79: Building Android apps in Meta's monorepository with Buck2

How do you keep Android build times under control when your codebase spans tens of thousands of modules and millions of lines of Kotlin? In this episode, Pascal talks with Iveta, Navid, and Joshua from Meta's Android Developer Experience team about the technical strategies that help Meta's engineers stay productive at scale. We discuss approaches like source-only ABIs and incremental compilation – clever solutions that have helped us tackle the challenges of building fast in a monorepo, as well as what you can do to keep your builds fast with Buck2. Got feedback? Send it to us on Threads (https://threads.net/@metatechpod), Instagram (https://instagram.com/metatechpod) and don't forget to follow our host Pascal (https://mastodon.social/@passy, https://threads.net/@passy_). Fancy working with us? Check out https://www.metacareers.com/. Timestamps Intro 0:06 Introducing Iveta 2:09 Introducing Joshua 3:29 Introducing Navid 4:00 Android DevX Team 4:36 The challenges of build speed 6:28 Buck2 and Android 7:34 How to add new language support to Buck2 9:01 What's new in Open Source? 11:02 Optimising Kotlin builds 12:55 Source-only ABI 14:25 Developer restrictions 17:33 From Jasabi to Kosabi 20:33 Strategies for keeping builds fast 22:08 Working with big modules 23:00 Bringing incremental Kotlin compilation to Buck2 24:48 Speed improvements 28:52 Third-party library upgrades 30:54 What's next? 33:56 Outro 36:14 Links Meta Connect 2025 Developer Talks: https://www.youtube.com/playlist?list=PLb0IAmt7-GS2cONiFVhtdKWEsyNkF6uUP  Buck2: https://buck2.build/ Incremental Kotlin compilation at Meta: https://engineering.fb.com/2025/08/26/open-source/enabling-kotlin-incremental-compilation-on-buck2/  Blog post about Jasabi (the Java counterpart to Kosabi): https://engineering.fb.com/2017/11/09/android/rethinking-android-app-compilation-with-buck/  Kotlin Conf talk about source-only ABI compilation: https://2025.kotlinconf.com/talks/857571/  Meta Connect 2025 Developer Talks: https://www.youtube.com/playlist?list=PLb0IAmt7-GS2cONiFVhtdKWEsyNkF6uUP  Buck2: https://buck2.build/ Incremental Kotlin compilation at Meta: https://engineering.fb.com/2025/08/26/open-source/enabling-kotlin-incremental-compilation-on-buck2/  Blog post about Jasabi (the Java counterpart to Kosabi): https://engineering.fb.com/2017/11/09/android/rethinking-android-app-compilation-with-buck/  Kotlin Conf talk about source-only ABI compilation: https://2025.kotlinconf.com/talks/857571/