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17a61e0015
value_to_json() converts CQL values to JSON for vector search filters.
For decimal and varint types, it used rjson::parse() on the JSON string,
which parses through a double and silently loses precision for values
exceeding ~15 significant digits — producing wrong filter results.
Additionally, for decimal type we need an exact string representation
that preserves the original (unscaled, scale) pair, because partition
keys use byte-level identity: different serialized representations of
the same numeric value are distinct rows, so the filter must reproduce
the exact representation stored in the key.
Add big_decimal::to_string_canonical() which follows the Java BigDecimal
toString() spec (JDK 8+), producing a bijective string representation
that uses exponential notation for extreme scales instead of expanding
trailing zeros (which could cause OOM). This could replace to_string(),
but doing so has wider consequences (e.g. hash/equality contract for
decimal_type) described in SCYLLADB-1574. Use it in value_to_json() for
decimal_type, and use rjson::from_string() for varint_type, both
bypassing the lossy double parse path.
Tests cover the new to_string_canonical() and the filter fix, as well as
existing decimal type behavior (key representation, clustering order,
toJson) that we rely on and must not break. The CQL decimal type tests
(test_type_decimal.py) also pass against Cassandra.
Fixes: SCYLLADB-2107
Refs: https://scylladb.atlassian.net/browse/SCYLLADB-1574
Closes scylladb/scylladb#29505
(cherry picked from commit 15493872b2)
Closes scylladb/scylladb#29957