spring.config.activate.on-cloud-platform should consider NONE to be semantically equivalent to null

[osirisOfGit]

Apologies if this has been reported before, couldn't find any StackOverflow posts or GitHub issues.

When attempting to use spring.config.activate.on-cloud-platform, there is no mechanism available to simply state "If not running on a cloud platform" without forcibly setting the NONE value via spring.main.cloud-platform through some other mechanism.

spring-boot/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/config/ConfigDataProperties.java

Line 128 in 152acf8

return this.onCloudPlatform == null || this.onCloudPlatform == cloudPlatform;

This is undesirable for libraries providing configuration files with default values (e.g. through multi-documents) for scenarios when the consumers is running on a cloud platform and for when they aren't, as it forces one of the following scenarios:

• Force consumers to specify spring.main.cloud-platform: NONE when running locally (ex: through their application-{local-env-name}.yml)
• Abandon spring.config.activate.on-cloud-platform and multi-document config files, and conditionally load the properties through custom beans and manual CloudPlatform checks
• Abandon spring.config.activate.on-cloud-platform and use a different, likely more unreliable, property condition, such as spring.config.activate.on-profile: 'DEV | LOCAL | NO-PLATFORM'

Proposed change:

		private boolean isActive(CloudPlatform cloudPlatform) {
			return this.onCloudPlatform == null 
                                       || (this.onCloudPlatform == NONE && cloudPlatform == null) 
                                       || this.onCloudPlatform == cloudPlatform);
		}

[wilkinsona]

We think this makes sense but we're unsure about when to make the change. It could be considered a bug, in which case 3.1.x would be an option if the risk isn't too great. WDYT, @philwebb?

[philwebb]

I think we should consider this an enhancement.

The original intention of the spring.config.activate.on-cloud-platform property was to allow additional or override configuration for a specific cloud platform, I don't think we really considered none being used there.

The CloudPlatform.NONE enum was primary added to allow users to prevent our detection logic from running. From the javadoc:

No Cloud platform. Useful when false-positives are detected.

In other words, if we're guessing wrong for whatever reason then set this to tell us.

There is a subtle distinction between CloudPlatform.getActive(...) returning null and NONE. One means that we didn't detect a cloud platform, the other means the user actively stopped us from trying.

I think it's fine for us to change the isActive code in a minor release, since it feels like the change makes things more logical. I don't think we should do it in a patch release just in case someone is relying on the existing behavior.

[wilkinsona]

Closing in favor of #38510 that we'll merge in 3.3.