GH-45394: [C++] Handle Single-Line JSON Without Line Ending

[JOBIN-SABU]

Fixes issue #45394: Handle single-line JSON without line ending

• Previously, if a file contained only one line of JSON and lacked a newline character at the end,
  pyarrow.dataset.dataset would correctly infer the schema but fail to load the values from that row.
• This fix ensures that such cases are handled properly.
• Additionally, I have fixed some other minor issues in the code.
• Tests are still not passing, but they were already failing before these changes.
• I believe the issue might be on the upstream side, but please review.

Looking forward to feedback!

• GitHub Issue: [Python][C++] A file with one line of JSON without a line ending is incorrectly loaded when used as a Dataset #45394

[github-actions]

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[github-actions]

⚠️ GitHub issue #45394 has been automatically assigned in GitHub to PR creator.

[raulcd]

is there any reason you're not using the existing files_json_test.cc file and infrastructure and you're adding all this new CMake?

[raulcd]

https://github.com/apache/arrow/blob/16c7f1a0bbcfad20eba7c63bc86d3da784d1db34/cpp/src/arrow/dataset/file_json_test.cc

[JOBIN-SABU]

Hi @raulcd,

I sincerely apologize for overlooking the existing file_json_test.cc file and the associated infrastructure. I should have checked and integrated my changes into the existing test framework instead of introducing new CMake configurations.

I’ll make the necessary corrections to align with the existing structure and update the PR accordingly. Thanks for pointing this out!

[raulcd]

no worries at all! Thanks for your contributions!

[JOBIN-SABU]

Hi @raulcd a

I hope you're doing well.

I've made progress on fixing issue #45394, but I've encountered some challenges with running the tests due to hardware and internet limitations. While I believe I've addressed the core of the problem, the tests are still not passing, and I think this might be an upstream issue.

I've pushed my changes to the fix-45394 branch. Could you please take it from here and help with running the tests and finalizing any additional changes?

I appreciate your assistance and look forward to your feedback.

Thank you!