Kotlin .gitignore template

Kotlin compiles to the same class files as Java on the default target, so the *.class rule and the archive rules for jar, war, nar and ear carry over unchanged. Anything the compiler emits is derived from the sources plus the build configuration, and the archives are deliverables rather than inputs.

.kotlin is the addition worth knowing about. The newer compiler writes session and error data there, in the project root rather than inside the build directory, which means a project that only ignores build will start showing an untracked directory after a compiler upgrade. It holds nothing durable: deleting it costs one recompile.

The .gradle directory and build are the build system's working state. .gradle in particular holds file hashes and daemon state keyed to absolute paths, and copying it between machines produces cache misses at best. Both are regenerated from the build scripts, which are the files that actually describe the project.

The three negation lines are inherited from the Java lineage and matter for the same reason. Ignoring *.jar would also ignore the Gradle wrapper jar, which is the bootstrapper that lets a fresh clone run ./gradlew without anyone installing Gradle first. Committing that jar is the recommended practice, not an oversight, so the negation restores it.

hs_err_pid and replay_pid are virtual machine crash dumps. They are useful for exactly one debugging session and contain the full environment of the machine that produced them. On a multiplatform project, note that the native and JavaScript targets write into build as well, so the single build rule covers more than it appears to.