For troubleshooting compiler, add -Vdebug-type-error (and remove -Yissue-debug)

project/ScalaOptionParser.scala

@@ -84,16 +84,16 @@ object ScalaOptionParser {
   // TODO retrieve these data programmatically, ala https://github.com/scala/scala-tool-support/blob/master/bash-completion/src/main/scala/BashCompletion.scala
   private def booleanSettingNames = List("-X", "-Xasync", "-Xcheckinit", "-Xdev", "-Xdisable-assertions", "-Xexperimental", "-Xfatal-warnings", "-Xlog-free-terms", "-Xlog-free-types", "-Xlog-implicit-conversions", "-Xlog-reflective-calls",
     "-Xno-forwarders", "-Xno-patmat-analysis", "-Xnon-strict-patmat-analysis", "-Xprint-pos", "-Xprint-types", "-Xprompt", "-Xresident", "-Xshow-phases", "-Xverify", "-Y",
-    "-Ybreak-cycles", "-Ydebug", "-Ycompact-trees", "-YdisableFlatCpCaching", "-Ydoc-debug",
+    "-Ybreak-cycles", "-Ydebug", "-Ydebug-type-error", "-Ycompact-trees", "-YdisableFlatCpCaching", "-Ydoc-debug",
     "-Yide-debug",
-    "-Yissue-debug", "-Ylog-classpath", "-Ymacro-debug-lite", "-Ymacro-debug-verbose", "-Ymacro-no-expand",
+    "-Ylog-classpath", "-Ymacro-debug-lite", "-Ymacro-debug-verbose", "-Ymacro-no-expand",
     "-Yno-completion", "-Yno-generic-signatures", "-Yno-imports", "-Yno-predef", "-Ymacro-annotations",
     "-Ypatmat-debug", "-Yno-adapted-args", "-Ypos-debug", "-Ypresentation-debug",
     "-Ypresentation-strict", "-Ypresentation-verbose", "-Yquasiquote-debug", "-Yrangepos", "-Yreify-copypaste", "-Yreify-debug", "-Yrepl-class-based",
     "-Yrepl-sync", "-Yshow-member-pos", "-Yshow-symkinds", "-Yshow-symowners", "-Yshow-syms", "-Yshow-trees", "-Yshow-trees-compact", "-Yshow-trees-stringified", "-Ytyper-debug",
     "-Ywarn-dead-code", "-Ywarn-numeric-widen", "-Ywarn-value-discard", "-Ywarn-extra-implicit", "-Ywarn-self-implicit",
     "-V",
-    "-Vclasspath", "-Vdebug", "-Vdebug-tasty", "-Vdoc", "-Vfree-terms", "-Vfree-types",
+    "-Vclasspath", "-Vdebug", "-Vdebug-tasty", "-Vdebug-type-error", "-Vdoc", "-Vfree-terms", "-Vfree-types",
     "-Vhot-statistics", "-Vide", "-Vimplicit-conversions", "-Vimplicits", "-Vissue",
     "-Vmacro", "-Vmacro-lite", "-Vpatmat", "-Vphases", "-Vpos", "-Vprint-pos",
     "-Vprint-types", "-Vquasiquote", "-Vreflective-calls", "-Vreify",

src/compiler/scala/tools/nsc/settings/ScalaSettings.scala

@@ -454,10 +454,11 @@ trait ScalaSettings extends StandardScalaSettings with Warnings { _: MutableSett
   val Vhelp              = BooleanSetting("-V", "Print a synopsis of verbose options.")
   val browse          = PhasesSetting("-Vbrowse", "Browse the abstract syntax tree after") withAbbreviation "-Ybrowse"
   val debug           = BooleanSetting("-Vdebug", "Increase the quantity of debugging output.") withAbbreviation "-Ydebug" withPostSetHook (s => if (s.value) StatisticsStatics.enableDebugAndDeoptimize())
-  val YdebugTasty      = BooleanSetting("-Vdebug-tasty", "Increase the quantity of debugging output when unpickling tasty.") withAbbreviation "-Ydebug-tasty"
-  val Ydocdebug          = BooleanSetting("-Vdoc", "Trace scaladoc activity.") withAbbreviation "-Ydoc-debug"
+  val YdebugTasty     = BooleanSetting("-Vdebug-tasty", "Increase the quantity of debugging output when unpickling tasty.") withAbbreviation "-Ydebug-tasty"
+  val VdebugTypeError = BooleanSetting("-Vdebug-type-error", "Print the stack trace when any error is caught.") withAbbreviation "-Ydebug-type-error"
+  val Ydocdebug       = BooleanSetting("-Vdoc", "Trace scaladoc activity.") withAbbreviation "-Ydoc-debug"
   val Yidedebug          = BooleanSetting("-Vide", "Generate, validate and output trees using the interactive compiler.") withAbbreviation "-Yide-debug"
-  val Yissuedebug        = BooleanSetting("-Vissue", "Print stack traces when a context issues an error.") withAbbreviation "-Yissue-debug"
+//  val Yissuedebug        = BooleanSetting("-Vissue", "Print stack traces when a context issues an error.") withAbbreviation "-Yissue-debug"
   val log                = PhasesSetting("-Vlog", "Log operations during") withAbbreviation "-Ylog"
   val Ylogcp             = BooleanSetting("-Vclasspath", "Output information about what classpath is being applied.") withAbbreviation "-Ylog-classpath"
   val YmacrodebugLite    = BooleanSetting("-Vmacro-lite", "Trace macro activities with less output.") withAbbreviation "-Ymacro-debug-lite"

