(
-                        ExpressionKind::Tuple(arguments),
+            ExpressionKind::Block(BlockExpression {
+                statements: vec![
+                    Statement { kind: StatementKind::Expression(lhs), span },
+                    Statement {
+                        kind: StatementKind::Expression(Expression::new(
+                            ExpressionKind::Tuple(arguments),
+                            span,
+                        )),
                         span,
-                    )),
-                    span,
-                },
-            ]))
+                    },
+                ],
+            })
         } else {
             ExpressionKind::Call(Box::new(CallExpression { func: Box::new(lhs), arguments }))
         };
@@ -452,19 +454,21 @@ pub struct IndexExpression {
 }
 
 #[derive(Debug, PartialEq, Eq, Clone)]
-pub struct BlockExpression(pub Vec<Statement>);
+pub struct BlockExpression {
+    pub statements: Vec<Statement>,
+}
 
 impl BlockExpression {
     pub fn pop(&mut self) -> Option<StatementKind> {
-        self.0.pop().map(|stmt| stmt.kind)
+        self.statements.pop().map(|stmt| stmt.kind)
     }
 
     pub fn len(&self) -> usize {
-        self.0.len()
+        self.statements.len()
     }
 
     pub fn is_empty(&self) -> bool {
-        self.0.is_empty()
+        self.statements.is_empty()
     }
 }
 
@@ -542,7 +546,7 @@ impl Display for Literal {
 impl Display for BlockExpression {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         writeln!(f, "{{")?;
-        for statement in &self.0 {
+        for statement in &self.statements {
             let statement = statement.kind.to_string();
             for line in statement.lines() {
                 writeln!(f, "    {line}")?;

compiler/noirc_frontend/src/ast/function.rs

@@ -83,7 +83,7 @@ impl NoirFunction {
         &mut self.def
     }
     pub fn number_of_statements(&self) -> usize {
-        self.def.body.0.len()
+        self.def.body.statements.len()
     }
     pub fn span(&self) -> Span {
         self.def.span

compiler/noirc_frontend/src/ast/statement.rs

@@ -603,10 +603,12 @@ impl ForRange {
                 };
 
                 let block_span = block.span;
-                let new_block = BlockExpression(vec![
-                    let_elem,
-                    Statement { kind: StatementKind::Expression(block), span: block_span },
-                ]);
+                let new_block = BlockExpression {
+                    statements: vec![
+                        let_elem,
+                        Statement { kind: StatementKind::Expression(block), span: block_span },
+                    ],
+                };
                 let new_block = Expression::new(ExpressionKind::Block(new_block), block_span);
                 let for_loop = Statement {
                     kind: StatementKind::For(ForLoopStatement {
@@ -618,7 +620,9 @@ impl ForRange {
                     span: for_loop_span,
                 };
 
-                let block = ExpressionKind::Block(BlockExpression(vec![let_array, for_loop]));
+                let block = ExpressionKind::Block(BlockExpression {
+                    statements: vec![let_array, for_loop],
+                });
                 StatementKind::Expression(Expression::new(block, for_loop_span))
             }
         }

compiler/noirc_frontend/src/debug/mod.rs

@@ -113,7 +113,7 @@ impl DebugInstrumenter {
             })
             .collect();
 
-        let func_body = &mut func.body.0;
+        let func_body = &mut func.body.statements;
         let mut statements = take(func_body);
 
         self.walk_scope(&mut statements, func.span);
@@ -243,7 +243,9 @@ impl DebugInstrumenter {
                 pattern: ast::Pattern::Tuple(vars_pattern, let_stmt.pattern.span()),
                 r#type: ast::UnresolvedType::unspecified(),
                 expression: ast::Expression {
-                    kind: ast::ExpressionKind::Block(ast::BlockExpression(block_stmts)),
+                    kind: ast::ExpressionKind::Block(ast::BlockExpression {
+                        statements: block_stmts,
+                    }),
                     span: let_stmt.expression.span,
                 },
             }),
@@ -330,11 +332,13 @@ impl DebugInstrumenter {
             kind: ast::StatementKind::Assign(ast::AssignStatement {
                 lvalue: assign_stmt.lvalue.clone(),
                 expression: ast::Expression {
-                    kind: ast::ExpressionKind::Block(ast::BlockExpression(vec![
-                        ast::Statement { kind: let_kind, span: expression_span },
-                        new_assign_stmt,
-                        ast::Statement { kind: ret_kind, span: expression_span },
-                    ])),
+                    kind: ast::ExpressionKind::Block(ast::BlockExpression {
+                        statements: vec![
+                            ast::Statement { kind: let_kind, span: expression_span },
+                            new_assign_stmt,
+                            ast::Statement { kind: ret_kind, span: expression_span },
+                        ],
+                    }),
                     span: expression_span,
                 },
             }),
@@ -344,7 +348,7 @@ impl DebugInstrumenter {
 
