Make errors are not swept under the carpet

Typer#ensureReported's comment outlines an example where errors
could go unreported, resulting in error trees after typer without
any reported error messages. This commit makes sure that at least
one error is reported if a tree node has an error type.

Fixes #1802.

1 files changed, 5 insertions, 2 deletions

diff --git a/compiler/src/dotty/tools/dotc/core/Symbols.scala b/compiler/src/dotty/tools/dotc/core/Symbols.scala
index cfd85c49c..b10b94ad8 100644
--- a/compiler/src/dotty/tools/dotc/core/Symbols.scala
+++ b/compiler/src/dotty/tools/dotc/core/Symbols.scala
@@ -22,6 +22,7 @@ import NameOps._
 import ast.tpd.Tree
 import ast.TreeTypeMap
 import Constants.Constant
+import reporting.diagnostic.Message
 import Denotations.{ Denotation, SingleDenotation, MultiDenotation }
 import collection.mutable
 import io.AbstractFile
@@ -290,9 +291,11 @@ trait Symbols { this: Context =>
    */
   def newSkolem(tp: Type) = newSymbol(defn.RootClass, nme.SKOLEM, SyntheticArtifact | Permanent, tp)
 
-  def newErrorSymbol(owner: Symbol, name: Name) =
+  def newErrorSymbol(owner: Symbol, name: Name, msg: => Message) = {
+    val errType = new ErrorType(msg)
     newSymbol(owner, name, SyntheticArtifact,
-      if (name.isTypeName) TypeAlias(ErrorType) else ErrorType)
+        if (name.isTypeName) TypeAlias(errType) else errType)
+  }
 
   /** Map given symbols, subjecting their attributes to the mappings
    *  defined in the given TreeTypeMap `ttmap`.