Serialization decoupling

[Mr3zee]

Subsystem
Compiler Plugin, kRPC

Problem Description
kotlinx.serialization was nailed down to our compiler plugin and core, which not always a proper coupling (like for gRPC it is unnecessary).

Solution
Move serialization responsibility to protocol side, switch generated objects to an array of parameters.

Note: Very are still coupled in core by RpcTypeKrpc class. Compiler plugin extensions are needed to resolve this, https://youtrack.jetbrains.com/issue/KRPC-178/General-Approach-for-custom-Service-Descriptors

[e5l]

Please add meaningful error message

[Mr3zee]

There can't be null, as this map doesn't hold nulls, NPE is unreachable

[Copilot]

Pull Request Overview

This PR decouples kotlinx.serialization from the compiler plugin core by moving serialization logic to the protocol side and generating RPC payloads as parameter arrays.

• Removed all direct serialization-plugin dependencies and diagnostics
• Introduced FirSerializablePropertiesProvider as a session component
• Simplified RPC service generator and strict-mode checker to use the new provider

Reviewed Changes

Copilot reviewed 74 out of 74 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
compiler-plugin-k2/.../RpcDiagnosticRendererFactory.kt	Removed the missing-serialization diagnostic mapping
compiler-plugin-k2/.../FirRpcDiagnostics.kt	Dropped the MISSING_SERIALIZATION_MODULE diagnostic
compiler-plugin-k2/.../SerializableProperties.kt	Added FirSerializablePropertiesProvider for custom serialization logic
compiler-plugin-k2/.../FirRpcStrictModeClassChecker.kt	Switched strict-mode checker to use new properties provider
compiler-plugin-k2/.../FirRpcCheckers.kt	Simplified checker registration, no longer toggled by serialization presence
compiler-plugin-k2/.../FirRpcAnnotationChecker.kt	Removed the serialization-module-missing check
compiler-plugin-k2/.../FirVersionSpecificApi.kt	Introduced toRegularClassSymbolVS extension
compiler-plugin-k2/.../FirRpcUtils.kt	Added doesMatchesClassId helper
compiler-plugin-k2/.../FirRpcServiceGenerator.kt	Stripped out nested class generation via the serialization plugin
compiler-plugin-k2/.../FirRpcExtensionRegistrar.kt	Always registers service generator and new session component
compiler-plugin-k2/.../FirRpcAdditionalCheckers.kt	Removed the serializationIsPresent flag
compiler-plugin-k2/.../FirGenerationKeys.kt	Eliminated RpcGeneratedRpcMethodClassKey
compiler-plugin-k2/build.gradle.kts	Removed serialization.plugin dependency
compiler-plugin-common/.../Names.kt	Updated Contextual → Transient ClassId and removed name helpers
compiler-plugin-backend/.../VersionSpecificApiImpl.kt	Added VS API overrides for constructor parameters and nullability
compiler-plugin-backend/.../extension/RpcIrContext.kt	Enhanced IR context with default rpc-type symbols and annotation utilities
compiler-plugin-backend/.../VersionSpecificApi.kt	Declared new IR API members for use by VS implementations

Comments suppressed due to low confidence (3)

compiler-plugin-k2/src/main/core/kotlinx/rpc/codegen/checkers/SerializableProperties.kt:64

• The logic for var properties is inverted: it currently includes only var properties marked with @Transient, but transient properties should be excluded. Change propertySymbol.hasSerialTransient(session) to !propertySymbol.hasSerialTransient(session).

else -> (propertySymbol.isVar && propertySymbol.hasSerialTransient(session))

compiler-plugin-k2/src/main/core/kotlinx/rpc/codegen/checkers/SerializableProperties.kt:41

• New SerializablePropertiesProvider logic covers complex scenarios (primary-constructor properties, inheritance, transient flags). Consider adding unit tests to verify each code path (val vs var, transient, private, superclass inheritance).

fun getSerializablePropertiesForClass(classSymbol: FirClassSymbol<*>): List<FirPropertySymbol> {

compiler-plugin-k2/src/main/core/kotlinx/rpc/codegen/checkers/SerializableProperties.kt:37

• [nitpick] Add KDoc to FirSerializablePropertiesProvider explaining its responsibility, caching behavior, and how it determines serializable properties (including handling of inheritance and @Transient).

internal class FirSerializablePropertiesProvider(session: FirSession) : FirExtensionSessionComponent(session) {