checker: check undefined ident of struct (#9164)

vlib/v/checker/checker.v

@@ -1063,6 +1063,9 @@ fn (mut c Checker) fail_if_immutable(expr ast.Expr) (string, token.Position) {
 			to_lock, pos = c.fail_if_immutable(expr.right)
 		}
 		ast.SelectorExpr {
+			if expr.expr_type == 0 {
+				return '', pos
+			}
 			// retrieve table.Field
 			c.ensure_type_exists(expr.expr_type, expr.pos) or { return '', pos }
 			mut typ_sym := c.table.get_final_type_symbol(c.unwrap_generic(expr.expr_type))

vlib/v/checker/tests/undefined_ident_of_struct.out

@@ -0,0 +1,7 @@
+vlib/v/checker/tests/undefined_ident_of_struct.vv:4:2: error: undefined ident: `f`
+    2 |
+    3 | fn get()  {
+    4 |     f.a = 'test'
+      |     ^
+    5 | }
+    6 |

vlib/v/checker/tests/undefined_ident_of_struct.vv

@@ -0,0 +1,9 @@
+module main
+
+fn get()  {
+	f.a = 'test'
+}
+
+fn main() {
+	println('hello')
+}