Fix #375: support OpenAPI 3.1 array-valued type (unions & nullable)

OpenAPI 3.1 / JSON Schema 2020-12 allows a schema's `type` to be an array,
e.g. type: ["string", "null"] (the nullable idiom that replaces 3.0's
`nullable: true`, and general unions). ApiTool.getType() read the type via
JsonNode.textValue(), which returns null for an array node and collapsed to
"", so every isObject/isArray/isString/isNumber/isDateTime predicate and
MapperUtil.getSimpleType failed -> the generator silently produced wrong or
empty types for those fields.

- ApiTool.getType: when `type` is an array, resolve to the first non-"null"
  entry ("null" only marks the type as nullable). All the isX predicates and
  getSimpleType then work unchanged for union/nullable types.
- MapperUtil.processNumber: read the type via ApiTool.getType instead of
  schema.get("type").asText(), so array-valued numeric types resolve.
- Add TypeConstants.NULL.
- Add a 3.1.0 regression fixture (testOpenApi31Types) covering ["string",
  "null"], ["integer","null"], ["number","null"]+double, int64 and a plain
  array, with golden assets.

Bumps version 6.3.2 -> 6.4.0 across the engine, maven and gradle modules.
Non-array `type` handling is unchanged, so existing 3.0 specs are unaffected.

Follow-up 3.1 items (examples array, $ref siblings, webhooks) tracked in #375.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: joseegarcia

multiapi-engine/pom.xml

@@ -4,7 +4,7 @@
 
   <groupId>com.sngular</groupId>
   <artifactId>multiapi-engine</artifactId>
-  <version>6.3.2</version>
+  <version>6.4.0</version>
   <packaging>jar</packaging>
 
   <properties>

multiapi-engine/src/main/java/com/sngular/api/generator/plugin/common/model/TypeConstants.java

@@ -18,6 +18,8 @@ public final class TypeConstants {
 
   public static final String ARRAY = "array";
 
+  public static final String NULL = "null";
+
   public static final String MAP = "map";
 
   public static final String BIG_DECIMAL = "bigDecimal";

multiapi-engine/src/main/java/com/sngular/api/generator/plugin/common/tools/ApiTool.java

@@ -220,7 +220,23 @@ public static boolean hasType(final JsonNode schema) {
   }
 
   public static String getType(final JsonNode schema) {
-    return hasType(schema) ? StringUtils.defaultIfEmpty(getNodeAsString(schema, "type"), "") : "";
+    if (!hasType(schema)) {
+      return "";
+    }
+    final JsonNode typeNode = getNode(schema, "type");
+    if (typeNode.isArray()) {
+      // OpenAPI 3.1 / JSON Schema 2020-12: "type" may be an array (e.g. ["string", "null"]).
+      // Resolve to the first non-"null" entry; "null" only marks the type as nullable.
+      String resolvedType = "";
+      for (final JsonNode element : typeNode) {
+        if (!TypeConstants.NULL.equalsIgnoreCase(element.asText())) {
+          resolvedType = element.asText();
+          break;
+        }
+      }
+      return resolvedType;
+    }
+    return StringUtils.defaultIfEmpty(typeNode.textValue(), "");
   }
 
   public static boolean hasItems(final JsonNode schema) {

multiapi-engine/src/main/java/com/sngular/api/generator/plugin/common/tools/MapperUtil.java

@@ -50,7 +50,7 @@ private static boolean checkIfNumber(final String nodeType) {
 
   private static String processNumber(final JsonNode schema) {
 
-    final var nodeType = schema.get("type").asText();
+    final var nodeType = ApiTool.getType(schema);
     final var formatType = schema.has("format") ? schema.get("format").asText() : null;
     String type = TypeConstants.INTEGER;
     if (TypeConstants.NUMBER.equalsIgnoreCase(nodeType)) {

multiapi-engine/src/test/java/com/sngular/api/generator/plugin/openapi/OpenApiGeneratorFixtures.java

@@ -147,6 +147,13 @@ public final class OpenApiGeneratorFixtures {
 					.clientPackage("com.sngular.multifileplugin.externalref.client").modelNamePrefix("Api")
 					.modelNameSuffix("DTO").build());
 
