Troubleshooting SQLDelight: The "KotlinSourceSet 'main' not found" Error in AGP 9

If you've recently tried jumping onto the bleeding edge with Android Gradle Plugin (AGP) 9.0, you might have hit a brick wall during project sync. A common culprit popping up lately is a cryptic error from SQLDelight:


KotlinSourceSet with name 'main' not found.

This issue, tracked under SQLDelight #6078, highlights a significant shift in how Android and Kotlin interact in the latest build tools. Here’s the breakdown of what's happening and how to fix it.

👉 KotlinSourceSet with name 'main' not found with AGP9 · Issue #6078 · sqldelight/sqldelight

🧑🏻‍💻 The Problem: Why is 'main' Missing?

The conflict arises because AGP 9 introduces a "New DSL" and changes how Kotlin source sets are managed. Historically, SQLDelight’s Gradle plugin looked for a source set explicitly named "main" to inject its generated code.

However, in AGP 9 (especially with the builtInKotlin flag enabled), the way source sets are registered has changed. The legacy "main" container that SQLDelight expects is either missing or hidden, causing the configuration phase to fail immediately.

🧑🏻‍💻 The Discussion Flow: From Discovery to Workaround

The GitHub thread reveals an interesting evolution of the fix:

The Discovery: Early adopters reported that even disabling the experimental newDsl didn't fix the crash.
The Culprit: Contributors identified that the SQLDelight plugin was making "unsafe" assumptions about the existence of the "main" source set.
The Temporary Fix: A specific flag in gradle.properties was found to restore the old behavior, allowing the plugin to find what it needs.

🧑🏻‍💻 How to Fix It (The Workaround)

Until the official patches in SQLDelight (specifically PR #6079 and #6091) are fully merged and released, you can unblock your development by adding these flags to your gradle.properties file:


# Temporary fix for SQLDelight + AGP 9
android.newDsl=false
android.builtInKotlin=true
android.disallowKotlinSourceSets=false

The key line here is android.disallowKotlinSourceSets=false. This tells AGP 9 to allow the traditional Kotlin source set structures that SQLDelight currently relies on.

🧑🏻‍💻 The Road Ahead: Permanent Fixes

The maintainers (including Jake Wharton and the CashApp team) are already working on a long-term solution. The goal is to move away from searching for "main" and instead use the proper AGP/Kotlin API to register generated code.

PR #6079: Focuses on implementing a more robust schema configuration.
PR #6091: Modernizes the plugin to play nice with the AGP 9 New DSL.

The takeaway?

AGP 9 is a major shift. If you’re using third-party plugins that generate code (like SQLDelight or Wire), expect a few bumps in the road as these libraries catch up to the new Gradle architecture.