JVM_IR: check for null when converting unboxed inline classes to strings

`C?` can be unboxed into `T?` if if wraps a reference type `T!!`, but in
this case `null` is not a valid value to pass to `toString-impl`.

 #KT-42005 Fixed

compiler/fir/fir2ir/tests/org/jetbrains/kotlin/codegen/ir/FirBlackBoxCodegenTestGenerated.java

@@ -13977,6 +13977,11 @@ public class FirBlackBoxCodegenTestGenerated extends AbstractFirBlackBoxCodegenT
             runTest("compiler/testData/codegen/box/inlineClasses/toStringCallingPrivateFun.kt");
         }
 
+        @TestMetadata("toStringOfUnboxedNullable.kt")
+        public void testToStringOfUnboxedNullable() throws Exception {
+            runTest("compiler/testData/codegen/box/inlineClasses/toStringOfUnboxedNullable.kt");
+        }
+
         @TestMetadata("typeChecksForInlineClasses.kt")
         public void testTypeChecksForInlineClasses() throws Exception {
             runTest("compiler/testData/codegen/box/inlineClasses/typeChecksForInlineClasses.kt");

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

@@ -14,6 +14,7 @@ import org.jetbrains.kotlin.backend.common.phaser.makeIrFilePhase
 import org.jetbrains.kotlin.backend.jvm.JvmBackendContext
 import org.jetbrains.kotlin.backend.jvm.ir.JvmIrBuilder
 import org.jetbrains.kotlin.backend.jvm.ir.createJvmIrBuilder
+import org.jetbrains.kotlin.backend.jvm.lower.inlineclasses.InlineClassAbi
 import org.jetbrains.kotlin.backend.jvm.lower.inlineclasses.unboxInlineClass
 import org.jetbrains.kotlin.ir.builders.*
 import org.jetbrains.kotlin.ir.declarations.IrClass
@@ -102,19 +103,23 @@ private class JvmStringConcatenationLowering(val context: JvmBackendContext) : F
         }
     }
 
-    private fun JvmIrBuilder.lowerInlineClassArgument(expression: IrExpression): IrExpression {
-        if (expression.type.unboxInlineClass() == expression.type)
-            return expression
-
+    private fun JvmIrBuilder.lowerInlineClassArgument(expression: IrExpression): IrExpression? {
+        if (InlineClassAbi.unboxType(expression.type) == null)
+            return null
         val toStringFunction = expression.type.classOrNull?.owner?.toStringFunction
-            ?: return expression
-
+            ?: return null
         val toStringReplacement = backendContext.inlineClassReplacements.getReplacementFunction(toStringFunction)
-            ?: return expression
-
-        return irCall(toStringReplacement).apply {
-            putValueArgument(0, expression)
-        }
+            ?: return null
+        // `C?` can only be unboxed if it wraps a reference type `T!!`, in which case the unboxed type
+        // is `T?`. We can't pass that to `C.toString-impl` without checking for `null`.
+        return if (expression.type.isNullable())
+            irLetS(expression) {
+                irIfNull(context.irBuiltIns.stringType, irGet(it.owner), irString(null.toString()), irCall(toStringReplacement).apply {
+                    putValueArgument(0, irGet(it.owner))
+                })
+            }
+        else
+            irCall(toStringReplacement).apply { putValueArgument(0, expression) }
     }
 
     override fun visitStringConcatenation(expression: IrStringConcatenation): IrExpression {
@@ -131,22 +136,19 @@ private class JvmStringConcatenationLowering(val context: JvmBackendContext) : F
                 else
                     this
 
