the issue for me is not the error... already found and solved that one. Question is if it is possible to have more context during a build when it fails? Something like a build log or a trace?
A failing build is less an issue when you create and publish a single rule, since you know the rule you're working on. However, when we later on start configuring and deploying Launch remotely via the API's, multiple data elements and rules will be created for a build.
This is also what we now run into with the migration scripts... things that work in DTM, are now failing in build in Launch, since it is more strict on syntax. A trace log on where the build actually stops (in which data element / extension / rule) would be very helpful...
Idea threads here in the community are specifically designed to take requests like that, and allow the community to vote on them. I'd recommend creating an idea thread around what you'd like build fail details to look like. Once the thread is created, post a link here so if anyone comes across this thread in the future, they can vote on the idea.