feat: add parens around unary expressions in in/instanceof (#564)

Author: nicolo-ribaudo

src/generation/generate.rs

@@ -3052,6 +3052,11 @@ fn gen_unary_expr<'a>(node: &UnaryExpr<'a>, context: &mut Context<'a>) -> PrintI
   let mut items = PrintItems::new();
   items.push_str(get_operator_text(node.op()));
   items.extend(gen_node(node.arg.into(), context));
+
+  if get_should_use_parens(node) {
+    items = surround_with_parens(items);
+  }
+
   return items;
 
   fn get_operator_text<'a>(op: UnaryOp) -> &'a str {
@@ -3065,6 +3070,13 @@ fn gen_unary_expr<'a>(node: &UnaryExpr<'a>, context: &mut Context<'a>) -> PrintI
       UnaryOp::Tilde => "~",
     }
   }
+
+  fn get_should_use_parens(node: &UnaryExpr) -> bool {
+    if let Node::BinExpr(parent) = node.parent() {
+      return matches!(parent.op(), BinaryOp::In | BinaryOp::InstanceOf);
+    }
+    false
+  }
 }
 
 fn gen_update_expr<'a>(node: &UpdateExpr<'a>, context: &mut Context<'a>) -> PrintItems {

tests/specs/expressions/BinaryExpression/BinaryExpression_Unary_In.txt

@@ -0,0 +1,39 @@
+== should properly parenthesize ! operator in in ==
+!foo in bar;
+(!foo in bar);
+!(foo in bar);
+(!foo) in bar;
+!!foo in bar;
+
+[expect]
+(!foo) in bar;
+(!foo) in bar;
+!(foo in bar);
+(!foo) in bar;
+(!!foo) in bar;
+
+== should properly parenthesize ! operator in instanceof ==
+!foo instanceof Bar;
+(!foo instanceof Bar);
+!(foo instanceof Bar);
+(!foo) instanceof Bar;
+!!foo instanceof bar;
+
+[expect]
+(!foo) instanceof Bar;
+(!foo) instanceof Bar;
+!(foo instanceof Bar);
+(!foo) instanceof Bar;
+(!!foo) instanceof bar;
+
+== should properly parenthesize void operator in instanceof ==
+void 0 in bar;
+(void 0 in bar);
+void (0 in bar);
+(void 0) in bar;
+
+[expect]
+(void 0) in bar;
+(void 0) in bar;
+void (0 in bar);
+(void 0) in bar;