ruby-grape / grape / 34580750600

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Let a parser's Grape errors through the formatter without re-raising

`Formatter#read_rack_input` answers a parser's StandardErrors with a 400,
and let Grape's own errors go on to the error middleware by rescuing them
first, `rescue Grape::Exceptions::Base => e; raise e`. Re-raising an
exception makes Ruby read its backtrace, which builds it as Strings, and
at request depth that is the dearest part of the error: about 25 µs. It
was paid by every malformed body, since the built-in parsers report one
as `InvalidMessageBody`.

A matcher module in the `rescue` clause now selects the errors to answer
here, StandardErrors that are not Grape errors, so a Grape error is
never rescued at this frame and travels on as it is.

A parser raising something that is not a StandardError, such as an
Interrupt or a SystemExit, keeps propagating rather than being answered
as a 400. Nothing pinned that; it now has a spec, which passes before and
after this change.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

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