From 481956a9330e2eac3d2c23cb376ab0deb5000aac Mon Sep 17 00:00:00 2001
From: Luke Cwik <lcwik@google.com>
Date: Tue, 17 Jul 2018 09:18:03 -0700
Subject: [PATCH] [BEAM-4769] Fix issue when performing coder inference for
 wildcard types.

---
 .../apache/beam/sdk/coders/CoderRegistry.java    |  6 +-----
 .../beam/sdk/coders/CoderRegistryTest.java       | 16 ++++++++++++++++
 2 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/sdks/java/core/src/main/java/org/apache/beam/sdk/coders/CoderRegistry.java b/sdks/java/core/src/main/java/org/apache/beam/sdk/coders/CoderRegistry.java
index 167ff84f01c3..865b24886085 100644
--- a/sdks/java/core/src/main/java/org/apache/beam/sdk/coders/CoderRegistry.java
+++ b/sdks/java/core/src/main/java/org/apache/beam/sdk/coders/CoderRegistry.java
@@ -621,11 +621,7 @@ private <T> Coder<T> getCoderFromTypeDescriptor(
     } else if (type instanceof WildcardType) {
       // No coder for an unknown generic type.
       throw new CannotProvideCoderException(
-          String.format(
-              "Cannot provide a coder for type variable %s"
-                  + " (declared by %s) because the actual type is unknown due to erasure.",
-              type, ((TypeVariable<?>) type).getGenericDeclaration()),
-          ReasonCode.TYPE_ERASURE);
+          String.format("Cannot provide a coder for wildcard type %s.", type), ReasonCode.UNKNOWN);
     } else {
       throw new RuntimeException("Internal error: unexpected kind of Type: " + type);
     }
diff --git a/sdks/java/core/src/test/java/org/apache/beam/sdk/coders/CoderRegistryTest.java b/sdks/java/core/src/test/java/org/apache/beam/sdk/coders/CoderRegistryTest.java
index de561dd1779b..4b21fd29fbf5 100644
--- a/sdks/java/core/src/test/java/org/apache/beam/sdk/coders/CoderRegistryTest.java
+++ b/sdks/java/core/src/test/java/org/apache/beam/sdk/coders/CoderRegistryTest.java
@@ -27,6 +27,7 @@
 import java.io.InputStream;
 import java.io.OutputStream;
 import java.io.Serializable;
+import java.lang.reflect.ParameterizedType;
 import java.lang.reflect.Type;
 import java.util.Collections;
 import java.util.List;
@@ -149,6 +150,21 @@ public void testParameterizedDefaultCoderUnknown() throws Exception {
     registry.getCoder(listUnknownToken);
   }
 
+  @Test
+  public void testParameterizedWildcardTypeIsUnknown() throws Exception {
+    CoderRegistry registry = CoderRegistry.createDefault();
+    TypeDescriptor<List<? extends MyValue>> wildcardUnknownToken =
+        new TypeDescriptor<List<? extends MyValue>>() {};
+
+    thrown.expect(CannotProvideCoderException.class);
+    thrown.expectMessage(
+        String.format(
+            "Cannot provide coder for parameterized type %s: Cannot provide a coder for wildcard type %s.",
+            wildcardUnknownToken,
+            ((ParameterizedType) wildcardUnknownToken.getType()).getActualTypeArguments()[0]));
+    registry.getCoder(wildcardUnknownToken);
+  }
+
   @Test
   public void testTypeParameterInferenceForward() throws Exception {
     CoderRegistry registry = CoderRegistry.createDefault();