[JVM_IR] Generate line numbers and nops for init blocks.

This seems to be what JVM does and it allows you to set a
breakpoint on the init line.

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

@@ -6,6 +6,7 @@
 package org.jetbrains.kotlin.backend.jvm.codegen
 
 import org.jetbrains.kotlin.backend.common.lower.BOUND_RECEIVER_PARAMETER
+import org.jetbrains.kotlin.backend.common.lower.SYNTHESIZED_INIT_BLOCK
 import org.jetbrains.kotlin.backend.jvm.JvmLoweredDeclarationOrigin
 import org.jetbrains.kotlin.backend.jvm.intrinsics.IrIntrinsicMethods
 import org.jetbrains.kotlin.backend.jvm.intrinsics.JavaClassProperty
@@ -324,15 +325,25 @@ class ExpressionCodegen(
 
     override fun visitBlock(expression: IrBlock, data: BlockInfo): PromisedValue {
         assert(expression !is IrReturnableBlock) { "unlowered returnable block: ${expression.dump()}" }
+        val isSynthesizedInitBlock = expression.origin == SYNTHESIZED_INIT_BLOCK
+        if (isSynthesizedInitBlock) {
+            expression.markLineNumber(startOffset = true)
+            mv.nop()
+        }
         if (expression.isTransparentScope)
             return super.visitBlock(expression, data)
         val info = BlockInfo(data)
         // Force materialization to avoid reading from out-of-scope variables.
-        return super.visitBlock(expression, info).materialized().also {
+        val value = super.visitBlock(expression, info).materialized().also {
             if (info.variables.isNotEmpty()) {
                 writeLocalVariablesInTable(info, markNewLabel())
             }
         }
+        if (isSynthesizedInitBlock) {
+            expression.markLineNumber(startOffset = false)
+            mv.nop()
+        }
+        return value
     }
 
     private val IrVariable.isVisibleInLVT: Boolean

compiler/testData/debug/stepping/initBlocks.kt

@@ -51,10 +51,8 @@ fun box() {
     Zoo()
 }
 
-// IGNORE_BACKEND: JVM_IR
-// The JVM_IR does not generate code that will break on the line
-// containing the `init`, nor the exit from the `init`. It only
-// contains lines for the contents of the init blocks.
+// JVM_IR has an extra step back to the line of the class
+// declaration for the return in the constructor.
 
 // LINENUMBERS
 // test.kt:48 box
@@ -64,6 +62,9 @@ fun box() {
 // test.kt:45 x
 // test.kt:7 <init>
 // test.kt:8 <init>
+// LINENUMBERS JVM_IR
+// test.kt:3 <init>
+// LINENUMBERS
 // test.kt:48 box
 // test.kt:49 box
 // test.kt:11 <init>
@@ -73,6 +74,9 @@ fun box() {
 // test.kt:16 <init>
 // test.kt:17 <init>
 // test.kt:18 <init>
+// LINENUMBERS JVM_IR
+// test.kt:11 <init>
+// LINENUMBERS
 // test.kt:49 box
 // test.kt:50 box
 // test.kt:21 <init>
@@ -85,6 +89,9 @@ fun box() {
 // test.kt:28 <init>
 // test.kt:29 <init>
 // test.kt:30 <init>
+// LINENUMBERS JVM_IR
+// test.kt:21 <init>
+// LINENUMBERS
 // test.kt:50 box
 // test.kt:51 box
 // test.kt:33 <init>
@@ -94,5 +101,8 @@ fun box() {
 // test.kt:39 <init>
 // test.kt:40 <init>
 // test.kt:42 <init>
+// LINENUMBERS JVM_IR
+// test.kt:33 <init>
+// LINENUMBERS
 // test.kt:51 box
 // test.kt:52 box

compiler/testData/debug/stepping/initBlocksCompanion.kt

@@ -0,0 +1,52 @@
+// FILE: test.kt
+
+class A {
+    companion object {
+        val s: String
+
+        init {
+            s = "OK"
+        }
+
+        val x = x()
+
+        init { val a = 32 }
+
+        init {
+            val b = 42
+        }
+
+        init
+        {
+            val c = 43
+        }
+    }
+}
+
+fun x() = ""
+
+fun box() {
+    A.x
+    A.s
+}
+
+// JVM backend has extra steps for getX and getS.
+
+// TODO: since these tests operate as step-into, we do not get any steps
+// in the <clinit> for the companion object. Maybe extend the test infrastructure
+// with directives to set break points in order to test this.
+
+// LINENUMBERS
+// test.kt:29 box
+// test.kt:11 getX
+// LINENUMBERS JVM
+// test.kt:11 getX
+// LINENUMBERS
+// test.kt:29 box
+// test.kt:30 box
+// test.kt:5 getS
+// LINENUMBERS JVM
+// test.kt:5 getS
+// LINENUMBERS
+// test.kt:30 box
+// test.kt:31 box

compiler/tests/org/jetbrains/kotlin/codegen/debugInformation/IrSteppingTestGenerated.java

@@ -193,6 +193,12 @@ public class IrSteppingTestGenerated extends AbstractIrSteppingTest {
         runTest("compiler/testData/debug/stepping/initBlocks.kt");
     }
 
+    @Test
+    @TestMetadata("initBlocksCompanion.kt")
+    public void testInitBlocksCompanion() throws Exception {
+        runTest("compiler/testData/debug/stepping/initBlocksCompanion.kt");
+    }
+
     @Test
     @TestMetadata("inlineCallableReference.kt")
     public void testInlineCallableReference() throws Exception {

compiler/tests/org/jetbrains/kotlin/codegen/debugInformation/SteppingTestGenerated.java

@@ -193,6 +193,12 @@ public class SteppingTestGenerated extends AbstractSteppingTest {
         runTest("compiler/testData/debug/stepping/initBlocks.kt");
     }
 
+    @Test
+    @TestMetadata("initBlocksCompanion.kt")
+    public void testInitBlocksCompanion() throws Exception {
+        runTest("compiler/testData/debug/stepping/initBlocksCompanion.kt");
+    }
+
     @Test
     @TestMetadata("inlineCallableReference.kt")
     public void testInlineCallableReference() throws Exception {

plugins/kotlin-serialization/kotlin-serialization-compiler/testData/codegen/Basic.ir.txt

@@ -25,6 +25,8 @@ public final class ListOfUsers$$serializer : java/lang/Object, kotlinx/serializa
           ALOAD (0)
           CHECKCAST
           PUTSTATIC (descriptor, Lkotlinx/serialization/SerialDescriptor;)
+        LABEL (L1)
+        LINENUMBER (13)
           RETURN
     }
 
@@ -332,6 +334,8 @@ public final class OptionalUser$$serializer : java/lang/Object, kotlinx/serializ
           ALOAD (0)
           CHECKCAST
           PUTSTATIC (descriptor, Lkotlinx/serialization/SerialDescriptor;)
+        LABEL (L1)
+        LINENUMBER (10)
           RETURN
     }
 
@@ -687,6 +691,8 @@ public final class User$$serializer : java/lang/Object, kotlinx/serialization/in
           ALOAD (0)
           CHECKCAST
           PUTSTATIC (descriptor, Lkotlinx/serialization/SerialDescriptor;)
+        LABEL (L1)
+        LINENUMBER (7)
           RETURN
     }
 
@@ -1000,4 +1006,4 @@ public final class User : java/lang/Object {
     public final java.lang.String getFirstName()
 
     public final java.lang.String getLastName()
-}
+}