Make sure to copy local symbols when reducing projections

If the result of reducing a projection has local bindings,
these bindings need to be copied.

Test case in run/Tuple.scala

Author: odersky

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

@@ -469,10 +469,13 @@ class Inliner(call: tpd.Tree, rhsToInline: tpd.Tree)(implicit ctx: Context) {
             val argInPlace =
               if (trailing.isEmpty) arg
               else letBindUnless(TreeInfo.Pure, arg)(seq(trailing, _))
-            seq(prefix, seq(leading, argInPlace))
-              .reporting(res => i"projecting $tree -> $res", inlining)
+            val fullArg = seq(prefix, seq(leading, argInPlace))
+            new TreeTypeMap().transform(fullArg) // make sure local bindings in argument have fresh symbols
+              .reporting(res => i"projecting $tree -> $res")
           }
           else tree
+        case Block(stats, expr) if stats.forall(isPureBinding) =>
+          cpy.Block(tree)(stats, reduceProjection(expr))
         case _ => tree
       }
     }

tests/run/Tuple.scala

@@ -0,0 +1,38 @@
+import annotation.showAsInfix
+
+sealed trait Tuple
+
+object Tuple {
+  object Empty extends Tuple
+
+  type Empty = Empty.type
+
+  @showAsInfix
+  final case class *: [H, T <: Tuple](hd: H, tl: T) extends Tuple
+
+  class HListDeco(val xs: Tuple) extends AnyVal {
+    transparent def *: [H] (x: H): Tuple = Tuple.*:.apply(x, xs)
+
+    transparent def size: Int = Tuple.size(xs)
+  }
+
+  transparent def size(xs: Tuple): Int = xs match {
+    case Empty => 0
+    case _ *: xs1 => size(xs1) + 1
+  }
+
+  transparent implicit def hlistDeco(xs: Tuple): HListDeco = new HListDeco(xs)
+
+  transparent def apply(): Tuple = Empty
+  transparent def apply(x1: Any): Tuple = x1 *: Empty
+  transparent def apply(x1: Any, x2: Any) = x1 *: x2 *: Empty
+
+  val xs0 = Tuple()
+  val xs1 = Tuple(2)
+  val xs2 = Tuple(2, "a")
+  val s0 = xs0.size
+  val s1 = xs1.size
+  val s2 = xs2.size
+}
+
+object Test extends App