Fix a number of errors in loops

shared/src/main/scala/io/kaitai/struct/ClassTypeProvider.scala

@@ -4,17 +4,24 @@ import io.kaitai.struct.datatype.DataType
 import io.kaitai.struct.datatype.DataType._
 import io.kaitai.struct.exprlang.Ast
 import io.kaitai.struct.format._
-import io.kaitai.struct.precompile.{EnumNotFoundError, FieldNotFoundError, TypeNotFoundError, TypeUndecidedError}
+import io.kaitai.struct.precompile.{EnumNotFoundError, ExpressionError, FieldNotFoundError, TypeNotFoundError, TypeUndecidedError}
 import io.kaitai.struct.translators.TypeProvider
 
 class ClassTypeProvider(classSpecs: ClassSpecs, var topClass: ClassSpec) extends TypeProvider {
   var nowClass = topClass
   val allClasses: ClassSpecs = classSpecs
 
-  var _currentIteratorType: Option[DataType] = None
+  /**
+    * Type of the `_` variable in the expression. That variable is defined in
+    * `repeat-until` and `valid: expr` contexts and refers to the attribute
+    * just parsed.
+    */
+  var _typeOfUnderscore: Option[DataType] = None
+  /**
+    * Type of the `_on` variable in the expression. That variable is defined in
+    * `cases.<case>` contexts and refers to the value of `switch-on` expression.
+    */
   var _currentSwitchType: Option[DataType] = None
-  def currentIteratorType: DataType = _currentIteratorType.get
-  def currentSwitchType: DataType = _currentSwitchType.get
 
   override def determineType(attrName: String): DataType = {
     determineType(nowClass, attrName)
@@ -30,14 +37,20 @@ class ClassTypeProvider(classSpecs: ClassSpecs, var topClass: ClassSpec) extends
         topClass.toDataType
       case Identifier.PARENT =>
         if (inClass.parentClass == UnknownClassSpec)
-          throw new RuntimeException(s"Unable to derive ${Identifier.PARENT} type in ${inClass.name.mkString("::")}")
+          throw new ExpressionError(s"Unable to derive '${Identifier.PARENT}' type in '${inClass.nameAsStr}'")
         inClass.parentClass.toDataType
       case Identifier.IO =>
         KaitaiStreamType
       case Identifier.ITERATOR =>
-        currentIteratorType
+        _typeOfUnderscore match {
+          case Some(value) => value
+          case None => throw new ExpressionError(s"Context variable '$attrName' is available only in the 'repeat-until' and 'valid/expr' attributes")
+        }
       case Identifier.SWITCH_ON =>
-        currentSwitchType
+        _currentSwitchType match {
+          case Some(value) => value
+          case None => throw new ExpressionError(s"Context variable '$attrName' is available only in the 'cases.<case>' expressions")
+        }
       case Identifier.INDEX =>
         CalcIntType
       case Identifier.SIZEOF =>

shared/src/main/scala/io/kaitai/struct/ConstructClassCompiler.scala

@@ -87,7 +87,8 @@ class ConstructClassCompiler(classSpecs: ClassSpecs, topClass: ClassSpec) extend
     case RepeatExpr(expr) =>
       s"Array(${translator.translate(expr)}, $typeStr)"
     case RepeatUntil(expr) =>
-      provider._currentIteratorType = Some(dataType)
+      // Set the type of the `_` variable in expression
+      provider._typeOfUnderscore = Some(dataType)
       s"RepeatUntil(lambda obj_, list_, this: ${translator.translate(expr)}, $typeStr)"
     case RepeatEos =>
       s"GreedyRange($typeStr)"

