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5530c529c2
When casting a float or double column to a string with `CAST(f AS TEXT)`,
Scylla is expected to print the number with enough digits so that reading
that string back to a float or double restores the original number
exactly. This expectation isn't documented anywhere, but makes sense,
and is what Cassandra does.
Before commit 71bbd7475c, this wasn't the
case in Scylla: `CAST(f AS TEXT)` always printed 6 digits of precision,
which was a bit under enough for a float (which can have 7 decimal digits
of precision), but very much not enough for a double (which can need 15
digits). The origin of this magic "6 digits" number was that Scylla uses
seastar::to_sstring() to print the float and double values, and before
the aforementioned commit those functions used sprintf with the "%g"
format - which always prints 6 decimal digits of precision! After that
commit, to_sstring() now uses a different approach (based on fmt) to
print the float and double values, that prints all significant digits.
This patch adds a regression test for this bug: We write float and double
values to the database, cast them to text, and then recover the float
or double number from that text - and check that we get back exactly the
same float or double object. The test *fails* before the aforementioned
commit, and passes after it. It also passes on Cassandra.
Refs #15127
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Closes #15131