[BUG][RUST] Twilio OpenAPI codegen errors

Created by: PiDelport

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?

Description

Twilio provides OpenAPI specifications for all of their APIs:

• https://www.twilio.com/blog/introducing-twilio-open-api-specification-beta
• https://www.twilio.com/docs/openapi

Twilio's documentation showcases using OpenAPI Generator to generate Rust clients: however, the code generation currently fails for a number of their APIs.

openapi-generator version

• 5.3.0-SNAPSHOT (latest)

OpenAPI declarations repository

• https://github.com/twilio/twilio-oai

Generation Details

openapi-generator-cli generate with options:

• --generator-name rust
• --library reqwest
• --additional-properties 'useSingleRequestParameter=true,supportMultipleResponses=true'

Steps to reproduce

See the failing checks in this PR:

• https://github.com/PiDelport/twilio-oai-rust/pull/1

Specifically, these specs are failing:

• twilio-oai-events-v1
• twilio-oai-proxy-v1
• twilio-oai-taskrouter-v1
• twilio-oai-verify-v2

Related issues/PRs

Suggest a fix

I made PRs for the issues I've encountered so far:

• #10419
• #10420
• #10432 (not a bug, but strongly affects API usability for Twilio)
• #10439

I collected the fixes into an integration testing branch:

• https://github.com/PiDelport/openapi-generator/compare/master...PiDelport:fix-rust-client

With the fixes, the twilio-oai 1.20.2 output builds successfully:

• https://github.com/PiDelport/twilio-oai-rust/compare/twilio-oai-1.20.2...twilio-oai-1.20.2-fixed
• Checks