[LL FIR] LLFirResolveTarget: make firFile property optional

Not all targets belonged to any files (e.g., fake overrides),
so we should be able to resolve them without a provided file

^KT-64243

analysis/low-level-api-fir/src/org/jetbrains/kotlin/analysis/low/level/api/fir/api/targets/LLFirResolveTarget.kt

@@ -25,9 +25,12 @@ import org.jetbrains.kotlin.fir.declarations.FirScript
  */
 internal sealed class LLFirResolveTarget(
     /**
-     * [FirFile] where the targets are located
+     * [FirFile] where the targets are located.
+     * Can be null if [target] does not belong to any file.
+     * E.g., fake overrides.
+     * @see org.jetbrains.kotlin.fir.scopes.impl.FirFakeOverrideGenerator
      */
-    val firFile: FirFile,
+    val firFile: FirFile?,
 
     /**
      * The list of [FirRegularClass] which are the required to go from file to target declarations in the top-down order.
@@ -48,19 +51,28 @@ internal sealed class LLFirResolveTarget(
 
     /**
      * Visit [path], [target] and optionally its subgraph.
-     * Each nested declaration will be wrapped with corresponding [withFile], [withClass] and [withScript] recursively.
+     * Each nested declaration will be wrapped with corresponding [LLFirResolveTargetVisitor.withFile],
+     * [LLFirResolveTargetVisitor.withRegularClass] and [LLFirResolveTargetVisitor.withScript] recursively.
      */
     fun visit(visitor: LLFirResolveTargetVisitor) {
         if (target is FirFile) {
             visitor.performAction(target)
         }
 
-        visitor.withFile(firFile) {
+        if (firFile != null) {
-            val pathIterator = path.iterator()
+            visitor.withFile(firFile) {
-            goToTarget(pathIterator, visitor)
+                goToTarget(visitor)
+            }
+        } else {
+            goToTarget(visitor)
         }
     }
 
+    private fun goToTarget(visitor: LLFirResolveTargetVisitor) {
+        val pathIterator = path.iterator()
+        goToTarget(pathIterator, visitor)
+    }
+
     private fun goToTarget(
         pathIterator: Iterator<FirDeclaration>,
         visitor: LLFirResolveTargetVisitor,
@@ -102,7 +114,7 @@ internal sealed class LLFirResolveTarget(
         append(this@LLFirResolveTarget::class.simpleName)
         append("(")
         buildList {
-            add(firFile.name)
+            firFile?.name?.let(::add)
             path.mapTo(this) {
                 when (it) {
                     is FirRegularClass -> it.name
@@ -130,8 +142,8 @@ internal sealed class LLFirResolveTarget(
     }
 }
 
-private fun pathWithScript(firFile: FirFile, path: List<FirRegularClass>, target: FirElementWithResolveState): List<FirDeclaration> {
+private fun pathWithScript(firFile: FirFile?, path: List<FirRegularClass>, target: FirElementWithResolveState): List<FirDeclaration> {
-    if (target is FirFile || target is FirFileAnnotationsContainer || target is FirScript) return path
+    if (firFile == null || target is FirFile || target is FirFileAnnotationsContainer || target is FirScript) return path
     val firScript = firFile.declarations.singleOrNull() as? FirScript ?: return path
     return listOf(firScript) + path
 }

analysis/low-level-api-fir/src/org/jetbrains/kotlin/analysis/low/level/api/fir/api/targets/LLFirSingleResolveTarget.kt

@@ -11,12 +11,16 @@ import org.jetbrains.kotlin.fir.declarations.*
 /**
  * [LLFirResolveTarget] representing single target to resolve. The [target] can be any of [FirElementWithResolveState]
  */
-internal class LLFirSingleResolveTarget(
+internal class LLFirSingleResolveTarget : LLFirResolveTarget {
-    firFile: FirFile,
+    constructor(firFile: FirFile) : super(firFile, emptyList(), firFile)
-    containerClasses: List<FirRegularClass>,
+
-    target: FirElementWithResolveState,
+    constructor(
-) : LLFirResolveTarget(firFile, containerClasses, target) {
+        firFile: FirFile,
-    constructor(firFile: FirFile) : this(firFile, emptyList(), firFile)
+        containerClasses: List<FirRegularClass>,
+        target: FirElementWithResolveState,
+    ) : super(firFile, containerClasses, target)
+
+    constructor(target: FirElementWithResolveState) : super(null, emptyList(), target)
 
     override fun visitTargetElement(
         element: FirElementWithResolveState,

analysis/low-level-api-fir/src/org/jetbrains/kotlin/analysis/low/level/api/fir/lazy/resolve/LLFirModuleLazyDeclarationResolver.kt

@@ -116,7 +116,7 @@ internal class LLFirModuleLazyDeclarationResolver(val moduleComponents: LLFirMod
         towerDataContextCollector: FirResolveContextCollector?,
     ) {
         try {
-            resolveFileToImportsWithLock(target.firFile)
+            target.firFile?.let(::resolveFileToImportsWithLock)
             if (toPhase == FirResolvePhase.IMPORTS) return
 
             lazyResolveTargets(

analysis/low-level-api-fir/src/org/jetbrains/kotlin/analysis/low/level/api/fir/transformers/LLFirTargetResolver.kt

@@ -73,7 +73,7 @@ internal abstract class LLFirTargetResolver(
      */
     private fun resolveDependencies(target: FirElementWithResolveState) {
         if (skipDependencyTargetResolutionStep || target is FirFileAnnotationsContainer) return
-        resolveTarget.firFile.annotationsContainer?.lazyResolveToPhase(resolverPhase)
+        resolveTarget.firFile?.annotationsContainer?.lazyResolveToPhase(resolverPhase)
 
         val originalDeclaration = (target as? FirCallableDeclaration)?.originalIfFakeOverrideOrDelegated()
         when {

analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/AbstractFirLazyDeclarationResolveOverAllPhasesTest.kt

@@ -12,7 +12,6 @@ import org.jetbrains.kotlin.fir.declarations.FirResolvePhase
 import org.jetbrains.kotlin.fir.declarations.resolvePhase
 import org.jetbrains.kotlin.fir.symbols.lazyResolveToPhaseRecursively
 import org.jetbrains.kotlin.psi.KtFile
-import org.jetbrains.kotlin.test.services.TestModuleStructure
 import org.jetbrains.kotlin.test.services.TestServices
 import org.jetbrains.kotlin.test.services.assertions
 
@@ -42,7 +41,7 @@ abstract class AbstractFirLazyDeclarationResolveOverAllPhasesTest : AbstractFirL
             } else {
                 val firFile = firResolveSession.getOrBuildFirFile(ktFile)
                 val designations = LLFirResolveMultiDesignationCollector.getDesignationsToResolve(elementToResolve)
-                listOf(firFile).plus(designations.map { it.firFile }).distinct()
+                listOf(firFile).plus(designations.mapNotNull { it.firFile }).distinct()
             }
 
             val basePhase = elementToResolve.resolvePhase