From 47e604db241cc776f11f5b3f7de3afc77a9cda5b Mon Sep 17 00:00:00 2001
From: Guillaume Martres <smarter@ubuntu.com>
Date: Fri, 19 Jan 2018 19:09:49 +0100
Subject: [PATCH] Fix #3873: Properly unpickle shared TypeTrees

When a TypeTree is represented by a SHAREDterm, we need to follow the
SHAREDterm and call `readTpt()` again. We cannot rely on `readTerm()`
following the SHAREDterm for us because a TypeTree can be pickled as
just a type.
---
 .../src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala   | 8 ++++++--
 tests/pos/i3873.scala                                     | 6 ++++++
 2 files changed, 12 insertions(+), 2 deletions(-)
 create mode 100644 tests/pos/i3873.scala

diff --git a/compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala b/compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala
index 3cb1c9034505..38ffe3963f05 100644
--- a/compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala
+++ b/compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala
@@ -1054,8 +1054,12 @@ class TreeUnpickler(reader: TastyReader,
       setPos(start, tree)
     }
 
-    def readTpt()(implicit ctx: Context) =
-      if (nextByte == SHAREDterm || isTypeTreeTag(nextUnsharedTag)) readTerm()
+    def readTpt()(implicit ctx: Context): Tree =
+      if (nextByte == SHAREDterm) {
+        readByte()
+        forkAt(readAddr()).readTpt()
+      }
+      else if (isTypeTreeTag(nextByte)) readTerm()
       else {
         val start = currentAddr
         val tp = readType()
diff --git a/tests/pos/i3873.scala b/tests/pos/i3873.scala
new file mode 100644
index 000000000000..ebb8b1cd70c9
--- /dev/null
+++ b/tests/pos/i3873.scala
@@ -0,0 +1,6 @@
+object Test {
+  inline def sum2(ys: List[Int]): Unit = {
+    ys.foldLeft(1)
+  }
+  val h1: ((List[Int]) => Unit) = sum2
+}