add support for path params in middle of the path

[dvjn]

Added support for path params in the middles of the paths as well

Earlier /user/@{username} didn't register username as a path param.
Similarly /{month}-{day}-{year} from chi's readme examples would only detect {month} as a param and nothing else.

After this change, all these path params should be detected and should work .

[dvjn]

I have tested these changes locally in a working project and am waiting for a maintainers review before adding specific test cases for this feature.

Please let me know if anything else is needed for this PR. Thanks.

[raphael]

Thanks for this PR! This is a great enhancement that brings Goa's path parameter detection in line with Chi router. The examples you mentioned (/user/@{username} and /{month}-{day}-{year}) are useful patterns. The core change seems simple, since it still requires valid parameter names [a-zA-Z0-9_]+, it won't accidentally match anything weird. And the OpenAPI generation should work fine since the surrounding characters (like @ or -) stay in place.

To make sure everything works end-to-end, could you add a few tests? I'm thinking http/mux_test.go would be a good place to add new mux tests. We should also add a validation test to make sure routes like /{year}-{month}-{day} properly validate that all three parameters exist in the method payload - you can extend the existing TestHTTPRouteValidation in expr/http_endpoint_test.go for this. Maybe add an OpenAPI test case with one of the new patterns to verify the generated spec looks right - adding a new DSL function to http/codegen/testdata/openapi_dsls.go should automatically generate the test cases.

That should cover it! The change itself is solid - just want to make sure the integration points work as expected.
Thanks for the contribution! 👍