From d73b38333c613cd2cee3630b858810c381a8fc80 Mon Sep 17 00:00:00 2001
From: Guillaume Martres <smarter@ubuntu.com>
Date: Tue, 15 Aug 2017 20:40:58 +0200
Subject: [PATCH] Fix #2980: Crash when inlining HK type parameters

When we inline we need to construct new trees with new symbols. This is
handled by TreeTypeMap which was missing a case for LambdaTypeTree (the
parameters of a type lambda are TypeDefs and thus have symbols that need
to be replaced). This caused a crash in pickling since we ended up
trying to pickle the same symbol twice.
---
 compiler/src/dotty/tools/dotc/ast/TreeTypeMap.scala |  3 +++
 tests/pos/i2980.scala                               | 13 +++++++++++++
 2 files changed, 16 insertions(+)
 create mode 100644 tests/pos/i2980.scala

diff --git a/compiler/src/dotty/tools/dotc/ast/TreeTypeMap.scala b/compiler/src/dotty/tools/dotc/ast/TreeTypeMap.scala
index cf529dfdaa12..c14423394573 100644
--- a/compiler/src/dotty/tools/dotc/ast/TreeTypeMap.scala
+++ b/compiler/src/dotty/tools/dotc/ast/TreeTypeMap.scala
@@ -98,6 +98,9 @@ final class TreeTypeMap(
             case ann => ann
           }
           res
+        case tdef @ LambdaTypeTree(tparams, body) =>
+          val (tmap1, tparams1) = transformDefs(tparams)
+          cpy.LambdaTypeTree(tdef)(tparams1, tmap1.transform(body))
         case blk @ Block(stats, expr) =>
           val (tmap1, stats1) = transformDefs(stats)
           val expr1 = tmap1.transform(expr)
diff --git a/tests/pos/i2980.scala b/tests/pos/i2980.scala
new file mode 100644
index 000000000000..b28b5614c921
--- /dev/null
+++ b/tests/pos/i2980.scala
@@ -0,0 +1,13 @@
+trait Foo {
+  def apply[~>[_,_]](x: Int ~> Int): Int ~> Int
+}
+
+object Foo {
+  inline def foo: Foo = new Foo {
+    def apply[~>[_,_]](x: Int ~> Int): Int ~> Int = x
+  }
+
+  def main(args: Array[String]): Unit = {
+    val x = foo((x: Int) => x)
+  }
+}