The lexer ignores whitespace like this:

         on whitespace      on non-ws   spontaneously
    IN_START --> IN_WHITESPACE --> JSON_SKIP --> IN_START
                    ^    |
                     \__/  on whitespace

This accumulates a whitespace token in state IN_WHITESPACE, only to
throw it away on the transition via JSON_SKIP to the start state.
Wasteful.  Go from IN_START to IN_START on whitspace directly,
dropping the whitespace character.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
---
 qobject/json-lexer.c      | 22 +++++-----------------
 qobject/json-parser-int.h |  1 -
 2 files changed, 5 insertions(+), 18 deletions(-)

diff --git a/qobject/json-lexer.c b/qobject/json-lexer.c
index 2a5561c917..a7df2093aa 100644
--- a/qobject/json-lexer.c
+++ b/qobject/json-lexer.c
@@ -115,7 +115,6 @@ enum json_lexer_state {
     IN_SIGN,
     IN_KEYWORD,
     IN_INTERP,
-    IN_WHITESPACE,
     IN_START,
     IN_START_INTERP,            /* must be IN_START + 1 */
 };
@@ -228,15 +227,6 @@ static const uint8_t json_lexer[][256] =  {
         ['a' ... 'z'] = IN_KEYWORD,
     },
 
-    /* whitespace */
-    [IN_WHITESPACE] = {
-        TERMINAL(JSON_SKIP),
-        [' '] = IN_WHITESPACE,
-        ['\t'] = IN_WHITESPACE,
-        ['\r'] = IN_WHITESPACE,
-        ['\n'] = IN_WHITESPACE,
-    },
-
     /* interpolation */
     [IN_INTERP] = {
         TERMINAL(JSON_INTERP),
@@ -263,10 +253,10 @@ static const uint8_t json_lexer[][256] =  {
         [','] = JSON_COMMA,
         [':'] = JSON_COLON,
         ['a' ... 'z'] = IN_KEYWORD,
-        [' '] = IN_WHITESPACE,
-        ['\t'] = IN_WHITESPACE,
-        ['\r'] = IN_WHITESPACE,
-        ['\n'] = IN_WHITESPACE,
+        [' '] = IN_START,
+        ['\t'] = IN_START,
+        ['\r'] = IN_START,
+        ['\n'] = IN_START,
     },
     [IN_START_INTERP]['%'] = IN_INTERP,
 };
@@ -323,10 +313,8 @@ static void json_lexer_feed_char(JSONLexer *lexer, char ch, bool flush)
             json_message_process_token(lexer, lexer->token, new_state,
                                        lexer->x, lexer->y);
             /* fall through */
-        case JSON_SKIP:
-            g_string_truncate(lexer->token, 0);
-            /* fall through */
         case IN_START:
+            g_string_truncate(lexer->token, 0);
             new_state = lexer->start_state;
             break;
         case JSON_ERROR:
diff --git a/qobject/json-parser-int.h b/qobject/json-parser-int.h
index 57cb8e79d3..16a25d00bb 100644
--- a/qobject/json-parser-int.h
+++ b/qobject/json-parser-int.h
@@ -31,7 +31,6 @@ typedef enum json_token_type {
     JSON_KEYWORD,
     JSON_STRING,
     JSON_INTERP,
-    JSON_SKIP,
     JSON_END_OF_INPUT,
     JSON_MAX = JSON_END_OF_INPUT
 } JSONTokenType;
-- 
2.17.1

On 08/27/2018 02:00 AM, Markus Armbruster wrote:
> The lexer ignores whitespace like this:
> 
>           on whitespace      on non-ws   spontaneously
>      IN_START --> IN_WHITESPACE --> JSON_SKIP --> IN_START
>                      ^    |
>                       \__/  on whitespace
> 
> This accumulates a whitespace token in state IN_WHITESPACE, only to
> throw it away on the transition via JSON_SKIP to the start state.
> Wasteful.  Go from IN_START to IN_START on whitspace directly,