+	static final List<SpecFile> TEST_OPEN_API_31_TYPES = List
+			.of(SpecFile.builder().filePath("openapigenerator/testOpenApi31Types/api-test.yml")
+					.apiPackage("com.sngular.multifileplugin.openapi31types")
+					.modelPackage("com.sngular.multifileplugin.openapi31types.model")
+					.clientPackage("com.sngular.multifileplugin.openapi31types.client")
+					.modelNameSuffix("DTO").build());
+
 	static final List<SpecFile> TEST_ANY_OF_IN_RESPONSE = List
 			.of(SpecFile.builder().filePath("openapigenerator/testAnyOfInResponse/api-test.yml")
 					.apiPackage("com.sngular.multifileplugin.testanyofinresponse")
@@ -763,6 +770,24 @@ static Function<Path, Boolean> validateExternalRefGeneration() {
 				DEFAULT_MODEL_API, expectedExceptionFiles, DEFAULT_EXCEPTION_API);
 	}
 
+	static Function<Path, Boolean> validateOpenApi31Types() {
+
+		final String DEFAULT_TARGET_API = "generated/com/sngular/multifileplugin/openapi31types";
+
+		final String DEFAULT_MODEL_API = "generated/com/sngular/multifileplugin/openapi31types/model";
+
+		final String COMMON_PATH = "openapigenerator/testOpenApi31Types/";
+
+		final String ASSETS_PATH = COMMON_PATH + "assets/";
+
+		final List<String> expectedTestApiFile = List.of(ASSETS_PATH + "ProfileApi.java");
+
+		final List<String> expectedTestApiModelFiles = List.of(ASSETS_PATH + "ProfileDTO.java");
+
+		return path -> commonTest(path, expectedTestApiFile, expectedTestApiModelFiles, DEFAULT_TARGET_API,
+				DEFAULT_MODEL_API, Collections.emptyList(), null);
+	}
+
 	static Function<Path, Boolean> validateAnyOfInResponse() {
 
 		final String DEFAULT_TARGET_API = "generated/com/sngular/multifileplugin/testanyofinresponse";

multiapi-engine/src/test/java/com/sngular/api/generator/plugin/openapi/OpenApiGeneratorTest.java

@@ -83,6 +83,8 @@ static Stream<Arguments> fileSpecToProcess() {
             OpenApiGeneratorFixtures.validateEnumsLombokGeneration()),
         Arguments.of("testExternalRefsGeneration", OpenApiGeneratorFixtures.TEST_EXTERNAL_REF_GENERATION,
             OpenApiGeneratorFixtures.validateExternalRefGeneration()),
+        Arguments.of("testOpenApi31Types", OpenApiGeneratorFixtures.TEST_OPEN_API_31_TYPES,
+            OpenApiGeneratorFixtures.validateOpenApi31Types()),
         Arguments.of("testAnyOfInResponse", OpenApiGeneratorFixtures.TEST_ANY_OF_IN_RESPONSE,
             OpenApiGeneratorFixtures.validateAnyOfInResponse()),
         Arguments.of("testOneOfInResponse", OpenApiGeneratorFixtures.TEST_ONE_OF_IN_RESPONSE,

multiapi-engine/src/test/resources/openapigenerator/testOpenApi31Types/api-test.yml

@@ -0,0 +1,49 @@
+---
+# Reproduction/regression for OpenAPI 3.1.x support (issue #375).
+# Exercises JSON Schema 2020-12 array-valued `type`, including the ["<type>", "null"]
+# nullable idiom that replaces 3.0's `nullable: true`, plus a int64 and a plain array.
+openapi: "3.1.0"
+info:
+  version: 1.0.0
+  title: Profile API (OpenAPI 3.1)
+  license:
+    name: MIT
+servers:
+  - url: http://localhost:8080/v1
+tags:
+  - name: profile
+paths:
+  /profile:
+    get:
+      summary: Get the profile
+      operationId: getProfile
+      tags:
+        - profile
+      responses:
+        '200':
+          description: The requested profile
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/Profile"
+components:
+  schemas:
+    Profile:
+      type: object
+      properties:
+        id:
+          type: string
+        nickname:
+          type: ["string", "null"]
+        age:
+          type: ["integer", "null"]
+        score:
+          type: ["number", "null"]
+          format: double
+        loginCount:
+          type: integer
+          format: int64
+        tags:
+          type: array
+          items:
+            type: string

multiapi-engine/src/test/resources/openapigenerator/testOpenApi31Types/assets/ProfileApi.java

