gen/c: Fix shared variable are not passed correctly to methods with shared type in recevier (#13320)

vlib/v/gen/c/fn.v

@@ -1006,7 +1006,8 @@ fn (mut g Gen) method_call(node ast.CallExpr) {
 			if !node.left.is_lvalue() {
 				g.write('ADDR($rec_cc_type, ')
 				has_cast = true
-			} else {
+				// if receiver has shared_f, the struct ptr itself is passed directly.
+			} else if !node.receiver_type.has_flag(.shared_f) {
 				g.write('&')
 			}
 		}
@@ -1062,7 +1063,8 @@ fn (mut g Gen) method_call(node ast.CallExpr) {
 			}
 			g.write(embed_name)
 		}
-		if node.left_type.has_flag(.shared_f) {
+		// if receiver has shared_f, the struct ptr itself is passed directly.
+		if node.left_type.has_flag(.shared_f) && !node.receiver_type.has_flag(.shared_f) {
 			g.write('->val')
 		}
 	}

vlib/v/tests/shared_lock_2_test.v

@@ -50,3 +50,27 @@ fn test_shared_receiver_lock() {
 		assert x.a == 7 && y.a == 5
 	}
 }
+
+struct St2 {
+mut:
+	a map[string]int
+}
+
+fn (shared x St2) f() {
+	lock x {
+		x.a["a"] = 123
+	}
+}
+
+fn test_shared_receiver_lock_2() {
+	shared x := St2 {
+		a: map[string]int
+	}
+
+	x.f()
+
+	rlock x {
+		assert x.a["a"] == 123
+	}
+}
+