pgsql: SQL/JSON: Correct jsonpath variable name matching

SQL/JSON: Correct jsonpath variable name matching

Previously, GetJsonPathVar() allowed a jsonpath expression to
reference any prefix of a PASSING variable's name. For example, the
following query would incorrectly work:

SELECT JSON_QUERY(context_item, jsonpath '$xy' PASSING val AS xyz);

The fix ensures that the length of the variable name mentioned in a
jsonpath expression matches exactly with the name of the PASSING
variable before comparing the strings using strncmp().

Reported-by: Alvaro Herrera (off-list)
Discussion: https://postgr.es/m/CA+HiwqFGkLWMvELBH6E4SQ45qUHthgcRH6gCJL20OsYDRtFx_w@mail.gmail.com

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/0f271e8e8d9c8db0ea86c0d12b3221009b81d8bf

Modified Files
--------------
src/backend/executor/execExpr.c | 1 +
src/backend/utils/adt/jsonpath_exec.c | 4 +++-
src/include/utils/jsonpath.h | 1 +
src/test/regress/expected/sqljson_queryfuncs.out | 11 +++++++++++
src/test/regress/sql/sqljson_queryfuncs.sql | 5 +++++
5 files changed, 21 insertions(+), 1 deletion(-)