[BUG] Multiple request-body content types generate a dangling request-model import

Description

Expected behavior

The generated sources compile. DefaultApi.java uses MultiArticleImporter as its
JSON request body and does not import a model that was never generated.

Actual behavior

During generation, OpenAPI Generator creates an inline schema for the multipart body
and then skips its model because skipFormModel defaults to true:

Inline schema created as createMultiArticleImporter_request.
Model createMultiArticleImporter_request not generated since it's marked as unused
(due to form parameters) and skipFormModel (global property) set to true (default)

openapi-generator version

openapi-generator:7.24.0

OpenAPI declaration file content or url

openapi: 3.0.3
info:
  title: OpenAPI Generator Bug Repro
  version: 1.0.0
paths:
  /api/multi_article_importer/:
    post:
      operationId: createMultiArticleImporter
      summary: Create a multi article importer
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/MultiArticleImporter'
          multipart/form-data:
            schema:
              type: object
              properties:
                file:
                  type: string
                  format: binary
      responses:
        '201':
          description: Created
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/MultiArticleImporter'
components:
  schemas:
    MultiArticleImporter:
      type: object
      properties:
        id:
          type: integer
          format: int64
        name:
          type: string

pom.xml:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>org.example</groupId>
  <artifactId>openapi-bug-repro</artifactId>
  <version>1.0-SNAPSHOT</version>
  <packaging>jar</packaging>

  <description>
    Minimal reproducer for openapi-generator bug:
    When a requestBody defines multiple content types (application/json + multipart/form-data),
    the generator emits an import for a *CreateRequest wrapper class that it never creates.
    See: https://github.com/OpenAPITools/openapi-generator/issues/...
  </description>

  <properties>
    <java.version>17</java.version>
    <maven.compiler.source>17</maven.compiler.source>
    <maven.compiler.target>17</maven.compiler.target>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <openapi-generator.version>7.24.0</openapi-generator.version>
  </properties>

  <dependencies>
    <!-- Required for generated Spring controller interfaces -->
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-web</artifactId>
      <version>6.1.14</version>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-context</artifactId>
      <version>6.1.14</version>
    </dependency>
    <!-- Required for @Valid / @NotNull annotations in generated code -->
    <dependency>
      <groupId>jakarta.validation</groupId>
      <artifactId>jakarta.validation-api</artifactId>
      <version>3.0.2</version>
    </dependency>
    <dependency>
      <groupId>jakarta.annotation</groupId>
      <artifactId>jakarta.annotation-api</artifactId>
      <version>2.1.1</version>
    </dependency>
    <dependency>
      <groupId>jakarta.servlet</groupId>
      <artifactId>jakarta.servlet-api</artifactId>
      <version>6.0.0</version>
      <scope>provided</scope>
    </dependency>
    <!-- Required for @Parameter / @Operation annotations in generated code -->
    <dependency>
      <groupId>io.swagger.core.v3</groupId>
      <artifactId>swagger-annotations</artifactId>
      <version>2.2.22</version>
    </dependency>
    <!-- Required for @JsonProperty in generated model classes -->
    <dependency>
      <groupId>com.fasterxml.jackson.core</groupId>
      <artifactId>jackson-annotations</artifactId>
      <version>2.17.2</version>
    </dependency>
    <dependency>
      <groupId>com.fasterxml.jackson.core</groupId>
      <artifactId>jackson-databind</artifactId>
      <version>2.17.2</version>
    </dependency>
  </dependencies>

  <build>
    <plugins>
      <plugin>
        <groupId>org.openapitools</groupId>
        <artifactId>openapi-generator-maven-plugin</artifactId>
        <version>${openapi-generator.version}</version>
        <executions>
          <execution>
            <id>generate-api</id>
            <goals>
              <goal>generate</goal>
            </goals>
            <configuration>
              <inputSpec>${project.basedir}/src/main/resources/api.yaml</inputSpec>
              <generatorName>spring</generatorName>
              <apiPackage>org.example.api</apiPackage>
              <modelPackage>org.example.model</modelPackage>
              <configOptions>
                <!-- Generate only interfaces, no full Spring Boot app needed -->
                <interfaceOnly>true</interfaceOnly>
                <useSpringBoot3>true</useSpringBoot3>
                <useTags>true</useTags>
                <!-- Keep the reproducer focused on the dangling request-model import. -->
                <openApiNullable>false</openApiNullable>
              </configOptions>
            </configuration>
          </execution>
        </executions>
      </plugin>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <version>3.13.0</version>
        <configuration>
          <source>17</source>
          <target>17</target>
        </configuration>
      </plugin>
    </plugins>
  </build>
</project>

Generation Details

error:

[ERROR] .../target/generated-sources/openapi/src/main/java/org/example/api/DefaultApi.java:[8,25]
error: cannot find symbol
symbol: class CreateMultiArticleImporterRequest
location: package org.example.model

the generated DefaultApi.java contains:

import org.example.model.CreateMultiArticleImporterRequest; // class is never generated

The import is unused, and no CreateMultiArticleImporterRequest.java exists anywhere
under target/generated-sources/.

Steps to reproduce

mvn clean compile

Related issues/PRs

Suggest a fix

Workarounds:

• Remove the multipart/form-data content so the operation has only one request-body type.
• Alternatively, set the global property skipFormModel to false. This generates the
  otherwise unused CreateMultiArticleImporterRequest model and makes the import resolvable.

Start by running mvn clean compile with src/main/resources/api.yaml and inspect the generated DefaultApi.java under target/generated-sources/openapi. Trace how the multipart request body produces the CreateMultiArticleImporterRequest import, then verify that the generated sources compile without an import for a missing model.