[BUG][Java][feign-hc5] templateResourcePath / templateDir is overwritten by feign-hc5 library in processOpts()

[BartPraats]

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?

Description

When using the java generator with library=feign-hc5, any user-provided templateResourcePath (or templateDir / -t) is silently ignored. The same configuration works correctly when using library=feign.

The root cause is in JavaClientCodegen.processOpts(), where the feign-hc5 branch unconditionally overwrites the template directory:

} else if (isLibrary(FEIGN_HC5)) {
    additionalProperties.put("feign-hc5", "true");
    setTemplateDir(FEIGN);   // Overwrites any user-provided templateDir/templateResourcePath
    setLibrary(FEIGN);
}

openapi-generator/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaClientCodegen.java

Lines 842 to 844 in e6304a8

	additionalProperties.put("feign-hc5", "true");
	setTemplateDir(FEIGN);
	setLibrary(FEIGN);

The setTemplateDir(FEIGN) call runs after the user's templateResourcePath/templateDir has already been set on the configurator, so it unconditionally replaces the user's custom template path with "feign". This means any custom templates the user provides are never picked up.

With library=feign, the if (isLibrary(FEIGN)) branch only sets additionalProperties.put("feign-okhttp", "true") and does not call setTemplateDir(), so the user's custom template path is preserved.

openapi-generator version

Latest master (commit e6304a8db2930fd3dd54a22dd220ac3bfc69e03f). The issue has existed since feign-hc5 was introduced.

OpenAPI declaration file content or url

Any valid OpenAPI spec will reproduce this. For example, the petstore spec:

openapi: "3.0.0"
info:
  title: Sample API
  version: "1.0.0"
paths:
  /pets:
    get:
      operationId: listPets
      summary: List all pets
      responses:
        '200':
          description: A list of pets
          content:
            application/json:
              schema:
                type: array
                items:
                  $ref: '#/components/schemas/Pet'
components:
  schemas:
    Pet:
      type: object
      properties:
        id:
          type: integer
          format: int64
        name:
          type: string

Generation Details

Maven plugin example (reproduces the bug):

<plugin>
    <groupId>org.openapitools</groupId>
    <artifactId>openapi-generator-maven-plugin</artifactId>
    <configuration>
        <inputSpec>${project.basedir}/src/main/resources/api.yaml</inputSpec>
        <generatorName>java</generatorName>
        <library>feign-hc5</library>
        <templateResourcePath>my-custom-templates/Java</templateResourcePath>
    </configuration>
</plugin>

CLI equivalent:

openapi-generator-cli generate \
  -g java \
  --library feign-hc5 \
  -t my-custom-templates/Java \
  -i api.yaml \
  -o output

Steps to reproduce

1. Create a custom template directory (e.g. my-custom-templates/Java/libraries/feign/) with a modified template file (e.g. a customized api.mustache).
2. Configure the generator with generatorName=java, library=feign-hc5, and templateResourcePath (or -t) pointing to my-custom-templates/Java.
3. Run the generator.
4. Observe: The custom templates are ignored; the built-in embedded templates are used instead.
5. Change the library to feign (keeping everything else the same).
6. Run the generator again.
7. Observe: The custom templates are now correctly picked up and used.

Actual output: With feign-hc5, the generator uses the built-in embedded templates, ignoring the user-provided templateResourcePath/templateDir.

Expected output: With feign-hc5, the generator should respect the user-provided templateResourcePath/templateDir and use custom templates, just as it does with the feign library.

Related issues/PRs

No directly related issues found.

Suggest a fix

The fix should be in JavaClientCodegen.java at line 842-844.

The feign-hc5 branch should not call setTemplateDir(FEIGN) unconditionally. Instead, it should only set the template directory if the user has not already provided a custom one. For example:

} else if (isLibrary(FEIGN_HC5)) {
    additionalProperties.put("feign-hc5", "true");
    // Only override templateDir if no custom template directory was provided by the user
    if (!isUserProvidedTemplateDir()) {
        setTemplateDir(FEIGN);
    }
    setLibrary(FEIGN);
}

Alternatively, the feign-hc5 library could be restructured to avoid calling setTemplateDir() entirely — for instance, by creating a libraries/feign-hc5/ resource directory (even if it just symlinks or delegates to the feign templates), so the standard library template resolution mechanism works without needing to override the template directory at the code level.

[wing328]

can you please file a PR with the suggested fix when you've time? 🙏

[BartPraats]

Sure, but can you (or someone) tell me what the preferred solution is? Add the if (!isUserProvidedTemplateDir()) condition or add the feign-hc5 resource dir?