[FIR] KT-57220 Avoid creating useless synthetic function providers

- This optimization applied to LL FIR can be extended to K2 as a whole.
  Likely, there won't be any performance benefits in CLI runs, but it's
  still better to avoid useless symbol providers.

analysis/low-level-api-fir/src/org/jetbrains/kotlin/analysis/low/level/api/fir/sessions/LLFirSessionCache.kt

@@ -164,13 +164,8 @@ internal class LLFirSessionCache(private val project: Project) {
             })
 
             val javaSymbolProvider = createJavaSymbolProvider(this, moduleData, project, contentScope)
-
+            val syntheticFunctionInterfaceProvider =
-            // We only need to add an extension synthetic function provider if the session's function type service even has extension kinds.
+                FirExtensionSyntheticFunctionInterfaceProvider.createIfNeeded(this, moduleData, scopeProvider)
-            // Otherwise, the provider will be completely useless.
-            val syntheticFunctionalInterfaceProvider = if (this.functionTypeService.hasExtensionKinds()) {
-                FirExtensionSyntheticFunctionInterfaceProvider(this, moduleData, scopeProvider)
-            } else null
-
             register(
                 FirSymbolProvider::class,
                 LLFirModuleWithDependenciesSymbolProvider(
@@ -179,7 +174,7 @@ internal class LLFirSessionCache(private val project: Project) {
                         provider.symbolProvider,
                         switchableExtensionDeclarationsSymbolProvider,
                         javaSymbolProvider,
-                        syntheticFunctionalInterfaceProvider,
+                        syntheticFunctionInterfaceProvider,
                     ),
                     dependencyProvider,
                 )

compiler/fir/entrypoint/src/org/jetbrains/kotlin/fir/session/FirAbstractSessionFactory.kt

@@ -16,7 +16,10 @@ import org.jetbrains.kotlin.fir.java.FirProjectSessionProvider
 import org.jetbrains.kotlin.fir.resolve.providers.DEPENDENCIES_SYMBOL_PROVIDER_QUALIFIED_KEY
 import org.jetbrains.kotlin.fir.resolve.providers.FirProvider
 import org.jetbrains.kotlin.fir.resolve.providers.FirSymbolProvider
-import org.jetbrains.kotlin.fir.resolve.providers.impl.*
+import org.jetbrains.kotlin.fir.resolve.providers.impl.FirCachingCompositeSymbolProvider
+import org.jetbrains.kotlin.fir.resolve.providers.impl.FirExtensionSyntheticFunctionInterfaceProvider
+import org.jetbrains.kotlin.fir.resolve.providers.impl.FirLibrarySessionProvider
+import org.jetbrains.kotlin.fir.resolve.providers.impl.FirProviderImpl
 import org.jetbrains.kotlin.fir.resolve.providers.symbolProvider
 import org.jetbrains.kotlin.fir.scopes.FirKotlinScopeProvider
 import org.jetbrains.kotlin.incremental.components.EnumWhenTracker
@@ -77,7 +80,7 @@ abstract class FirAbstractSessionFactory {
         createProviders: (
             FirSession, FirKotlinScopeProvider, FirSymbolProvider,
             FirSwitchableExtensionDeclarationsSymbolProvider?,
-            FirExtensionSyntheticFunctionInterfaceProvider,
+            FirExtensionSyntheticFunctionInterfaceProvider?,
             dependencies: List<FirSymbolProvider>,
         ) -> List<FirSymbolProvider>
     ): FirSession {
@@ -109,7 +112,8 @@ abstract class FirAbstractSessionFactory {
 
             val dependencyProviders = computeDependencyProviderList(moduleData)
             val generatedSymbolsProvider = FirSwitchableExtensionDeclarationsSymbolProvider.create(this)
-            val syntheticFunctionInterfaceProvider = FirExtensionSyntheticFunctionInterfaceProvider(this, moduleData, kotlinScopeProvider)
+            val syntheticFunctionInterfaceProvider =
+                FirExtensionSyntheticFunctionInterfaceProvider.createIfNeeded(this, moduleData, kotlinScopeProvider)
 
             val providers = createProviders(
                 this,

compiler/fir/entrypoint/src/org/jetbrains/kotlin/fir/session/FirJsSessionFactory.kt

