Adds support for Iterable but not Collection parameters.

This was removed as part of #48.

fixes gh-135

spring-cloud-openfeign-core/pom.xml

@@ -220,6 +220,12 @@
 			<version>3.4.0</version>
 			<scope>test</scope>
 		</dependency>
+		<dependency>
+			<groupId>io.vavr</groupId>
+			<artifactId>vavr</artifactId>
+			<version>0.10.0</version>
+			<scope>test</scope>
+		</dependency>
 	</dependencies>
 	<profiles>
 		<profile>

spring-cloud-openfeign-core/src/main/java/org/springframework/cloud/openfeign/support/SpringMvcContract.java

@@ -45,6 +45,7 @@ import org.springframework.context.ResourceLoaderAware;
 import org.springframework.core.DefaultParameterNameDiscoverer;
 import org.springframework.core.MethodParameter;
 import org.springframework.core.ParameterNameDiscoverer;
+import org.springframework.core.ResolvableType;
 import org.springframework.core.annotation.AnnotationUtils;
 import org.springframework.core.convert.ConversionService;
 import org.springframework.core.convert.TypeDescriptor;
@@ -129,8 +130,8 @@ public class SpringMvcContract extends Contract.BaseContract
 		// Feign applies the Param.Expander to each element of an Iterable, so in those
 		// cases we need to provide a TypeDescriptor of the element.
 		if (typeDescriptor.isAssignableTo(ITERABLE_TYPE_DESCRIPTOR)) {
-			TypeDescriptor elementTypeDescriptor = typeDescriptor
-					.getElementTypeDescriptor();
+			TypeDescriptor elementTypeDescriptor = getElementTypeDescriptor(
+					typeDescriptor);
 
 			checkState(elementTypeDescriptor != null,
 					"Could not resolve element type of Iterable type %s. Not declared?",
@@ -141,6 +142,22 @@ public class SpringMvcContract extends Contract.BaseContract
 		return typeDescriptor;
 	}
 
+	private static TypeDescriptor getElementTypeDescriptor(
+			TypeDescriptor typeDescriptor) {
+		TypeDescriptor elementTypeDescriptor = typeDescriptor.getElementTypeDescriptor();
+		// that means it's not a collection but it is iterable, gh-135
+		if (elementTypeDescriptor == null
+				&& Iterable.class.isAssignableFrom(typeDescriptor.getType())) {
+			ResolvableType type = typeDescriptor.getResolvableType().as(Iterable.class)
+					.getGeneric(0);
+			if (type.resolve() == null) {
+				return null;
+			}
+			return new TypeDescriptor(type, null, typeDescriptor.getAnnotations());
+		}
+		return elementTypeDescriptor;
+	}
+
 	@Override
 	public void setResourceLoader(ResourceLoader resourceLoader) {
 		this.resourceLoader = resourceLoader;

spring-cloud-openfeign-core/src/test/java/org/springframework/cloud/openfeign/valid/IterableParameterTests.java

@@ -0,0 +1,105 @@
+/*
+ * Copyright 2013-2019 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.cloud.openfeign.valid;
+
+import com.netflix.loadbalancer.Server;
+import com.netflix.loadbalancer.ServerList;
+import io.vavr.collection.HashSet;
+import io.vavr.collection.Set;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.boot.test.context.SpringBootTest.WebEnvironment;
+import org.springframework.boot.web.server.LocalServerPort;
+import org.springframework.cloud.netflix.ribbon.RibbonClient;
+import org.springframework.cloud.netflix.ribbon.StaticServerList;
+import org.springframework.cloud.openfeign.EnableFeignClients;
+import org.springframework.cloud.openfeign.FeignClient;
+import org.springframework.cloud.openfeign.test.NoSecurityConfiguration;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.context.annotation.Import;
+import org.springframework.test.annotation.DirtiesContext;
+import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RequestParam;
+import org.springframework.web.bind.annotation.RestController;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * @author Spencer Gibb
+ */
+@RunWith(SpringJUnit4ClassRunner.class)
+@SpringBootTest(classes = IterableParameterTests.Application.class, webEnvironment = WebEnvironment.RANDOM_PORT, value = {
+		"spring.application.name=iterableparametertest",
+		"logging.level.org.springframework.cloud.openfeign.valid=DEBUG",
+		"feign.httpclient.enabled=false", "feign.okhttp.enabled=false",
+		"feign.hystrix.enabled=false" })
+@DirtiesContext
+public class IterableParameterTests {
+
+	@Autowired
+	private TestClient testClient;
+
+	@Test
+	public void testClient() {
+		assertThat(this.testClient).as("testClient was null").isNotNull();
+		String results = this.testClient.echo(HashSet.of("a", "b"));
+		assertThat(results).isEqualTo("a,b");
+	}
+
+	@FeignClient(name = "localapp")
+	protected interface TestClient {
+
+		@GetMapping("/echo")
+		String echo(@RequestParam Set<String> set);
+
+	}
+
+	@Configuration
+	@EnableAutoConfiguration
+	@RestController
+	@EnableFeignClients(clients = TestClient.class)
+	@RibbonClient(name = "localapp", configuration = LocalRibbonClientConfiguration.class)
+	@Import(NoSecurityConfiguration.class)
+	protected static class Application {
+
+		@GetMapping("/echo")
+		public String echo(@RequestParam String set) {
+			return set;
+		}
+
+	}
+
+	// Load balancer with fixed server list for "local" pointing to localhost
+	public static class LocalRibbonClientConfiguration {
+
+		@LocalServerPort
+		private int port = 0;
+
+		@Bean
+		public ServerList<Server> ribbonServerList() {
+			return new StaticServerList<>(new Server("localhost", this.port));
+		}
+
+	}
+
+}

src/checkstyle/checkstyle-suppressions.xml

@@ -9,6 +9,7 @@
 	<suppress files=".*FeignRibbonOkHttpClientConfigurationTests.*" checks="LineLengthCheck" />
 	<suppress files=".*InvoiceClient.*" checks="LineLengthCheck" />
 	<suppress files=".*InvoiceResource.*" checks="LineLengthCheck" />
+	<suppress files=".*IterableParameterTests.*" checks="LineLengthCheck" />
 	<suppress files=".*LoadBalancerFeignClientOverrideTests.*" checks="LineLengthCheck" />
 	<suppress files=".*ProtobufSpringEncoderTest.*" checks="LineLengthCheck" />
 	<suppress files=".*ProtobufTest.*" checks="LineLengthCheck" />