[JS IR] Improve debug info for if and when statements

#KT-46276

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/ir/IrBuilder.kt

@@ -157,9 +157,29 @@ object JsIrBuilder {
     fun buildBreak(type: IrType, loop: IrLoop) = IrBreakImpl(UNDEFINED_OFFSET, UNDEFINED_OFFSET, type, loop)
     fun buildContinue(type: IrType, loop: IrLoop) = IrContinueImpl(UNDEFINED_OFFSET, UNDEFINED_OFFSET, type, loop)
 
-    fun buildIfElse(type: IrType, cond: IrExpression, thenBranch: IrExpression, elseBranch: IrExpression? = null): IrWhen = buildIfElse(
-        UNDEFINED_OFFSET, UNDEFINED_OFFSET, type, cond, thenBranch, elseBranch, JsStatementOrigins.SYNTHESIZED_STATEMENT
-    )
+    fun buildIfElse(
+        type: IrType,
+        cond: IrExpression,
+        thenBranch: IrExpression,
+        elseBranch: IrExpression? = null,
+        thenBranchStartOffset: Int = cond.startOffset,
+        thenBranchEndOffset: Int = thenBranch.endOffset,
+        elseBranchStartOffset: Int = UNDEFINED_OFFSET,
+        elseBranchEndOffset: Int = elseBranch?.endOffset ?: UNDEFINED_OFFSET,
+    ): IrWhen =
+        buildIfElse(
+            startOffset = UNDEFINED_OFFSET,
+            endOffset = UNDEFINED_OFFSET,
+            type = type,
+            cond = cond,
+            thenBranch = thenBranch,
+            elseBranch = elseBranch,
+            origin = JsStatementOrigins.SYNTHESIZED_STATEMENT,
+            thenBranchStartOffset = thenBranchStartOffset,
+            thenBranchEndOffset = thenBranchEndOffset,
+            elseBranchStartOffset = elseBranchStartOffset,
+            elseBranchEndOffset = elseBranchEndOffset
+        )
 
     fun buildIfElse(
         startOffset: Int,
@@ -168,13 +188,17 @@ object JsIrBuilder {
         cond: IrExpression,
         thenBranch: IrExpression,
         elseBranch: IrExpression? = null,
-        origin: IrStatementOrigin? = null
+        origin: IrStatementOrigin? = null,
+        thenBranchStartOffset: Int = cond.startOffset,
+        thenBranchEndOffset: Int = thenBranch.endOffset,
+        elseBranchStartOffset: Int = UNDEFINED_OFFSET,
+        elseBranchEndOffset: Int = elseBranch?.endOffset ?: UNDEFINED_OFFSET,
     ): IrWhen {
         val element = IrIfThenElseImpl(startOffset, endOffset, type, origin)
-        element.branches.add(IrBranchImpl(cond, thenBranch))
+        element.branches.add(IrBranchImpl(thenBranchStartOffset, thenBranchEndOffset, cond, thenBranch))
         if (elseBranch != null) {
-            val irTrue = IrConstImpl.boolean(UNDEFINED_OFFSET, UNDEFINED_OFFSET, cond.type, true)
-            element.branches.add(IrElseBranchImpl(irTrue, elseBranch))
+            val irTrue = IrConstImpl.constTrue(UNDEFINED_OFFSET, UNDEFINED_OFFSET, cond.type)
+            element.branches.add(IrElseBranchImpl(elseBranchStartOffset, elseBranchEndOffset, irTrue, elseBranch))
         }
 
         return element

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/lower/BlockDecomposerLowering.kt

@@ -12,6 +12,7 @@ import org.jetbrains.kotlin.backend.common.ir.isPure
 import org.jetbrains.kotlin.descriptors.DescriptorVisibilities
 import org.jetbrains.kotlin.ir.IrElement
 import org.jetbrains.kotlin.ir.IrStatement
+import org.jetbrains.kotlin.ir.UNDEFINED_OFFSET
 import org.jetbrains.kotlin.ir.backend.js.JsCommonBackendContext
 import org.jetbrains.kotlin.ir.backend.js.JsIrBackendContext
 import org.jetbrains.kotlin.ir.backend.js.ir.JsIrBuilder
@@ -424,13 +425,17 @@ class BlockDecomposerTransformer(
                         isElseBranch(orig) -> (res as? IrBlock)?.statements ?: listOf(res)
                         else -> listOf(
                             JsIrBuilder.buildIfElse(
-                                orig.startOffset,
-                                orig.endOffset,
-                                unitType,
-                                condValue,
-                                res,
-                                elseBlock,
-                                expression.origin
+                                startOffset = UNDEFINED_OFFSET,
+                                endOffset = UNDEFINED_OFFSET,
+                                type = unitType,
+                                cond = condValue,
+                                thenBranch = res,
+                                elseBranch = elseBlock,
+                                origin = expression.origin,
+                                thenBranchStartOffset = orig.startOffset,
+                                thenBranchEndOffset = orig.endOffset,
+                                elseBranchStartOffset = UNDEFINED_OFFSET,
+                                elseBranchEndOffset = UNDEFINED_OFFSET,
                             )
                         )
                     }

compiler/testData/debug/stepping/if.kt

@@ -26,6 +26,6 @@ inline fun getB(): Int {
 
 // EXPECTATIONS JS_IR
 // test.kt:14 box
-// test.kt:5 box
+// test.kt:4 box
 // test.kt:11 getA
 // test.kt:14 box

compiler/testData/debug/stepping/ifWithInlineInCondition.kt

@@ -66,13 +66,13 @@ fun nop() {}
 // test.kt:8 box
 // test.kt:24 box
 // test.kt:9 box
-// test.kt:10 box
+// test.kt:7 box
 // test.kt:11 box
 // test.kt:30 nop
 // test.kt:24 box
 // test.kt:16 box
 // test.kt:27 box
-// test.kt:15 box
+// test.kt:14 box
 // test.kt:19 box
 // test.kt:30 nop
 // test.kt:21 box