[BUG][RUBY-NEXTGEN] Nothing autoloads when moduleName is not the camelized gemName

[wiebren]

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 moduleName is not the camelized gemName (e.g. gemName=things_api, moduleName=Things), none of the generated constants load. For a single-level moduleName, gem.mustache sets Zeitwerk up with Zeitwerk::Loader.for_gem, which expects lib/things_api/** to define constants under ThingsApi. The generated files define them under Things, so Things::Client is never autoloaded and eager_load fails on ThingsApi.

gem.mustache already has a loader that works (Zeitwerk::Loader.new + push_dir(..., namespace: self)), but it only emits it when moduleName is nested.

openapi-generator version

master, 7.26.0-SNAPSHOT, 05b61f34d7fb0199330e1d6c57e6159f72427837

OpenAPI declaration file content or url

openapi: 3.0.3
info:
  title: zeitwerk
  version: 1.0.0
paths:
  /things:
    get:
      operationId: listThings
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                type: array
                items:
                  $ref: '#/components/schemas/Thing'
components:
  schemas:
    Thing:
      type: object
      properties:
        name:
          type: string

Generation Details

java -jar openapi-generator-cli.jar generate -g ruby-nextgen -i spec.yaml -o out \
  --additional-properties=gemName=things_api,moduleName=Things

Generated lib/things_api.rb (comments trimmed):

module Things
  class << self
    attr_reader :loader
  end

  @loader = Zeitwerk::Loader.for_gem
  @loader.setup

  def self.eager_load!
    @loader.eager_load
  end
end

Steps to reproduce

$LOAD_PATH.unshift 'out/lib'
require 'things_api'

Things::Client.new(base_url: 'http://localhost')

Actual (ruby 3.3, zeitwerk 2.8.3):

uninitialized constant Things::Client (NameError)

Things.eager_load! raises uninitialized constant ThingsApi (NameError).

Expected: the client loads, as it does with gemName=things.

Related issues/PRs

None found.

Suggest a fix

Always use the explicit loader. push_dir(namespace: self) doesn't depend on gemName matching moduleName. With this change the snippet works for both gemName=things_api and gemName=things, and Things::VERSION still resolves.

--- a/modules/openapi-generator/src/main/resources/ruby-nextgen/gem.mustache
+++ b/modules/openapi-generator/src/main/resources/ruby-nextgen/gem.mustache
@@ -21,10 +21,9 @@
     attr_reader :loader
   end
 
-{{#moduleNameNested}}
-  # Nested moduleName: for_gem can't target a nested namespace, so drive Zeitwerk
-  # explicitly. The parent module(s) above are pre-defined so `module {{moduleName}}`
-  # (here and in every generated file) reopens rather than raising NameError.
+  # for_gem derives the namespace from gemName, which need not match moduleName (and
+  # can't target a nested one), so drive Zeitwerk explicitly. Any parent module(s) above
+  # are pre-defined so `module {{moduleName}}` reopens rather than raising NameError.
   @loader = Zeitwerk::Loader.new
   @loader.push_dir("#{__dir__}/{{gemName}}", namespace: self)
   # version.rb defines VERSION (not a `Version` class). for_gem's GemInflector special-cases
@@ -32,10 +31,6 @@
   # {{moduleName}}::VERSION available.
   @loader.ignore("#{__dir__}/{{gemName}}/version.rb")
   require_relative "{{gemName}}/version"
-{{/moduleNameNested}}
-{{^moduleNameNested}}
-  @loader = Zeitwerk::Loader.for_gem
-{{/moduleNameNested}}
 {{#zeitwerkInflections.0}}
   # Model names keep their acronym casing (e.g. HTTPConfig), but Zeitwerk's default
   # inflector would expect HttpConfig from the file name. Register the exceptions so

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