Auto generate unknown fallback (#1561)

Resolve #1537.
#1462

# Summary

Previously, in the line-bot-sdk-java, the `Unknown` class was manually
implemented and used as the `defaultImpl` (fallback) in `@JsonTypeInfo`.
However, with the transition to generating code from OpenAPI
definitions, generating the `Unknown` class directly from the OpenAPI
spec became challenging. Consequently, the fallback option was disabled.

This change created an issue when decoding webhooks. The type field in
webhooks may receive new values as future features are developed. If an
older SDK version encounters these new values, it could crash while
parsing the webhook.

This PR aims to re-enable the fallback option by adding code that
automatically generates the `Unknown` class from the Java code produced
by OpenAPI, ~even if the method is a bit rough or not entirely elegant~
. This ensures that we can maintain the fallback mechanism under OpenAPI
management.

Author: habara-k

clients/line-bot-messaging-api-client/.openapi-generator/FILES

@@ -153,6 +153,8 @@ src/main/java/com/linecorp/bot/messaging/model/TextMessage.java
 src/main/java/com/linecorp/bot/messaging/model/TextMessageV2.java
 src/main/java/com/linecorp/bot/messaging/model/URIAction.java
 src/main/java/com/linecorp/bot/messaging/model/URIImagemapAction.java
+src/main/java/com/linecorp/bot/messaging/model/UnknownMentionTarget.java
+src/main/java/com/linecorp/bot/messaging/model/UnknownSubstitutionObject.java
 src/main/java/com/linecorp/bot/messaging/model/UpdateRichMenuAliasRequest.java
 src/main/java/com/linecorp/bot/messaging/model/UserMentionTarget.java
 src/main/java/com/linecorp/bot/messaging/model/UserProfileResponse.java

clients/line-bot-messaging-api-client/src/main/java/com/linecorp/bot/messaging/model/MentionTarget.java

@@ -34,5 +34,6 @@
     use = JsonTypeInfo.Id.NAME,
     include = JsonTypeInfo.As.PROPERTY,
     property = "type",
+    defaultImpl = UnknownMentionTarget.class,
     visible = true)
 public interface MentionTarget {}

clients/line-bot-messaging-api-client/src/main/java/com/linecorp/bot/messaging/model/SubstitutionObject.java

@@ -34,5 +34,6 @@
     use = JsonTypeInfo.Id.NAME,
     include = JsonTypeInfo.As.PROPERTY,
     property = "type",
+    defaultImpl = UnknownSubstitutionObject.class,
     visible = true)
 public interface SubstitutionObject {}

clients/line-bot-messaging-api-client/src/main/java/com/linecorp/bot/messaging/model/UnknownMentionTarget.java

@@ -0,0 +1,41 @@
+/*
+ * Copyright 2023 LINE Corporation
+ *
+ * LINE Corporation licenses this file to you 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.
+ */
+
+/**
+ * NOTE: This class is auto generated by OpenAPI Generator (https://openapi-generator.tech).
+ * https://openapi-generator.tech Do not edit the class manually.
+ */
+package com.linecorp.bot.messaging.model;
+
+
+
+import com.fasterxml.jackson.annotation.JsonInclude;
+import com.fasterxml.jackson.annotation.JsonInclude.Include;
+
+/** UnknownMentionTarget */
+@JsonInclude(Include.NON_NULL)
+@javax.annotation.Generated(value = "")
+public record UnknownMentionTarget() implements MentionTarget {
+
+  public static class Builder {
+
+    public Builder() {}
+
+    public UnknownMentionTarget build() {
+      return new UnknownMentionTarget();
+    }
+  }
+}

clients/line-bot-messaging-api-client/src/main/java/com/linecorp/bot/messaging/model/UnknownSubstitutionObject.java

