ruby-grape / grape / 33726996561

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Share content-type tables between middleware instances (#2885)

Grape builds one content-type-aware middleware per API instance, and each
one memoized its own derived tables. A memory profile of an app mounting 13
APIs held 42 of them (20 Formatter, 20 Error, 2 Versioner) covering four
distinct content-type registrations: 42 lookup tables and 41 mime-type
tables for four distinct values, 15.1 kB of the 849.7 kB retained.

Both tables are derived from nothing but the registry, so they now live in
value-keyed caches on Grape::ContentTypes — Hash keys compare by value, so
every API registering the same content types shares one table. On the same
app that is 42 lookup tables down to 4 and 41 mime-type tables down to 3,
17.4 kB down to 4.9 kB. What is left is the registry Hash itself, which
InheritableSetting builds fresh per API instance.

The cached tables are frozen now that they are shared, and each cache keeps
a frozen copy of the registry as its key: the caller's Hash stays reachable
through `middleware.options[:content_types]`, and mutating a live key would
corrupt a cache that is now process-wide.

Formatter is the only middleware that reads `mime_types` — Error resolves
`content_type` through the lookup, and the versioners read the registry
directly — so it warms that table itself instead of PrecomputedContentTypes
building one for all 42 instances.

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

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