We use the current parsing position instead.  The line and column in the
error weren't used (nor very accurate to begin with) and the user can
easily compute them when needed.  The line number calculation is kept
just in case but deprecated, for removal in Emacs 32.

* src/json.c (struct json_parser, json_parser_init): Update parser state.
(json_signal_error): New position computation.
(json_skip_whitespace_internal): Remove.
(is_json_whitespace): New.
(json_skip_whitespace, json_skip_whitespace_if_possible)
(json_parse_unicode, json_parse_string, json_parse_number)
(json_parse_value): Simplify and rewrite for efficiency.
(count_chars, count_newlines)
(string_byte_to_pos, string_byte_to_line)
(buffer_byte_to_pos, buffer_byte_to_line): New.
(Fjson_parse_string, Fjson_parse_buffer): Adapt to new parser state.
* test/src/json-tests.el (json-tests--parse-string-error-pos)
(json-tests--parse-buffer-error-pos, json-parse-error-position): New.
* etc/NEWS: Note deprecation of line and column.

* src/json.c (Fjson_insert): Simplify 'memcpy' argument.
(Fjson_parse_buffer): Only read to ZV, not all the way to Z.
* test/src/json-tests.el (with-all-gap-positions-in-temp-buffer):
New macro.
(json-parse-buffer/restricted): New test.

* test/lisp/emacs-lisp/bytecomp-tests.el (bytecomp-reify-function):
* test/lisp/emacs-lisp/cl-extra-tests.el (cl-getf):
* test/lisp/emacs-lisp/cl-macs-tests.el
(cl-macs-loop-for-as-arith-order-side-effects)
(cl-macs-loop-for-as-equals-then, cl-macs-loop-do, cl-macs-loop-finally)
(cl-macs-loop-in-ref, cl-macs-loop-being-elements-of-ref)
(cl-macs-test--symbol-macrolet, cl-the):
* test/lisp/emacs-lisp/cl-seq-tests.el (cl-lib-test-remove)
(cl-lib-test-remove-if-not):
* test/lisp/emacs-lisp/edebug-resources/edebug-test-code.el
(edebug-test-code-range):
* test/lisp/emacs-lisp/edebug-tests.el (edebug-tests-deduplicate):
* test/lisp/emacs-lisp/generator-tests.el (cps-while-incf):
(cps-test-iter-cleanup-once-only):
* test/lisp/emacs-lisp/hierarchy-tests.el
(hierarchy-labelfn-button-if-does-not-button-unless-condition)
(hierarchy-labelfn-button-if-does-button-when-condition):
* test/lisp/emacs-lisp/let-alist-tests.el (let-alist-evaluate-once):
* test/lisp/emacs-lisp/lisp-mode-tests.el
(indent-sexp, lisp-indent-region):
* test/lisp/emacs-lisp/map-tests.el (test-map-elt-gv)
(test-setf-map-with-function):
* test/lisp/emacs-lisp/multisession-tests.el (multi-test-sqlite-simple)
(multi-test-sqlite-busy, multi-test-files-simple)
(multi-test-files-busy):
* test/lisp/emacs-lisp/oclosure-tests.el
(oclosure-test, oclosure-test-mutate):
* test/lisp/emacs-lisp/track-changes-tests.el
(track-changes-tests--random):
* test/lisp/files-tests.el (files-tests--with-buffer-offer-save):
* test/lisp/net/shr-tests.el (shr-test/zoom-image):
* test/lisp/replace-tests.el (replace-tests-with-undo):
* test/src/buffer-tests.el (test-overlay-randomly):
* test/src/data-tests.el (test-bool-vector-bv-from-hex-string):
* test/src/fns-tests.el (fns-tests-sort):
* test/src/json-tests.el (json-insert/signal, json-insert/throw):
* test/src/minibuf-tests.el (minibuf-tests--strings-to-symbol-alist)
(minibuf-tests--strings-to-string-alist)
(minibuf-tests--strings-to-string-hashtable)
(minibuf-tests--strings-to-symbol-hashtable):
* test/src/process-tests.el (make-process/file-handler/found): Prefer
incf to cl-incf.

Run "TZ=UTC0 admin/update-copyright".

The JSON format is defined as a byte sequence and will always be used as
such, so returning a multibyte string makes little sense.

* src/json.c (json_out_to_string): Remove.
(Fjson_serialize): Return unibyte string.
* test/src/json-tests.el (json-serialize/roundtrip)
(json-serialize/roundtrip-scalars, json-serialize/string):
Update tests.
* doc/lispref/text.texi (Parsing JSON): Document.
* etc/NEWS: Announce.

Previously, a unibyte target buffer could be put in an incorrect state
if json-insert was used to insert non-ASCII characters.

* src/json.c (Fjson_insert): Simplify.  Don't attempt to decode the data
being inserted: it is guaranteed to be correct UTF-8 and is correct for
both unibyte and multibyte buffers.
* test/src/json-tests.el (json-serialize/roundtrip)
(json-serialize/roundtrip-scalars): Extend tests.

* test/src/json-tests.el (json-parse-string/object):
Duplicated object keys are now retained in alist and plist output.
* etc/NEWS: Mention it.

* src/json.c (json_parse_value): Generate a plain parse error.
* test/src/json-tests.el (json-parse-string/short): Adapt test.

Speed up JSON parsing substantially by only UTF-8-parsing string
literals and only exactly once.  Previously, json-parse-string always
first parsed the entire input and copied it to a new string, and then
validated each string literal twice.

We no longer create an extra new string when interning an alist key,
nor do we garble plist keys with Unicode characters.

* src/lread.c (intern_c_multibyte): New.
* src/json.c (json_encode): Remove.
(utf8_error): New.
(json_parse_string): Faster and more careful UTF-8 decoding.
Create and return a new multibyte string or symbol without extra
decoding.  All callers adapted.
(Fjson_parse_string): Skip expensive input pre-decoding.
* test/src/json-tests.el (json-parse-string/object-unicode-keys)
(json-parse-string/short): New.
(json-parse-string/string, json-parse-string/invalid-unicode):
Adapt tests.
* etc/NEWS: Mentioned change in errors.

* lisp/progmodes/sh-script.el (sh--json-read): Remove.
(sh-shellcheck-flymake): Call json-parse-buffer directly.
* test/src/json-tests.el: Don't check for function availability.