     fn walk_expr(&mut self, expr: &mut ast::Expression) {
         match &mut expr.kind {
-            ast::ExpressionKind::Block(ast::BlockExpression(ref mut statements)) => {
+            ast::ExpressionKind::Block(ast::BlockExpression { ref mut statements, .. }) => {
                 self.scope.push(HashMap::default());
                 self.walk_scope(statements, expr.span);
             }
@@ -415,14 +419,16 @@ impl DebugInstrumenter {
 
         self.walk_expr(&mut for_stmt.block);
         for_stmt.block = ast::Expression {
-            kind: ast::ExpressionKind::Block(ast::BlockExpression(vec![
-                set_stmt,
-                ast::Statement {
-                    kind: ast::StatementKind::Semi(for_stmt.block.clone()),
-                    span: for_stmt.block.span,
-                },
-                drop_stmt,
-            ])),
+            kind: ast::ExpressionKind::Block(ast::BlockExpression {
+                statements: vec![
+                    set_stmt,
+                    ast::Statement {
+                        kind: ast::StatementKind::Semi(for_stmt.block.clone()),
+                        span: for_stmt.block.span,
+                    },
+                    drop_stmt,
+                ],
+            }),
             span: for_stmt.span,
         };
     }

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

@@ -252,7 +252,7 @@ impl<'a> Resolver<'a> {
                 typ: typ.clone(),
                 span: name.span(),
             }),
-            body: BlockExpression(Vec::new()),
+            body: BlockExpression { statements: Vec::new() },
             span: name.span(),
             where_clause: where_clause.to_vec(),
             return_type: return_type.clone(),
@@ -1952,8 +1952,8 @@ impl<'a> Resolver<'a> {
 
     fn resolve_block(&mut self, block_expr: BlockExpression) -> HirExpression {
         let statements =
-            self.in_new_scope(|this| vecmap(block_expr.0, |stmt| this.intern_stmt(stmt)));
-        HirExpression::Block(HirBlockExpression(statements))
+            self.in_new_scope(|this| vecmap(block_expr.statements, |stmt| this.intern_stmt(stmt)));
+        HirExpression::Block(HirBlockExpression { statements })
     }
 
     pub fn intern_block(&mut self, block: BlockExpression) -> ExprId {

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

@@ -468,7 +468,8 @@ mod test {
             expression: expr_id,
         };
         let stmt_id = interner.push_stmt(HirStatement::Let(let_stmt));
-        let expr_id = interner.push_expr(HirExpression::Block(HirBlockExpression(vec![stmt_id])));
+        let expr_id = interner
+            .push_expr(HirExpression::Block(HirBlockExpression { statements: vec![stmt_id] }));
         interner.push_expr_location(expr_id, Span::single_char(0), file);
 
         // Create function to enclose the let statement

compiler/noirc_frontend/src/hir_def/expr.rs

@@ -37,7 +37,7 @@ pub enum HirExpression {
 impl HirExpression {
     /// Returns an empty block expression
     pub const fn empty_block() -> HirExpression {
-        HirExpression::Block(HirBlockExpression(vec![]))
+        HirExpression::Block(HirBlockExpression { statements: vec![] })
     }
 }
 
@@ -249,11 +249,13 @@ pub struct HirIndexExpression {
 }
 
 #[derive(Debug, Clone)]
-pub struct HirBlockExpression(pub Vec<StmtId>);
+pub struct HirBlockExpression {
+    pub statements: Vec<StmtId>,
+}
 
 impl HirBlockExpression {
     pub fn statements(&self) -> &[StmtId] {
-        &self.0
+        &self.statements
     }
 }
 

compiler/noirc_frontend/src/monomorphization/mod.rs

@@ -430,7 +430,7 @@ impl<'interner> Monomorphizer<'interner> {
                 }
             },
             HirExpression::Literal(HirLiteral::Unit) => ast::Expression::Block(vec![]),
-            HirExpression::Block(block) => self.block(block.0)?,
+            HirExpression::Block(block) => self.block(block.statements)?,
 
             HirExpression::Prefix(prefix) => {
                 let location = self.interner.expr_location(&expr);