[BUG] [Elixir] Invalid client module names generated from Paypal API spec

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• 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?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

When generating an Elixir client using Paypal's OpenAPI spec files, invalid module names are sometimes created. This prevents the application from compiling.

Actual: defmodule Orders.Model.400DetailsInner do

Expected: uncertain.

• Every part of a module name separated by a . must begin with an upper-case letter. So, prefixing the 400DetailsInner portion with something arbitrary like X would work: defmodule Orders.Model.X400DetailsInner do.
• Alternatively, module names are just atoms that start with Elixir. Creating modules (and referencing them throughout the code base) like this should work: :"Elixir.Orders.Model.400DetailsInner"
• There may be another, better solution that I'm not thinking of.

openapi-generator version

latest

OpenAPI declaration file content or url

https://github.com/paypal/paypal-rest-api-specifications/blob/main/openapi/checkout_orders_v2.json

Generation Details

docker run --rm -v "${PWD}:/local" openapitools/openapi-generator-cli:latest generate \
    -i /local/checkout_orders_v2.json \
    -g elixir \
    -o /local/out/

Steps to reproduce

1. git clone git@github.com:paypal/paypal-rest-api-specifications.git
2. cd paypal-rest-api-specifications/openapi
3. Run the above generation command
4. less out/lib/orders/model/_400_details_inner.ex
5. Observe invalid module definition: defmodule Orders.Model.400DetailsInner do

Related issues/PRs

Suggest a fix

See above.

Reproduce generation with the Paypal checkout_orders_v2.json spec and the shown Docker command. Inspect out/lib/orders/model/_400_details_inner.ex and the generated references to determine a valid Elixir module name. Done means the generated client uses valid module definitions and compiles successfully.