Keep a :version path capture when the API declares no version

[ericproulx]

Summary

Grape::Request#make_params dropped :version from the routing args unconditionally, alongside :route_info:

filtered = routing_args&.except(:version, :route_info)

That is right when Grape put it there — a path-versioned API captures the version as a segment and exposes it through env['api.version'] rather than params. But it is not always Grape's. An API that declares no version can name a param :version:

class API < Grape::API
  format :json
  route_param :version do
    get { { v: params[:version] } }   # => {"v": null}
  end
end

GET /abc matched, Mustermann captured version => "abc", and the value was filtered out before the endpoint saw it — params[:version] nil and the key absent from params altogether. Same for a bare get '/:version'. A segment silently lost on a route that had matched.

API	params[:version] before	after
no version declared, route_param :version	nil	"abc"
no version declared, get '/:version'	nil	"abc"
version 'v1', using: :path	absent (correct)	absent
version 'v1', using: :header	absent (correct)	absent
version 'v1', using: :param	absent (correct)	absent

Approach

A route reports a #version only when the API declared one — Grape::Router::BaseRoute already delegates it to the pattern — so that distinguishes the two cases without any new API. Drop the capture when the route carries a version, keep it otherwise.

All three versioning strategies are unaffected: their routes report a version, so :version stays out of params and env['api.version'] remains the way to read it. A path-versioned API with a nested route_param :id still gets only id.

Backward compatibility

No UPGRADING entry. The change only adds a param that was being discarded, on APIs that declare no version — where nothing could have depended on it being absent, since the route matched but the value was unreachable.

request_spec.rb's "cuts version and route_info" asserted the old unconditional rule against a synthetic route_info; it now covers both branches with a route double that does and does not report a version.

Longstanding, not a regression: identical in 3.3.4.

Test plan

• request_spec.rb split into version-carrying and version-less routes; verified the version-less case fails without the lib/ change.
• Full RSpec suite passes locally (2544 examples, 0 failures).
• RuboCop clean.
• CI green.

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* [#UUUU](https://github.com/ruby-grape/grape/pull/UUUU): Keep a `:version` path capture in `params` when the API declares no version, instead of always dropping it as Grape's own - [@ericproulx](https://github.com/ericproulx).
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