JVM IR: replace unoverridden Number.toChar with toInt().toChar()

This fixes failing tests for JVM_IR in
`box/primitiveTypes/numberToChar`.

 #KT-23447 Fixed
 #KT-46465

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

@@ -162,8 +162,11 @@ class IrIntrinsicMethods(val irBuiltIns: IrBuiltIns, val symbols: JvmSymbols) {
     private fun binaryOp(methodName: String, opcode: Int) = binaryFunForPrimitivesAcrossPrimitives(methodName, BinaryOp(opcode))
 
     private fun numberConversionMethods(): List<Pair<Key, IntrinsicMethod>> =
-        PrimitiveType.NUMBER_TYPES.flatMap { type -> numberConversionMethods(type.symbol) } +
+        PrimitiveType.NUMBER_TYPES.flatMap { type ->
-                numberConversionMethods(irBuiltIns.numberClass)
+            OperatorConventions.NUMBER_CONVERSIONS.map { method ->
+                createKeyMapping(NumberCast, type.symbol, method.asString())
+            }
+        }
 
     private fun arrayMethods(): List<Pair<Key, IntrinsicMethod>> =
         symbols.primitiveArraysToPrimitiveTypes.flatMap { (array, primitiveType) -> arrayMethods(primitiveType.symbol, array) } +
@@ -234,12 +237,5 @@ class IrIntrinsicMethods(val irBuiltIns: IrBuiltIns, val symbols: JvmSymbols) {
         ): Pair<Key, IntrinsicMethod> =
             Key(klass.owner.fqNameWhenAvailable!!, null, name, args.map { getParameterFqName(it) }) to
                     intrinsic
-
-        private fun numberConversionMethods(numberClass: IrClassSymbol) =
-            OperatorConventions.NUMBER_CONVERSIONS.map { method ->
-                createKeyMapping(NumberCast, numberClass, method.asString())
-            }
-
-
     }
 }

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

@@ -444,6 +444,7 @@ private val jvmFilePhases = listOf(
     kotlinNothingValueExceptionPhase,
     makePropertyDelegateMethodsStaticPhase,
     addSuperQualifierToJavaFieldAccessPhase,
+    replaceNumberToCharCallSitesPhase,
 
     renameFieldsPhase,
     fakeInliningLocalVariablesLowering,

compiler/ir/backend.jvm/lower/src/org/jetbrains/kotlin/backend/jvm/lower/ReplaceNumberToCharCallSitesLowering.kt

@@ -0,0 +1,61 @@
+/*
+ * Copyright 2010-2023 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.backend.jvm.lower
+
+import org.jetbrains.kotlin.backend.common.FileLoweringPass
+import org.jetbrains.kotlin.backend.common.phaser.makeIrFilePhase
+import org.jetbrains.kotlin.backend.jvm.JvmBackendContext
+import org.jetbrains.kotlin.backend.jvm.functionByName
+import org.jetbrains.kotlin.ir.declarations.IrFile
+import org.jetbrains.kotlin.ir.expressions.IrCall
+import org.jetbrains.kotlin.ir.expressions.IrExpression
+import org.jetbrains.kotlin.ir.expressions.impl.IrCallImpl
+import org.jetbrains.kotlin.ir.types.isNumber
+import org.jetbrains.kotlin.ir.util.irCall
+import org.jetbrains.kotlin.ir.util.resolveFakeOverride
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformerVoid
+import org.jetbrains.kotlin.ir.visitors.transformChildrenVoid
+import org.jetbrains.kotlin.types.expressions.OperatorConventions
+
+internal val replaceNumberToCharCallSitesPhase = makeIrFilePhase(
+    ::ReplaceNumberToCharCallSitesLowering,
+    name = "ReplaceNumberToCharCallSites",
+    description = "Replace `Number.toChar` call sites with `toInt().toChar()`",
+)
+
+// This lowering replaces call sites of the form `x.toChar()` to `x.toInt().toChar()`, but only if the declaration of `toChar`
+// in the scope of `x` comes from the library class `kotlin.Number`. For example, if `x` is some `MyNumber` which overrides
+// `toChar`, we won't replace it because there might be some custom logic, different from `toInt().toChar()`.
+//
+// This allows us to migrate usages of deprecated `Number.toChar` less painfully in order to remove it in the future (KT-56822).
+// Also, this allows to invoke `toChar` on `Number` subclasses declared in Java, which do not have it declared, even though the
+// compiler sees it there because `java.lang.Number` is mapped to `kotlin.Number`.
+class ReplaceNumberToCharCallSitesLowering(val context: JvmBackendContext) : FileLoweringPass, IrElementTransformerVoid() {
+    override fun lower(irFile: IrFile) {
+        irFile.transformChildrenVoid(this)
+    }
+
+    override fun visitCall(expression: IrCall): IrExpression {
+        expression.transformChildrenVoid(this)
+
+        val callee = expression.symbol.owner
+        if (callee.name != OperatorConventions.CHAR) return expression
+
+        val declaration = callee.resolveFakeOverride() ?: callee
+        val declaringClassType = declaration.dispatchReceiverParameter?.type ?: return expression
+        if (!declaringClassType.isNumber()) return expression
+
+        val dispatchReceiver = expression.dispatchReceiver ?: return expression
+        expression.dispatchReceiver = IrCallImpl(
+            dispatchReceiver.startOffset, dispatchReceiver.endOffset,
+            context.irBuiltIns.intType, context.irBuiltIns.numberClass.functionByName("toInt"), 0, 0,
+        ).also { toInt ->
+            toInt.dispatchReceiver = dispatchReceiver
+        }
+
+        return irCall(expression, context.irBuiltIns.intClass.functionByName("toChar"))
+    }
+}

compiler/testData/codegen/box/primitiveTypes/numberToChar/javaSubclass.kt

@@ -2,6 +2,9 @@
 // ISSUE: KT-23447
 // WITH_STDLIB
 
+// IGNORE_BACKEND_K2: JVM_IR
+// Ignore reason: KT-57217
+
 // FILE: MyNumber.java
 
 public class MyNumber extends Number {