Fix build failure source plugin

[wind57]

No description provided.

[wind57]

@ryanjbaxter fixes our build failure. its a intermediate solution until I figure out exactly what causes it and why. thank you

[ryanjbaxter]

I think actually this dependency upgrade broke things
spring-cloud/spring-cloud-build#277

I am not sure why, but I reverted the change and so far the build looks pretty good.

[wind57]

well yes, that is the PR that broke things, but downgrading is not really a solution, imho. I don't know (yet) a smart way to solve this, but here is the issue:

The problem is in 3 things at the same time:

• spring-boot-maven-plugin
• maven itself
• maven-source-plugin

When we want an image to be generated, we use the spring-boot-maven-plugin and our configuration is like this (simplified):

<executions>
  <execution>
	<id>build-image</id>
	<phase>package</phase>
	<goals>
		<goal>build-image</goal>
	</goals>
....

As such, when we run mvn clean install everything up to phase package runs, including the maven-source-plugin. In simpler words, it will look like this:

// this one generates the sources
maven-source-plugin:3.3.1:jar (attach-sources) > generate-sources ....

// this one builds the actual source jar, for example: spring-cloud-kubernetes-configuration-watcher-3.1.4-SNAPSHOT-sources.jar
maven-source-plugin:3.3.1:jar (attach-sources) 

// now build the image
spring-boot-maven-plugin:3.2.7:repackage

The problem here is that this spring-boot-maven-plugin requires the package phase : https://github.com/spring-projects/spring-boot/blob/c67d99f0528b57394e3575991d2458c2cdac46e4/spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/main/java/org/springframework/boot/maven/BuildImageMojo.java#L65

And this means: run the package phase again. maven does not have a way to detect what was run before in the same build (there might one here : https://issues.apache.org/jira/browse/MNG-6566 , but its maven 4.0.0), as such starts all goals from that phase again, meaning some of the goals will run two times. This is how the boot plugin worked for a very long time.

This was not a problem until maven-source-plugin:3.3.1. Before 3.3.1 version, if the plugin would see that a source jar was already present, it would show a warning and move on. From 3.3.1 it fails, saying that : "you already have a sources jar, I'm to fail", in our case the error message is : "Presumably you have configured maven-source-plugin to execute twice in your build." which makes perfect sense.

---

I'm still thinking how to properly solve this, since we can't downgrade forever and it seems that all future versions will have this problem too. Of course, a proper solution has to come from spring-boot-maven-plugin, but I don't really know how that would be doable :(

[ryanjbaxter]

Thanks for the investigation here. I agree that eventually we want to upgrade, but there isn't much harm in staying where we are for now and IMO is preferable to making the changes to work around the issue in this PR.

I think it is worth opening an issue with Spring Boot with the details above and see if they have some thoughts on this. My guess is that we are not the only ones running into this and maybe they have some suggestions.

[wind57]

done: spring-projects/spring-boot#41601

[wind57]

you were right Ryan, it was us who were configuring things incorrectly... To properly fix this, you will have to upgrade in the commons and I will fix it here. wdyt?

[ryanjbaxter]

I merged the change in spring cloud build, once the build finishes and the snapshots are available you can test things out. It should only take a few minutes for the build to finish

[wind57]

this is the actual fix

[wind57]

I removed the plugin from children and placed it in the parent pom, but the fix is the same

[wind57]

Nice. Good to go!