WebApplicationType does not consider modules when deduced from classpath

[matthew-js-porter]

When using an application that is using spring-boot-starter-webclient and NOT spring-boot-starter-webflux
@ConditionalOnWebApplication is evaluating to true when it should be false duirng @SpringBootTest runs.
It does not appear to be the case on normal application runs.

Steps to Reproduce

1. Go to https://start.spring.io/
2. Select Spring Boot 4.0.0 and add Reactive HTTP Client dependencies only.
3. Generate the project.
4. Add the following test code:

package com.example.conditional_on_web_demo;

import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.autoconfigure.condition.ConditionalOnWebApplication;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.context.annotation.Configuration;

import static org.assertj.core.api.Assertions.assertThat;
import static org.junit.jupiter.api.Assertions.assertAll;

@SpringBootTest
class ConditionalOnWebDemoApplicationTests {

	@Configuration
	@ConditionalOnWebApplication(type = ConditionalOnWebApplication.Type.SERVLET)
    static class MyServletConfiguration {
	}

	@Configuration
	@ConditionalOnWebApplication(type = ConditionalOnWebApplication.Type.REACTIVE)
	static class MyReactiveConfiguration {
	}

	@Configuration
	@ConditionalOnWebApplication
	static class MyGenericWebConfiguration {
	}

	@Test
	void contextLoads(
			@Autowired(required = false) MyServletConfiguration myServletConfiguration,
			@Autowired(required = false) MyReactiveConfiguration myReactiveConfiguration,
			@Autowired(required = false) MyGenericWebConfiguration myGenericWebConfiguration
	) {
		assertAll(
				() -> assertThat(myServletConfiguration).isNull(),
				() -> assertThat(myReactiveConfiguration).isNull(),
				() -> assertThat(myGenericWebConfiguration).isNull()
		);
	}
}

5. Run the Test and observe the assertion errors (servlet will pass, reactive and generic will fail)

[philwebb]

I think the issue is with org.springframework.boot.WebApplicationType.deduceFromClasspath(). It sees WebFlux without WebMvc and assumes that a reactive web application is needed. Unfortunately we don't have a great signal that WebFlux isn't needed when we only consider classes from spring-webflux.jar because it contains bother server and client code.

I wonder if instead of looking for the core framework classes we should instead use classes from our own modules. We could use org.springframework.boot.webflux.autoconfigure.WebFluxAutoConfiguration and org.springframework.boot.webmvc.autoconfigure.WebMvcAutoConfiguration.

We'll need to discuss this as a team. For now, you can add this to your tests:

@SpringBootTest(properties = "spring.main.web-application-type=none")

[matthew-js-porter]

Thanks @philwebb!

[wilkinsona]

I think it makes sense to now use something from our own modules. If we want to avoid the loose cycle between spring-boot and spring-boot-webmvc/spring-boot-webflux, we could make use of spring.factories in a similar fashion to ApplicationContextFactory.