Re: [Qemu-devel] [PATCH 5/6] json: Eliminate lexer state IN_ERROR

[Markus Armbruster <armbru@redhat.com>]

Eric Blake <eblake@redhat.com> writes:

> On 08/28/2018 10:01 AM, Eric Blake wrote:
>> The question remains, then, if a fixed-size gap (by making JSON_MIN
>> be exactly 100) is any smarter than a contiguous layout (by making
>> JSON_MIN be IN_START_INTERP + 1).  I can't see any strong reason for
>> preferring one form over the other, so keeping the gap doesn't hurt.
>
> And having said that, this patch series also introduced a second gap
> for LOOKAHEAD defined at 0x80, along with assertions that it doesn't
> collide with either IN_* or JSON_*. It may be just as easy to make
> JSON_MIN start at LOOKAHEAD+1 than to assert that all of JSON_* fits
> in the space between 100 and 0x80 - 1.  Although in the long run, I
> seriously doubt we'll be adding many new enum values to either the
> lexer or the parser.

LOOKAHEAD is semantically independent from the lexer state.  Evidence:
we use both IN_START and IN_START | LOOKAHEAD in json_lexer[].