[BUG] CAST string to timestamp produces null for some valid timestamps

[andygrove]

Describe the bug
Casting the following strings to timestamp produces null values instead of valid timestamps.

"\nT2\n", // today, 02:00:00.0
"\nT\n", // today, midnight
"\n:\n", // today, midnight
"\n1:\n", // today, 01:00:00.0
"\n5:24\n", // today, 05:24:00.0
"\n:2\n", // today, 2 minutes after midnight
"\n1::2\n" // today, 01:00:02.0

Steps/Code to reproduce bug

I will check in the fuzzer used to generate these values as part of the PR that fixes the issue.

Expected behavior
We should produce the same values as Spark.

Additional context
None

[sameerz]

This will be partially addressed in 21.08 and completed in 21.10.

[andygrove]

Rather than try and support these edge cases I am now leaning towards having a regex to detect them instead and fail if we see them and tell the user to disable spark.rapids.sql.castStringToTimestamp.enabled if they run into this error.