From ac3c4300216a80d8329429840d78e9b80df399ef Mon Sep 17 00:00:00 2001
From: Liu Fengyun <liu@fengy.me>
Date: Fri, 19 Jul 2019 16:45:29 +0200
Subject: [PATCH] Fix #6142: remove unreasonable type change for _

The logic was introduced in f618e47, which is hard to justify.
The problem is exhibited in tests/pos/i6142.scala, where
we have code lik the following:

    implicit val _: scala.quoted.Type = ...
    {
      def $anon$ = _
      closure($anon$)
    }

Changing the type of `_` will break LambdLift (`_` is not free anymore),
and the compiler crashes at backend when generating code for the unfound local variable `_`,
whose symbol is `scala.quoted.Type`.
---
 compiler/src/dotty/tools/dotc/transform/Erasure.scala |  5 +----
 tests/pos/i6142.scala                                 | 10 ++++++++++
 2 files changed, 11 insertions(+), 4 deletions(-)
 create mode 100644 tests/pos/i6142.scala

diff --git a/compiler/src/dotty/tools/dotc/transform/Erasure.scala b/compiler/src/dotty/tools/dotc/transform/Erasure.scala
index 825419b7daac..76f03286a4fb 100644
--- a/compiler/src/dotty/tools/dotc/transform/Erasure.scala
+++ b/compiler/src/dotty/tools/dotc/transform/Erasure.scala
@@ -614,10 +614,7 @@ object Erasure {
           if (sym.isConstructor) defn.UnitType
           else sym.info.resultType
         var vparamss1 = (outer.paramDefs(sym) ::: ddef.vparamss.flatten) :: Nil
-        var rhs1 = ddef.rhs match {
-          case id @ Ident(nme.WILDCARD) => untpd.TypedSplice(id.withType(restpe))
-          case _ => ddef.rhs
-        }
+        var rhs1 = ddef.rhs
         if (sym.isAnonymousFunction && vparamss1.head.length > MaxImplementedFunctionArity) {
           val bunchedParam = ctx.newSymbol(sym, nme.ALLARGS, Flags.TermParam, JavaArrayType(defn.ObjectType))
           def selector(n: Int) = ref(bunchedParam)
diff --git a/tests/pos/i6142.scala b/tests/pos/i6142.scala
new file mode 100644
index 000000000000..9b0485bc5f19
--- /dev/null
+++ b/tests/pos/i6142.scala
@@ -0,0 +1,10 @@
+import scala.quoted._
+
+object O {
+  def foo given QuoteContext = {
+    type T
+    implicit val _: scala.quoted.Type[T] = ???
+    '[List[T]]
+    ()
+  }
+}