checker,cgen: fix cast_expr() for alias

vlib/v/checker/checker.v

@@ -3539,6 +3539,12 @@ fn (mut c Checker) cast_expr(mut node ast.CastExpr) ast.Type {
 	} else {
 		to_type
 	}
+
+	if final_to_sym == final_from_sym {
+		// type alias
+		return to_type
+	}
+
 	final_to_is_ptr := to_type.is_ptr() || final_to_type.is_ptr()
 	c.markused_castexpr(mut node, to_type, mut final_to_sym)
 	if to_type.has_flag(.result) {

vlib/v/tests/casts/cast_to_alias_test.v

@@ -49,3 +49,29 @@ fn test_cast_to_alias_of_ref_struct() {
 	println(typeof(bar).name)
 	assert typeof(bar).name == '&Alias'
 }
+
+type Bar1 = Foo
+type Bar2 = Foo
+type Bar3 = Foo
+
+fn test_cast_to_from_alias() {
+	bar2 := Bar2{
+		x: 100
+	}
+	foo := Foo(bar2)
+	bar1 := Bar1(bar2)
+	bar3 := Bar3(bar2)
+	assert typeof(foo).name == 'Foo'
+	assert typeof(bar1).name == 'Bar1'
+	assert typeof(bar2).name == 'Bar2'
+	assert typeof(bar3).name == 'Bar3'
+
+	foo1_1 := Foo(foo)
+	bar1_1 := Bar1(foo)
+	bar2_1 := Bar2(foo)
+	bar3_1 := Bar3(foo)
+	assert typeof(foo1_1).name == 'Foo'
+	assert typeof(bar1_1).name == 'Bar1'
+	assert typeof(bar2_1).name == 'Bar2'
+	assert typeof(bar3_1).name == 'Bar3'
+}