Support iterable and array-based OkHttp Part parts.

Also forbid OkHttp Part parts in iterables and arrays when a part name was specified.

retrofit/src/main/java/retrofit2/ServiceMethod.java

@@ -540,12 +540,33 @@ final class ServiceMethod<T> {
         String partName = part.value();
         Class<?> rawParameterType = Utils.getRawType(type);
         if (partName.isEmpty()) {
-          if (!MultipartBody.Part.class.isAssignableFrom(rawParameterType)) {
+          if (Iterable.class.isAssignableFrom(rawParameterType)) {
+            if (!(type instanceof ParameterizedType)) {
+              throw parameterError(p, rawParameterType.getSimpleName()
+                  + " must include generic type (e.g., "
+                  + rawParameterType.getSimpleName()
+                  + "<String>)");
+            }
+            ParameterizedType parameterizedType = (ParameterizedType) type;
+            Type iterableType = Utils.getParameterUpperBound(0, parameterizedType);
+            if (!MultipartBody.Part.class.isAssignableFrom(Utils.getRawType(iterableType))) {
+              throw parameterError(p,
+                  "@Part annotation must supply a name or use MultipartBody.Part parameter type.");
+            }
+            return ParameterHandler.RawPart.INSTANCE.iterable();
+          } else if (rawParameterType.isArray()) {
+            Class<?> arrayComponentType = rawParameterType.getComponentType();
+            if (!MultipartBody.Part.class.isAssignableFrom(arrayComponentType)) {
+              throw parameterError(p,
+                  "@Part annotation must supply a name or use MultipartBody.Part parameter type.");
+            }
+            return ParameterHandler.RawPart.INSTANCE.array();
+          } else if (MultipartBody.Part.class.isAssignableFrom(rawParameterType)) {
+            return ParameterHandler.RawPart.INSTANCE;
+          } else {
             throw parameterError(p,
                 "@Part annotation must supply a name or use MultipartBody.Part parameter type.");
           }
-
-          return ParameterHandler.RawPart.INSTANCE;
         } else {
           Headers headers =
               Headers.of("Content-Disposition", "form-data; name=\"" + partName + "\"",
@@ -560,11 +581,19 @@ final class ServiceMethod<T> {
             }
             ParameterizedType parameterizedType = (ParameterizedType) type;
             Type iterableType = Utils.getParameterUpperBound(0, parameterizedType);
+            if (MultipartBody.Part.class.isAssignableFrom(Utils.getRawType(iterableType))) {
+              throw parameterError(p, "@Part parameters using the MultipartBody.Part must not "
+                  + "include a part name in the annotation.");
+            }
             Converter<?, RequestBody> converter =
                 retrofit.requestBodyConverter(iterableType, annotations, methodAnnotations);
             return new ParameterHandler.Part<>(headers, converter).iterable();
           } else if (rawParameterType.isArray()) {
             Class<?> arrayComponentType = boxIfPrimitive(rawParameterType.getComponentType());
+            if (MultipartBody.Part.class.isAssignableFrom(arrayComponentType)) {
+              throw parameterError(p, "@Part parameters using the MultipartBody.Part must not "
+                  + "include a part name in the annotation.");
+            }
             Converter<?, RequestBody> converter =
                 retrofit.requestBodyConverter(arrayComponentType, annotations, methodAnnotations);
             return new ParameterHandler.Part<>(headers, converter).array();

retrofit/src/test/java/retrofit2/RequestBuilderTest.java

@@ -1446,6 +1446,44 @@ public final class RequestBuilderTest {
     }
   }
 
+  @Test public void multipartIterableRequiresName() {
+    class Example {
+      @Multipart //
+      @POST("/foo/bar/") //
+      Call<ResponseBody> method(@Part List<RequestBody> part) {
+        return null;
+      }
+    }
+
+    try {
+      buildRequest(Example.class, new Object[] { null });
+      fail();
+    } catch (IllegalArgumentException e) {
+      assertThat(e).hasMessage(
+          "@Part annotation must supply a name or use MultipartBody.Part parameter type. (parameter #1)\n"
+              + "    for method Example.method");
+    }
+  }
+
+  @Test public void multipartArrayRequiresName() {
+    class Example {
+      @Multipart //
+      @POST("/foo/bar/") //
+      Call<ResponseBody> method(@Part RequestBody[] part) {
+        return null;
+      }
+    }
+
+    try {
+      buildRequest(Example.class, new Object[] { null });
+      fail();
+    } catch (IllegalArgumentException e) {
+      assertThat(e).hasMessage(
+          "@Part annotation must supply a name or use MultipartBody.Part parameter type. (parameter #1)\n"
+              + "    for method Example.method");
+    }
+  }
+
   @Test public void multipartOkHttpPartForbidsName() {
     class Example {
       @Multipart //
@@ -1491,6 +1529,71 @@ public final class RequestBuilderTest {
         .contains("\r\nkat\r\n--");
   }
 
