Preserve VM throw sites in stack traces

lynglib/src/androidMain/kotlin/net/sergeych/lyng/obj/ObjListBoundsGuardAndroid.kt

@@ -17,4 +17,5 @@
 
 package net.sergeych.lyng.obj
 
-internal actual fun objListBoundsViolationMessageOrNull(size: Int, index: Int): String? = null
+internal actual fun objListBoundsViolationMessageOrNull(size: Int, index: Int): String? =
+    if (index < 0 || index >= size) "Index $index out of bounds for length $size" else null

lynglib/src/commonMain/kotlin/net/sergeych/lyng/Pos.kt

@@ -33,6 +33,17 @@ data class Pos(val source: Source, val line: Int, val column: Int) {
         if( end ) "EOF"
         else if( line >= 0 ) source.lines[line] else "<no line information>"
 
+    val currentLineTrimmedStart: String get() = currentLine.trimStart()
+
+    val currentLineIndentWidth: Int
+        get() {
+            val lineText = currentLine
+            val firstNonWhitespace = lineText.indexOfFirst { !it.isWhitespace() }
+            return if (firstNonWhitespace >= 0) firstNonWhitespace else 0
+        }
+
+    val visualColumn: Int get() = (column - currentLineIndentWidth).coerceAtLeast(0)
+
     val end: Boolean get() = line >= source.lines.size
 
     companion object {

lynglib/src/commonMain/kotlin/net/sergeych/lyng/ScriptError.kt

@@ -25,14 +25,15 @@ open class ScriptError(val pos: Pos, val errorMessage: String, cause: Throwable?
     """
         $pos: Error: $errorMessage
         
-        ${pos.currentLine}
+        ${pos.currentLineTrimmedStart}
-        ${if( pos.column >= 0 ) "-".repeat(pos.column) + "^" else ""}
+        ${if( pos.column >= 0 ) "-".repeat(pos.visualColumn) + "^" else ""}
     """.trimIndent(),
     cause
 )
 
 class ScriptFlowIsNoMoreCollected: Exception()
 
-class ExecutionError(val errorObject: Obj, pos: Pos, message: String) : ScriptError(pos, message)
+class ExecutionError(val errorObject: Obj, pos: Pos, message: String, cause: Throwable? = null) :
+    ScriptError(pos, message, cause)
 
-class ImportException(pos: Pos, message: String) : ScriptError(pos, message)
+class ImportException(pos: Pos, message: String) : ScriptError(pos, message)

lynglib/src/commonMain/kotlin/net/sergeych/lyng/bytecode/BytecodeCompiler.kt

@@ -3650,11 +3650,14 @@ class BytecodeCompiler(
     }
 
     private fun compileIndexRef(ref: IndexRef): CompiledValue? {
+        val indexPos = refPosOrCurrent(ref.targetRef)
+        setPos(indexPos)
         val receiver = compileRefWithFallback(ref.targetRef, null, Pos.builtIn) ?: return null
         val elementSlotType = indexElementSlotType(receiver.slot, ref.targetRef)
         val dst = allocSlot()
         if (!ref.optionalRef) {
             val index = compileRefWithFallback(ref.indexRef, null, Pos.builtIn) ?: return null
+            setPos(indexPos)
             if (elementSlotType == SlotType.INT && index.type == SlotType.INT) {
                 builder.emit(Opcode.GET_INDEX_INT, receiver.slot, index.slot, dst)
                 updateSlotType(dst, SlotType.INT)

lynglib/src/commonMain/kotlin/net/sergeych/lyng/bytecode/CmdRuntime.kt

@@ -43,9 +43,10 @@ class CmdVm {
                 }
                 break
             } catch (e: Throwable) {
-                if (!frame.handleException(e)) {
+                val throwable = frame.normalizeThrowable(e)
+                if (!frame.handleException(throwable)) {
                     frame.cancelIterators()
-                    throw e
+                    throw throwable
                 }
             }
         }
@@ -4432,6 +4433,19 @@ class CmdFrame(
         return scope
     }
 
+    suspend fun normalizeThrowable(t: Throwable): Throwable {
+        if (t is ExecutionError || t is ReturnException || t is LoopBreakContinueException) return t
+        val parentScope = ensureScope()
+        val pos = (t as? ScriptError)?.pos ?: currentErrorPos() ?: parentScope.pos
+        val throwScope = parentScope.createChildScope(pos = pos)
+        val message = when (t) {
+            is ScriptError -> t.errorMessage
+            else -> t.message ?: t.toString()
+        }
+        val errorObject = ObjUnknownException(throwScope, message).apply { getStackTrace() }
+        return ExecutionError(errorObject, pos, message, t)
+    }
+
     suspend fun handleException(t: Throwable): Boolean {
         val handler = tryStack.lastOrNull() ?: return false
         vmIterDebug {

lynglib/src/commonMain/kotlin/net/sergeych/lyng/obj/ObjException.kt

@@ -106,16 +106,18 @@ open class ObjException(
                     val pos = s.pos
                     if (pos != lastPos && !pos.currentLine.isEmpty()) {
                         if (lastPos == null || (lastPos.source != pos.source || lastPos.line != pos.line)) {
+                            val sourceLine = pos.currentLineTrimmedStart
+                            val visualColumn = pos.visualColumn
                             val fallback =
-                                ObjString("#${pos.source.objSourceName}:${pos.line+1}:${pos.column+1}: ${pos.currentLine}")
+                                ObjString("#${pos.source.objSourceName}:${pos.line+1}:${visualColumn+1}: $sourceLine")
                             if (maybeCls != null) {
                                 try {
                                     result.list += maybeCls.callWithArgs(
                                         scope,
                                         pos.source.objSourceName,
                                         ObjInt(pos.line.toLong()),
-                                        ObjInt(pos.column.toLong()),
+                                        ObjInt(visualColumn.toLong()),
-                                        ObjString(pos.currentLine)
+                                        ObjString(sourceLine)
                                     )
                                 } catch (e: Throwable) {
                                     // Fallback textual entry if StackTraceEntry fails to instantiate

