Forbid accessing to a mut object in a func

compiler/erg_compiler/effectcheck.rs

@@ -374,6 +374,16 @@ impl SideEffectChecker {
             Expr::TypeAsc(type_asc) => {
                 self.check_expr(&type_asc.expr);
             }
+            Expr::Accessor(acc) => {
+                if !self.in_context_effects_allowed() && acc.ref_t().is_mut_type() {
+                    self.errs.push(EffectError::touch_mut_error(
+                        self.cfg.input.clone(),
+                        line!() as usize,
+                        expr,
+                        self.full_path(),
+                    ));
+                }
+            }
             _ => {}
         }
     }

compiler/erg_compiler/error.rs

@@ -1383,6 +1383,25 @@ impl EffectError {
             caused_by,
         )
     }
+
+    pub fn touch_mut_error(input: Input, errno: usize, expr: &Expr, caused_by: String) -> Self {
+        Self::new(
+            ErrorCore::new(
+                vec![SubMessage::only_loc(expr.loc())],
+                switch_lang!(
+                    "japanese" => "関数中で可変オブジェクトにアクセスすることは出来ません",
+                    "simplified_chinese" => "函数中不能访问可变对象",
+                    "traditional_chinese" => "函數中不能訪問可變對象",
+                    "english" => "cannot access a mutable object in a function",
+                ),
+                errno,
+                HasEffect,
+                expr.loc(),
+            ),
+            input,
+            caused_by,
+        )
+    }
 }
 
 pub type OwnershipError = TyCheckError;

tests/should_ok/control_expr.er

@@ -23,3 +23,9 @@ print! counter
 w! do!(not(counter == 0)), do!:
     print! "counter = {counter}"
     counter.update!(i -> i - 1)
+
+counter2 = !2
+not_zero!() = not counter2 == 0
+while! not_zero!, do!:
+    print! "aaa"
+    counter2.update!(i -> i - 1)