shared/src/main/scala/io/kaitai/struct/GraphvizClassCompiler.scala

@@ -196,7 +196,8 @@ class GraphvizClassCompiler(classSpecs: ClassSpecs, topClass: ClassSpec) extends
           case ValidationInEnum() =>
             "must be defined in the enum"
           case ValidationExpr(expr) =>
-            provider._currentIteratorType = Some(dataType)
+            // Set the type of the `_` variable in expression
+            provider._typeOfUnderscore = Some(dataType)
             s"must satisfy ${expression(expr, fullPortName, STYLE_EDGE_VALID)}"
         }
       case None => return
@@ -212,7 +213,8 @@ class GraphvizClassCompiler(classSpecs: ClassSpecs, topClass: ClassSpec) extends
           expression(ex, s"$currentTable:$portName", STYLE_EDGE_REPEAT) +
           " times</TD></TR>")
       case RepeatUntil(ex) =>
-        provider._currentIteratorType = Some(dataType)
+        // Set the type of the `_` variable in expression
+        provider._typeOfUnderscore = Some(dataType)
         out.puts("<TR><TD COLSPAN=\"4\" PORT=\"" + portName + "\">repeat until " +
           expression(ex, s"$currentTable:$portName", STYLE_EDGE_REPEAT) +
           "</TD></TR>")

shared/src/main/scala/io/kaitai/struct/languages/CSharpCompiler.scala

@@ -272,7 +272,7 @@ class CSharpCompiler(typeProvider: ClassTypeProvider, config: RuntimeConfig)
     out.puts(s"${privateMemberName(id)} = new ${kaitaiType2NativeType(ArrayTypeInStream(dataType))}();")
   }
 
-  override def condRepeatEosHeader(id: Identifier, io: String, dataType: DataType): Unit = {
+  override def condRepeatEosHeader(io: String): Unit = {
     out.puts("{")
     out.inc
     out.puts("var i = 0;")
@@ -292,8 +292,8 @@ class CSharpCompiler(typeProvider: ClassTypeProvider, config: RuntimeConfig)
     out.puts("}")
   }
 
-  override def condRepeatExprHeader(id: Identifier, io: String, dataType: DataType, repeatExpr: expr): Unit = {
-    out.puts(s"for (var i = 0; i < ${expression(repeatExpr)}; i++)")
+  override def condRepeatExprHeader(countExpr: expr): Unit = {
+    out.puts(s"for (var i = 0, _end = ${expression(countExpr)}; i < _end; ++i)")
     out.puts("{")
     out.inc
   }
@@ -303,12 +303,12 @@ class CSharpCompiler(typeProvider: ClassTypeProvider, config: RuntimeConfig)
 
   override def condRepeatExprFooter: Unit = fileFooter(null)
 
-  override def condRepeatUntilHeader(id: Identifier, io: String, dataType: DataType, untilExpr: expr): Unit = {
+  override def condRepeatUntilHeader(itemType: DataType): Unit = {
     out.puts("{")
     out.inc
     out.puts("var i = 0;")
-    out.puts(s"${kaitaiType2NativeType(dataType)} ${translator.doName("_")};")
-    out.puts("do {")
+    out.puts(s"${kaitaiType2NativeType(itemType)} ${translator.doName(Identifier.ITERATOR)};")
+    out.puts("while (true) {")
     out.inc
   }
 
@@ -322,13 +322,17 @@ class CSharpCompiler(typeProvider: ClassTypeProvider, config: RuntimeConfig)
     out.puts(s"${privateMemberName(id)}.Add($tempVar);")
   }
 
-  override def condRepeatUntilFooter(id: Identifier, io: String, dataType: DataType, untilExpr: expr): Unit = {
-    typeProvider._currentIteratorType = Some(dataType)
-    out.puts("i++;")
-    out.dec
-    out.puts(s"} while (!(${expression(untilExpr)}));")
+  override def condRepeatUntilFooter(untilExpr: expr): Unit = {
+    out.puts(s"if (${expression(untilExpr)}) {")
+    out.inc
+    out.puts("break;")
     out.dec
     out.puts("}")
+    out.puts("++i;")
+    out.dec
+    out.puts("}") // close while (true)
+    out.dec
+    out.puts("}") // close scope of i and _ variables
   }
 
   override def handleAssignmentSimple(id: Identifier, expr: String): Unit =

shared/src/main/scala/io/kaitai/struct/languages/CppCompiler.scala

@@ -563,7 +563,7 @@ class CppCompiler(
     outSrc.puts(s"${privateMemberName(id)} = ${newVector(dataType)};")
   }
 
