From 0894cd3c69d1c22819027d0788954981d8c22429 Mon Sep 17 00:00:00 2001
From: Som Snytt <som.snytt@gmail.com>
Date: Fri, 7 Feb 2020 10:52:41 -0800
Subject: [PATCH] Restore warn-any improvement

---
 .../scala/tools/nsc/typechecker/Infer.scala   | 19 ++++++++++++++-----
 test/files/neg/warn-inferred-any.check        |  5 +----
 2 files changed, 15 insertions(+), 9 deletions(-)

diff --git a/src/compiler/scala/tools/nsc/typechecker/Infer.scala b/src/compiler/scala/tools/nsc/typechecker/Infer.scala
index f86eb2f67bec..1688c0eb4aec 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Infer.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Infer.scala
@@ -13,11 +13,10 @@
 package scala.tools.nsc
 package typechecker
 
-import scala.collection.mutable.ListBuffer
-import scala.collection.{immutable, mutable}
+import scala.collection.{immutable, mutable}, mutable.ListBuffer
+import scala.reflect.internal.Depth
 import scala.util.control.ControlThrowable
 import symtab.Flags._
-import scala.reflect.internal.Depth
 
 /** This trait contains methods related to type parameter inference.
  *
@@ -589,8 +588,18 @@ trait Infer extends Checkable {
         // ...or lower bound of a type param, since they're asking for it.
         var checked, warning = false
         def checkForAny(): Unit = {
-          val collector = new ContainsAnyCollector(topTypes)
-          @`inline` def containsAny(t: Type) = t.dealiasWidenChain.exists(collector.collect)
+          val collector = new ContainsAnyCollector(topTypes) {
+            val seen = mutable.Set.empty[Type]
+            override def apply(t: Type): Unit = {
+              def saw(dw: Type): Unit =
+                if (!result && !seen(dw)) {
+                  seen += dw
+                  if (!dw.typeSymbol.isRefinementClass) super.apply(dw)
+                }
+              if (!result && !seen(t)) t.dealiasWidenChain.foreach(saw)
+            }
+          }
+          @`inline` def containsAny(t: Type) = collector.collect(t)
           val hasAny = containsAny(pt) || containsAny(restpe) ||
             formals.exists(containsAny) ||
             argtpes.exists(containsAny) ||
diff --git a/test/files/neg/warn-inferred-any.check b/test/files/neg/warn-inferred-any.check
index 862a74d664f8..e9809a04c723 100644
--- a/test/files/neg/warn-inferred-any.check
+++ b/test/files/neg/warn-inferred-any.check
@@ -13,9 +13,6 @@ warn-inferred-any.scala:27: warning: a type was inferred to be `Any`; this may i
 warn-inferred-any.scala:37: warning: a type was inferred to be `Object`; this may indicate a programming error.
   cs.contains(new C2)             // warns
      ^
-warn-inferred-any.scala:52: warning: a type was inferred to be `Any`; this may indicate a programming error.
-  stream.mapM(f)                  // should not warn
-         ^
 error: No warnings can be incurred under -Werror.
-6 warnings
+5 warnings
 1 error