springboot Dependencies enforced without applying plugin

starting with spring-boot-2.3.0 dependencies seem to be enforced even without applying spring-boot plugin / dependency management.

I couldn't find any changes documented in that respect.

Comment From: wilkinsona

That shouldn’t be the case. An opinion will be expressed about the dependency version (via Gradle’s module metadata) but it shouldn’t be enforced. Can you please provide a minimal example that reproduces the problem that you’re seeing?

Comment From: masc3d

sure. following example uses h2 which both spring-boot 2.2.8 and 2.3.1 dependencies would resolve to 1.4.200.

plugins {
    id 'java'
}

ext {
    v_h2 = '1.4.199'
    v_springboot = '2.3.1.RELEASE'
}

repositories {
    mavenCentral()
}

dependencies {
    implementation(
            "org.springframework.boot:spring-boot-starter:$v_springboot",
            "com.h2database:h2:$v_h2"
    )
}

using spring-boot-2.2.8 resolves to h2-1.4.199 as expected. using spring-boot-2.3.1 resolves to h2-1.4.200 instead.

Comment From: wilkinsona

Thanks. I see what you mean now. That change in behaviour wasn't intentional. It's happening because the Gradle module metadata for spring-boot-starter is pulling in the version constraints defined in spring-boot-dependencies and applying them to the resolution of implementation as a whole rather than just to the transitive dependencies of spring-boot-starter.

Ideally, the constraints would only be applied that broadly if you used the dependency management plugin or declared a platform dependency on spring-boot-dependencies. I'll have a chat with the Gradle team and see what we can do to make that the case.

If you want to upgrade the version from the one that Spring Boot specifies in spring-boot-dependencies, the configuration you've shared above will work unaltered. If you want to downgrade the version (as you are attempting with H2), you'll need to do things slightly differently for now at least. The following will result in 1.4.199 being used:

dependencies {
    implementation("org.springframework.boot:spring-boot-starter:$v_springboot")
    implementation("com.h2database:h2") {
        version { strictly v_h2 }
    }
}