src/compiler/scala/tools/nsc/typechecker/Contexts.scala

@@ -808,7 +808,7 @@ trait Contexts { self: Analyzer =>
     /** Issue/buffer/throw the given implicit ambiguity error according to the current mode for error reporting. */
     private[typechecker] def issueAmbiguousError(err: AbsAmbiguousTypeError) = reporter.issueAmbiguousError(err)(this)
     /** Issue/throw the given error message according to the current mode for error reporting. */
-    def error(pos: Position, msg: String)                                    = reporter.error(fixPosition(pos), msg)
+    def error(pos: Position, msg: String)                                    = reporter.errorAndDumpIfDebug(fixPosition(pos), msg)
     /** Issue/throw the given error message according to the current mode for error reporting. */
     def warning(pos: Position, msg: String, category: WarningCategory)       = reporter.warning(fixPosition(pos), msg, category, owner)
     def warning(pos: Position, msg: String, category: WarningCategory, site: Symbol) = reporter.warning(fixPosition(pos), msg, category, site)
@@ -1643,7 +1643,7 @@ trait Contexts { self: Analyzer =>
     type Error = AbsTypeError
     type Warning = (Position, String, WarningCategory, Symbol)
 
-    def issue(err: AbsTypeError)(implicit context: Context): Unit = error(context.fixPosition(err.errPos), addDiagString(err.errMsg))
+    def issue(err: AbsTypeError)(implicit context: Context): Unit = errorAndDumpIfDebug(context.fixPosition(err.errPos), addDiagString(err.errMsg))
 
     def echo(msg: String): Unit = echo(NoPosition, msg)
 
@@ -1655,6 +1655,13 @@ trait Contexts { self: Analyzer =>
 
     def error(pos: Position, msg: String): Unit
 
+    final def errorAndDumpIfDebug(pos: Position, msg: String): Unit = {
+      error(pos, msg)
+      if (settings.VdebugTypeError.value) {
+        Thread.dumpStack()
+      }
+    }
+
     protected def handleSuppressedAmbiguous(err: AbsAmbiguousTypeError): Unit = ()
 
     def makeImmediate: ContextReporter = this
@@ -1686,7 +1693,7 @@ trait Contexts { self: Analyzer =>
           if (target.isBuffering) {
             target ++= errors
           } else {
-            errors.foreach(e => target.error(e.errPos, e.errMsg))
+            errors.foreach(e => target.errorAndDumpIfDebug(e.errPos, e.errMsg))
           }
           // TODO: is clearAllErrors necessary? (no tests failed when dropping it)
           // NOTE: even though `this ne target`, it may still be that `target.errorBuffer eq _errorBuffer`,

test/files/run/debug-type-error.check

@@ -0,0 +1,5 @@
+newSource1.scala:3: error: object dummy is not a member of package org
+  val a: org.dummy.Dummy = ???
+             ^
+java.lang.Exception: Stack trace
+java.lang.Exception: Stack trace

test/files/run/debug-type-error.scala

@@ -0,0 +1,25 @@
+// filter: (\s*)at(.*)
+
+import scala.tools.partest._
+
+object Test extends DirectTest {
+  override def extraSettings: String = "-usejavacp -Vdebug-type-error"
+
+  def code: String = ""
+
+  def noSuchType: String = """
+object Example
+{
+  val a: org.dummy.Dummy = ???
+}
+  """
+
+  def show(): Unit = {
+    val global = newCompiler()
+
+    def run(code: String): Unit =
+      compileString(global)(code.trim)
+
+    run(noSuchType)
+  }
+}