-
-            val arguments = expression.arguments.map { lowerInlineClassArgument(it) }
-
+            val arguments = expression.arguments
             when {
                 arguments.isEmpty() ->
                     irString("")
 
                 arguments.size == 1 ->
-                    callToString(arguments.single().unwrapImplicitNotNull())
+                    lowerInlineClassArgument(arguments[0]) ?: callToString(arguments[0].unwrapImplicitNotNull())
 
                 arguments.size == 2 && arguments[0].type.isStringClassType() ->
                     irCall(backendContext.ir.symbols.intrinsicStringPlus).apply {
-                        putValueArgument(0, arguments[0].unwrapImplicitNotNull())
-
+                        putValueArgument(0, lowerInlineClassArgument(arguments[0]) ?: arguments[0].unwrapImplicitNotNull())
                         // Unwrapping IMPLICIT_NOTNULL is not strictly necessary on 2nd argument (parameter type is `Any?`)
-                        putValueArgument(1, arguments[1])
+                        putValueArgument(1, lowerInlineClassArgument(arguments[1]) ?: arguments[1])
                     }
 
                 else -> {
@@ -156,10 +158,9 @@ private class JvmStringConcatenationLowering(val context: JvmBackendContext) : F
                         val appendFunction = typeToAppendFunction(argument.type)
                         stringBuilder = irCall(appendFunction).apply {
                             dispatchReceiver = stringBuilder
-
                             // Unwrapping IMPLICIT_NOTNULL is necessary for ALL arguments. There could be a call to `String.plus(Any?)`
                             // anywhere in the flattened IrStringConcatenation expression, e.g., `"foo" + (Java.platformString() + 123)`.
-                            putValueArgument(0, argument.unwrapImplicitNotNull())
+                            putValueArgument(0, lowerInlineClassArgument(argument) ?: argument.unwrapImplicitNotNull())
                         }
                     }
                     irCall(toStringFunction).apply {

compiler/testData/codegen/box/inlineClasses/toStringOfUnboxedNullable.kt

@@ -0,0 +1,21 @@
+// !LANGUAGE: +InlineClasses
+// IGNORE_BACKEND: JVM
+// IGNORE_LIGHT_ANALYSIS
+inline class IC(val x: String)
+
+fun IC?.foo() = toString() // `IC?` unboxed into `String?`
+fun IC?.bar() = "$this"
+
+fun assertEquals(a: String, b: String) {
+    if (a != b) throw AssertionError("$a != $b")
+}
+
+fun box(): String {
+    assertEquals((null as IC?).foo(), "null")
+    assertEquals((null as IC?).foo(), (null as IC?).toString())
+    assertEquals((null as IC?).foo(), (null as IC?).bar())
+    assertEquals(IC("x").foo(), "IC(x=x)")
+    assertEquals(IC("x").foo(), IC("x").toString())
+    assertEquals(IC("x").foo(), IC("x").bar())
+    return "OK"
+}

compiler/testData/codegen/bytecodeText/inlineClasses/toStringIsCalledByInlineClass.kt

@@ -1,13 +0,0 @@
-// !LANGUAGE: +InlineClasses
-
-// FILE: Z.kt
-inline class Z(val x: Int)
-
-// FILE: test.kt
-fun testZ(z: Z) = z.toString()
-fun testNZ(z: Z?) = z?.toString()
-
-// @TestKt.class:
-// 0 INVOKESTATIC Z\$Erased\.toString
-// 0 INVOKESTATIC Z\-Erased\.toString
-// 2 INVOKESTATIC Z\.toString-impl \(I\)Ljava/lang/String;

compiler/testData/codegen/bytecodeText/inlineClasses/toStringOfInlineClassValue.kt

@@ -0,0 +1,15 @@
+// !LANGUAGE: +InlineClasses
+
+// FILE: Z.kt
+inline class Z(val x: Int)
+
+// FILE: test.kt
+fun testZ(z: Z) = z.toString()
+fun testZT(z: Z) = "$z"
+fun testNZ(z: Z?) = z?.toString() // unboxed into Int after the null check
+fun testNZA(z: Z?) = z.toString() // calls Any?.toString() on boxed value
+fun testNZT(z: Z?) = "$z" // same
+
+// @TestKt.class:
+// 3 INVOKESTATIC Z\.toString-impl \(I\)Ljava/lang/String;
+// 2 INVOKESTATIC java/lang/String.valueOf

compiler/testData/codegen/bytecodeText/inlineClasses/toStringOfReferenceInlineClassValue.kt

