From c13400a889276f540c35f5509d344514e05e5704 Mon Sep 17 00:00:00 2001
From: Guillaume Martres <smarter@ubuntu.com>
Date: Thu, 29 Mar 2018 15:34:59 +0200
Subject: [PATCH] Fix #4203: Don't expand implicit functions in patterns

---
 compiler/src/dotty/tools/dotc/typer/Typer.scala | 2 ++
 tests/pos/i4203.scala                           | 9 +++++++++
 2 files changed, 11 insertions(+)
 create mode 100644 tests/pos/i4203.scala

diff --git a/compiler/src/dotty/tools/dotc/typer/Typer.scala b/compiler/src/dotty/tools/dotc/typer/Typer.scala
index 954bd38ec216..431721dc44e6 100644
--- a/compiler/src/dotty/tools/dotc/typer/Typer.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Typer.scala
@@ -1821,6 +1821,7 @@ class Typer extends Namer
             xtree.isTerm &&
             !untpd.isImplicitClosure(xtree) &&
             !ctx.mode.is(Mode.ImplicitShadowing) &&
+            !ctx.mode.is(Mode.Pattern) &&
             !ctx.isAfterTyper)
           makeImplicitFunction(xtree, ifpt)
         else xtree match {
@@ -2317,6 +2318,7 @@ class Typer extends Namer
       if (defn.isImplicitFunctionClass(wtp.underlyingClassRef(refinementOK = false).classSymbol) &&
           !untpd.isImplicitClosure(tree) &&
           !isApplyProto(pt) &&
+          !ctx.mode.is(Mode.Pattern) &&
           !ctx.isAfterTyper) {
         typr.println(i"insert apply on implicit $tree")
         typed(untpd.Select(untpd.TypedSplice(tree), nme.apply), pt, locked)
diff --git a/tests/pos/i4203.scala b/tests/pos/i4203.scala
new file mode 100644
index 000000000000..3549237bff2a
--- /dev/null
+++ b/tests/pos/i4203.scala
@@ -0,0 +1,9 @@
+case class Box[Z](unbox: Z)
+
+object Test {
+  def foo(b: Box[implicit Int => Int]): Int = b match {
+    case Box(f) =>
+      implicit val i: Int = 1
+      f
+  }
+}