Kotlin + Lombok mixed-mode compilation breaks (missing Lombok-generated methods)

[abdi810103]

Kotlin + Lombok mixed-mode compilation breaks (missing Lombok-generated methods)

Environment

• Bazel: (add your version)

• rules_kotlin: 1.9.x

• rules_java: bundled

• rules_jvm_external: (version)

• Platform: macOS (dev), Linux (CI)

---

🚨 Summary of the Problem

Our project contains mixed Java + Kotlin source sets where:

1. Kotlin code calls Java classes

2. Java classes use Lombok, generating getters/setters

3. Java code also references Kotlin classes

This creates a circular dependency:

Kotlin → needs Lombok-generated Java methods
Java → needs Kotlin classes
Lombok → needs Java compilation before Kotlin

Under Maven/Gradle this works because Java + Kotlin + Lombok compile in a unified phase.

Under rules_kotlin, the Kotlin compiler sees the raw Java source before Lombok runs, causing missing symbol errors.

---

❌ Errors We Get

error: cannot find symbol
        sessionStorage.setUserId(...)
                      ^
  symbol:   method setUserId(String)
  location: variable sessionStorage of type SessionStorage

But these methods are generated by Lombok — they should exist.

---

✔ What We Have Tried

Attempt | Result -- | -- Adding Lombok via kt_compiler_plugin | ❌ Not recognized / no effect Using kapt | ❌ Fails with internal FIR errors Forcing annotation processors | ❌ Kotlin still sees raw Java Disabling header compilation | ❌ Did not fix Splitting sources into multiple libraries | ❌ Breaks circular dependencies Converting Java → Kotlin | ⚠ Works but not viable long-term

Nothing resolves the core issue:

rules_kotlin does not support mixed Java + Kotlin compilation where annotation processors must run before Kotlin.

---

🧪 Minimal Reproduction

Java (with Lombok)

@Data
public class SessionStorage {
    private String userId;
}

Kotlin (uses Lombok-generated getter)

class PremiumClient(private val session: SessionStorage) {
    fun test() = session.userId // Fails: no getter found
}

Java referencing Kotlin

public class AuthService {
    private final PremiumClient client = new PremiumClient(new SessionStorage());
}

---

🤔 Expected Behavior

• Lombok should generate getters/setters before Kotlin is compiled.

• Kotlin should compile against bytecode, not the raw Java source.

• Mixed Java/Kotlin source sets should be supported, like Gradle or Maven.

---

💥 Actual Behavior

• Kotlin compiler is invoked before Lombok-generated bytecode exists.

• It cannot resolve methods that Lombok would generate.

• Java compilation then fails because Kotlin compilation failed.

---

🎯 What We Are Requesting

1️⃣ Official Lombok support for mixed Java + Kotlin compilation

Something equivalent to:

• Java annotation processing

• Kotlin + Java compilation in a single step

• kapt compatibility or alternative

2️⃣ A unified compile action

Where:

• Java annotation processors run first

• Kotlin compiles against their bytecode

3️⃣ Documentation or recommended path

For projects migrating from Maven → Bazel that use:

• Spring Boot

• Lombok

• Kotlin

• Java legacy code

This combination is extremely common in enterprise projects.

---

🧩 Why This Matters

Many real-world projects depend on:

• Spring Boot

• Lombok

• Kotlin for new features

• Java for legacy components

These mixed source sets are widely used and currently cannot compile in Bazel using rules_kotlin without major restructuring.

A unified solution would benefit many teams across the ecosystem.

---

[agluszak]

Could you provide a minimal repro project, ideally using the latest version of rules_kotlin?

[abdi810103]

Yes, I will do that soon.

[adrianimboden]

I have the same problem in our codebase. I created a minimal reproducer using the latest rules_kotlin:

https://github.com/adrianimboden/bazel-kotlin-lombok-repro

bazelisk build //...
INFO: Analyzed 3 targets (1 packages loaded, 7 targets configured).
ERROR: .../bazel-kotlin-lombok-repro/BUILD:23:15: KotlinCompile //:lib { kt: 1, java: 1, srcjars: 0 } for x86_64 failed: (Exit 1): build failed: error executing KotlinCompile command (from kt_jvm_library rule target //:lib) bazel-out/k8-opt-exec/bin/external/rules_kotlin+/src/main/kotlin/build '--flagfile=bazel-out/k8-fastbuild/bin/lib-kt.jar-0.params'
src/main/java/com/example/User.kt:4:18: error: unresolved reference 'builder'.
    val a = Data.builder().abc(1).build()
                 ^^^^^^^
Feb 03, 2026 3:25:14 PM worker request 0
SEVERE: Compilation failure: compile phase failed:
src/main/java/com/example/User.kt:4:18: error: unresolved reference 'builder'.
    val a = Data.builder().abc(1).build()
                 ^^^^^^^
INFO: Elapsed time: 0.468s, Critical Path: 0.19s
INFO: 2 processes: 4 action cache hit, 2 internal.
ERROR: Build did NOT complete successfully