Fix stack overflow when testing for shadowing

Shadowing tests could go into an infinite recursion when
the found sahdwoing member itself needs an implicit that
is resolved and then shadowed again by the same member.

A test case is neg/arrayclone-new.scala. This caused
a SO before, now gives two errors.

1 files changed, 3 insertions, 2 deletions

diff --git a/src/dotty/tools/dotc/typer/Implicits.scala b/src/dotty/tools/dotc/typer/Implicits.scala
index b03bcfcf9..841390ef1 100644
--- a/src/dotty/tools/dotc/typer/Implicits.scala
+++ b/src/dotty/tools/dotc/typer/Implicits.scala
@@ -491,7 +491,7 @@ trait Implicits { self: Typer =>
             pt)
         val generated1 = adapt(generated, pt)
         lazy val shadowing =
-          typed(untpd.Ident(ref.name) withPos pos.toSynthetic, funProto)(nestedContext.setNewTyperState)
+          typed(untpd.Ident(ref.name) withPos pos.toSynthetic, funProto)(nestedContext.setNewTyperState.addMode(Mode.ImplicitShadowing))
         def refMatches(shadowing: Tree): Boolean =
           ref.symbol == closureBody(shadowing).symbol || {
             shadowing match {
@@ -501,7 +501,8 @@ trait Implicits { self: Typer =>
           }
         if (ctx.typerState.reporter.hasErrors)
           nonMatchingImplicit(ref)
-        else if (contextual && !shadowing.tpe.isError && !refMatches(shadowing)) {
+        else if (contextual && !ctx.mode.is(Mode.ImplicitShadowing) &&
+                 !shadowing.tpe.isError && !refMatches(shadowing)) {
           implicits.println(i"SHADOWING $ref in ${ref.termSymbol.owner} is shadowed by $shadowing in ${shadowing.symbol.owner}")
           shadowedImplicit(ref, methPart(shadowing).tpe)
         }