From a1d17e528ecd8df383665b471cee9b39fe2cdd4e Mon Sep 17 00:00:00 2001
From: Miles Sabin <miles@milessabin.com>
Date: Wed, 3 Jul 2019 13:55:38 +0100
Subject: [PATCH] Reject incomplete implicit dictionaries

If any RHS of a recursive implicit dictionary (after pruning) is an
EmptyTree, then this indicates that implicit search failed and we should
report the overall search as a failure.

Fixes scala/bug#11591.
---
 src/compiler/scala/tools/nsc/typechecker/Contexts.scala | 3 ++-
 test/files/neg/t11591.check                             | 4 ++++
 test/files/neg/t11591.scala                             | 9 +++++++++
 3 files changed, 15 insertions(+), 1 deletion(-)
 create mode 100644 test/files/neg/t11591.check
 create mode 100644 test/files/neg/t11591.scala

diff --git a/src/compiler/scala/tools/nsc/typechecker/Contexts.scala b/src/compiler/scala/tools/nsc/typechecker/Contexts.scala
index a981c4aa58c0..544f18cb3204 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Contexts.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Contexts.scala
@@ -351,7 +351,8 @@ trait Contexts { self: Analyzer =>
         }
 
         val pruned = prune(List(result.tree), implicitDictionary.map(_._2), Nil)
-        if(pruned.isEmpty) result
+        if (pruned.isEmpty) result
+        else if (pruned.exists(_._2 == EmptyTree)) SearchFailure
         else {
           val pos = result.tree.pos
           val (dictClassSym, dictClass0) = {
diff --git a/test/files/neg/t11591.check b/test/files/neg/t11591.check
new file mode 100644
index 000000000000..2f7e70ba803f
--- /dev/null
+++ b/test/files/neg/t11591.check
@@ -0,0 +1,4 @@
+byname-implicits-bug.scala:8: error: could not find implicit value for parameter e: Test.A
+  implicitly[A]
+            ^
+one error found
diff --git a/test/files/neg/t11591.scala b/test/files/neg/t11591.scala
new file mode 100644
index 000000000000..407304e9822d
--- /dev/null
+++ b/test/files/neg/t11591.scala
@@ -0,0 +1,9 @@
+object Test {
+  class A
+  class B
+
+  implicit def mkA(implicit b: => B): A = ???
+  implicit def mkB(implicit a: A, i: Int): B = ???
+
+  implicitly[A]
+}