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14e13ecbd4
This is a backport of https://github.com/scylladb/scylla/pull/10420 to branch 5.0.
Branch 5.0 had somewhat different code in this expression area, so the backport was not automatically, but nevertheless was fairly straightforward - just copy the exact same checking code to its right place, and keep the exact same tests to see we indeed fixed the bug.
Refs #10535.
The original cover letter from https://github.com/scylladb/scylla/pull/10420:
In the filtering expression "WHERE m[?] = 2", our implementation was buggy when either the map, or the subscript, was NULL (and also when the latter was an UNSET_VALUE). Our code ended up dereferencing null objects, yielding bizarre errors when we were lucky, or crashes when we were less lucky - see examples of both in issues https://github.com/scylladb/scylla/issues/10361, https://github.com/scylladb/scylla/issues/10399, https://github.com/scylladb/scylla/pull/10401. The existing test test_null.py::test_map_subscript_null reproduced all these bugs sporadically.
In this series we improve the test to reproduce the separate bugs separately, and also reproduce additional problems (like the UNSET_VALUE). We then define both m[NULL] and NULL[2] to result in NULL instead of the existing undefined (and buggy, and crashing) behavior. This new definition is consistent with our usual SQL-inspired tradition that NULL "wins" in expressions - e.g., NULL < 2 is also defined as resulting in NULL.
However, this decision differs from Cassandra, where m[NULL] is considered an error but NULL[2] is allowed. We believe that making m[NULL] be a NULL instead of an error is more consistent, and moreover - necessary if we ever want to support more complicate expressions like m[a], where the column a can be NULL for some rows and non-NULL for others, and it doesn't make sense to return an "invalid query" error in the middle of the scan.
Fixes https://github.com/scylladb/scylla/issues/10361
Fixes https://github.com/scylladb/scylla/issues/10399
Fixes https://github.com/scylladb/scylla/pull/10401
Closes #11142
* github.com:scylladb/scylla:
test/cql-pytest: reproducer for CONTAINS NULL bug
expressions: don't dereference invalid map subscript in filter
expressions: fix invalid dereference in map subscript evaluation
test/cql-pytest: improve tests for map subscripts and nulls
(cherry picked from commit 23a34d7e42)