@@ -0,0 +1,17 @@
+// !LANGUAGE: +InlineClasses
+// Completely incorrect bytecode - see `box/inlineClasses/toStringOfUnboxedNullable.kt`
+// IGNORE_BACKEND: JVM
+
+// FILE: Z.kt
+inline class Z(val x: Any)
+
+// FILE: test.kt
+fun testZ(z: Z) = z.toString()
+fun testZT(z: Z) = "$z"
+fun testNZ(z: Z?) = z?.toString() // `Z?` is unboxed into `Any?` even before the null check
+fun testNZA(z: Z?) = z.toString() // so all of these call toString-impl
+fun testNZT(z: Z?) = "$z"
+
+// @TestKt.class:
+// 5 INVOKESTATIC Z\.toString-impl \(Ljava/lang/Object;\)Ljava/lang/String;
+// 0 INVOKESTATIC java/lang/String.valueOf

compiler/tests/org/jetbrains/kotlin/codegen/BlackBoxCodegenTestGenerated.java

@@ -15372,6 +15372,11 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
             runTest("compiler/testData/codegen/box/inlineClasses/toStringCallingPrivateFun.kt");
         }
 
+        @TestMetadata("toStringOfUnboxedNullable.kt")
+        public void testToStringOfUnboxedNullable() throws Exception {
+            runTest("compiler/testData/codegen/box/inlineClasses/toStringOfUnboxedNullable.kt");
+        }
+
         @TestMetadata("typeChecksForInlineClasses.kt")
         public void testTypeChecksForInlineClasses() throws Exception {
             runTest("compiler/testData/codegen/box/inlineClasses/typeChecksForInlineClasses.kt");

compiler/tests/org/jetbrains/kotlin/codegen/BytecodeTextTestGenerated.java

@@ -3192,9 +3192,14 @@ public class BytecodeTextTestGenerated extends AbstractBytecodeTextTest {
             runTest("compiler/testData/codegen/bytecodeText/inlineClasses/suspendFunctionMangling.kt");
         }
 
-        @TestMetadata("toStringIsCalledByInlineClass.kt")
-        public void testToStringIsCalledByInlineClass() throws Exception {
-            runTest("compiler/testData/codegen/bytecodeText/inlineClasses/toStringIsCalledByInlineClass.kt");
+        @TestMetadata("toStringOfInlineClassValue.kt")
+        public void testToStringOfInlineClassValue() throws Exception {
+            runTest("compiler/testData/codegen/bytecodeText/inlineClasses/toStringOfInlineClassValue.kt");
+        }
+
+        @TestMetadata("toStringOfReferenceInlineClassValue.kt")
+        public void testToStringOfReferenceInlineClassValue() throws Exception {
+            runTest("compiler/testData/codegen/bytecodeText/inlineClasses/toStringOfReferenceInlineClassValue.kt");
         }
 
         @TestMetadata("uIntArrayIteratorWithoutBoxing.kt")

compiler/tests/org/jetbrains/kotlin/codegen/LightAnalysisModeTestGenerated.java

@@ -14669,6 +14669,11 @@ public class LightAnalysisModeTestGenerated extends AbstractLightAnalysisModeTes
             runTest("compiler/testData/codegen/box/inlineClasses/simpleSecondaryConstructor.kt");
         }
 
+        @TestMetadata("toStringOfUnboxedNullable.kt")
+        public void ignoreToStringOfUnboxedNullable() throws Exception {
+            runTest("compiler/testData/codegen/box/inlineClasses/toStringOfUnboxedNullable.kt");
+        }
+
         private void runTest(String testDataFilePath) throws Exception {
             KotlinTestUtils.runTest(this::doTest, TargetBackend.JVM, testDataFilePath);
         }

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

@@ -13977,6 +13977,11 @@ public class IrBlackBoxCodegenTestGenerated extends AbstractIrBlackBoxCodegenTes
             runTest("compiler/testData/codegen/box/inlineClasses/toStringCallingPrivateFun.kt");
         }
 
