Fix crash when warnings are issued

Author: odersky

compiler/src/dotty/tools/dotc/reporting/Reporter.scala

@@ -230,7 +230,7 @@ abstract class Reporter extends interfaces.ReporterResult {
     ctx.mode.is(Mode.Printing)
 
   /** Does this reporter contain not yet reported errors or warnings? */
-  def hasPending(implicit ctx: Context): Boolean = false
+  def hasPendingErrors: Boolean = false
 
   /** If this reporter buffers messages, remove and return all buffered messages. */
   def removeBufferedMessages(implicit ctx: Context): List[MessageContainer] = Nil

compiler/src/dotty/tools/dotc/reporting/StoreReporter.scala

@@ -30,14 +30,8 @@ class StoreReporter(outer: Reporter) extends Reporter {
     infos += m
   }
 
-  override def hasPending(implicit ctx: Context): Boolean = infos != null && {
-    infos exists {
-      case _: Error => true
-      case m: ConditionalWarning => m.enablingOption.value
-      case _: Warning => true
-      case _ => false
-    }
-  }
+  override def hasPendingErrors: Boolean =
+    infos != null && infos.exists(_.isInstanceOf[Error])
 
   override def removeBufferedMessages(implicit ctx: Context): List[MessageContainer] =
     if (infos != null) try infos.toList finally infos = null

compiler/src/dotty/tools/dotc/typer/ProtoTypes.scala

@@ -249,13 +249,12 @@ object ProtoTypes {
           targ = arg.withType(WildcardType)
         else {
           targ = typerFn(arg)
-          if (!ctx.reporter.hasPending) {
-            // There is something fishy going on. Run pos/t1756.scala with -feature.
-            // You will get an orphan type parameter for CI when pickling.
-            // The difference is that with -feature an `implicitConversions` warning
-            // is issued, which means the next two statements are not executed.
-            // It seems we are missing then some constraint instantiations because `evalState`
-            // is not updated.
+          if (!ctx.reporter.hasPendingErrors) {
+            // FIXME: This can swallow warnings by updating the typerstate from a nested
+            // context that gets discarded later. But we do have to update the
+            // typerstate if there are no errors. If we also omitted the next two lines
+            // when warning were emitted, `pos/t1756.scala` would fail when run with -feature.
+            // It would produce an orphan type parameter for CI when pickling.
             myTypedArg = myTypedArg.updated(arg, targ)
             evalState = evalState.updated(arg, (ctx.typerState, ctx.typerState.constraint))
           }