Hand a Proc passed as the last middleware argument to the middleware

[ericproulx]

Summary

A callable passed as the last argument to use, insert_before or insert_after was taken for the middleware's block:

class Reporter
  def initialize(app, on_error)
    @app = app
    @on_error = on_error
  end
  # ...
end

use Reporter, ->(e) { Sentry.capture_exception(e) }
# => ArgumentError: wrong number of arguments (given 1, expected 2)

The DSL recorded a registration as [operation, *args] and appended the block only when one was given, so Stack#merge_with told the block apart by its class and popped whatever Proc came last. The middleware was then built without its callable. Reproduced on 2.1.3, 3.0.1, 3.3.5 and 4.0.1; the pop dates from c2e41f7 (2016).

Every registration now ends in its block, nil when none was given, and merge_with always takes the last element as the block.

Contract change

API.middleware returns those entries, so each one now ends in nil when no block was given:

use SomeMiddleware, 'abc'
API.middleware # before: [[:use, SomeMiddleware, 'abc']]
               # after:  [[:use, SomeMiddleware, 'abc', nil]]

Covered in UPGRADING. grape-swagger's own check (middleware.flatten.include?(auth_wrapper)) is unaffected.

Test plan

• New specs: a Proc argument reaches the middleware through use and insert_before, and a block given alongside it stays the block; the two argument cases fail without the fix.
• Updated the specs that pinned the old entry shape.
• Full RSpec suite passes locally (2945 examples, 0 failures); RuboCop clean.
• CI green.

🤖 Generated with Claude Code

[github-actions]

Danger Report

No issues found.

View run