fix: Parse an if followed by a tuple as a block (#1924)

* Fix parsing an if followed by a tuple as a function call

* Fix test

crates/noirc_frontend/src/ast/expression.rs

@@ -158,8 +158,17 @@ impl Expression {
     }
 
     pub fn call(lhs: Expression, arguments: Vec<Expression>, span: Span) -> Expression {
-        let func = Box::new(lhs);
-        let kind = ExpressionKind::Call(Box::new(CallExpression { func, arguments }));
+        // Need to check if lhs is an if expression since users can sequence if expressions
+        // 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::Expression(lhs),
+                Statement::Expression(Expression::new(ExpressionKind::Tuple(arguments), span)),
+            ]))
+        } else {
+            ExpressionKind::Call(Box::new(CallExpression { func: Box::new(lhs), arguments }))
+        };
         Expression::new(kind, span)
     }
 }

crates/noirc_frontend/src/parser/parser.rs

@@ -1531,6 +1531,19 @@ mod test {
     fn parse_block() {
         parse_with(block(expression()), "{ [0,1,2,3,4] }").unwrap();
 
+        // Regression for #1310: this should be parsed as a block and not a function call
+        let res = parse_with(block(expression()), "{ if true { 1 } else { 2 } (3, 4) }").unwrap();
+        match unwrap_expr(res.0.last().unwrap()) {
+            // The `if` followed by a tuple is currently creates a block around both in case
+            // there was none to start with, so there is an extra block here.
+            ExpressionKind::Block(block) => {
+                assert_eq!(block.0.len(), 2);
+                assert!(matches!(unwrap_expr(&block.0[0]), ExpressionKind::If(_)));
+                assert!(matches!(unwrap_expr(&block.0[1]), ExpressionKind::Tuple(_)));
+            }
+            _ => unreachable!(),
+        }
+
         parse_all_failing(
             block(expression()),
             vec![
@@ -1544,6 +1557,14 @@ mod test {
         );
     }
 
+    /// Extract an Statement::Expression from a statement or panic
+    fn unwrap_expr(stmt: &Statement) -> &ExpressionKind {
+        match stmt {
+            Statement::Expression(expr) => &expr.kind,
+            _ => unreachable!(),
+        }
+    }
+
     /// Deprecated constrain usage test
     #[test]
     fn parse_constrain() {