From c90bf34bb76744fc523bbec2a7e39ecd17a031a7 Mon Sep 17 00:00:00 2001
From: GreasySlug <9619abgoni@gmail.com>
Date: Wed, 31 Dec 2025 20:28:34 +0900
Subject: [PATCH 1/2] fix(parser): handle unmatched closing parenthesis

---
 crates/erg_parser/error.rs | 17 +++++++++++++++++
 crates/erg_parser/parse.rs |  7 +++++++
 2 files changed, 24 insertions(+)

diff --git a/crates/erg_parser/error.rs b/crates/erg_parser/error.rs
index ea9211442..ad990ffde 100644
--- a/crates/erg_parser/error.rs
+++ b/crates/erg_parser/error.rs
@@ -175,6 +175,23 @@ impl LexError {
         ))
     }
 
+    pub fn parenthesize_error(errno: usize, loc: Location, got: &str) -> Self {
+        let msg = switch_lang!(
+            "japanese" => "不適切な閉じ括弧があります",
+            "simplified_chinese" => "存在不匹配的右括号",
+            "traditional_chinese" => "存在不匹配的右括號",
+            "english" => "unmatched closing parenthesis found",
+        );
+        let got = StyledStr::new(got, Some(ERR), Some(ATTR));
+        let hint = switch_lang!(
+            "japanese" => format!("この{}は対応する開き括弧がないため、削除するか開き括弧を追加してください", got),
+            "simplified_chinese" => format!("{}缺少对应的左括号，请删除或添加左括号", got),
+            "traditional_chinese" => format!("{}缺少對應的左括號，請刪除或添加左括號", got),
+            "english" => format!("{} has no matching opening parenthesis - either remove it or add an opening parenthesis", got),
+        );
+        Self::syntax_error(errno, loc, msg, Some(hint))
+    }
+
     pub fn expect_next_line_error(errno: usize, loc: Location, caused: &str) -> Self {
         Self::new(ErrorCore::new(
             vec![SubMessage::ambiguous_new(
diff --git a/crates/erg_parser/parse.rs b/crates/erg_parser/parse.rs
index 6236de1d7..cde39f981 100644
--- a/crates/erg_parser/parse.rs
+++ b/crates/erg_parser/parse.rs
@@ -2050,6 +2050,13 @@ impl Parser {
                     debug_exit_info!(self);
                     return Err(());
                 }
+                Some(t) if t.is(RParen) => {
+                    let err = ParseError::parenthesize_error(line!() as usize, t.loc(), ")");
+                    self.errs.push(err);
+                    self.next_expr();
+                    debug_exit_info!(self);
+                    return Err(());
+                }
                 _ => {
                     if stack.len() <= 1 {
                         break;

From f09f704cc1e4555740f2597002eedb35c0e497bd Mon Sep 17 00:00:00 2001
From: GreasySlug <9619abgoni@gmail.com>
Date: Wed, 31 Dec 2025 20:32:56 +0900
Subject: [PATCH 2/2] test(parse): add neg test

---
 crates/erg_parser/tests/parse_test.rs      | 5 +++++
 crates/erg_parser/tests/unmatched_paren.er | 1 +
 2 files changed, 6 insertions(+)
 create mode 100644 crates/erg_parser/tests/unmatched_paren.er

diff --git a/crates/erg_parser/tests/parse_test.rs b/crates/erg_parser/tests/parse_test.rs
index 8b780a362..6f56729f1 100644
--- a/crates/erg_parser/tests/parse_test.rs
+++ b/crates/erg_parser/tests/parse_test.rs
@@ -84,6 +84,11 @@ fn parse_invalid_class_definition() -> Result<(), ()> {
     expect_failure("tests/invalid_class_definition.er", 0, 7)
 }
 
+#[test]
+fn parse_missing_paren() -> Result<(), ()> {
+    expect_failure("tests/unmatched_paren.er", 0, 1)
+}
+
 #[test]
 fn parse_warns() -> Result<(), ()> {
     expect_success("tests/warns.er", 1)
diff --git a/crates/erg_parser/tests/unmatched_paren.er b/crates/erg_parser/tests/unmatched_paren.er
new file mode 100644
index 000000000..fdcb10430
--- /dev/null
+++ b/crates/erg_parser/tests/unmatched_paren.er
@@ -0,0 +1 @@
+func a, b) = a + b
\ No newline at end of file