Re: [Qemu-devel] [PATCH 2/6] json: Clean up how lexer consumes "end of input"

[Eric Blake <eblake@redhat.com>]

On 08/27/2018 02:00 AM, Markus Armbruster wrote:
> When the lexer isn't in its start state at the end of input, it's
> working on a token.  To flush it out, it needs to transit to its start
> state on "end of input" lookahead.
> 
> There are two ways to the start state, depending on the current state:
> 
> * If the lexer is in a TERMINAL(JSON_FOO) state, it can emit a
>    JSON_FOO token.
> 
> * Else, it can go to IN_ERROR state, and emit a JSON_ERROR token.
> 
> There are complications, however:
> 
> * The transition to IN_ERROR state consumes the input character and
>    adds it to the JSON_ERROR token.  The latter is inappropriate for
>    the "end of input" character, so we suppress that.  See also recent
>    commit "json: Fix lexer to include the bad character in JSON_ERROR
>    token".

Now commit a2ec6be7

> 
> * The transition to a TERMINAL(JSON_FOO) state doesn't consume the
>    input character.  In that case, the lexer normally loops until it is
>    consumed.  We have to suppress that for the "end of input" input
>    character.  If we didn't, the lexer would consume it by entering
>    IN_ERROR state, emitting a bogus JSON_ERROR token.  We fixed that in
>    commit bd3924a33a6.
> 
> However, simply breaking the loop this way assumes that the lexer
> needs exactly one state transition to reach its start state.  That
> assumption is correct now, but it's unclean, and I'll soon break it.
> Clean up: instead of breaking the loop after one iteration, break it
> after it reached the start state.
> 
> Signed-off-by: Markus Armbruster <armbru@redhat.com>
> ---
>   qobject/json-lexer.c | 17 +++++++++--------
>   1 file changed, 9 insertions(+), 8 deletions(-)
> 
> diff --git a/qobject/json-lexer.c b/qobject/json-lexer.c
> index 4867839f66..ec3aec726f 100644
> --- a/qobject/json-lexer.c
> +++ b/qobject/json-lexer.c
> @@ -261,7 +261,8 @@ void json_lexer_init(JSONLexer *lexer, bool enable_interpolation)
>   
>   static void json_lexer_feed_char(JSONLexer *lexer, char ch, bool flush)
>   {
> -    int char_consumed, new_state;
> +    int new_state;
> +    bool char_consumed = false;

Yay for the switch to bool.

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org