fix(formatter): omit call parens only around a sole, uncommented argument

crates/emmylua_formatter/src/formatter/expr.rs

@@ -1366,7 +1366,7 @@ fn format_single_arg_call_without_parens(
             .is_single_arg_no_parens()
             .then(|| args_list.get_single_arg_expr())
             .flatten(),
-        SingleArgCallParens::Omit => args_list.get_single_arg_expr(),
+        SingleArgCallParens::Omit => sole_arg_expr(args_list),
     }?;
 
     Some(match single_arg {
@@ -1380,6 +1380,22 @@ fn format_single_arg_call_without_parens(
     })
 }
 
+/// The argument of a parenthesized call that has exactly one argument and no comments,
+/// i.e. one whose parentheses can be dropped without losing anything.
+fn sole_arg_expr(args_list: &LuaCallArgList) -> Option<LuaSingleArgExpr> {
+    let mut args = args_list.get_args();
+    let arg = args.next()?;
+    if args.next().is_some()
+        || args_list
+            .syntax()
+            .children()
+            .any(|child| LuaComment::cast(child).is_some())
+    {
+        return None;
+    }
+    LuaSingleArgExpr::cast(arg.syntax().clone())
+}
+
 fn format_table_expr(ctx: &FormatContext, plan: &FormatPlan, expr: &LuaTableExpr) -> Vec<DocIR> {
     let has_direct_comments = expr
         .syntax()

crates/emmylua_formatter/src/test/config_tests.rs

@@ -486,6 +486,50 @@ local t = {
         );
     }
 
+    #[test]
+    fn test_single_arg_call_parens_omit_keeps_parens_for_multiple_args() {
+        let config = LuaFormatConfig {
+            output: OutputConfig {
+                single_arg_call_parens: SingleArgCallParens::Omit,
+                ..Default::default()
+            },
+            ..Default::default()
+        };
+
+        for code in [
+            "print(\"a\", \"b\")\n",
+            "local n = select(\"#\", ...)\n",
+            "obj:method({ 1 }, 2)\n",
+            // the string/table is not the first argument
+            "foo(x, \"a\")\n",
+            "foo(1, { 2 })\n",
+        ] {
+            assert_format_with_config!(code, code, config.clone());
+        }
+    }
+
+    #[test]
+    fn test_single_arg_call_parens_omit_keeps_parens_around_a_comment() {
+        let config = LuaFormatConfig {
+            output: OutputConfig {
+                single_arg_call_parens: SingleArgCallParens::Omit,
+                ..Default::default()
+            },
+            ..Default::default()
+        };
+
+        // same layout as with the default `Preserve`: the comment keeps the call parenthesized
+        assert_format_with_config!(
+            r#"foo("a" --[[note]])
+"#,
+            r#"foo(
+    "a" --[[note]]
+)
+"#,
+            config
+        );
+    }
+
     #[test]
     fn test_simple_lambda_single_line_always_collapses_eligible_multiline_lambda() {
         let config = LuaFormatConfig {