The builder that accept() runs stores no nodes, but still decoded every string
with escapes into the arena (slow_string(): memcpy of the runs between escapes
and the UTF-8 of every \u escape). It now calls check_string() instead, which
has the same checks and the same errors and error positions (control characters,
ill-formed UTF-8, bad escapes, bad hex digits, lone and unpaired surrogates, a
missing closing quote) and skips the text between them with scan_string_run(),
without writing anything. The builder that stores keeps slow_string().
The flag that passes the request from accept() to build() now sits next to
`discarded` in document_data, where it uses padding: no member of document_data
moves (the first version put it after `nodes`, which moved all members behind it
by eight bytes).
Tests: the new section of the accept test checks runs of text of every length from
0 to 40 between valid and invalid escapes, UTF-8 sequences and control characters,
in values and in keys, cut near the end of the text, against json::accept().
Checked against a checker that accepts a lone low surrogate.
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Niels Lohmann
9ba25b1b66