-  override def condRepeatEosHeader(id: Identifier, io: String, dataType: DataType): Unit = {
+  override def condRepeatEosHeader(io: String): Unit = {
     outSrc.puts("{")
     outSrc.inc
     outSrc.puts("int i = 0;")
@@ -583,10 +583,8 @@ class CppCompiler(
     outSrc.puts("}")
   }
 
-  override def condRepeatExprHeader(id: Identifier, io: String, dataType: DataType, repeatExpr: Ast.expr): Unit = {
-    val lenVar = s"l_${idToStr(id)}"
-    outSrc.puts(s"const int $lenVar = ${expression(repeatExpr)};")
-    outSrc.puts(s"for (int i = 0; i < $lenVar; i++) {")
+  override def condRepeatExprHeader(countExpr: Ast.expr): Unit = {
+    outSrc.puts(s"for (int i = 0, _end = ${expression(countExpr)}; i < _end; ++i) {")
     outSrc.inc
   }
 
@@ -598,12 +596,12 @@ class CppCompiler(
     outSrc.puts("}")
   }
 
-  override def condRepeatUntilHeader(id: Identifier, io: String, dataType: DataType, untilExpr: expr): Unit = {
+  override def condRepeatUntilHeader(itemType: DataType): Unit = {
     outSrc.puts("{")
     outSrc.inc
     outSrc.puts("int i = 0;")
-    outSrc.puts(s"${kaitaiType2NativeType(dataType.asNonOwning())} ${translator.doName("_")};")
-    outSrc.puts("do {")
+    outSrc.puts(s"${kaitaiType2NativeType(itemType.asNonOwning())} ${translator.doName(Identifier.ITERATOR)};")
+    outSrc.puts("while (true) {")
     outSrc.inc
   }
 
@@ -632,13 +630,17 @@ class CppCompiler(
     outSrc.puts(s"${privateMemberName(id)}->push_back($wrappedTempVar);")
   }
 
-  override def condRepeatUntilFooter(id: Identifier, io: String, dataType: DataType, untilExpr: expr): Unit = {
-    typeProvider._currentIteratorType = Some(dataType)
-    outSrc.puts("i++;")
-    outSrc.dec
-    outSrc.puts(s"} while (!(${expression(untilExpr)}));")
+  override def condRepeatUntilFooter(untilExpr: expr): Unit = {
+    outSrc.puts(s"if (${expression(untilExpr)}) {")
+    outSrc.inc
+    outSrc.puts("break;")
     outSrc.dec
     outSrc.puts("}")
+    outSrc.puts("++i;")
+    outSrc.dec
+    outSrc.puts("}") // close while (true)
+    outSrc.dec
+    outSrc.puts("}") // close scope of i and _ variables
   }
 
   override def handleAssignmentSimple(id: Identifier, expr: String): Unit = {

shared/src/main/scala/io/kaitai/struct/languages/GoCompiler.scala

@@ -277,12 +277,12 @@ class GoCompiler(typeProvider: ClassTypeProvider, config: RuntimeConfig)
     // function works even on `nil` slices (https://go.dev/tour/moretypes/15)
   }
 
-  override def condRepeatEosHeader(id: Identifier, io: String, dataType: DataType): Unit = {
+  override def condRepeatEosHeader(io: String): Unit = {
     out.puts(s"for i := 0;; i++ {")
     out.inc
 
     val eofVar = translator.allocateLocalVar()
-    out.puts(s"${translator.localVarName(eofVar)}, err := this._io.EOF()")
+    out.puts(s"${translator.localVarName(eofVar)}, err := $io.EOF()")
     translator.outAddErrCheck()
     out.puts(s"if ${translator.localVarName(eofVar)} {")
     out.inc
@@ -297,8 +297,8 @@ class GoCompiler(typeProvider: ClassTypeProvider, config: RuntimeConfig)
     out.puts(s"$name = append($name, $expr)")
   }
 