lynglib/src/commonTest/kotlin/ScriptTest.kt

@@ -5261,6 +5261,35 @@ class ScriptTest {
         )
     }
 
+    @Test
+    fun testUnexpectedThrowablePreservesThrowSiteStackTrace() = runTest {
+        val caught = evalNamed(
+            "baderrorstack", """
+            fun boom() {
+                val arr = [10, 20, 30]
+                arr[10]
+            }
+            try {
+                boom()
+                "unreachable"
+            } catch (e) {
+                e
+            }
+        """.trimIndent()
+        )
+        val trace = caught.getLyngExceptionMessageWithStackTrace()
+        assertContains(trace, "\n    at baderrorstack:3:1: arr[10]")
+        assertContains(trace, "\n    at baderrorstack:6:1: boom()")
+        assertFalse(trace.contains("catch (e)"))
+    }
+
+    @Test
+    fun testScriptErrorMessageTrimsSourceIndent() = runTest {
+        val x = ScriptError(Pos(Source("trimraw", "    arr[10]"), 0, 4), "boom")
+        assertContains(x.message!!, "\narr[10]\n")
+        assertFalse(x.message!!.contains("\n    arr[10]\n"))
+    }
+
     @Test
     fun testMapIteralAmbiguity() = runTest {
         eval(

lynglib/src/commonTest/kotlin/net/sergeych/lyng/PrintlnOverrideTest.kt

@@ -22,6 +22,8 @@ import net.sergeych.lyng.bridge.globalBinder
 import net.sergeych.lyng.obj.ObjVoid
 import kotlin.test.Test
 import kotlin.test.assertEquals
+import kotlin.test.assertFalse
+import kotlin.test.assertTrue
 
 class PrintlnOverrideTest {
 
@@ -84,4 +86,46 @@ class PrintlnOverrideTest {
 
         assertEquals(listOf("gb top level", "gb inside function"), output)
     }
+
+    @Test
+    fun testExceptionPrintStackTraceFormatsPrimaryFrameBlock() = runTest {
+        val scope = Script.newScope()
+        val output = mutableListOf<String>()
+
+        scope.globalBinder().bindGlobalFun("println") {
+            val sb = StringBuilder()
+            for (i in 0 until args.size) {
+                if (i > 0) sb.append(" ")
+                sb.append(string(i))
+            }
+            output.add(sb.toString())
+            ObjVoid
+        }
+
+        scope.eval(
+            """
+            fun boom() {
+                val arr = [10, 20, 30]
+                var a = 10
+                var b = arr[a]
+                b
+            }
+            try {
+                boom()
+            } catch (e) {
+                e.printStackTrace()
+            }
+            """.trimIndent()
+        )
+
+        assertTrue(output.isNotEmpty())
+        assertEquals(
+            "IndexOutOfBoundsException: Index 10 out of bounds for length 3 at eval:4:9:",
+            output[0]
+        )
+        assertEquals("var b = arr[a]", output[1])
+        assertEquals("--------^", output[2])
+        assertTrue(output.size >= 4)
+        assertFalse(output.any { it == "        at eval:4:9: var b = arr[a]" })
+    }
 }

lynglib/src/jvmMain/kotlin/net/sergeych/lyng/obj/ObjListBoundsGuardJvm.kt

@@ -17,4 +17,5 @@
 
 package net.sergeych.lyng.obj
 
-internal actual fun objListBoundsViolationMessageOrNull(size: Int, index: Int): String? = null
+internal actual fun objListBoundsViolationMessageOrNull(size: Int, index: Int): String? =
+    if (index < 0 || index >= size) "Index $index out of bounds for length $size" else null

lynglib/src/nativeMain/kotlin/net/sergeych/lyng/obj/ObjListBoundsGuardNative.kt

@@ -17,4 +17,5 @@
 
 package net.sergeych.lyng.obj
 
-internal actual fun objListBoundsViolationMessageOrNull(size: Int, index: Int): String? = null
+internal actual fun objListBoundsViolationMessageOrNull(size: Int, index: Int): String? =
+    if (index < 0 || index >= size) "Index $index out of bounds for length $size" else null

lynglib/stdlib/lyng/root.lyng

@@ -441,9 +441,25 @@ static fun List<T>.fill(size: Int, block: (Int)->T): List<T> {
 
 /* Print this exception and its stack trace to standard output. */
 fun Exception.printStackTrace(): void {
-    println(this)
+    if( stackTrace.size == 0 ) {
+        println(this)
+        return
+    }
+    val first = stackTrace[0] as StackTraceEntry
+    var arrow = "^"
+    for( i in 0..<first.column ) {
+        arrow = "-" + arrow
+    }
+    println("%s: %s at %s:"(this::class.className, message, first.at))
+    println(first.sourceString)
+    println(arrow)
+    var skipFirst = true
     for( entry in stackTrace ) {
-        println("\tat "+entry.toString())
+        if( skipFirst ) {
+            skipFirst = false
+        } else {
+            println("        at " + entry.toString())
+        }
     }
 }