Reject conditional @ComponentScan declarations that rely on the REGISTER_BEAN phase

[wangxing-git]

spring boot version

2.1.5.RELEASE

TestConfig.java

package org.xyattic.boot.calkin.demo.oauth2.server.config;

import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;
import org.springframework.core.io.Resource;

/**
 * @author wangxing
 * @create 2019/6/28
 */
@Configuration
@Import(TestConfig.Test.class)
@ConditionalOnBean(Resource.class)
public class TestConfig {

    @ConditionalOnClass(Resource.class)
    @ComponentScan("org.xyattic.boot.calkin.demo.oauth2.test")
    class Test {

    }

}

The package org.xyattic.boot.calkin.demo.oauth2.test by default is not scanned.
When I activated it under certain conditions, I found that @ComponentScan was also activated when the condition was not met.

TestConfig:
      Did not match:
         - @ConditionalOnBean (types: org.springframework.core.io.Resource; SearchStrategy: all) did not find any beans of type org.springframework.core.io.Resource (OnBeanCondition)

   TestConfig.Test:
      Did not match:
         - Ancestor org.xyattic.boot.calkin.demo.oauth2.server.config.TestConfig did not match (ConditionEvaluationReport.AncestorsMatchedCondition)
      Matched:
         - @ConditionalOnClass found required class 'org.springframework.core.io.Resource' (OnClassCondition)

The log shows as not matching.
And the following will not accidentally activate.

@Configuration
@Import(TestConfig.Test.class)
//@ConditionalOnBean(Resource.class)
@ConditionalOnProperty("test.enabled")
public class TestConfig {

    @ConditionalOnClass(Resource.class)
    @ComponentScan("org.xyattic.boot.calkin.demo.oauth2.test")
    class Test {

    }

}

[wilkinsona]

Thanks for the report. The behaviour that you have observed is part of Spring Framework.

In the first example the unexpected behaviour is occurring because Framework does not consistently consider the conditions on TestConfig when evaluating the conditions on its Test inner-class. When it's deciding whether or not to process the @ComponentScan it only considers the conditions on Test. Later on, when it's deciding whether to process any @Bean definitions on Test it does consider the conditions on TestConfig. In implementation terms this is because of the use of TrackedConditionEvaluator in the latter case.

The second example avoids the problem of the first example because @ConditionalOnProperty is a different sort of condition to @ConditionalOnBean. Condition evaluation is split into two phases, configuration parsing and bean registration. @ConditionalOnProperty can be evaluated in the configuration parsing phase, whereas @ConditionalOnBean can only be evaluated in the bean registration phase. In the second example, when TestConfig is processed during configuration parsing, @ConditionalOnProperty does not match so TestConfig is skipped along with its inner-classes. By contrast, in the first example @ConditionalOnBean is not considered during the configuration parsing phase so Test and its @ComponentScan are then processed.

In short, we need to move this to spring-projects/spring-framework so that the Framework team can take a look.

[echooymxq]

version:5.2.1.RELEASE

@ConditionalOnBean(EnableSvcConfiguration.Marker.class)
@ComponentScan("com.github.bzi.service")
@Configuration
public class SvcAutoConfiguration {
}

In my case, when i use ConditionalOnBean meet condition, the @ComponentScan can't be activated.

[wangxing-git]

version:5.2.1.RELEASE

@ConditionalOnBean(EnableSvcConfiguration.Marker.class)
@ComponentScan("com.github.bzi.service")
@Configuration
public class SvcAutoConfiguration {
}

In my case, when i use ConditionalOnBean meet condition, the @ComponentScan can't be activated.

@echooymxq
My example is by the outer class @Import inner class, @ComponentScan is marked on the inner class, and the condition of the outer class uses @ConditionalOnBean and the condition is not met, but @ComponentScan on the inner class is still activated.