feat(openapi): convert parameter models to plain objects with serialize/parse functions

[ALagoni97]

Summary

• OpenAPI parameter models are now generated as TypeScript interfaces instead of classes, with two accompanying standalone functions per model: serializeXxxUrl(parameters, basePath): string and parseXxxFromUrl(url, basePath): XxxType
• buildUrlWithParameters in http/common-types.ts now accepts a serializeFn callback instead of a generic with a structural constraint, decoupling the URL builder from the parameter shape
• Import statements for parameter-bearing channels are updated to include the serialize/parse function names alongside the interface
• All OpenAPI runtime test files and snapshots updated to match the new output

Why plain objects?

Class instances carry runtime overhead (prototype chain, new keyword, instanceof checks) that is unnecessary for parameter objects which are pure data bags. Interfaces + standalone functions are:

• Tree-shakeable: bundlers can drop unused serialize/parse functions; a class always pulls its methods in
• Simpler to construct: callers pass a plain object literal — no new FindPetsByStatusAndCategoryParameters(...) required
• Easier to test: no need to instantiate; just pass { status: 'available' } directly

Possibility of extending to AsyncAPI

AsyncAPI parameters currently remain class-based (getChannelWithParameters, createFromChannel static methods). The same refactor could be applied there:

• Each AsyncAPI parameter class would become an interface + serializeXxxChannel(parameters): string / parseXxxFromChannel(channel): XxxType pair
• The NATS/AMQP/Kafka/MQTT/WebSocket/EventSource channel renderers in src/codegen/generators/typescript/channels/protocols/ each have their own addParametersToDependencies wiring that would need updating (analogous to what was done for HTTP here)
• The AsyncAPI runtime test suite (test/runtime/typescript/test/parameters.spec.ts, AsyncAPI section) would need the class-based assertions replaced with interface + function assertions

The main reason it was left out of this PR was scope — the HTTP path was self-contained and testable in isolation. The AsyncAPI side touches more protocol renderers and would be a good follow-up PR.

Test plan

• npm test — 646/647 tests pass (1 pre-existing skip), all 78 snapshots clean
• npm run build — TypeScript compilation succeeds
• npm run generate:assets — asset generation succeeds
• npm run runtime:typescript:generate — runtime code regenerated and matches committed files

🤖 Generated with Claude Code

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated (UTC)
the-codegen-project	Ready	Preview, Comment	Jul 14, 2026 4:17pm
the-codegen-project-mcp	Ready	Preview, Comment	Jul 14, 2026 4:17pm