Compiler plugins

Active contributors: Dmitriy Novozhilov, Andrei Shikov, Leonid Startsev

The plugins/ directory hosts compiler plugins — extensions that hook into FIR (the K2 frontend) and/or IR (the backend representation) to add language features without changing the compiler core. The largest are widely used by Kotlin programmers: Compose, kotlinx.serialization, kapt, parcelize, allopen, lombok, atomicfu, power-assert.

This page is the index. Each plugin has its own short page below; small plugins are batched.

Pages in this section

• Compose — plugins/compose/
• kotlinx.serialization — plugins/kotlinx-serialization/
• kapt — plugins/kapt/
• Parcelize — plugins/parcelize/
• Spring/JPA helpers (allopen, noarg, sam-with-receiver, lombok) — plugins/{allopen,noarg,sam-with-receiver,lombok}/
• Other plugins — assign-plugin, atomicfu, jvm-abi-gen, js-plain-objects, power-assert, scripting, kotlin-dataframe, plugin-sandbox

Top-level layout

plugins/
├── allopen/                    Open declarations matching annotations (Spring, JPA)
├── assign-plugin/              Custom assignment-operator overloading
├── atomicfu/                   Atomic field updaters (kotlinx.atomicfu compiler plugin)
├── compose/                    Jetpack Compose / Compose Multiplatform plugin
├── js-plain-objects/           "Plain JS objects" support
├── jvm-abi-gen/                Stripped-ABI jar generator for incremental builds
├── kapt/                       Kotlin Annotation Processing Tool
├── kotlin-dataframe/           DataFrame's compile-time schema generation
├── kotlinx-serialization/      kotlinx.serialization plugin
├── lombok/                     Lombok interop on Kotlin sources
├── noarg/                      Synthesize no-arg constructors (JPA)
├── parcelize/                  Android Parcelable generation
├── plugin-sandbox/             A "sandbox" plugin used as a learning example/test bed
├── plugins-interactions-testing/ Tests that exercise multiple plugins together
├── power-assert/               Detailed assertion failure messages
├── sam-with-receiver/          SAM conversion with extension receiver
├── scripting/                  Compiler plugin behind libraries/scripting/
└── test-plugins/               Plugins used purely as test fixtures

Plugin extension points

Compiler plugins hook in via two main extension surfaces:

Surface	Where it's defined	What it does
FIR extensions	compiler/fir/plugin-utils/ and the K2 FirExtension API	Add new top-level declarations, modify resolved declarations, supply types for synthesized members.
IR generation	compiler/plugin-api/ and the IrGenerationExtension interface	Walk and rewrite IR after frontend resolution.

Older plugins (kapt, parcelize, allopen) had K1 paths. Most have been updated to ship K2 (FIR-based) implementations alongside the K1 ones.

Build and ship

Each plugin is built as two artifacts (typically):

• A compiler plugin jar — loaded by kotlinc via -Xplugin=....
• A runtime/companion jar — supplies the runtime types the generated code references.

KGP and the Maven plugin expose user-friendly DSL/configuration for each, hiding the -Xplugin= mechanics.

How plugins integrate with KGP

KGP-side modules wrap compiler plugins in Gradle DSLs:

• libraries/tools/kotlin-allopen/ (DSL) ↔ plugins/allopen/ (compiler plugin)
• libraries/tools/kotlin-noarg/ ↔ plugins/noarg/
• libraries/tools/kotlin-serialization/ ↔ plugins/kotlinx-serialization/
• libraries/tools/kotlin-compose-compiler/ ↔ plugins/compose/
• libraries/tools/kotlin-power-assert/ ↔ plugins/power-assert/
• libraries/tools/kotlin-lombok/ ↔ plugins/lombok/
• libraries/tools/kotlin-dataframe/ ↔ plugins/kotlin-dataframe/
• libraries/tools/kotlin-assignment/ ↔ plugins/assign-plugin/
• libraries/tools/kotlin-sam-with-receiver/ ↔ plugins/sam-with-receiver/
• libraries/tools/atomicfu/ ↔ plugins/atomicfu/

(Maven counterparts exist for most — see Maven plugin.)

Where to start

Read the plugin-extension-API in compiler/plugin-api/ plus the FIR extension API in compiler/fir/plugin-utils/. Browse plugins/plugin-sandbox/ for a teaching example. To prototype a new plugin, copy plugins/plugin-sandbox/ and adapt it.

For specific plugins: each has its own page; pick from the list above.