From 119752fd6be2179c8ab10641206046b6d3c027a7 Mon Sep 17 00:00:00 2001
From: Martin Odersky <odersky@gmail.com>
Date: Thu, 29 Aug 2019 14:03:52 +0200
Subject: [PATCH 1/3] Don't interpolate downwards to a bottom type

If the result of a covariant type variable interpolation would be a bottom type,
wait instead. This could make the variable be inferred to its upper bound after all,
if we do not need a fully instantiated type right away.
---
 compiler/src/dotty/tools/dotc/typer/Inferencing.scala | 9 ++++++++-
 tests/{ => pending}/pos/enum-interop.scala            | 0
 tests/{ => pending}/pos/i536.scala                    | 0
 tests/run/type-propagation.scala                      | 7 +++++++
 4 files changed, 15 insertions(+), 1 deletion(-)
 rename tests/{ => pending}/pos/enum-interop.scala (100%)
 rename tests/{ => pending}/pos/i536.scala (100%)
 create mode 100644 tests/run/type-propagation.scala

diff --git a/compiler/src/dotty/tools/dotc/typer/Inferencing.scala b/compiler/src/dotty/tools/dotc/typer/Inferencing.scala
index 45c7c74ae459..06c9f1e51443 100644
--- a/compiler/src/dotty/tools/dotc/typer/Inferencing.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Inferencing.scala
@@ -433,7 +433,14 @@ trait Inferencing { this: Typer =>
             else if (!hasUnreportedErrors)
               if (v.intValue != 0) {
                 typr.println(i"interpolate $tvar in $state in $tree: $tp, fromBelow = ${v.intValue == 1}, $constraint")
-                tvar.instantiate(fromBelow = v.intValue == 1)
+                if (true) {
+                  val fromBelow = v.intValue == 1
+                  val instType = ctx.typeComparer.instanceType(tvar.origin, fromBelow)
+                  if (!(fromBelow && instType.isRef(defn.NothingClass)))
+                    tvar.instantiateWith(instType)
+                }
+                else
+                  tvar.instantiate(fromBelow = v.intValue == 1)
               }
               else typr.println(i"no interpolation for nonvariant $tvar in $state")
           }
diff --git a/tests/pos/enum-interop.scala b/tests/pending/pos/enum-interop.scala
similarity index 100%
rename from tests/pos/enum-interop.scala
rename to tests/pending/pos/enum-interop.scala
diff --git a/tests/pos/i536.scala b/tests/pending/pos/i536.scala
similarity index 100%
rename from tests/pos/i536.scala
rename to tests/pending/pos/i536.scala
diff --git a/tests/run/type-propagation.scala b/tests/run/type-propagation.scala
new file mode 100644
index 000000000000..b01d716269ac
--- /dev/null
+++ b/tests/run/type-propagation.scala
@@ -0,0 +1,7 @@
+object Test extends App {
+  def foo: String = {
+    "abc".asInstanceOf
+  }
+
+  assert(foo == "abc")
+}

From 1d48a9308e46e8660d4f9046f3f4b3889d2900cf Mon Sep 17 00:00:00 2001
From: Martin Odersky <odersky@gmail.com>
Date: Thu, 29 Aug 2019 15:42:47 +0200
Subject: [PATCH 2/3] Reclassify test

i536.scala previously compiled since the type argument was inferred to be Nothing.
But that inference is useless; it just hides a runtime failure. The issue #536
only complained that the compiler crashed, so having a negative outcome
is permissible.
---
 tests/{pending/pos => neg}/i536.scala | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
 rename tests/{pending/pos => neg}/i536.scala (62%)

diff --git a/tests/pending/pos/i536.scala b/tests/neg/i536.scala
similarity index 62%
rename from tests/pending/pos/i536.scala
rename to tests/neg/i536.scala
index f2b8f9ce6b28..e96ff48d12f7 100644
--- a/tests/pending/pos/i536.scala
+++ b/tests/neg/i536.scala
@@ -8,5 +8,5 @@ object Max {
   val m1 = max(xs)
   val m2 = max(null)
 
-  java.util.Collections.max(null)
+  java.util.Collections.max(null)  // error: Type argument Comparable[_] does not conform to upper bound Comparable[_ >: LazyRef(Comparable[_])]
 }

From fd218352a7511b039daa119da51f2a2732b2684f Mon Sep 17 00:00:00 2001
From: Martin Odersky <odersky@gmail.com>
Date: Thu, 29 Aug 2019 17:22:24 +0200
Subject: [PATCH 3/3] Update fastparse to work around #7130

---
 community-build/community-projects/fastparse | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/community-build/community-projects/fastparse b/community-build/community-projects/fastparse
index 5bb27834d584..d13f34b47079 160000
--- a/community-build/community-projects/fastparse
+++ b/community-build/community-projects/fastparse
@@ -1 +1 @@
-Subproject commit 5bb27834d58422282bc12a1b5a03a69dc081338e
+Subproject commit d13f34b470790536bf64deed062b7da53b098c05