GH-50109: [C++][Gandiva] Fix incorrect error messages

[lriggs]

Rationale for this change

Three small, independent bugs in Gandiva's runtime error messages: in two cases the message misrepresents what actually failed, and in one case a copy-paste error left the wrong function name in a message.

What changes are included in this PR?

1. levenshtein reported OOM as a length error

cpp/src/gandiva/precompiled/string_ops.cc:1738-1742 — when gdv_fn_context_arena_malloc returned null (i.e. memory allocation failed), the function set the error to "String length must be greater than 0". The condition is an OOM, not a length issue. Now reports "LEVENSHTEIN: could not allocate working memory".

2. levenshtein length-bound message was off by one

cpp/src/gandiva/precompiled/string_ops.cc:1702-1708 — the precondition is in1_len < 0 || in2_len < 0, which rejects only negative lengths (zero is valid). The message said "must be greater than 0", implying zero was rejected too. Corrected to "LEVENSHTEIN: input lengths must be non-negative, got <a> and <b>", which now also echoes the offending values.

3. gdv_fn_aes_decrypt reported the wrong direction

cpp/src/gandiva/gdv_function_stubs.cc:411 — inside the AES decrypt function, the OOM message said "Could not allocate memory for returning aes encrypt cypher text". Pure copy-paste from the sibling encrypt function. Corrected the direction wording.

Test updates

cpp/src/gandiva/precompiled/string_ops_test.cc:1133-1135 — the levenshtein test was asserting HasSubstr("String length must be greater than 0"), which was matching the bug message — i.e. the test was effectively verifying the wrong behavior. Updated to assert the corrected message substring.

Are these changes tested?

cd cpp/debug
cmake --build . --target gandiva_shared gandiva-precompiled-test gandiva-internals-test gandiva-projector-test -j4
./debug/gandiva-precompiled-test     # 130/130 pass
./debug/gandiva-internals-test       # 156/156 pass
./debug/gandiva-projector-test       # 218/218 pass

Are there any user-facing changes?

Yes, improved error message accuracy.

• GitHub Issue: [C++][Gandiva] Fix incorrect error messages #50109

[github-actions]

⚠️ GitHub issue #50109 has been automatically assigned in GitHub to PR creator.