[AA Standalone] Implement KotlinDirectInheritorsProvider

- We are relying on static indexing to find candidates for sealed
  inheritors, hence the extension to the index.
- The direct usage of `KotlinStaticDeclarationProviderFactory` in
  `KotlinStandaloneDirectInheritorsProvider` is not pretty, but a proper
  design requires making the static index available as a service and
  moving "static" services to the Standalone API (from AA providers).

^KT-66013

analysis/analysis-api-providers/src/org/jetbrains/kotlin/analysis/providers/impl/KotlinStaticDeclarationIndex.kt

@@ -6,6 +6,7 @@
 package org.jetbrains.kotlin.analysis.providers.impl
 
 import org.jetbrains.kotlin.name.FqName
+import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.psi.*
 
 internal class KotlinStaticDeclarationIndex {
@@ -16,4 +17,9 @@ internal class KotlinStaticDeclarationIndex {
     internal val typeAliasMap: MutableMap<FqName, MutableSet<KtTypeAlias>> = mutableMapOf()
     internal val topLevelFunctionMap: MutableMap<FqName, MutableSet<KtNamedFunction>> = mutableMapOf()
     internal val topLevelPropertyMap: MutableMap<FqName, MutableSet<KtProperty>> = mutableMapOf()
+
+    /**
+     * Allows quickly finding [KtClassOrObject]s which have a given simple name as a supertype. The map may contain local classes as well.
+     */
+    internal val classesBySupertypeName: MutableMap<Name, MutableSet<KtClassOrObject>> = mutableMapOf()
 }

analysis/analysis-api-providers/src/org/jetbrains/kotlin/analysis/providers/impl/KotlinStaticDeclarationProvider.kt

@@ -35,6 +35,7 @@ import org.jetbrains.kotlin.fileClasses.javaFileFacadeFqName
 import org.jetbrains.kotlin.idea.KotlinLanguage
 import org.jetbrains.kotlin.name.*
 import org.jetbrains.kotlin.psi.*
+import org.jetbrains.kotlin.psi.psiUtil.getSuperNames
 import org.jetbrains.kotlin.psi.stubs.KotlinClassOrObjectStub
 import org.jetbrains.kotlin.psi.stubs.elements.KtStubElementTypes
 import org.jetbrains.kotlin.psi.stubs.impl.*
@@ -203,7 +204,7 @@ public class KotlinStaticDeclarationProviderFactory(
         }
 
         override fun visitClassOrObject(classOrObject: KtClassOrObject) {
-            addToClassMap(classOrObject)
+            indexClassOrObject(classOrObject)
             super.visitClassOrObject(classOrObject)
         }
 
@@ -236,6 +237,11 @@ public class KotlinStaticDeclarationProviderFactory(
         }.add(script)
     }
 
+    private fun indexClassOrObject(classOrObject: KtClassOrObject) {
+        addToClassMap(classOrObject)
+        indexSupertypeNames(classOrObject)
+    }
+
     private fun addToClassMap(classOrObject: KtClassOrObject) {
         classOrObject.getClassId()?.let { classId ->
             index.classMap.computeIfAbsent(classId.packageFqName) {
@@ -244,6 +250,14 @@ public class KotlinStaticDeclarationProviderFactory(
         }
     }
 
+    private fun indexSupertypeNames(classOrObject: KtClassOrObject) {
+        classOrObject.getSuperNames().forEach { superName ->
+            index.classesBySupertypeName
+                .computeIfAbsent(Name.identifier(superName)) { mutableSetOf() }
+                .add(classOrObject)
+        }
+    }
+
     private fun addToTypeAliasMap(typeAlias: KtTypeAlias) {
         typeAlias.getClassId()?.let { classId ->
             index.typeAliasMap.computeIfAbsent(classId.packageFqName) {
@@ -307,12 +321,12 @@ public class KotlinStaticDeclarationProviderFactory(
     private fun indexStub(stub: StubElement<*>) {
         when (stub) {
             is KotlinClassStubImpl -> {
-                addToClassMap(stub.psi)
+                indexClassOrObject(stub.psi)
                 // member functions and properties
                 stub.childrenStubs.forEach(::indexStub)
             }
             is KotlinObjectStubImpl -> {
-                addToClassMap(stub.psi)
+                indexClassOrObject(stub.psi)
                 // member functions and properties
                 stub.childrenStubs.forEach(::indexStub)
             }
@@ -399,6 +413,9 @@ public class KotlinStaticDeclarationProviderFactory(
     }
 
     public fun getAllKtClasses(): List<KtClassOrObject> = index.classMap.values.flattenTo(mutableListOf())
+
+    public fun getDirectInheritorCandidates(baseClassName: Name): Set<KtClassOrObject> =
+        index.classesBySupertypeName[baseClassName].orEmpty()
 }
 
 /**