* Dubbo version: 2.7.7

EG:

SPI interface in apache dubbo
```
package org.apache.dubbo.common.extension;

/**
 * ExtensionFactory
 */
@SPI
public interface ExtensionFactory {
...
}
```
compatible class with alibaba dubbo

```
package com.alibaba.dubbo.common.extension;

@Deprecated
public interface ExtensionFactory extends org.apache.dubbo.common.extension.ExtensionFactory {

}
```

Not ADD @SPI annotation

``` java
    public static <T> ExtensionLoader<T> getExtensionLoader(Class<T> type) {
         .....
        if (!withExtensionAnnotation(type)) {
            throw new IllegalArgumentException("Extension type (" + type +
                    ") is not an extension, because it is NOT annotated with @" + SPI.class.getSimpleName() + "!");
        }
       ....
        return loader;
    }
```
In ExtensionLoader#getExtensionLoader  will check failed and throw Exception.

BTW,  ExtensionLoader not provided  compatible class.



/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.alibaba.dubbo.common.extension;
@Deprecated
public interface ExtensionFactory extends org.apache.dubbo.common.extension.ExtensionFactory {
}