IntelliJ IDEA .gitignore template

.idea is the project directory the editor creates, and this template ignores all of it. That is the blunt option, and it is defensible: the directory mixes genuinely shared configuration, such as code style and inspection profiles, with pure session state, such as which files you had open and where your breakpoints are, and separating them takes a list of negations that has changed with every editor version.

The cost is that a team giving up on the directory also gives up on sharing a code style. The usual replacement is a formatter configuration file that lives outside the editor directory and that other tools read too, which sidesteps the argument entirely.

The module files are the other half. *.iml describes one module: its source roots, its dependencies and its language level. *.iws is the workspace, holding entirely personal state. *.ipr is the older single file project format. In a project built by a real build tool, the module files are regenerated on import, so tracking them means constant conflicts over machine specific paths.

out is the compiler output directory the editor uses when it compiles a project itself rather than delegating to the build tool. It is the editor's equivalent of a build directory and it is regenerated on demand. Because the rule is unanchored, it also matches a source directory named out anywhere in the repository, which is worth checking on a project that uses that name for something else.

The remaining rules cover plugin leftovers: atlassian-ide-plugin.xml, fabric.properties, crashlytics.properties, crashlytics-build.properties and com_crashlytics_export_strings.xml. Those last few can contain identifiers tied to a crash reporting account, which is a better reason to ignore them than tidiness. They are also generated during a build rather than written by hand, so nothing is lost by keeping them out of the repository entirely.