On 2024-03-26 Tu 17:52, Jacob Champion wrote:
On Mon, Mar 25, 2024 at 3:14 PM Jacob Champion
<jacob.champ...@enterprisedb.com> wrote:
- add Assert calls in impossible error cases [2]
To expand on this one, I think these parts of the code (marked with
`<- here`) are impossible to reach:
switch (top)
{
case JSON_TOKEN_STRING:
if (next_prediction(pstack) == JSON_TOKEN_COLON)
ctx = JSON_PARSE_STRING;
else
ctx = JSON_PARSE_VALUE; <- here
break;
case JSON_TOKEN_NUMBER: <- here
case JSON_TOKEN_TRUE: <- here
case JSON_TOKEN_FALSE: <- here
case JSON_TOKEN_NULL: <- here
case JSON_TOKEN_ARRAY_START: <- here
case JSON_TOKEN_OBJECT_START: <- here
ctx = JSON_PARSE_VALUE;
break;
case JSON_TOKEN_ARRAY_END: <- here
ctx = JSON_PARSE_ARRAY_NEXT;
break;
case JSON_TOKEN_OBJECT_END: <- here
ctx = JSON_PARSE_OBJECT_NEXT;
break;
case JSON_TOKEN_COMMA: <- here
if (next_prediction(pstack) == JSON_TOKEN_STRING)
ctx = JSON_PARSE_OBJECT_NEXT;
else
ctx = JSON_PARSE_ARRAY_NEXT;
break;
Since none of these cases are non-terminals, the only way to get to
this part of the code is if (top != tok). But inspecting the
productions and transitions that can put these tokens on the stack, it
looks like the only way for them to be at the top of the stack to
begin with is if (tok == top). (Otherwise, we would have chosen a
different production, or else errored out on a non-terminal.)
This case is possible...
case JSON_TOKEN_STRING:
if (next_prediction(pstack) == JSON_TOKEN_COLON)
ctx = JSON_PARSE_STRING;
...if we're in the middle of JSON_PROD_[MORE_]KEY_PAIRS. But the
corresponding else case is not, because if we're in the middle of a
_KEY_PAIRS production, the next_prediction() _must_ be
JSON_TOKEN_COLON.
Do you agree, or am I missing a way to get there?
One good way of testing would be to add the Asserts, build with
-DFORCE_JSON_PSTACK, and run the standard regression suite, which has a
fairly comprehensive set of JSON errors. I'll play with that.
cheers
andrew
--
Andrew Dunstan
EDB: https://www.enterprisedb.com