@@ -0,0 +1,46 @@
+package com.sngular.multifileplugin.openapi31types;
+
+import java.util.Optional;
+import java.util.List;
+import java.util.Map;
+import javax.validation.Valid;
+
+import io.swagger.v3.oas.annotations.Operation;
+import io.swagger.v3.oas.annotations.Parameter;
+import io.swagger.v3.oas.annotations.media.Content;
+import io.swagger.v3.oas.annotations.media.Schema;
+import io.swagger.v3.oas.annotations.responses.ApiResponse;
+import org.springframework.http.MediaType;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.*;
+import org.springframework.web.context.request.NativeWebRequest;
+
+import com.sngular.multifileplugin.openapi31types.model.ProfileDTO;
+
+public interface ProfileApi {
+
+  /**
+   * GET /profile: Get the profile
+   * @return  The requested profile; (status code 200)
+   */
+
+  @Operation(
+    operationId = "getProfile",
+    summary = "Get the profile",
+    tags = {"profile"},
+    responses = {
+      @ApiResponse(responseCode = "200", description = "The requested profile", content = @Content(mediaType = "application/json", schema = @Schema(implementation = ProfileDTO.class)))
+    }
+  )
+  @RequestMapping(
+    method = RequestMethod.GET,
+    value = "/profile",
+    produces = {"application/json"}
+  )
+
+  default ResponseEntity<ProfileDTO> getProfile() {
+    return new ResponseEntity<>(HttpStatus.NOT_IMPLEMENTED);
+  }
+
+}

multiapi-engine/src/test/resources/openapigenerator/testOpenApi31Types/assets/ProfileDTO.java

