Improve script and REPL result handling:

- implement error result
- refactor other result classes
- implement handling in the script evaluation extension - also restores
  previous script error reporting functionality
- add possibility to customize result fileds in script and REPL
- refactor result calculation in the backend: cleanup, rename (since
  it is not only about REPL now)

libraries/scripting/common/src/kotlin/script/experimental/api/errorHandling.kt

@@ -7,7 +7,9 @@
 
 package kotlin.script.experimental.api
 
+import com.sun.xml.internal.messaging.saaj.util.ByteOutputStream
 import java.io.File
+import java.io.PrintStream
 
 /**
  * The single script diagnostic report
@@ -28,11 +30,28 @@ data class ScriptDiagnostic(
      */
     enum class Severity { FATAL, ERROR, WARNING, INFO, DEBUG }
 
-    override fun toString(): String = buildString {
-        append(severity.name)
-        append(' ')
+    override fun toString(): String = render()
+
+    /**
+     * Render diagnostics message as a string in a form:
+     * "[SEVERITY ]message[ (file:line:column)][: exception message[\n exception stacktrace]]"
+     * @param withSeverity add severity prefix, true by default
+     * @param withLocation add error location in the compiled script, if present, true by default
+     * @param withException add exception message, if present, true by default
+     * @param withStackTrace add exception stacktrace, if exception is present and [withException] is true, false by default
+     */
+    fun render(
+        withSeverity: Boolean = true,
+        withLocation: Boolean = true,
+        withException: Boolean = true,
+        withStackTrace: Boolean = false
+    ): String = buildString {
+        if (withSeverity) {
+            append(severity.name)
+            append(' ')
+        }
         append(message)
-        if (sourcePath != null || location != null) {
+        if (withLocation && (sourcePath != null || location != null)) {
             append(" (")
             sourcePath?.let { append(it.substringAfterLast(File.separatorChar)) }
             location?.let {
@@ -43,9 +62,18 @@ data class ScriptDiagnostic(
             }
             append(')')
         }
-        if (exception != null) {
+        if (withException && exception != null) {
             append(": ")
             append(exception)
+            if (withStackTrace) {
+                ByteOutputStream().use { os ->
+                    val ps = PrintStream(os)
+                    exception.printStackTrace(ps)
+                    ps.flush()
+                    append("\n")
+                    append(os.toString())
+                }
+            }
         }
     }
 }

libraries/scripting/common/src/kotlin/script/experimental/api/replData.kt

@@ -6,6 +6,7 @@
 package kotlin.script.experimental.api
 
 import java.io.Serializable
+import kotlin.script.experimental.util.PropertiesCollection
 
 const val REPL_SNIPPET_FIRST_NO = 1
 const val REPL_SNIPPET_FIRST_GEN = 1
@@ -29,3 +30,21 @@ data class ReplSnippetIdImpl(override val no: Int, override val generation: Int,
         private val serialVersionUID: Long = 1L
     }
 }
+
+interface ReplScriptCompilationConfigurationKeys
+
+open class ReplScriptCompilationConfigurationBuilder : PropertiesCollection.Builder(),
+    ReplScriptCompilationConfigurationKeys {
+    companion object : ReplScriptCompilationConfigurationKeys
+}
+
+val ScriptCompilationConfigurationKeys.repl
+    get() = ReplScriptCompilationConfigurationBuilder()
+
+
+/**
+ * The prefix of the name of the generated script class field to assign the snipped results to, empty means disabled
+ * see also ScriptCompilationConfigurationKeys.resultField
+ */
+val ReplScriptCompilationConfigurationKeys.resultFieldPrefix by PropertiesCollection.key<String>("res")
+

libraries/scripting/common/src/kotlin/script/experimental/api/scriptCompilation.kt

@@ -99,6 +99,12 @@ val ScriptCompilationConfigurationKeys.defaultImports by PropertiesCollection.ke
  */
 val ScriptCompilationConfigurationKeys.importScripts by PropertiesCollection.key<List<SourceCode>>()
 
+/**
+ * The name of the generated script class field to assign the script results to, empty means disabled
+ * see also ReplScriptCompilationConfigurationKeys.resultFieldPrefix
+ */
+val ScriptCompilationConfigurationKeys.resultField by PropertiesCollection.key<String>("\$\$result")
+
 /**
  * The list of script dependencies - platform specific
  */

libraries/scripting/common/src/kotlin/script/experimental/api/scriptEvaluation.kt

@@ -121,17 +121,40 @@ data class RefineEvaluationConfigurationData(
 /**
  * The script evaluation result value
  */
-sealed class ResultValue {
-    class Value(val name: String, val value: Any?, val type: String, val scriptInstance: Any) : ResultValue() {
+sealed class ResultValue(val scriptInstance: Any? = null) {
+
+    /**
+     * The result value representing a script return value - the value of the last expression in the script
+     * @param name assigned name of the result field - used e.g. in REPL
+     * @param value actual result value
+     * @param type name of the result type
+     * @param scriptInstance instance of the script class
+     */
+    class Value(val name: String, val value: Any?, val type: String, scriptInstance: Any) : ResultValue(scriptInstance) {
         override fun toString(): String = "$name: $type = $value"
     }
 
-    class UnitValue(val scriptInstance: Any) : ResultValue() {
+    /**
+     * The result value representing unit result, e.g. when the script ends with a statement
+     * @param scriptInstance instance of the script class
+     */
+    class Unit(scriptInstance: Any) : ResultValue(scriptInstance) {
         override fun toString(): String = "Unit"
     }
 
-    // TODO: obsolete it, use differently named value in the saving evaluators
-    object Unit : ResultValue()
+    /**
+     * The result value representing an exception from script itself
+     * @param error the actual exception thrown on script evaluation
+     * @param wrappingException the wrapping exception e.g. InvocationTargetException, sometimes useful for calculating the relevant stacktrace
+     */
+    class Error(val error: Throwable, val wrappingException: Throwable? = null) : ResultValue() {
+        override fun toString(): String = error.toString()
+    }
+
+    /**
+     * The result value used in non-evaluating "evaluators"
+     */
+    object NotEvaluated : ResultValue()
 }
 
 /**