[FIR] Optimize synthetic function symbol provider with ClassId heuristic

- Similar to the implementation of `isNameForFunctionClass` in
  `FirSymbolProvider`, `FirSyntheticFunctionInterfaceProvider` benefits
  from checking the `ClassId` for a digit before accessing its class
  cache.

compiler/fir/providers/src/org/jetbrains/kotlin/fir/resolve/providers/FirSymbolProvider.kt

@@ -9,6 +9,7 @@ import org.jetbrains.kotlin.fir.FirSession
 import org.jetbrains.kotlin.fir.FirSessionComponent
 import org.jetbrains.kotlin.fir.resolve.fullyExpandedType
 import org.jetbrains.kotlin.fir.resolve.getSymbolByLookupTag
+import org.jetbrains.kotlin.fir.resolve.providers.impl.FirSyntheticFunctionInterfaceProviderBase.Companion.mayBeSyntheticFunctionClassName
 import org.jetbrains.kotlin.fir.scopes.FirScope
 import org.jetbrains.kotlin.fir.scopes.getDeclaredConstructors
 import org.jetbrains.kotlin.fir.scopes.getFunctions
@@ -16,14 +17,10 @@ import org.jetbrains.kotlin.fir.scopes.getProperties
 import org.jetbrains.kotlin.fir.scopes.impl.declaredMemberScope
 import org.jetbrains.kotlin.fir.symbols.FirBasedSymbol
 import org.jetbrains.kotlin.fir.symbols.impl.*
-import org.jetbrains.kotlin.fir.types.ConeLookupTagBasedType
-import org.jetbrains.kotlin.fir.types.ConeSimpleKotlinType
-import org.jetbrains.kotlin.fir.types.FirTypeRef
-import org.jetbrains.kotlin.fir.types.coneTypeSafe
+import org.jetbrains.kotlin.fir.types.*
 import org.jetbrains.kotlin.name.ClassId
 import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.name.Name
-import org.jetbrains.kotlin.fir.types.functionTypeService
 
 @RequiresOptIn
 annotation class FirSymbolProviderInternals
@@ -144,10 +141,9 @@ fun Set<String>.mayHaveTopLevelClassifier(
 private inline fun Set<String>.mayHaveTopLevelClassifier(shortClassName: Name): Boolean =
     shortClassName.asString() in this || shortClassName.isSpecial
 
+@OptIn(FirSymbolProviderInternals::class)
 private fun isNameForFunctionClass(classId: ClassId, session: FirSession): Boolean {
-    // Optimization: `classId` can only be a name for a generated function class if it ends with a digit. See `FunctionTypeKind`.
-    if (classId.relativeClassName.asString().lastOrNull()?.isDigit() != true) return false
-
+    if (!classId.mayBeSyntheticFunctionClassName()) return false
     return session.functionTypeService.getKindByClassNamePrefix(classId.packageFqName, classId.shortClassName.asString()) != null
 }
 

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

@@ -70,6 +70,7 @@ abstract class FirSyntheticFunctionInterfaceProviderBase(
     val kotlinScopeProvider: FirKotlinScopeProvider
 ) : FirSymbolProvider(session) {
     override fun getClassLikeSymbolByClassId(classId: ClassId): FirRegularClassSymbol? {
+        if (!classId.mayBeSyntheticFunctionClassName()) return null
         return cache.getValue(classId)
     }
 
@@ -233,4 +234,14 @@ abstract class FirSyntheticFunctionInterfaceProviderBase(
     }
 
     private fun FunctionTypeKind.classId(arity: Int) = ClassId(packageFqName, numberedClassName(arity))
+
+    companion object {
+        /**
+         * A [ClassId] can only be a name for a generated function class if it ends with a digit. See [FunctionTypeKind].
+         *
+         * Checking this first is usually faster than checking `functionTypeService.getKindByClassNamePrefix` or a class cache.
+         */
+        @FirSymbolProviderInternals
+        fun ClassId.mayBeSyntheticFunctionClassName(): Boolean = relativeClassName.asString().lastOrNull()?.isDigit() == true
+    }
 }