-  override def condRepeatExprHeader(id: Identifier, io: String, dataType: DataType, repeatExpr: Ast.expr): Unit = {
-    out.puts(s"for i := 0; i < int(${expression(repeatExpr)}); i++ {")
+  override def condRepeatExprHeader(countExpr: Ast.expr): Unit = {
+    out.puts(s"for i, _end := 0, int(${expression(countExpr)}); i < _end; i++ {")
     out.inc
     // FIXME: Go throws a fatal compile error when the `i` variable is not used (unused variables
     // can only use the blank identifier `_`, see https://go.dev/doc/effective_go#blank), so we have
@@ -311,8 +311,11 @@ class GoCompiler(typeProvider: ClassTypeProvider, config: RuntimeConfig)
   override def handleAssignmentRepeatExpr(id: Identifier, r: TranslatorResult): Unit =
     handleAssignmentRepeatEos(id, r)
 
-  override def condRepeatUntilHeader(id: Identifier, io: String, dataType: DataType, untilExpr: Ast.expr): Unit = {
-    out.puts(s"for i := 1;; i++ {")
+  override def condRepeatUntilHeader(itemType: DataType): Unit = {
+    out.puts("{")
+    out.inc
+    out.puts("i := 0")
+    out.puts(s"for {")
     out.inc
   }
 
@@ -323,15 +326,17 @@ class GoCompiler(typeProvider: ClassTypeProvider, config: RuntimeConfig)
     out.puts(s"${privateMemberName(id)} = append(${privateMemberName(id)}, $tempVar)")
   }
 
-  override def condRepeatUntilFooter(id: Identifier, io: String, dataType: DataType, untilExpr: Ast.expr): Unit = {
-    typeProvider._currentIteratorType = Some(dataType)
+  override def condRepeatUntilFooter(untilExpr: Ast.expr): Unit = {
     out.puts(s"if ${expression(untilExpr)} {")
     out.inc
     out.puts("break")
     out.dec
     out.puts("}")
+    out.puts("i++;")
     out.dec
-    out.puts("}")
+    out.puts("}") // close for
+    out.dec
+    out.puts("}") // close scope of i variable
   }
 
   private def castToType(r: TranslatorResult, dataType: DataType): TranslatorResult = {

shared/src/main/scala/io/kaitai/struct/languages/JavaCompiler.scala

@@ -560,7 +560,7 @@ class JavaCompiler(typeProvider: ClassTypeProvider, config: RuntimeConfig)
     out.puts(s"${privateMemberName(id)} = new ArrayList<${kaitaiType2JavaTypeBoxed(dataType)}>();")
   }
 
-  override def condRepeatEosHeader(id: Identifier, io: String, dataType: DataType): Unit = {
+  override def condRepeatEosHeader(io: String): Unit = {
     out.puts("{")
     out.inc
     out.puts("int i = 0;")
@@ -580,8 +580,8 @@ class JavaCompiler(typeProvider: ClassTypeProvider, config: RuntimeConfig)
     out.puts("}")
   }
 
-  override def condRepeatExprHeader(id: Identifier, io: String, dataType: DataType, repeatExpr: expr): Unit = {
-    out.puts(s"for (int i = 0; i < ${expression(repeatExpr)}; i++) {")
+  override def condRepeatExprHeader(countExpr: expr): Unit = {
+    out.puts(s"for (int i = 0, _end = ${expression(countExpr)}; i < _end; ++i) {")
     out.inc
   }
 
@@ -594,12 +594,12 @@ class JavaCompiler(typeProvider: ClassTypeProvider, config: RuntimeConfig)
   override def handleAssignmentRepeatExpr(id: Identifier, expr: String): Unit =
     handleAssignmentRepeatEos(id, expr)
 
-  override def condRepeatUntilHeader(id: Identifier, io: String, dataType: DataType, untilExpr: expr): Unit = {
+  override def condRepeatUntilHeader(itemType: DataType): Unit = {
     out.puts("{")
     out.inc
-    out.puts(s"${kaitaiType2JavaType(dataType)} ${translator.doName(Identifier.ITERATOR)};")
+    out.puts(s"${kaitaiType2JavaType(itemType)} ${translator.doName(Identifier.ITERATOR)};")
     out.puts("int i = 0;")
-    out.puts("do {")
+    out.puts("while (true) {")
     out.inc
   }
 
