Fix unreachable warning in deeply nested sealed hierarchy (#18706)

Author: dwijnand

compiler/src/dotty/tools/dotc/core/TypeOps.scala

@@ -883,7 +883,7 @@ object TypeOps:
           else if symbol.is(Module) then
             TermRef(this(tref.prefix), symbol.sourceModule)
           else if (prefixTVar != null)
-            this(tref)
+            this(tref.applyIfParameterized(tref.typeParams.map(_ => WildcardType)))
           else {
             prefixTVar = WildcardType  // prevent recursive call from assigning it
             // e.g. tests/pos/i15029.more.scala, create a TypeVar for `Instances`' B, so we can disregard `Ints`

compiler/test/dotty/tools/dotc/reporting/TestReporter.scala

@@ -32,9 +32,6 @@ extends Reporter with UniqueMessagePositions with HideNonSensicalMessages with M
   protected final val _consoleReporter = new ConsoleReporter(null, new PrintWriter(_consoleBuf))
   final def consoleOutput: String = _consoleBuf.toString
 
-  private var _didCrash = false
-  final def compilerCrashed: Boolean = _didCrash
-
   private var _skip: Boolean = false
   final def setSkip(): Unit = _skip = true
   final def skipped: Boolean = _skip
@@ -50,14 +47,6 @@ extends Reporter with UniqueMessagePositions with HideNonSensicalMessages with M
   def log(msg: String) =
     _messageBuf.append(msg)
 
-  def logStackTrace(thrown: Throwable): Unit = {
-    _didCrash = true
-    val sw = new java.io.StringWriter
-    val pw = new java.io.PrintWriter(sw)
-    thrown.printStackTrace(pw)
-    log(sw.toString)
-  }
-
   /** Prints the message with the given position indication. */
   def printMessageAndPos(dia: Diagnostic, extra: String)(using Context): Unit = {
     val msg = messageAndPos(dia)

compiler/test/dotty/tools/vulpix/ParallelTesting.scala

@@ -244,7 +244,7 @@ trait ParallelTesting extends RunnerOrchestration { self =>
 
     final def countErrors  (reporters: Seq[TestReporter]) = countErrorsAndWarnings(reporters)._1
     final def countWarnings(reporters: Seq[TestReporter]) = countErrorsAndWarnings(reporters)._2
-    final def reporterFailed(r: TestReporter) = r.compilerCrashed || r.errorCount > 0
+    final def reporterFailed(r: TestReporter) = r.errorCount > 0
 
     /**
      * For a given test source, returns a check file against which the result of the test run
@@ -733,22 +733,20 @@ trait ParallelTesting extends RunnerOrchestration { self =>
       lazy val (map, expCount) = getWarnMapAndExpectedCount(testSource.sourceFiles.toIndexedSeq)
       lazy val obtCount = reporters.foldLeft(0)(_ + _.warningCount)
       lazy val (expected, unexpected) = getMissingExpectedWarnings(map, reporters.iterator.flatMap(_.diagnostics))
+      lazy val diagnostics = reporters.flatMap(_.diagnostics.toSeq.sortBy(_.pos.line).map(e => s" at ${e.pos.line + 1}: ${e.message}"))
+      def showLines(title: String, lines: Seq[String]) = if lines.isEmpty then "" else title + lines.mkString("\n", "\n", "")
       def hasMissingAnnotations = expected.nonEmpty || unexpected.nonEmpty
-      def showDiagnostics = "-> following the diagnostics:\n" +
-        reporters.flatMap(_.diagnostics.toSeq.sortBy(_.pos.line).map(e => s"${e.pos.line + 1}: ${e.message}")).mkString(" at ", "\n at ", "")
+      def showDiagnostics = showLines("-> following the diagnostics:", diagnostics)
       Option:
-        if reporters.exists(_.compilerCrashed) then s"Compiler crashed when compiling: ${testSource.title}"
-        else if reporters.exists(_.errorCount > 0) then
+        if reporters.exists(_.errorCount > 0) then
           s"""Compilation failed for: ${testSource.title}
              |$showDiagnostics
              |""".stripMargin.trim.linesIterator.mkString("\n", "\n", "")
-        else if obtCount == 0 then s"\nNo warnings found when compiling warn test $testSource"
-        else if expCount == 0 then s"\nNo warning expected/defined in $testSource -- use // warn"
         else if expCount != obtCount then
           s"""|Wrong number of warnings encountered when compiling $testSource
               |expected: $expCount, actual: $obtCount
-              |${expected.mkString("Unfulfilled expectations:\n", "\n", "")}
-              |${unexpected.mkString("Unexpected warnings:\n", "\n", "")}
+              |${showLines("Unfulfilled expectations:", expected)}
+              |${showLines("Unexpected warnings:", unexpected)}
               |$showDiagnostics
               |""".stripMargin.trim.linesIterator.mkString("\n", "\n", "")
         else if hasMissingAnnotations then s"\nWarnings found on incorrect row numbers when compiling $testSource\n$showDiagnostics"
@@ -862,7 +860,6 @@ trait ParallelTesting extends RunnerOrchestration { self =>
     override def suppressErrors = true
 
     override def maybeFailureMessage(testSource: TestSource, reporters: Seq[TestReporter]): Option[String] =
-      def compilerCrashed = reporters.exists(_.compilerCrashed)
       lazy val (errorMap, expectedErrors) = getErrorMapAndExpectedCount(testSource.sourceFiles.toIndexedSeq)
       lazy val actualErrors = reporters.foldLeft(0)(_ + _.errorCount)
       lazy val (expected, unexpected) = getMissingExpectedErrors(errorMap, reporters.iterator.flatMap(_.errors))
@@ -871,8 +868,7 @@ trait ParallelTesting extends RunnerOrchestration { self =>
         reporters.flatMap(_.allErrors.sortBy(_.pos.line).map(e => s"${e.pos.line + 1}: ${e.message}")).mkString(" at ", "\n at ", "")
 
       Option {
-        if compilerCrashed then s"Compiler crashed when compiling: ${testSource.title}"
-        else if actualErrors == 0 then s"\nNo errors found when compiling neg test $testSource"
+        if actualErrors == 0 then s"\nNo errors found when compiling neg test $testSource"
         else if expectedErrors == 0 then s"\nNo errors expected/defined in $testSource -- use // error or // nopos-error"
         else if expectedErrors != actualErrors then
           s"""|Wrong number of errors encountered when compiling $testSource

tests/warn/i18661.scala

@@ -0,0 +1,28 @@
+class Jacket[T]:
+  sealed trait BodyType:
+    sealed trait OrganType:
+      case class Heart() extends Body.Organ
+      case class Brain() extends Body.Organ
+    object Organ extends OrganType
+    sealed trait Organ
+  object Body extends BodyType
+  sealed trait Body
+
+type AnyJacket         = Jacket[?]
+type AnyBodyOrgan      = AnyJacket#BodyType#Organ
+type AnyBodyOrganHeart = AnyJacket#BodyType#OrganType#Heart
+type AnyBodyOrganBrain = AnyJacket#BodyType#OrganType#Brain
+
+def check( asr : AnyBodyOrgan ) : String =
+  asr match
+    case c : AnyBodyOrganHeart => "Heart"
+    case s : AnyBodyOrganBrain => "Brain" // was: unreachable
+
+val jacket = new Jacket[Unit]
+val heart = new jacket.Body.Organ.Heart()
+val brain = new jacket.Body.Organ.Brain()
+
+@main
+def go =
+  println( check( heart ) )
+  println( check( brain ) )