+  @Test public void multipartOkHttpIterablePart() throws IOException {
+    class Example {
+      @Multipart //
+      @POST("/foo/bar/") //
+      Call<ResponseBody> method(@Part List<MultipartBody.Part> part) {
+        return null;
+      }
+    }
+
+    MultipartBody.Part part1 = MultipartBody.Part.createFormData("foo", "bar");
+    MultipartBody.Part part2 = MultipartBody.Part.createFormData("kit", "kat");
+    Request request = buildRequest(Example.class, Arrays.asList(part1, part2));
+    assertThat(request.method()).isEqualTo("POST");
+    assertThat(request.headers().size()).isZero();
+    assertThat(request.url().toString()).isEqualTo("http://example.com/foo/bar/");
+
+    RequestBody body = request.body();
+    Buffer buffer = new Buffer();
+    body.writeTo(buffer);
+    String bodyString = buffer.readUtf8();
+
+    assertThat(bodyString)
+        .contains("Content-Disposition: form-data;")
+        .contains("name=\"foo\"\r\n")
+        .contains("\r\nbar\r\n--");
+
+    assertThat(bodyString)
+        .contains("Content-Disposition: form-data;")
+        .contains("name=\"kit\"\r\n")
+        .contains("\r\nkat\r\n--");
+  }
+
+  @Test public void multipartOkHttpArrayPart() throws IOException {
+    class Example {
+      @Multipart //
+      @POST("/foo/bar/") //
+      Call<ResponseBody> method(@Part MultipartBody.Part[] part) {
+        return null;
+      }
+    }
+
+    MultipartBody.Part part1 = MultipartBody.Part.createFormData("foo", "bar");
+    MultipartBody.Part part2 = MultipartBody.Part.createFormData("kit", "kat");
+    Request request =
+        buildRequest(Example.class, new Object[] { new MultipartBody.Part[] { part1, part2 } });
+    assertThat(request.method()).isEqualTo("POST");
+    assertThat(request.headers().size()).isZero();
+    assertThat(request.url().toString()).isEqualTo("http://example.com/foo/bar/");
+
+    RequestBody body = request.body();
+    Buffer buffer = new Buffer();
+    body.writeTo(buffer);
+    String bodyString = buffer.readUtf8();
+
+    assertThat(bodyString)
+        .contains("Content-Disposition: form-data;")
+        .contains("name=\"foo\"\r\n")
+        .contains("\r\nbar\r\n--");
+
+    assertThat(bodyString)
+        .contains("Content-Disposition: form-data;")
+        .contains("name=\"kit\"\r\n")
+        .contains("\r\nkat\r\n--");
+  }
+
   @Test public void multipartOkHttpPartWithFilename() throws IOException {
     class Example {
       @Multipart //
@@ -1548,6 +1651,44 @@ public final class RequestBuilderTest {
         .contains("\r\npong2\r\n--");
   }
 
+  @Test public void multipartIterableOkHttpPart() {
+    class Example {
+      @Multipart //
+      @POST("/foo/bar/") //
+      Call<ResponseBody> method(@Part("ping") List<MultipartBody.Part> part) {
+        return null;
+      }
+    }
+
+    try {
+      buildRequest(Example.class, new Object[] { null });
+      fail();
+    } catch (IllegalArgumentException e) {
+      assertThat(e).hasMessage(
+          "@Part parameters using the MultipartBody.Part must not include a part name in the annotation. (parameter #1)\n"
+              + "    for method Example.method");
+    }
+  }
+
+  @Test public void multipartArrayOkHttpPart() {
+    class Example {
+      @Multipart //
+      @POST("/foo/bar/") //
+      Call<ResponseBody> method(@Part("ping") MultipartBody.Part[] part) {
+        return null;
+      }
+    }
+
+    try {
+      buildRequest(Example.class, new Object[] { null });
+      fail();
+    } catch (IllegalArgumentException e) {
+      assertThat(e).hasMessage(
+          "@Part parameters using the MultipartBody.Part must not include a part name in the annotation. (parameter #1)\n"
+              + "    for method Example.method");
+    }
+  }
+
   @Test public void multipartWithEncoding() throws IOException {
     class Example {
       @Multipart //