[IR] Add optIn to IrDeclarationContainer.declarations

Accessing list of declaration may trigger lazy declaration list computation for lazy class,
   which requires computation of fake-overrides for this class. So it's unsafe to access it
   before IR for all sources is built (because fake-overrides of lazy classes may depend on
   declaration of source classes, e.g. for java source classes)

So this OptIn is needed to carefully handle all cases of .declarations access in FIR2IR

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/lazy/Fir2IrLazyClass.kt

@@ -24,6 +24,7 @@ import org.jetbrains.kotlin.ir.declarations.lazy.IrMaybeDeserializedClass
 import org.jetbrains.kotlin.ir.declarations.lazy.lazyVar
 import org.jetbrains.kotlin.ir.expressions.IrConstructorCall
 import org.jetbrains.kotlin.ir.symbols.IrClassSymbol
+import org.jetbrains.kotlin.ir.symbols.IrSymbolInternals
 import org.jetbrains.kotlin.ir.types.IrSimpleType
 import org.jetbrains.kotlin.ir.types.IrType
 import org.jetbrains.kotlin.ir.types.impl.IrSimpleTypeImpl
@@ -154,6 +155,7 @@ class Fir2IrLazyClass(
             .also(converter::bindFakeOverridesOrPostpone)
     }
 
+    @IrSymbolInternals
     override val declarations: MutableList<IrDeclaration> by lazyVar(lock) {
         val result = mutableListOf<IrDeclaration>()
         // NB: it's necessary to take all callables from scope,

compiler/ir/ir.tree/gen/org/jetbrains/kotlin/ir/declarations/IrDeclarationContainer.kt

@@ -8,6 +8,7 @@
 
 package org.jetbrains.kotlin.ir.declarations
 
+import org.jetbrains.kotlin.ir.symbols.IrSymbolInternals
 
 /**
  * A non-leaf IR tree element.
@@ -15,5 +16,12 @@ package org.jetbrains.kotlin.ir.declarations
  * Generated from: [org.jetbrains.kotlin.ir.generator.IrTree.declarationContainer]
  */
 interface IrDeclarationContainer : IrDeclarationParent {
+    /**
+     * Accessing list of declaration may trigger lazy declaration list computation for lazy class,
+     *   which requires computation of fake-overrides for this class. So it's unsafe to access it
+     *   before IR for all sources is built (because fake-overrides of lazy classes may depend on
+     *   declaration of source classes, e.g. for java source classes)
+     */
+    @IrSymbolInternals
     val declarations: MutableList<IrDeclaration>
 }

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrClassImpl.kt

@@ -10,6 +10,7 @@ import org.jetbrains.kotlin.ir.ObsoleteDescriptorBasedAPI
 import org.jetbrains.kotlin.ir.declarations.*
 import org.jetbrains.kotlin.ir.expressions.IrConstructorCall
 import org.jetbrains.kotlin.ir.symbols.IrClassSymbol
+import org.jetbrains.kotlin.ir.symbols.IrSymbolInternals
 import org.jetbrains.kotlin.ir.types.IrSimpleType
 import org.jetbrains.kotlin.ir.types.IrType
 import org.jetbrains.kotlin.name.Name
@@ -47,6 +48,7 @@ open class IrClassImpl(
 
     override var thisReceiver: IrValueParameter? = null
 
+    @IrSymbolInternals
     override val declarations: MutableList<IrDeclaration> = ArrayList()
 
     override var typeParameters: List<IrTypeParameter> = emptyList()

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrExternalPackageFragmentImpl.kt

@@ -24,6 +24,7 @@ import org.jetbrains.kotlin.ir.UNDEFINED_OFFSET
 import org.jetbrains.kotlin.ir.declarations.IrDeclaration
 import org.jetbrains.kotlin.ir.declarations.IrExternalPackageFragment
 import org.jetbrains.kotlin.ir.symbols.IrExternalPackageFragmentSymbol
+import org.jetbrains.kotlin.ir.symbols.IrSymbolInternals
 import org.jetbrains.kotlin.ir.symbols.impl.IrExternalPackageFragmentSymbolImpl
 import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.serialization.deserialization.descriptors.DeserializedContainerSource
@@ -51,6 +52,7 @@ class IrExternalPackageFragmentImpl(
     override val moduleDescriptor: ModuleDescriptor
         get() = packageFragmentDescriptor.containingDeclaration
 
