Versioning your IDEA module meta-data (.iml)

On one of our larger client projects, we’ve been tackling an array of improvements to the development environment. This is largely motivated by the fact that it’s a big project with lots of modules and engineers and time lost dealing with environment issues was expensive and frustrating. Everyone wants to be productive without having to wrestle with their tools or understand the ins and outs of things on the periphery, like build systems and IDE configuration.

We migrated to Maven 2 for builds partially because it’s convention driven, so when questions of how we should do something come up we can default to Maven best practices. Another reason is that it enabled us to stick to the Don’t Repeat Yourself (DRY) principle. We didn’t want to duplicate build meta-data by maintaining both command-line configuration (Maven pom.xmls) and IntelliJ IDEA configuration. Maven deals with this pretty well via the maven-idea-plugin.

The downside to running “mvn idea:module” every time there’s a pom change is that it eats at least a few minutes with all of the checks for sources and javadocs. To make matters worse, we always had to run it from the master directory so that intra-module dependencies were modeled correctly as IDEA module dependencies, not jar dependencies. Each developer would go through this routine when there was a change because we weren’t versioning our IDEA meta-data in subversion. When considering all of the engineer’s time, this process would consume over half an hour in total.

I wanted to change the process so that we still used the maven-idea-plugin to generate the meta-data (staying true to DRY), but then commit the generated files to subversion so that only one person would have to go through the pain of re-generating (presumably whoever made the changes to the poms) and the rest of the team could continue without much disruption. The problem is that each generated .iml file contains absolute paths which are specific to their machine.

After a bit of sleuthing, I discovered an IDEA option called Path Variables which is available in the general settings section. There isn’t much to tell you what it does, so it’s easily overlooked. You can specify one or more variables and IDEA will automatically replace file paths in project (.ipr) and module files (.iml) with the provided variables. Everyone on the development team added a Path Variable called “M2_REPO” which points to their local maven repository (~/.m2/repository).

After running “mvn idea:module” we just open the project in IDEA and it will do the replacing behind the scenes. Now the module meta-data can be versioned and shared.

It’s a small feature, but it’s helping us streamline everyone’s day-to-day.

IDEA 7 includes native Maven support which is getting better with each point release. The process described herein works great with the native plugin as well.