@@ -613,13 +613,17 @@ class JavaCompiler(typeProvider: ClassTypeProvider, config: RuntimeConfig)
     out.puts(s"${privateMemberName(id)}.add($tempVar);")
   }
 
-  override def condRepeatUntilFooter(id: Identifier, io: String, dataType: DataType, untilExpr: expr): Unit = {
-    typeProvider._currentIteratorType = Some(dataType)
-    out.puts("i++;")
-    out.dec
-    out.puts(s"} while (!(${expression(untilExpr)}));")
+  override def condRepeatUntilFooter(untilExpr: expr): Unit = {
+    out.puts(s"if (${expression(untilExpr)}) {")
+    out.inc
+    out.puts("break;")
     out.dec
     out.puts("}")
+    out.puts("++i;")
+    out.dec
+    out.puts("}") // close while (true)
+    out.dec
+    out.puts("}") // close scope of i and _ variables
   }
 
   override def handleAssignmentSimple(id: Identifier, expr: String): Unit =

shared/src/main/scala/io/kaitai/struct/languages/JavaScriptCompiler.scala

@@ -293,7 +293,7 @@ class JavaScriptCompiler(typeProvider: ClassTypeProvider, config: RuntimeConfig)
   override def condRepeatInitAttr(id: Identifier, dataType: DataType): Unit =
     out.puts(s"${privateMemberName(id)} = [];")
 
-  override def condRepeatEosHeader(id: Identifier, io: String, dataType: DataType): Unit = {
+  override def condRepeatEosHeader(io: String): Unit = {
     out.puts("var i = 0;")
     out.puts(s"while (!$io.isEof()) {")
     out.inc
@@ -309,8 +309,8 @@ class JavaScriptCompiler(typeProvider: ClassTypeProvider, config: RuntimeConfig)
     out.puts("}")
   }
 
-  override def condRepeatExprHeader(id: Identifier, io: String, dataType: DataType, repeatExpr: expr): Unit = {
-    out.puts(s"for (var i = 0; i < ${expression(repeatExpr)}; i++) {")
+  override def condRepeatExprHeader(countExpr: expr): Unit = {
+    out.puts(s"for (var i = 0, _end = ${expression(countExpr)}; i < _end; ++i) {")
     out.inc
   }
 
@@ -322,9 +322,10 @@ class JavaScriptCompiler(typeProvider: ClassTypeProvider, config: RuntimeConfig)
     out.puts("}")
   }
 
-  override def condRepeatUntilHeader(id: Identifier, io: String, dataType: DataType, untilExpr: expr): Unit = {
+  override def condRepeatUntilHeader(itemType: DataType): Unit = {
+    // "var" variables in any case have a scope of surrounding function, no need a scope to isolate them
     out.puts("var i = 0;")
-    out.puts("do {")
+    out.puts("while (true) {")
     out.inc
   }
 
@@ -334,11 +335,15 @@ class JavaScriptCompiler(typeProvider: ClassTypeProvider, config: RuntimeConfig)
     out.puts(s"${privateMemberName(id)}.push($tmpName);")
   }
 
-  override def condRepeatUntilFooter(id: Identifier, io: String, dataType: DataType, untilExpr: expr): Unit = {
-    typeProvider._currentIteratorType = Some(dataType)
-    out.puts("i++;")
+  override def condRepeatUntilFooter(untilExpr: expr): Unit = {
+    out.puts(s"if (${expression(untilExpr)}) {")
+    out.inc
+    out.puts("break;")
+    out.dec
+    out.puts("}")
+    out.puts("++i;")
     out.dec
-    out.puts(s"} while (!(${expression(untilExpr)}));")
+    out.puts("}") // close while (true)
   }
 
   override def handleAssignmentSimple(id: Identifier, expr: String): Unit = {