fix(type_checker,tests): handle redefining variables in type_checker

compiler/src/compiler/type_checker.cpp

@@ -457,6 +457,9 @@ void type_checker::visit_if_stmt(if_stmt *obj) {
 }
 void type_checker::visit_let_stmt(let_stmt *obj) {
   auto name = obj->name_->token_;
+  if (scope_.is_defined(name)) {
+    error(obj->name_, "Redefining a variable is not allowed");
+  }
   auto placeholder = ykobject(obj->data_type_);
   if (obj->expression_ != nullptr) {
     obj->expression_->accept(this);

compiler/test_data/bug_fixes/redefining_vars.yaka

@@ -0,0 +1,7 @@
+def a() -> int:
+    b: int = 1
+    b: u8 = 1u8
+    return 0
+
+def main() -> int:
+    return 0

compiler/test_data/bug_fixes/redefining_vars_params.yaka

@@ -0,0 +1,7 @@
+def a(b: int) -> int:
+    b: u8 = 1u8
+    return 0
+
+def main() -> int:
+    a(1)
+    return 0

compiler/tests/test_type_checker.cpp

@@ -481,4 +481,12 @@ TEST_CASE(
     "type checker: only 1 argument is allowed for binarydata()") {
   TEST_SNIPPET("a: Ptr[Const[u8]] = binarydata(1, 2, 3)",
                "binarydata() builtin expects 1 argument");
+}
+TEST_CASE("type checker: Redefining variables in a function different data types") {
+  TEST_FILE("../test_data/bug_fixes/redefining_vars.yaka",
+            "Redefining a variable is not allowed");
+}
+TEST_CASE("type checker: Redefining variables in a function - params") {
+  TEST_FILE("../test_data/bug_fixes/redefining_vars_params.yaka",
+            "Redefining a variable is not allowed");
 }