andygrove opened a new issue, #5271:
URL: https://github.com/apache/datafusion-comet/issues/5271
## Describe the bug
A bare `-0.0` literal in a Comet SQL file test does not produce a negative
zero. Spark parses `-0.0` as `decimal(1,1)`, decimal has no signed zero, and
the coercion to `double` or `float` yields `+0.0`. `CAST(-0.0 AS DOUBLE)` has
the same problem, because the cast source is still the decimal literal.
The result is that a number of our SQL fixtures read as signed-zero coverage
while testing nothing. To get an actual negative zero you have to go through
the string form, `double('-0.0')` or `float('-0.0')`.
## How this was found
While reviewing #5235 I wrote a nested-array fixture using bare `-0.0` and
it passed against the *unpatched* merge-base, which it should not have.
Switching the literals to `double('-0.0')` made it fail as expected:
```
!== Spark Answer == == Comet Answer
(unpatched) ==
![List(List(-0.0)),List(List(0.0)),true]
[List(List(-0.0)),List(List(0.0)),false]
![List(List(0.0)),List(List(-0.0)),true]
[List(List(0.0)),List(List(-0.0)),false]
![List(List(1.0, -0.0)),List(List(1.0, 0.0)),true] [List(List(1.0,
-0.0)),List(List(1.0, 0.0)),false]
```
## Known instance
`spark/src/test/resources/sql-tests/expressions/array/arrays_overlap.sql:120`
```sql
INSERT INTO test_overlap_dbl VALUES ..., (array(0.0), array(-0.0)), ...
```
Both sides store `[0.0]`, so the row is not exercising signed zero at all.
## What needs doing
Audit `spark/src/test/resources/sql-tests/` for the pattern and convert the
affected literals. About 35 files mention `-0.0`, in three shapes, and the
first two are the broken ones:
- bare `-0.0` in a `VALUES` row for a `double`/`float` column
- `CAST(-0.0 AS DOUBLE)` / `CAST(-0.0 AS FLOAT)`
- `double('-0.0')` / `float('-0.0')`, which is correct
Files worth checking first, since they are specifically about float edge
cases: `arrays_overlap.sql`, `array_union.sql`, `array_except.sql`,
`array_intersect.sql`, `array_distinct.sql`, `array_min.sql`,
`array_insert.sql`, `array_compact.sql`, `array_repeat.sql`,
`sort_array_strict_fp.sql`, `shuffle.sql`, `shuffle_with_seed.sql`.
Each conversion should be checked to confirm the query still passes. Some of
them may start failing, which would surface real signed-zero divergences that
the vacuous form has been hiding.
Worth a note in the SQL file test docs as well, so the next person writing
float edge-case fixtures does not hit this.
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