@@ -0,0 +1,177 @@
+package com.sngular.multifileplugin.openapi31types.model;
+
+import java.util.Objects;
+
+import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
+import com.fasterxml.jackson.databind.annotation.JsonPOJOBuilder;
+import com.fasterxml.jackson.annotation.JsonProperty;
+import io.swagger.v3.oas.annotations.media.Schema;
+import java.util.List;
+import java.util.ArrayList;
+
+@JsonDeserialize(builder = ProfileDTO.ProfileDTOBuilder.class)
+public class ProfileDTO {
+
+  @JsonProperty(value ="tags")
+  private List<String> tags;
+  @JsonProperty(value ="id")
+  private String id;
+  @JsonProperty(value ="loginCount")
+  private Long loginCount;
+  @JsonProperty(value ="age")
+  private Integer age;
+  @JsonProperty(value ="score")
+  private Double score;
+  @JsonProperty(value ="nickname")
+  private String nickname;
+
+  private ProfileDTO(ProfileDTOBuilder builder) {
+    this.tags = builder.tags;
+    this.id = builder.id;
+    this.loginCount = builder.loginCount;
+    this.age = builder.age;
+    this.score = builder.score;
+    this.nickname = builder.nickname;
+
+  }
+
+  public static ProfileDTO.ProfileDTOBuilder builder() {
+    return new ProfileDTO.ProfileDTOBuilder();
+  }
+
+  @JsonPOJOBuilder(buildMethodName = "build", withPrefix = "")
+  public static class ProfileDTOBuilder {
+
+    private List<String> tags = new ArrayList<String>();
+    private String id;
+    private Long loginCount;
+    private Integer age;
+    private Double score;
+    private String nickname;
+
+    public ProfileDTO.ProfileDTOBuilder tags(List<String> tags) {
+      if (!tags.isEmpty()) {
+        this.tags.addAll(tags);
+      }
+      return this;
+    }
+
+    public ProfileDTO.ProfileDTOBuilder tag(String tag) {
+      if (Objects.nonNull(tag)) {
+        this.tags.add(tag);
+      }
+      return this;
+    }
+
+    public ProfileDTO.ProfileDTOBuilder id(String id) {
+      this.id = id;
+      return this;
+    }
+
+    public ProfileDTO.ProfileDTOBuilder loginCount(Long loginCount) {
+      this.loginCount = loginCount;
+      return this;
+    }
+
+    public ProfileDTO.ProfileDTOBuilder age(Integer age) {
+      this.age = age;
+      return this;
+    }
+
+    public ProfileDTO.ProfileDTOBuilder score(Double score) {
+      this.score = score;
+      return this;
+    }
+
+    public ProfileDTO.ProfileDTOBuilder nickname(String nickname) {
+      this.nickname = nickname;
+      return this;
+    }
+
+    public ProfileDTO build() {
+      ProfileDTO profileDTO = new ProfileDTO(this);
+      return profileDTO;
+    }
+  }
+
+  @Schema(name = "tags", required = false)
+  public List<String> getTags() {
+    return tags;
+  }
+  public void setTags(List<String> tags) {
+    this.tags = tags;
+  }
+
+  @Schema(name = "id", required = false)
+  public String getId() {
+    return id;
+  }
+  public void setId(String id) {
+    this.id = id;
+  }
+
+  @Schema(name = "loginCount", required = false)
+  public Long getLoginCount() {
+    return loginCount;
+  }
+  public void setLoginCount(Long loginCount) {
+    this.loginCount = loginCount;
+  }
+
+  @Schema(name = "age", required = false)
+  public Integer getAge() {
+    return age;
+  }
+  public void setAge(Integer age) {
+    this.age = age;
+  }
+
+  @Schema(name = "score", required = false)
+  public Double getScore() {
+    return score;
+  }
+  public void setScore(Double score) {
+    this.score = score;
+  }
+
+  @Schema(name = "nickname", required = false)
+  public String getNickname() {
+    return nickname;
+  }
+  public void setNickname(String nickname) {
+    this.nickname = nickname;
+  }
+
+  @Override
+  public boolean equals(Object o) {
+    if (this == o) {
+      return true;
+    }
+    if (o == null || getClass() != o.getClass()) {
+      return false;
+    }
+    ProfileDTO profileDTO = (ProfileDTO) o;
+    return Objects.equals(this.tags, profileDTO.tags) && Objects.equals(this.id, profileDTO.id) && Objects.equals(this.loginCount, profileDTO.loginCount) && Objects.equals(this.age, profileDTO.age) && Objects.equals(this.score, profileDTO.score) && Objects.equals(this.nickname, profileDTO.nickname);
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash(tags, id, loginCount, age, score, nickname);
+  }
+
+  @Override
+  public String toString() {
+    StringBuilder sb = new StringBuilder();
+    sb.append("ProfileDTO{");
+    sb.append(" tags:").append(tags).append(",");
+    sb.append(" id:").append(id).append(",");
+    sb.append(" loginCount:").append(loginCount).append(",");
+    sb.append(" age:").append(age).append(",");
+    sb.append(" score:").append(score).append(",");
+    sb.append(" nickname:").append(nickname);
+    sb.append("}");
+    return sb.toString();
+  }
+
+
+}

scs-multiapi-gradle-plugin/build.gradle

@@ -21,7 +21,7 @@ repositories {
 }
 
 group = 'com.sngular'
-version = '6.3.2'
+version = '6.4.0'
 
 def SCSMultiApiPluginGroupId = group
 def SCSMultiApiPluginVersion = version
@@ -31,7 +31,7 @@ dependencies {
   shadow localGroovy()
   shadow gradleApi()
 
-  implementation 'com.sngular:multiapi-engine:6.3.2'
+  implementation 'com.sngular:multiapi-engine:6.4.0'
   testImplementation 'org.assertj:assertj-core:3.24.2'
   testImplementation 'com.puppycrawl.tools:checkstyle:10.12.3'
   testImplementation 'org.junit.platform:junit-platform-launcher:1.9.2'