It looks like the TestFlight Plugin expands variables placed into the “Build Notes” field, so the question is: how can we get the changes for the current build into an environment variable?
As far as I’m aware, the Subversion plugin doesn’t provide this information via an environment variable. However, all Jenkins SCM plugins integrate changelog information, as you can see via the “Changes” link in the web UI for each build.
This information is also available via the Jenkins API, even while a build is in progress.
For example, if you add an “Execute shell” build step where you run this command:
curl -s "http://jenkins/job/my-job/$BUILD_NUMBER/api/xml?wrapper=changes&xpath=//changeSet//comment"
You’ll get an XML document similar to this:
<changes>
<comment>First commit.</comment>
<comment>Second commit.</comment>
</changes>
You can then format this information however you like and place it into an environment variable which can then be referenced in the TestFlight “Build Notes” section.
However, setting an environment variable in a build step isn’t persistent by default — to do so requires using the EnvInject Plugin.
In this case, you could write your changelog text to a temporary file with contents like:
CHANGELOG="New in this build:\n- First commit.\n- Second commit."
Then, by using a build step with the Environment Properties File Path option to load this file, the $CHANGELOG variable would exist in your environment and persist until the end of the build, allowing you to use it in the “Build Notes” field.
Note: I haven’t used the TestFlight plugin myself (though I took a quick look at the code), and I only tested the changes API with a Git repository. Similarly, I didn’t test how newlines should be encoded with the EnvInject plugin, so that could cause issues.