fix(judge): treat empty output files as existing

[Ujimatsu-Chiya]

fix(judge): treat empty output files as existing

When using file IO mode, HydroJudge checked output file existence with a truthy value check on ret.files[outname].

This caused a valid zero-byte output file, such as an empty user.out, to be treated as missing because an empty string is falsy in JavaScript. As a result, pretests with empty output incorrectly failed with Output file not found.

Check whether the output file key exists instead of checking whether its content is truthy, and preserve empty stdout/stderr with nullish coalescing.

Summary by CodeRabbit

• Bug Fixes
  • Improved handling of sandbox output files so missing results are reported more reliably.
  • Preserved empty stdout and stderr content instead of treating it as missing.
  • If an expected output file is not found, the run now surfaces a clearer runtime error.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

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Plan: Pro

Run ID: b8884a43-ce02-4d5e-94f6-c1769cc6e33c

📥 Commits

Reviewing files that changed from the base of the PR and between 99ce691 and a93fb5a.

📒 Files selected for processing (1)

• packages/hydrojudge/src/sandbox.ts

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Walkthrough

adaptResult now distinguishes missing output entries from falsy values when checking output file IDs and files. It copies the output filename’s file ID into ret.fileIds.stdout when present, sets an output-not-found runtime error when neither output artifact exists, and uses nullish-coalescing to preserve empty-string stdout and stderr contents.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly matches the main fix: treating empty judge output files as existing.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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Warning

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packages/hydrojudge/src/sandbox.ts

ESLint skipped: missing config or dependency (missing-dependency). The ESLint configuration references a package that is not available in the sandbox.

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[Ujimatsu-Chiya]

I have read the CLA Document and I hereby sign the CLA

[undefined-moe]

Please provide a non-working example (problem package & code / hydro.ac submission link)

[Ujimatsu-Chiya]

Please provide a non-working example (problem package & code / hydro.ac submission link)

https://hydro.ac/p/loj-P3891 这是一道需要文件freopen的题目，对于自测样例的空输出，它打印的是RE：Output file not found:

期望行为应该是空输出，而不是文件不存在。

https://hydro.ac/p/luogu-B4177 对于一个标准输入输出的题目，期望的自测样例的空输出应该是：