+    @IrSymbolInternals
     override val declarations: MutableList<IrDeclaration> = ArrayList()
 
     @OptIn(ObsoleteDescriptorBasedAPI::class)

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrFileImpl.kt

@@ -26,6 +26,7 @@ import org.jetbrains.kotlin.ir.declarations.IrModuleFragment
 import org.jetbrains.kotlin.ir.declarations.MetadataSource
 import org.jetbrains.kotlin.ir.expressions.IrConstructorCall
 import org.jetbrains.kotlin.ir.symbols.IrFileSymbol
+import org.jetbrains.kotlin.ir.symbols.IrSymbolInternals
 import org.jetbrains.kotlin.ir.symbols.impl.IrFileSymbolImpl
 import org.jetbrains.kotlin.name.FqName
 
@@ -79,6 +80,7 @@ class IrFileImpl(
                 packageFragmentDescriptor.containingDeclaration
         }
 
+    @IrSymbolInternals
     override val declarations: MutableList<IrDeclaration> = ArrayList()
 
     override var annotations: List<IrConstructorCall> = emptyList()

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/lazy/IrLazyClass.kt

@@ -11,6 +11,7 @@ import org.jetbrains.kotlin.ir.ObsoleteDescriptorBasedAPI
 import org.jetbrains.kotlin.ir.declarations.*
 import org.jetbrains.kotlin.ir.expressions.IrConstructorCall
 import org.jetbrains.kotlin.ir.symbols.IrClassSymbol
+import org.jetbrains.kotlin.ir.symbols.IrSymbolInternals
 import org.jetbrains.kotlin.ir.types.IrSimpleType
 import org.jetbrains.kotlin.ir.types.IrType
 import org.jetbrains.kotlin.ir.util.*
@@ -55,7 +56,7 @@ class IrLazyClass(
         }
     }
 
-
+    @IrSymbolInternals
     override val declarations: MutableList<IrDeclaration> by lazyVar(stubGenerator.lock) {
         ArrayList<IrDeclaration>().also {
             typeTranslator.buildWithScope(this) {

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/types/impl/IrErrorClassImpl.kt

@@ -13,6 +13,7 @@ import org.jetbrains.kotlin.ir.declarations.*
 import org.jetbrains.kotlin.ir.declarations.impl.IrClassImpl
 import org.jetbrains.kotlin.ir.expressions.IrConstructorCall
 import org.jetbrains.kotlin.ir.symbols.IrFileSymbol
+import org.jetbrains.kotlin.ir.symbols.IrSymbolInternals
 import org.jetbrains.kotlin.ir.symbols.impl.IrClassSymbolImpl
 import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.name.Name
@@ -31,6 +32,8 @@ object IrErrorClassImpl : IrClassImpl(
             override var annotations: List<IrConstructorCall>
                 get() = shouldNotBeCalled()
                 set(_) {}
+
+            @IrSymbolInternals
             override val declarations: MutableList<IrDeclaration>
                 get() = shouldNotBeCalled()
             override val symbol: IrFileSymbol

compiler/ir/ir.tree/tree-generator/src/org/jetbrains/kotlin/ir/generator/IrTree.kt

@@ -343,7 +343,17 @@ object IrTree : AbstractTreeBuilder() {
 
         parent(declarationParent)
 
-        +listField("declarations", declaration, mutability = List, isChild = true)
+        +listField("declarations", declaration, mutability = List, isChild = true) {
+            kDoc = """
+                 Accessing list of declaration may trigger lazy declaration list computation for lazy class,
+                   which requires computation of fake-overrides for this class. So it's unsafe to access it
+                   before IR for all sources is built (because fake-overrides of lazy classes may depend on
+                   declaration of source classes, e.g. for java source classes)
+            """.trimIndent()
+            generationCallback = {
+                addAnnotation(ClassName("org.jetbrains.kotlin.ir.symbols", "IrSymbolInternals"))
+            }
+        }
     }
     val typeParametersContainer: ElementConfig by element(Declaration) {
         ownsChildren = false