MDEV-22224: Support JSON Path negative index

This patch can be viewed as combination of two parts:
1) Enabling '-' in the path so that the parser does not give out a warning.
2) Setting the negative index to a correct value and returning the
   appropriate value.

1) To enable using the negative index in the path:
To make the parser not return warning when negative index is used in path
'-' needs to be allowed in json path characters. P_NEG is added
to enable this and is made recognizable by setting the 45th index of
json_path_chr_map[] to P_NEG (instead of previous P_ETC)
because 45 corresponds to '-' in unicode.
When the path is being parsed and '-' is encountered, the parser should
recognize it as parsing '-' sign, so a new json state PS_NEG is required.
When the state is PS_NEG, it means that a negative integer is
going to be parsed so set is_negative_index of current step to 1 and
n_item is set accordingly when integer is encountered after '-'.
Next proceed with parsing rest of the path and get the correct path.
Next thing is parsing the json and returning correct value.

2) Setting the negative index to a correct value and returning the value:
While parsing json if we encounter array and the path step for the array
is a negative index (n_item < 0), then we can count the number of elements
in the array and set n_item to correct corresponding value. This is done in
json_skip_array_and_count.

1 files changed, 1 insertions, 1 deletions

diff --git a/unittest/json_lib/json_lib-t.c b/unittest/json_lib/json_lib-t.c
index 378ebe201f5..c5a6df54e1d 100644
--- a/unittest/json_lib/json_lib-t.c
+++ b/unittest/json_lib/json_lib-t.c
@@ -140,7 +140,7 @@ test_search()
   json_path_t p;
   json_path_step_t *cur_step;
   int n_matches, scal_values;
-  uint array_counters[JSON_DEPTH_LIMIT];
+  int array_counters[JSON_DEPTH_LIMIT];
 
   if (json_scan_start(&je, ci, s_e(fj0)) ||
       json_path_setup(&p, ci, s_e(fp0)))