JVM IR: retain optional annotations as package private classes

Similarly to how it's done in the old backend (see
PackageCodegenImpl.generateClassesAndObjectsInFile and
AnnotationCodegen.genAnnotation)

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/ExpectDeclarationsRemoveLowering.kt

@@ -15,9 +15,9 @@ import org.jetbrains.kotlin.ir.visitors.acceptVoid
 /**
  * This pass removes all declarations with `isExpect == true`.
  */
-class ExpectDeclarationsRemoveLowering(val context: BackendContext) : FileLoweringPass {
+class ExpectDeclarationsRemoveLowering(val context: BackendContext, keepOptionalAnnotations: Boolean = false) : FileLoweringPass {
 
-    val visitor = ExpectDeclarationRemover(context.ir.symbols.externalSymbolTable, true)
+    val visitor = ExpectDeclarationRemover(context.ir.symbols.externalSymbolTable, doRemove = true, keepOptionalAnnotations)
 
     override fun lower(irFile: IrFile) {
         irFile.acceptVoid(visitor)

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/JvmLower.kt

@@ -74,8 +74,8 @@ private val arrayConstructorPhase = makeIrFilePhase(
     description = "Transform `Array(size) { index -> value }` into a loop"
 )
 
-private val expectDeclarationsRemovingPhase = makeIrModulePhase(
-    ::ExpectDeclarationsRemoveLowering,
+private val expectDeclarationsRemovingPhase = makeIrModulePhase<JvmBackendContext>(
+    { context -> ExpectDeclarationsRemoveLowering(context, keepOptionalAnnotations = true) },
     name = "ExpectDeclarationsRemoving",
     description = "Remove expect declaration from module fragment"
 )

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/codegen/AnnotationCodegen.kt

@@ -35,6 +35,7 @@ import org.jetbrains.kotlin.ir.types.isNullable
 import org.jetbrains.kotlin.ir.util.*
 import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.name.Name
+import org.jetbrains.kotlin.resolve.checkers.ExpectedActualDeclarationChecker
 import org.jetbrains.kotlin.synthetic.isVisibleOutside
 import org.jetbrains.org.objectweb.asm.AnnotationVisitor
 import org.jetbrains.org.objectweb.asm.Type
@@ -156,6 +157,13 @@ class AnnotationCodegen(
         val retentionPolicy = getRetentionPolicy(annotationClass)
         if (retentionPolicy == RetentionPolicy.SOURCE) return null
 
+        // We do not generate annotations whose classes are optional (annotated with `@OptionalExpectation`) because if an annotation entry
+        // is resolved to the expected declaration, this means that annotation has no actual class, and thus should not be generated.
+        // (Otherwise we would've resolved the entry to the actual annotation class.)
+        if (ExpectedActualDeclarationChecker.isOptionalAnnotationClass(annotationClass.descriptor)) {
+            return null
+        }
+
         innerClassConsumer.addInnerClassInfoFromAnnotation(annotationClass)
 
         val asmTypeDescriptor = typeMapper.mapType(annotation.type).descriptor

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/ExpectDeclarationRemover.kt

@@ -5,6 +5,7 @@
 
 package org.jetbrains.kotlin.ir.util
 
+import org.jetbrains.kotlin.descriptors.ClassDescriptor
 import org.jetbrains.kotlin.descriptors.MemberDescriptor
 import org.jetbrains.kotlin.ir.IrElement
 import org.jetbrains.kotlin.ir.declarations.*
@@ -22,7 +23,11 @@ import org.jetbrains.kotlin.resolve.descriptorUtil.module
 import org.jetbrains.kotlin.resolve.multiplatform.ExpectedActualResolver
 
 // `doRemove` means should expect-declaration be removed from IR
-class ExpectDeclarationRemover(val symbolTable: ReferenceSymbolTable, private val doRemove: Boolean) : IrElementVisitorVoid {
+class ExpectDeclarationRemover(
+    val symbolTable: ReferenceSymbolTable,
+    private val doRemove: Boolean,
+    private val keepOptionalAnnotations: Boolean
+) : IrElementVisitorVoid {
     override fun visitElement(element: IrElement) {
         element.acceptChildrenVoid(this)
     }
@@ -30,12 +35,16 @@ class ExpectDeclarationRemover(val symbolTable: ReferenceSymbolTable, private va
     override fun visitFile(declaration: IrFile) {
         // All declarations with `isExpect == true` are nested into a top-level declaration with `isExpect == true`.
         declaration.declarations.removeAll {
+            // TODO: rewrite findCompatibleActualForExpected using IR structures instead of descriptors
             val descriptor = it.descriptor
-            if (descriptor is MemberDescriptor && descriptor.isExpect) {
+            if (descriptor !is MemberDescriptor || !descriptor.isExpect ||
+                (keepOptionalAnnotations && descriptor is ClassDescriptor &&
+                        ExpectedActualDeclarationChecker.shouldGenerateExpectClass(descriptor))
+            ) {
+                false
+            } else {
                 copyDefaultArgumentsFromExpectToActual(it)
                 doRemove
-            } else {
-                false
             }
         }
     }
@@ -56,9 +65,7 @@ class ExpectDeclarationRemover(val symbolTable: ReferenceSymbolTable, private va
                 assert(function.valueParameters[index] == declaration)
 