+        @TestMetadata("toStringOfUnboxedNullable.kt")
+        public void testToStringOfUnboxedNullable() throws Exception {
+            runTest("compiler/testData/codegen/box/inlineClasses/toStringOfUnboxedNullable.kt");
+        }
+
         @TestMetadata("typeChecksForInlineClasses.kt")
         public void testTypeChecksForInlineClasses() throws Exception {
             runTest("compiler/testData/codegen/box/inlineClasses/typeChecksForInlineClasses.kt");

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

@@ -3287,9 +3287,14 @@ public class IrBytecodeTextTestGenerated extends AbstractIrBytecodeTextTest {
             runTest("compiler/testData/codegen/bytecodeText/inlineClasses/suspendFunctionMangling.kt");
         }
 
-        @TestMetadata("toStringIsCalledByInlineClass.kt")
-        public void testToStringIsCalledByInlineClass() throws Exception {
-            runTest("compiler/testData/codegen/bytecodeText/inlineClasses/toStringIsCalledByInlineClass.kt");
+        @TestMetadata("toStringOfInlineClassValue.kt")
+        public void testToStringOfInlineClassValue() throws Exception {
+            runTest("compiler/testData/codegen/bytecodeText/inlineClasses/toStringOfInlineClassValue.kt");
+        }
+
+        @TestMetadata("toStringOfReferenceInlineClassValue.kt")
+        public void testToStringOfReferenceInlineClassValue() throws Exception {
+            runTest("compiler/testData/codegen/bytecodeText/inlineClasses/toStringOfReferenceInlineClassValue.kt");
         }
 
         @TestMetadata("uIntArrayIteratorWithoutBoxing.kt")

js/js.tests/test/org/jetbrains/kotlin/js/test/es6/semantics/IrJsCodegenBoxES6TestGenerated.java

@@ -12017,6 +12017,11 @@ public class IrJsCodegenBoxES6TestGenerated extends AbstractIrJsCodegenBoxES6Tes
             runTest("compiler/testData/codegen/box/inlineClasses/toStringCallingPrivateFun.kt");
         }
 
+        @TestMetadata("toStringOfUnboxedNullable.kt")
+        public void testToStringOfUnboxedNullable() throws Exception {
+            runTest("compiler/testData/codegen/box/inlineClasses/toStringOfUnboxedNullable.kt");
+        }
+
         @TestMetadata("typeChecksForInlineClasses.kt")
         public void testTypeChecksForInlineClasses() throws Exception {
             runTest("compiler/testData/codegen/box/inlineClasses/typeChecksForInlineClasses.kt");

js/js.tests/test/org/jetbrains/kotlin/js/test/ir/semantics/IrJsCodegenBoxTestGenerated.java

@@ -12017,6 +12017,11 @@ public class IrJsCodegenBoxTestGenerated extends AbstractIrJsCodegenBoxTest {
             runTest("compiler/testData/codegen/box/inlineClasses/toStringCallingPrivateFun.kt");
         }
 
+        @TestMetadata("toStringOfUnboxedNullable.kt")
+        public void testToStringOfUnboxedNullable() throws Exception {
+            runTest("compiler/testData/codegen/box/inlineClasses/toStringOfUnboxedNullable.kt");
+        }
+
         @TestMetadata("typeChecksForInlineClasses.kt")
         public void testTypeChecksForInlineClasses() throws Exception {
             runTest("compiler/testData/codegen/box/inlineClasses/typeChecksForInlineClasses.kt");

js/js.tests/test/org/jetbrains/kotlin/js/test/semantics/JsCodegenBoxTestGenerated.java

@@ -12082,6 +12082,11 @@ public class JsCodegenBoxTestGenerated extends AbstractJsCodegenBoxTest {
             runTest("compiler/testData/codegen/box/inlineClasses/toStringCallingPrivateFun.kt");
         }
 
+        @TestMetadata("toStringOfUnboxedNullable.kt")
+        public void testToStringOfUnboxedNullable() throws Exception {
+            runTest("compiler/testData/codegen/box/inlineClasses/toStringOfUnboxedNullable.kt");
+        }
+
         @TestMetadata("typeChecksForInlineClasses.kt")
         public void testTypeChecksForInlineClasses() throws Exception {
             runTest("compiler/testData/codegen/box/inlineClasses/typeChecksForInlineClasses.kt");