s/whitspace/whitespace/

> dropping the whitespace character.
> 
> Signed-off-by: Markus Armbruster <armbru@redhat.com>
> ---
>   qobject/json-lexer.c      | 22 +++++-----------------
>   qobject/json-parser-int.h |  1 -
>   2 files changed, 5 insertions(+), 18 deletions(-)
> 
> @@ -263,10 +253,10 @@ static const uint8_t json_lexer[][256] =  {
>           [','] = JSON_COMMA,
>           [':'] = JSON_COLON,
>           ['a' ... 'z'] = IN_KEYWORD,
> -        [' '] = IN_WHITESPACE,
> -        ['\t'] = IN_WHITESPACE,
> -        ['\r'] = IN_WHITESPACE,
> -        ['\n'] = IN_WHITESPACE,
> +        [' '] = IN_START,
> +        ['\t'] = IN_START,
> +        ['\r'] = IN_START,
> +        ['\n'] = IN_START,
>       },
>       [IN_START_INTERP]['%'] = IN_INTERP,

Don't you need to set [IN_START_INTERP][' '] to IN_START_INTERP, rather 
than IN_START?  Otherwise, the presence of skipped whitespace would 
change whether interpolation happens.  (At least, that's what you had in 
an earlier version of this patch).

>   };
> @@ -323,10 +313,8 @@ static void json_lexer_feed_char(JSONLexer *lexer, char ch, bool flush)
>               json_message_process_token(lexer, lexer->token, new_state,
>                                          lexer->x, lexer->y);
>               /* fall through */
> -        case JSON_SKIP:
> -            g_string_truncate(lexer->token, 0);
> -            /* fall through */
>           case IN_START:
> +            g_string_truncate(lexer->token, 0);
>               new_state = lexer->start_state;

Oh, I see. We are magically reverting to the correct start state if the 
requested transition reports IN_START, rather than blindly using IN_START.

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

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

Eric Blake <eblake@redhat.com> writes:

> On 08/27/2018 02:00 AM, Markus Armbruster wrote:
>> The lexer ignores whitespace like this:
>>
>>           on whitespace      on non-ws   spontaneously
>>      IN_START --> IN_WHITESPACE --> JSON_SKIP --> IN_START
>>                      ^    |
>>                       \__/  on whitespace
>>
>> This accumulates a whitespace token in state IN_WHITESPACE, only to
>> throw it away on the transition via JSON_SKIP to the start state.
>> Wasteful.  Go from IN_START to IN_START on whitspace directly,
>
> s/whitspace/whitespace/

Will fix.

>> dropping the whitespace character.
>>
>> Signed-off-by: Markus Armbruster <armbru@redhat.com>
>> ---
>>   qobject/json-lexer.c      | 22 +++++-----------------
>>   qobject/json-parser-int.h |  1 -
>>   2 files changed, 5 insertions(+), 18 deletions(-)
>>
>> @@ -263,10 +253,10 @@ static const uint8_t json_lexer[][256] =  {
>>           [','] = JSON_COMMA,
>>           [':'] = JSON_COLON,
>>           ['a' ... 'z'] = IN_KEYWORD,
>> -        [' '] = IN_WHITESPACE,
>> -        ['\t'] = IN_WHITESPACE,
>> -        ['\r'] = IN_WHITESPACE,
>> -        ['\n'] = IN_WHITESPACE,
>> +        [' '] = IN_START,
>> +        ['\t'] = IN_START,
>> +        ['\r'] = IN_START,
>> +        ['\n'] = IN_START,
>>       },
>>       [IN_START_INTERP]['%'] = IN_INTERP,
>
> Don't you need to set [IN_START_INTERP][' '] to IN_START_INTERP,
> rather than IN_START?  Otherwise, the presence of skipped whitespace
> would change whether interpolation happens.  (At least, that's what
> you had in an earlier version of this patch).
>
>>   };
>> @@ -323,10 +313,8 @@ static void json_lexer_feed_char(JSONLexer *lexer, char ch, bool flush)
>>               json_message_process_token(lexer, lexer->token, new_state,
>>                                          lexer->x, lexer->y);
>>               /* fall through */
>> -        case JSON_SKIP:
>> -            g_string_truncate(lexer->token, 0);
>> -            /* fall through */
>>           case IN_START:
>> +            g_string_truncate(lexer->token, 0);
>>               new_state = lexer->start_state;
>
> Oh, I see. We are magically reverting to the correct start state if
> the requested transition reports IN_START, rather than blindly using
> IN_START.

Correct.  Less repetitive this way.

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

Thanks!