@@ -5,21 +5,25 @@
 
 package org.jetbrains.kotlin.fir.session
 
-import org.jetbrains.kotlin.config.*
+import org.jetbrains.kotlin.config.LanguageVersionSettings
-import org.jetbrains.kotlin.fir.*
+import org.jetbrains.kotlin.config.LanguageVersionSettingsImpl
+import org.jetbrains.kotlin.fir.FirModuleData
+import org.jetbrains.kotlin.fir.FirSession
+import org.jetbrains.kotlin.fir.FirVisibilityChecker
+import org.jetbrains.kotlin.fir.SessionConfiguration
 import org.jetbrains.kotlin.fir.analysis.FirOverridesBackwardCompatibilityHelper
 import org.jetbrains.kotlin.fir.checkers.registerJsCheckers
 import org.jetbrains.kotlin.fir.deserialization.ModuleDataProvider
 import org.jetbrains.kotlin.fir.extensions.FirExtensionRegistrar
 import org.jetbrains.kotlin.fir.java.FirProjectSessionProvider
 import org.jetbrains.kotlin.fir.resolve.calls.ConeCallConflictResolverFactory
-import org.jetbrains.kotlin.fir.resolve.providers.impl.*
+import org.jetbrains.kotlin.fir.resolve.providers.impl.FirBuiltinSymbolProvider
+import org.jetbrains.kotlin.fir.resolve.providers.impl.FirExtensionSyntheticFunctionInterfaceProvider
 import org.jetbrains.kotlin.fir.scopes.FirKotlinScopeProvider
 import org.jetbrains.kotlin.fir.scopes.FirPlatformClassMapper
 import org.jetbrains.kotlin.fir.scopes.impl.FirEnumEntriesSupport
 import org.jetbrains.kotlin.incremental.components.LookupTracker
 import org.jetbrains.kotlin.library.KotlinLibrary
-import org.jetbrains.kotlin.library.metadata.resolver.KotlinResolvedLibrary
 import org.jetbrains.kotlin.name.Name
 
 object FirJsSessionFactory : FirAbstractSessionFactory() {
@@ -75,13 +79,13 @@ object FirJsSessionFactory : FirAbstractSessionFactory() {
         },
         createKotlinScopeProvider = { FirKotlinScopeProvider { _, declaredMemberScope, _, _ -> declaredMemberScope } },
         createProviders = { session, builtinsModuleData, kotlinScopeProvider ->
-            listOf(
+            listOfNotNull(
                 KlibBasedSymbolProvider(session, moduleDataProvider, kotlinScopeProvider, resolvedLibraries),
                 // (Most) builtins should be taken from the dependencies in JS compilation, therefore builtins provider is the last one
                 // TODO: consider using "poisoning" provider for builtins to ensure that proper ones are taken from dependencies
                 // NOTE: it requires precise filtering for true nuiltins, like Function*
                 FirBuiltinSymbolProvider(session, builtinsModuleData, kotlinScopeProvider),
-                FirExtensionSyntheticFunctionInterfaceProvider(session, builtinsModuleData, kotlinScopeProvider),
+                FirExtensionSyntheticFunctionInterfaceProvider.createIfNeeded(session, builtinsModuleData, kotlinScopeProvider),
             )
         }
     )

compiler/fir/entrypoint/src/org/jetbrains/kotlin/fir/session/FirJvmSessionFactory.kt

