Issue recursion overflows in variance checking where they happen

Author: odersky

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

@@ -180,7 +180,7 @@ class VarianceChecker()(implicit ctx: Context) {
         sym.is(PrivateLocal) ||
         sym.name.is(InlineAccessorName) || // TODO: should we exclude all synthetic members?
         sym.is(TypeParam) && sym.owner.isClass // already taken care of in primary constructor of class
-      tree match {
+      try tree match {
         case defn: MemberDef if skip =>
           ctx.debuglog(s"Skipping variance check of ${sym.showDcl}")
         case tree: TypeDef =>
@@ -197,6 +197,9 @@ class VarianceChecker()(implicit ctx: Context) {
           vparamss foreach (_ foreach traverse)
         case _ =>
       }
+      catch {
+        case ex: TypeError => ctx.error(ex.toMessage, tree.sourcePos.focus)
+      }
     }
   }
 }

tests/neg-custom-args/matchtype-loop.scala

@@ -11,7 +11,7 @@ object Test {
   val x: Int = g[Int]     // error: found: L[Int], required: Int
 
   def aa: LL[Boolean] = ???
-  def bb: LL[Int] = ???   // error: recursion limit exceeded with  reduce type  LazyRef(Test.LL[Int]) match ...
+  def bb: LL[Int] = ???   // error: recursion limit exceeded with  reduce type  LazyRef(Test.LL[Int]) match ... // error
   def gg[X]: LL[X] = ???
   val xx: Int = gg[Int]   // error: recursion limit exceeded with  reduce type  LazyRef(Test.LL[Int]) match ...
 }