Debugging

One major downside to generating IR directly is that developers cannot step into generated source code with the debugger. This is an accepted trade-off with Metro (or any other compiler plugin).

Metro does offer a debug option in its plugin options/Gradle extension that will print verbose Kotlin pseudocode for all generated IR classes. This can be further tuned to print just certain classes.

metro {
  debug.set(true)
}

In the future, we could possibly explore including information in IR to synthesize call stack information similar to coroutines, but will save that for if/when it’s asked for.

Reports

Similar to Compose, Metro supports a reportsDestination property in its Gradle DSL and can output various graph reports to this destination if specified. This is very much a WIP, feedback is welcome!

metro {
  reportsDestination.set(layout.buildDirectory.dir("metro/reports"))
}

Warning

The Kotlin Gradle Plugin does not include file inputs like reportsDestination as build inputs, so you may need to compile with --rerun to force recompilation after adding this flag.

Decompiled Bytecode

Compiled java class files of Metro-generated types are fairly friendly to the IntelliJ “decompile to Java” action. Simply open the class file in the IDE (usually seen as a Kotlin bytecode class) then run the “decompile to Java” action. For JVM projects they are under build/classes. For Android projects, it’s build/tmp/kotlin-classes.