@@ -5,8 +5,11 @@
 
 package org.jetbrains.kotlin.fir.session
 
-import org.jetbrains.kotlin.config.*
+import org.jetbrains.kotlin.config.LanguageVersionSettings
-import org.jetbrains.kotlin.fir.*
+import org.jetbrains.kotlin.config.LanguageVersionSettingsImpl
+import org.jetbrains.kotlin.fir.FirModuleData
+import org.jetbrains.kotlin.fir.FirSession
+import org.jetbrains.kotlin.fir.SessionConfiguration
 import org.jetbrains.kotlin.fir.checkers.registerJvmCheckers
 import org.jetbrains.kotlin.fir.declarations.FirDeclarationOrigin
 import org.jetbrains.kotlin.fir.deserialization.ModuleDataProvider
@@ -16,7 +19,9 @@ import org.jetbrains.kotlin.fir.java.FirProjectSessionProvider
 import org.jetbrains.kotlin.fir.java.JavaSymbolProvider
 import org.jetbrains.kotlin.fir.java.deserialization.JvmClassFileBasedSymbolProvider
 import org.jetbrains.kotlin.fir.java.deserialization.OptionalAnnotationClassesProvider
-import org.jetbrains.kotlin.fir.resolve.providers.impl.*
+import org.jetbrains.kotlin.fir.resolve.providers.impl.FirBuiltinSymbolProvider
+import org.jetbrains.kotlin.fir.resolve.providers.impl.FirCloneableSymbolProvider
+import org.jetbrains.kotlin.fir.resolve.providers.impl.FirExtensionSyntheticFunctionInterfaceProvider
 import org.jetbrains.kotlin.fir.resolve.scopes.wrapScopeWithJvmMapped
 import org.jetbrains.kotlin.fir.scopes.FirKotlinScopeProvider
 import org.jetbrains.kotlin.fir.session.environment.AbstractProjectEnvironment
@@ -48,7 +53,7 @@ object FirJvmSessionFactory : FirAbstractSessionFactory() {
             },
             createKotlinScopeProvider = { FirKotlinScopeProvider(::wrapScopeWithJvmMapped) },
             createProviders = { session, builtinsModuleData, kotlinScopeProvider ->
-                listOf(
+                listOfNotNull(
                     JvmClassFileBasedSymbolProvider(
                         session,
                         moduleDataProvider,
@@ -58,7 +63,7 @@ object FirJvmSessionFactory : FirAbstractSessionFactory() {
                         projectEnvironment.getFirJavaFacade(session, moduleDataProvider.allModuleData.last(), scope)
                     ),
                     FirBuiltinSymbolProvider(session, builtinsModuleData, kotlinScopeProvider),
-                    FirExtensionSyntheticFunctionInterfaceProvider(session, builtinsModuleData, kotlinScopeProvider),
+                    FirExtensionSyntheticFunctionInterfaceProvider.createIfNeeded(session, builtinsModuleData, kotlinScopeProvider),
                     FirCloneableSymbolProvider(session, builtinsModuleData, kotlinScopeProvider),
                     OptionalAnnotationClassesProvider(
                         session,

compiler/fir/entrypoint/src/org/jetbrains/kotlin/fir/session/FirNativeSessionFactory.kt

@@ -45,11 +45,11 @@ object FirNativeSessionFactory : FirAbstractSessionFactory() {
                 ).apply {
                     bindSession(session)
                 }
-                listOf(
+                listOfNotNull(
                     KlibBasedSymbolProvider(session, moduleDataProvider, kotlinScopeProvider, resolvedLibraries.map { it.library }),
                     NativeForwardDeclarationsSymbolProvider(session, forwardDeclarationsModuleData, kotlinScopeProvider, resolvedLibraries),
                     FirBuiltinSymbolProvider(session, builtinsModuleData, kotlinScopeProvider),
-                    FirExtensionSyntheticFunctionInterfaceProvider(session, builtinsModuleData, kotlinScopeProvider),
+                    FirExtensionSyntheticFunctionInterfaceProvider.createIfNeeded(session, builtinsModuleData, kotlinScopeProvider),
                     FirCloneableSymbolProvider(session, builtinsModuleData, kotlinScopeProvider),
                 )
             })

compiler/fir/providers/src/org/jetbrains/kotlin/fir/resolve/providers/impl/FirExtensionSyntheticFunctionInterfaceProvider.kt

@@ -46,6 +46,21 @@ class FirExtensionSyntheticFunctionInterfaceProvider(
     moduleData: FirModuleData,
     kotlinScopeProvider: FirKotlinScopeProvider
 ) : FirSyntheticFunctionInterfaceProviderBase(session, moduleData, kotlinScopeProvider) {
+    companion object {
+        /**
+         * A [FirExtensionSyntheticFunctionInterfaceProvider] only needs to be created if the session's function type service has extension
+         * function kinds. Otherwise, the provider would be useless.
+         */
+        fun createIfNeeded(
+            session: FirSession,
+            moduleData: FirModuleData,
+            kotlinScopeProvider: FirKotlinScopeProvider,
+        ): FirExtensionSyntheticFunctionInterfaceProvider? {
+            if (!session.functionTypeService.hasExtensionKinds()) return null
+            return FirExtensionSyntheticFunctionInterfaceProvider(session, moduleData, kotlinScopeProvider)
+        }
+    }
+
     override fun FunctionTypeKind.isAcceptable(): Boolean {
         return !this.isBuiltin
     }