avoid UndeclaredThrowableException when UNWRAP unwraps checked causes

Author: gitshabh

core/src/main/java/feign/SynchronousMethodHandler.java

@@ -56,7 +56,9 @@ public Object invoke(Object[] argv) throws Throwable {
           retryer.continueOrPropagate(e);
         } catch (RetryableException th) {
           Throwable cause = th.getCause();
-          if (methodHandlerConfiguration.getPropagationPolicy() == UNWRAP && cause != null) {
+          if (methodHandlerConfiguration.getPropagationPolicy() == UNWRAP
+              && cause != null
+              && (cause instanceof RuntimeException || cause instanceof Error)) {
             throw cause;
           } else {
             throw th;

core/src/test/java/feign/FeignTest.java

@@ -50,6 +50,7 @@
 import feign.querymap.FieldQueryMapEncoder;
 import java.io.IOException;
 import java.lang.reflect.Type;
+import java.net.ProtocolException;
 import java.net.URI;
 import java.time.Clock;
 import java.time.Instant;
@@ -708,6 +709,22 @@ void throwsRetryableExceptionIfNoUnderlyingCause() throws Exception {
     assertThat(exception.getMessage()).contains(message);
   }
 
+  @Test
+  void doesNotUnwrapCheckedCauseWhenPropagationPolicyIsUnwrap() {
+    TestInterface api =
+        Feign.builder()
+            .exceptionPropagationPolicy(UNWRAP)
+            .retryer(new DefaultRetryer(1, 1, 1))
+            .client(
+                (_, _) -> {
+                  throw new ProtocolException("missing Location header for redirect");
+                })
+            .target(TestInterface.class, "http://localhost:" + server.getPort());
+
+    RetryableException exception = assertThrows(RetryableException.class, () -> api.post());
+    assertThat(exception.getCause()).isInstanceOf(ProtocolException.class);
+  }
+
   @Test
   void whenReturnTypeIsResponseNoErrorHandling() {
     Map<String, Collection<String>> headers = new LinkedHashMap<>();