[C++][Gandiva] Fix castVARCHAR memory inefficiencies, unused bool allocation, and missing len<=0 handling

[dmitry-chirkov-dremio]

Describe the enhancement requested

The castVARCHAR functions have several issues:

Functional issues:

• bool - allocates 5 bytes from arena, then immediately overwrites the pointer with a string literal; the allocation is never used
• int32/int64 - missing handling for len=0 (should return empty string) and len<0 (should set error)

Performance issues:

• int32/int64 - max output is 11/20 bytes, but allocates len bytes upfront
• date64 - output is always 10 bytes ("YYYY-MM-DD"), but allocates len bytes
• float32/float64 - max output is ~15-24 bytes, but allocates len bytes

Proposed fixes:

1. Integer types: Format to stack buffer, allocate only min(len, actual_size) bytes, add len<=0 handling
2. Date/Float types: Allocate only min(len, max_output_size) bytes upfront instead of len bytes
3. Boolean type: Return string literal directly without arena allocation
4. Tests: Add coverage for len=0 and len<0 edge cases

Component(s)

C++, Gandiva

[dmitry-chirkov-dremio]

take

[AnshikaJain-code]

Hi, I’m interested in working on this issue.

I see a commit referencing it, but I don’t see a linked PR in the Development section. Is this still open for contribution, or is there an active PR addressing it?

Thanks!

[dmitry-chirkov-dremio]

Thank you for your interest, @AnshikaJain-code!
I'm already working on the PR #49421 - feel free to review.