ast: fix `new_struct := MyStruct{...(*old_struct)}` (#8544)

vlib/v/ast/ast.v

@@ -1254,6 +1254,8 @@ pub fn (expr Expr) is_lvalue() bool {
 		CTempVar { return true }
 		IndexExpr { return expr.left.is_lvalue() }
 		SelectorExpr { return expr.expr.is_lvalue() }
+		ParExpr { return expr.expr.is_lvalue() } // for var := &{...(*pointer_var)}
+		PrefixExpr { return expr.right.is_lvalue() }
 		else {}
 	}
 	return false

vlib/v/tests/struct_test.v

@@ -170,6 +170,14 @@ fn test_assoc_with_vars() {
 	}
 	assert merged.a == 42
 	assert merged.b == 7
+
+	def3 := &Def{ 100, 200 }
+	merged1 := Def{...(*def3)}
+	merged2 := &Def{...(*def3)}
+	assert merged1.a == 100
+	assert merged1.b == 200
+	assert merged2.a == 100
+	assert merged2.b == 200
 }
 
 const (