Add unreachable

compiler/erg_compiler/context/initialize/mod.rs

@@ -1800,6 +1800,7 @@ impl Context {
         let t_exit = t_quit.clone();
         let t_repr = nd_func(vec![kw("object", Obj)], None, Str);
         let t_round = nd_func(vec![kw("number", Float)], None, Int);
+        let t_unreachable = nd_func(vec![], None, Never);
         self.register_builtin_py_impl("abs", t_abs, Immutable, Private, Some("abs"));
         self.register_builtin_py_impl("ascii", t_ascii, Immutable, Private, Some("ascii"));
         self.register_builtin_impl("assert", t_assert, Const, Private); // assert casting に悪影響が出る可能性があるため、Constとしておく
@@ -1852,6 +1853,14 @@ impl Context {
         self.register_builtin_py_impl("quit", t_quit, Immutable, Private, Some("quit"));
         self.register_builtin_py_impl("repr", t_repr, Immutable, Private, Some("repr"));
         self.register_builtin_py_impl("round", t_round, Immutable, Private, Some("round"));
+        // TODO: original implementation
+        self.register_builtin_py_impl(
+            "unreachable",
+            t_unreachable,
+            Immutable,
+            Private,
+            Some("exit"),
+        );
     }
 
     fn init_builtin_const_funcs(&mut self) {

compiler/erg_parser/tests/desugar_param_pat.er

@@ -3,9 +3,9 @@ sum2 [x, y]: [Nat; 2] =
 
 print! sum2 [1, 2]
 
-x = match "c" + "":
+x = match "a" + "":
     "a" -> 1
     "b" -> 2
-    _ -> 3
+    _ -> unreachable()
 
 print! x