"Basil L. Contovounesios" <contovob@tcd.ie> writes:

> I have a local WIP branch where I am refactoring parts of json.el to
> improve performance, and avoiding the proposed copy-sequence is one of
> the fixes.

Large patch attached (fear not (too much); the bulk of it is new
regression tests).  CCing João because it also touches jsonrpc.el.

The only backward-incompatible part of it should be the stricter number
parsing.  Until now[1], json.el accepted numbers with a leading plus
sign, leading zeros, and no integer component, all of which are
forbidden by the JSON spec[2] and rejected by Emacs' native JSON parsing
functions.  I was initially willing to ignore this according to "be
liberal in what you accept and strict in what you output," but given
that libraries are already treating json.el and json.c functions as
interchangeable, I think json.el should be fixed.  Who knows, it may
even help to catch some bad JSON generation somewhere, somewhen.

[1]: (json-read-number): New arg.  Handle explicitly signed numbers.
7712319db8 2008-08-28 20:19:17 +0000
https://git.savannah.gnu.org/cgit/emacs.git/commit/?id=7712319db8db97391059925b27ae71f304eee7d2

[2]: https://tools.ietf.org/html/rfc8259#section-6

> I've also found a couple of test JSON files to benchmark against.

I downloaded the three large (sizes 617KB-2.2MB) JSON files here:

https://github.com/miloyip/nativejson-benchmark/tree/master/data

and ran the following benchmark: