raghav-reglobe opened a new pull request, #69219:
URL: https://github.com/apache/doris/pull/69219
### What problem does this PR solve?
Issue Number: close #69218
Related PR: none
Problem Summary:
`format_json_double` in `variant_string_parse.cpp` formatted a double with
`digits10 + 1` = 16 significant digits, one
short of what a binary64 can need, so `0.30000000000000004` rendered as
`0.3` and `1997.6000000000001` as `1997.6`: two
different doubles, and every reader that parsed a number out of
`CAST(variant AS STRING)` stored the neighbour. The
element path (`v['s']`) was already exact; the loss was in the document
writer. fmt's default `{}` (Dragonbox) is the
shortest representation that round-trips.
### Release note
Fix the JSON text of a VARIANT value rendering some doubles with 16
significant digits (not round-trip safe); the
document text now uses the shortest representation that parses back to the
same double.
### Check List (For Author)
- Test
- [x] Unit Test —
`DataTypeVariantV2SerdeOutputTest.DoublesRenderWithTheirShortestRoundTripForm`:
seven doubles
through both text surfaces and one document.
- Behavior changed:
- [x] Yes. The text form of a double inside a VARIANT document can now
carry 17 significant digits where the value
needs them (e.g. `0.30000000000000004` instead of `0.3`).
- Does this need documentation?
- [x] No.
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