Better diagnostic for Element has no prototype error

j2k/src/org/jetbrains/jet/j2k/CodeBuilder.kt

@@ -46,6 +46,8 @@ fun CodeBuilder.append(elements: Collection<Element>, separator: String, prefix:
     return append(elements.filter { !it.isEmpty }.map { { append(it) } }, separator, prefix, suffix)
 }
 
+class ElementCreationStackTraceRequiredException : RuntimeException()
+
 class CodeBuilder(private val topElement: PsiElement?) {
     private val builder = StringBuilder()
     private var endOfLineCommentAtEnd = false
@@ -81,11 +83,16 @@ class CodeBuilder(private val topElement: PsiElement?) {
         if (element.isEmpty) return this // do not insert comment and spaces for empty elements to avoid multiple blank lines
 
         if (element.prototypes == null && topElement != null) {
+            if (element.createdAt == null) {
+                throw ElementCreationStackTraceRequiredException()
+            }
+            else {
                 val s = "Element $element has no prototypes assigned.\n" +
                         "Use Element.assignPrototype() or Element.assignNoPrototype().\n" +
                         "Element created at:\n${element.createdAt}"
                 throw RuntimeException(s)
             }
+        }
 
         if (topElement == null || element.prototypes!!.isEmpty()) {
             element.generateCode(this)

j2k/src/org/jetbrains/jet/j2k/Converter.kt

@@ -99,9 +99,11 @@ public class Converter private(val project: Project,
                         State(state.methodReturnType, state.expressionVisitorFactory, state.statementVisitorFactory, state.specialContext, state.importList, importsToAdd))
 
     public fun elementToKotlin(element: PsiElement): String {
+        try {
             val converted = convertTopElement(element) ?: return ""
             val builder = CodeBuilder(element)
             builder.append(converted)
+
             if (postProcessor != null) {
                 return AfterConversionPass(project, postProcessor).run(builder.result)
             }
@@ -109,6 +111,17 @@ public class Converter private(val project: Project,
                 return builder.result
             }
         }
+        catch(e: ElementCreationStackTraceRequiredException) {
+            // if we got this exception then we need to turn element creation stack traces on to get better diagnostic
+            Element.saveCreationStacktraces = true
+            try {
+                return elementToKotlin(element)
+            }
+            finally {
+                Element.saveCreationStacktraces = false
+            }
+        }
+    }
 
     private fun convertTopElement(element: PsiElement?): Element? = when (element) {
         is PsiJavaFile -> convertFile(element)

j2k/src/org/jetbrains/jet/j2k/ast/Element.kt

@@ -67,7 +67,11 @@ abstract class Element {
           $prototypes = value
       }
 
-    public var createdAt: String = "Element creation stacktraces turned off. Uncomment initializer of Element.createdAt." //Exception().getStackTrace().joinToString("\n")
+    public var createdAt: String?
+            = if (saveCreationStacktraces)
+                  Exception().getStackTrace().joinToString("\n")
+              else
+                  null
 
     /** This method should not be used anywhere except for CodeBuilder! Use CodeBuilder.append instead. */
     public abstract fun generateCode(builder: CodeBuilder)
@@ -80,4 +84,8 @@ abstract class Element {
         override fun generateCode(builder: CodeBuilder) { }
         override val isEmpty: Boolean get() = true
     }
+
+    class object {
+        var saveCreationStacktraces = false
+    }
 }