                 if (function is IrConstructor &&
-                    ExpectedActualDeclarationChecker.isOptionalAnnotationClass(
-                        function.descriptor.constructedClass
-                    )
+                    ExpectedActualDeclarationChecker.isOptionalAnnotationClass(function.descriptor.constructedClass)
                 ) {
                     return
                 }
@@ -145,4 +152,4 @@ class ExpectDeclarationRemover(val symbolTable: ReferenceSymbolTable, private va
             else -> error(parent)
         }
     }
-}
+}

compiler/ir/serialization.js/src/org/jetbrains/kotlin/ir/backend/js/klib.kt

@@ -136,7 +136,7 @@ fun generateKLib(
     val moduleName = configuration[CommonConfigurationKeys.MODULE_NAME]!!
 
     if (!configuration.klibMpp) {
-        moduleFragment.acceptVoid(ExpectDeclarationRemover(psi2IrContext.symbolTable, false))
+        moduleFragment.acceptVoid(ExpectDeclarationRemover(psi2IrContext.symbolTable, doRemove = false, keepOptionalAnnotations = false))
     }
 
     serializeModuleIntoKlib(

compiler/testData/compileKotlinAgainstKotlin/optionalAnnotation.kt

@@ -1,6 +1,5 @@
 // !LANGUAGE: +MultiPlatformProjects
 // !USE_EXPERIMENTAL: kotlin.ExperimentalMultiplatform
-// IGNORE_BACKEND: JVM_IR
 // TARGET_BACKEND: JVM
 // FULL_JDK
 // FILE: A.kt

compiler/testData/writeFlags/multiplatform/optionalExpectation.kt

@@ -0,0 +1,12 @@
+// !LANGUAGE: +MultiPlatformProjects
+// !USE_EXPERIMENTAL: kotlin.ExperimentalMultiplatform
+// WITH_RUNTIME
+
+@file:Suppress("OPTIONAL_DECLARATION_USAGE_IN_NON_COMMON_SOURCE") // TODO: support common sources in the test infrastructure
+
+@OptionalExpectation
+expect annotation class Anno(val s: String)
+
+// TESTED_OBJECT_KIND: class
+// TESTED_OBJECTS: Anno
+// FLAGS: ACC_INTERFACE, ACC_ABSTRACT, ACC_ANNOTATION

compiler/tests/org/jetbrains/kotlin/codegen/flags/WriteFlagsTestGenerated.java

@@ -872,6 +872,24 @@ public class WriteFlagsTestGenerated extends AbstractWriteFlagsTest {
         }
     }
 
+    @TestMetadata("compiler/testData/writeFlags/multiplatform")
+    @TestDataPath("$PROJECT_ROOT")
+    @RunWith(JUnit3RunnerWithInners.class)
+    public static class Multiplatform extends AbstractWriteFlagsTest {
+        private void runTest(String testDataFilePath) throws Exception {
+            KotlinTestUtils.runTest(this::doTest, TargetBackend.JVM, testDataFilePath);
+        }
+
+        public void testAllFilesPresentInMultiplatform() throws Exception {
+            KotlinTestUtils.assertAllTestsPresentByMetadataWithExcluded(this.getClass(), new File("compiler/testData/writeFlags/multiplatform"), Pattern.compile("^(.+)\\.kt$"), null, TargetBackend.JVM, true);
+        }
+
+        @TestMetadata("optionalExpectation.kt")
+        public void testOptionalExpectation() throws Exception {
+            runTest("compiler/testData/writeFlags/multiplatform/optionalExpectation.kt");
+        }
+    }
+
     @TestMetadata("compiler/testData/writeFlags/property")
     @TestDataPath("$PROJECT_ROOT")
     @RunWith(JUnit3RunnerWithInners.class)

compiler/tests/org/jetbrains/kotlin/codegen/ir/IrWriteFlagsTestGenerated.java

@@ -872,6 +872,24 @@ public class IrWriteFlagsTestGenerated extends AbstractIrWriteFlagsTest {
         }
     }
 
+    @TestMetadata("compiler/testData/writeFlags/multiplatform")
+    @TestDataPath("$PROJECT_ROOT")
+    @RunWith(JUnit3RunnerWithInners.class)
+    public static class Multiplatform extends AbstractIrWriteFlagsTest {
+        private void runTest(String testDataFilePath) throws Exception {
+            KotlinTestUtils.runTest(this::doTest, TargetBackend.JVM_IR, testDataFilePath);
+        }
+
+        public void testAllFilesPresentInMultiplatform() throws Exception {
+            KotlinTestUtils.assertAllTestsPresentByMetadataWithExcluded(this.getClass(), new File("compiler/testData/writeFlags/multiplatform"), Pattern.compile("^(.+)\\.kt$"), null, TargetBackend.JVM_IR, true);
+        }
+
+        @TestMetadata("optionalExpectation.kt")
+        public void testOptionalExpectation() throws Exception {
+            runTest("compiler/testData/writeFlags/multiplatform/optionalExpectation.kt");
+        }
+    }
+
     @TestMetadata("compiler/testData/writeFlags/property")
     @TestDataPath("$PROJECT_ROOT")
     @RunWith(JUnit3RunnerWithInners.class)