IR: undeprecate IrUninitializedType

It's no longer a temporary hack, see the comment.

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

@@ -24,6 +24,7 @@ import org.jetbrains.kotlin.ir.expressions.IrBody
 import org.jetbrains.kotlin.ir.expressions.IrConstructorCall
 import org.jetbrains.kotlin.ir.symbols.IrConstructorSymbol
 import org.jetbrains.kotlin.ir.types.IrType
+import org.jetbrains.kotlin.ir.types.impl.IrUninitializedType
 import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.serialization.deserialization.descriptors.DeserializedContainerSource
 
@@ -51,9 +52,8 @@ class IrConstructorImpl(
     override lateinit var parent: IrDeclarationParent
     override var annotations: List<IrConstructorCall> = emptyList()
 
-    @Suppress("DEPRECATION")
     override var returnType: IrType = returnType
-        get() = if (field === org.jetbrains.kotlin.ir.types.impl.IrUninitializedType) {
+        get() = if (field === IrUninitializedType) {
             error("Return type is not initialized")
         } else {
             field

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

@@ -16,6 +16,7 @@ import org.jetbrains.kotlin.ir.expressions.IrConstructorCall
 import org.jetbrains.kotlin.ir.symbols.IrPropertySymbol
 import org.jetbrains.kotlin.ir.symbols.IrSimpleFunctionSymbol
 import org.jetbrains.kotlin.ir.types.IrType
+import org.jetbrains.kotlin.ir.types.impl.IrUninitializedType
 import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.serialization.deserialization.descriptors.DeserializedContainerSource
 
@@ -41,9 +42,8 @@ abstract class IrFunctionCommonImpl(
     override lateinit var parent: IrDeclarationParent
     override var annotations: List<IrConstructorCall> = emptyList()
 
-    @Suppress("DEPRECATION")
     override var returnType: IrType = returnType
-        get() = if (field === org.jetbrains.kotlin.ir.types.impl.IrUninitializedType) {
+        get() = if (field === IrUninitializedType) {
             error("Return type is not initialized")
         } else {
             field

compiler/ir/ir.tree.persistent/src/org/jetbrains/kotlin/ir/declarations/persistent/PersistentIrConstructor.kt

@@ -26,6 +26,7 @@ import org.jetbrains.kotlin.ir.expressions.IrBody
 import org.jetbrains.kotlin.ir.expressions.IrConstructorCall
 import org.jetbrains.kotlin.ir.symbols.IrConstructorSymbol
 import org.jetbrains.kotlin.ir.types.IrType
+import org.jetbrains.kotlin.ir.types.impl.IrUninitializedType
 import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.serialization.deserialization.descriptors.DeserializedContainerSource
 
@@ -70,10 +71,9 @@ internal class PersistentIrConstructor(
             }
         }
 
-    @Suppress("DEPRECATION")
     override var returnType: IrType
         get() = returnTypeField.let {
-            if (it !== org.jetbrains.kotlin.ir.types.impl.IrUninitializedType) it else error("Return type is not initialized")
+            if (it !== IrUninitializedType) it else error("Return type is not initialized")
         }
         set(c) {
             returnTypeField = c

compiler/ir/ir.tree.persistent/src/org/jetbrains/kotlin/ir/declarations/persistent/PersistentIrFunction.kt

@@ -18,6 +18,7 @@ import org.jetbrains.kotlin.ir.expressions.IrConstructorCall
 import org.jetbrains.kotlin.ir.symbols.IrPropertySymbol
 import org.jetbrains.kotlin.ir.symbols.IrSimpleFunctionSymbol
 import org.jetbrains.kotlin.ir.types.IrType
+import org.jetbrains.kotlin.ir.types.impl.IrUninitializedType
 import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.serialization.deserialization.descriptors.DeserializedContainerSource
 
@@ -60,10 +61,9 @@ internal abstract class PersistentIrFunctionCommon(
             }
         }
 
-    @Suppress("DEPRECATION")
     final override var returnType: IrType
         get() = returnTypeField.let {
-            if (it !== org.jetbrains.kotlin.ir.types.impl.IrUninitializedType) it else error("Return type is not initialized")
+            if (it !== IrUninitializedType) it else error("Return type is not initialized")
         }
         set(c) {
             returnTypeField = c

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

@@ -46,7 +46,16 @@ object IrStarProjectionImpl : IrStarProjection {
     override fun hashCode(): Int = System.identityHashCode(this)
 }
 
-@Deprecated("Hack to temporary cover late type initialization")
+/**
+ * An instance which should be used when creating an IR element whose type cannot be determined at the moment of creation.
+ *
+ * Example: when translating generic functions in psi2ir, we're creating an IrFunction first, then adding IrTypeParameter instances to it,
+ * and only then translating the function's return type with respect to those created type parameters.
+ *
+ * Instead of using this special instance, we could just make IrFunction/IrConstructor constructors allow to accept no return type,
+ * however this could lead to a situation where we forget to set return type sometimes. This would result in crashes at unexpected moments,
+ * especially in Kotlin/JS where function return types are not present in the resulting binary files.
+ */
 object IrUninitializedType : IrType {
     override val annotations: List<IrConstructorCall> = emptyList()