@@ -0,0 +1,41 @@
+/*
+ * Copyright 2023 LINE Corporation
+ *
+ * LINE Corporation licenses this file to you 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.
+ */
+
+/**
+ * NOTE: This class is auto generated by OpenAPI Generator (https://openapi-generator.tech).
+ * https://openapi-generator.tech Do not edit the class manually.
+ */
+package com.linecorp.bot.messaging.model;
+
+
+
+import com.fasterxml.jackson.annotation.JsonInclude;
+import com.fasterxml.jackson.annotation.JsonInclude.Include;
+
+/** UnknownSubstitutionObject */
+@JsonInclude(Include.NON_NULL)
+@javax.annotation.Generated(value = "")
+public record UnknownSubstitutionObject() implements SubstitutionObject {
+
+  public static class Builder {
+
+    public Builder() {}
+
+    public UnknownSubstitutionObject build() {
+      return new UnknownSubstitutionObject();
+    }
+  }
+}

generator/src/main/java/com/linecorp/bot/codegen/LineJavaCodegenGenerator.java

@@ -22,9 +22,11 @@
 import java.io.InputStream;
 import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.NoSuchElementException;
+import java.util.Set;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
@@ -137,6 +139,72 @@ public ModelsMap postProcessModels(ModelsMap objs) {
         return modelsMap;
     }
 
+    @Override
+    public Map<String, ModelsMap> postProcessAllModels(Map<String, ModelsMap> objs) {
+        super.postProcessAllModels(objs);
+
+        Map<String, ModelsMap> additionalModels = new HashMap<>();
+
+        // List of interfaces for which an Unknown class should not be generated for backward compatibility
+        List<String> definedInterfaces = List.of(
+                "Event", "MessageContent", "Message", "Action", "DemographicFilter",
+                "FlexBoxBackground", "FlexComponent", "FlexContainer", "ImagemapAction",
+                "Mentionee", "ModuleContent", "Recipient", "RichMenuBatchOperation",
+                "Source", "Template", "ThingsContent"
+        );
+
+        // Set additional unknown* class for jackson's defaultImpl to have unknwon* class as fallback
+        for (ModelsMap modelsAttrs : objs.values()) {
+            String packageName = modelsAttrs.containsKey("packageName")
+                    ? modelsAttrs.get("packageName").toString()
+                    : null;
+            String _package = modelsAttrs.containsKey("package")
+                    ? modelsAttrs.get("package").toString()
+                    : packageName;
+
+            for (ModelMap mo : modelsAttrs.getModels()) {
+                CodegenModel codegenModel = mo.getModel();
+                if (codegenModel.discriminator != null) {
+                    String baseName = codegenModel.classname;
+
+                    // skip for excluded interfaces
+                    if (definedInterfaces.contains(baseName)) {
+                        continue;
+                    }
+
+                    String fallbackModelName = "Unknown" + baseName;
+                    CodegenModel fallbackModel = new CodegenModel();
+                    fallbackModel.name = fallbackModelName;
+                    fallbackModel.schemaName = fallbackModelName;
+                    fallbackModel.parent = baseName;
+                    fallbackModel.interfaces = List.of(baseName);
+                    fallbackModel.allOf = Set.of(baseName);
+                    fallbackModel.classname = fallbackModelName;
+                    fallbackModel.classVarName = camelize(fallbackModelName);
+                    fallbackModel.dataType = baseName;
+                    fallbackModel.classFilename = fallbackModelName;
+                    fallbackModel.imports = Set.of(baseName);
+                    fallbackModel.setIsAnyType(true);
+                    addImplements(fallbackModel, baseName);
+                    ModelMap fallbackModelMap = new ModelMap();
+                    fallbackModelMap.setModel(fallbackModel);
+
+                    ModelsMap fallbackModelsMap = new ModelsMap();
+                    fallbackModelsMap.setModels(List.of(fallbackModelMap));
+                    fallbackModelsMap.setImports(List.of(Map.of("import", _package + "." + baseName)));
+                    fallbackModelsMap.put("packageName", packageName);
+                    fallbackModelsMap.put("package", _package);
+                    fallbackModelsMap.put("classname", fallbackModelName);
+
+                    additionalModels.put(fallbackModelName, fallbackModelsMap);
+                }
+            }
+        }
+        objs.putAll(additionalModels);
+
+        return objs;
+    }
+
     private String readPartialBody(String path) {
         // fill src/main/resources/body/*.java to the body of the class.
         try (InputStream inputStream = getClass().getClassLoader()

