Let rescue_from :grape_exceptions outrank a catch-all class handler

[ericproulx]

Summary

rescue_from :grape_exceptions is an opt-in to keep Grape's own errors rendering with their own status — a validation failure answers 400 rather than whatever the application's catch-all returns.

It only ever worked against rescue_from :all, which lives in all_rescue_handler and is consulted last. Written as a class instead, rescue_from StandardError is a registered handler, matched first, and Grape's exceptions are StandardErrors — so the opt-in silently did nothing:

rescue_from StandardError { error!('server error', 500) }
rescue_from :grape_exceptions          # inert

Measured on GET / against requires :n, type: Integer:

config	before	after
no rescue_from	400	400
:all	500	500
:all + :grape_exceptions	400	400
StandardError	500	500
StandardError + :grape_exceptions	500	400
:grape_exceptions + StandardError	500	400
ValidationErrors + StandardError + :grape_exceptions	422	422
raising ArgumentError with the above	500 catch-all	500 catch-all

Approach

Let the opt-in win over a handler that only matched through a non-Grape ancestor. A handler registered for a Grape exception class is more precise than the opt-in and still wins, so an explicit rescue_from Grape::Exceptions::ValidationErrors keeps its handler.

registered_rescue_handler gains an _entry variant returning the matched class alongside its handler, since deciding this needs to know which class matched, not just that one did. find_handler resolves the entry once and passes it down, so there is no extra lookup.

Grape::Exceptions::InvalidVersionHeader is explicitly left alone — it must keep reaching Rack so the next versioned route is tried.

Backward compatibility

UPGRADING entry added. An API that registers a catch-all as a class and opts into :grape_exceptions will now answer Grape's own status for Grape's own errors, where it previously answered the catch-all's — which is what the opt-in asks for, and makes the two spellings of "catch everything" agree. An API that does not use rescue_from :grape_exceptions is unaffected.

Test plan

• 4 new examples in api_spec.rb: validation stays 400 under a class catch-all, application errors still reach the catch-all, an explicit grape-class handler still wins, and a non-Grape exception is not intercepted. The last three are invariant guards against the change over-reaching; verified the behavioural one fails without the lib/ change.
• Full RSpec suite passes locally (2547 examples, 0 failures).
• RuboCop clean.
• CI green.

🤖 Generated with Claude Code

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