Set api.version when the version is the only path segment

[ericproulx]

Problem

Grape::Middleware::Versioner::Path extracts the version from the first path segment — but only when a second slash follows it:

slash_position = path_info.index('/', 1) # omit the first one
return unless slash_position

For the root route of a path-versioned API there is no second segment, so the middleware returned early and never set env['api.version']:

class API < Grape::API
  version 'v1', using: :path
  get '/' do
    { version_seen: version }
  end
end

GET /v1 → 200 with {"version_seen":null}. The route matches (the version lives in the compiled route pattern), but everything that reads env['api.version'] sees nothing: the version helper, Grape::DSL::Entity#entity_representation_for (entities lose their version: embed, breaking conditional exposures), and ErrorFormatter::Base#present. The same happens with a format suffix (GET /v1.json) and behind a prefix (GET /api/v1).

Only the versioner middlewares write api.version, so nothing downstream recovers it from the route's version capture either. The logic is identical at least as far back as v2.4.0 — long-standing, not a regression.

Fix

When the (prefix-stripped) path is a single segment, record the version on an exact match against the declared versions, trimming a trailing .format suffix right-to-left so dotted versions still work:

• /v1 → v1
• /v1.json → v1 (suffix trimmed)
• /v1.2.json with version 'v1.2' → v1.2 (rightmost dot trimmed first)
• /awesome → no version, no 404 — the segment is left for the router to resolve

The single-segment branch deliberately never raises version_not_found!: with no following segment there is nothing to disambiguate a version from a plain path, so an unknown segment falls through to the router's 404 exactly as before. Multi-segment behavior (/v3/foo → 404 with X-Cascade: pass for an undeclared version) is unchanged.

Tests

• Middleware-level cases for all of the above in versioner/path_spec.rb.
• A sets the API version for the root route example added to the shared versioning examples, so the root route is now covered end-to-end for all four strategies (:path — previously failing — plus :param, :header, :accept_version_header).

🤖 Generated with Claude Code

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