generator/src/main/resources/line-java-codegen/model/interface.pebble

@@ -14,12 +14,7 @@
     use = JsonTypeInfo.Id.NAME,
     include = JsonTypeInfo.As.PROPERTY,
     property = "{{model.discriminator.propertyName}}",
-    {# Unknown{{className}} is not auto-generated, so the defaultImpl for newly added classes needs to be disabled. #}
-    {% if ["Event", "MessageContent", "Message", "Action", "DemographicFilter", "FlexBoxBackground", "FlexComponent",
-       "FlexContainer", "ImagemapAction", "Mentionee", "ModuleContent", "Recipient", "RichMenuBatchOperation",
-       "Source", "Template", "ThingsContent"] contains model.classname %}
     defaultImpl = Unknown{{model.classname}}.class,
-    {% endif %}
     visible = true
 )
 public interface {{model.classname}} {

line-bot-webhook/.openapi-generator/FILES

@@ -56,6 +56,7 @@ src/main/java/com/linecorp/bot/webhook/model/TextMessageContent.java
 src/main/java/com/linecorp/bot/webhook/model/ThingsContent.java
 src/main/java/com/linecorp/bot/webhook/model/ThingsEvent.java
 src/main/java/com/linecorp/bot/webhook/model/UnfollowEvent.java
+src/main/java/com/linecorp/bot/webhook/model/UnknownMembershipContent.java
 src/main/java/com/linecorp/bot/webhook/model/UnlinkThingsContent.java
 src/main/java/com/linecorp/bot/webhook/model/UnsendDetail.java
 src/main/java/com/linecorp/bot/webhook/model/UnsendEvent.java

line-bot-webhook/src/main/java/com/linecorp/bot/webhook/model/MembershipContent.java

@@ -35,5 +35,6 @@
     use = JsonTypeInfo.Id.NAME,
     include = JsonTypeInfo.As.PROPERTY,
     property = "type",
+    defaultImpl = UnknownMembershipContent.class,
     visible = true)
 public interface MembershipContent {}

line-bot-webhook/src/main/java/com/linecorp/bot/webhook/model/UnknownMembershipContent.java

@@ -0,0 +1,41 @@
+/*
+ * Copyright 2023 LINE Corporation
+ *
+ * LINE Corporation licenses this file to you 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.
+ */
+
+/**
+ * NOTE: This class is auto generated by OpenAPI Generator (https://openapi-generator.tech).
+ * https://openapi-generator.tech Do not edit the class manually.
+ */
+package com.linecorp.bot.webhook.model;
+
+
+
+import com.fasterxml.jackson.annotation.JsonInclude;
+import com.fasterxml.jackson.annotation.JsonInclude.Include;
+
+/** UnknownMembershipContent */
+@JsonInclude(Include.NON_NULL)
+@javax.annotation.Generated(value = "")
+public record UnknownMembershipContent() implements MembershipContent {
+
+  public static class Builder {
+
+    public Builder() {}
+
+    public UnknownMembershipContent build() {
+      return new UnknownMembershipContent();
+    }
+  }
+}

line-bot-webhook/src/test/java/com/linecorp/bot/webhook/model/UnknownFallbackTest.java

@@ -50,7 +50,8 @@ public static Stream<Arguments> targets() {
                 arguments(MessageContent.class, UnknownMessageContent.class),
                 arguments(ModuleContent.class, UnknownModuleContent.class),
                 arguments(Source.class, UnknownSource.class),
-                arguments(ThingsContent.class, UnknownThingsContent.class)
+                arguments(ThingsContent.class, UnknownThingsContent.class),
+                arguments(MembershipContent.class, UnknownMembershipContent.class)
         );
     }
 }