fix(vasp): report frames dropped for a missing OUTCAR energy

[njzjz]

Ref #566.

State of the issue

The crash in the report — TypeError: Mismatch between array dtype ('object') and format specifier ('%.18e') from np.savetxt — no longer reproduces. #844 added a None guard in _get_frames_lower, so a truncated OUTCAR now yields a clean float64 energies array. I confirmed this by cutting tests/poscars/OUTCAR.h2o.md just before its last TOTEN record: 2 frames, dtype('float64'), no exception.

What #844 left behind is a bare break:

if energy is None:
    break

So the damaged frame and every frame after it vanish with no diagnostic at all. A user converting an interrupted run silently gets fewer frames than the run produced, which is the half of njzjz's comment ("there should be an error, or dpdata should ignore the frame") that is still unaddressed.

Change

Warn before breaking, naming the frame and stating that nothing after it is read either:

UserWarning: no energy found in frame 3; it and any frame after it are not read.
This usually means the calculation was interrupted before it finished writing.

The same break is also the normal loop exit — after the last ionic step, get_outcar_block returns the trailing timing report, which has no energy either. Warning unconditionally would fire on every well-formed OUTCAR (this is what my first attempt did, and test_complete_file_is_silent caught it). The warning is therefore limited to blocks that had already started emitting step data, i.e. where coord, cell, or force is non-empty.

No parsed data changes; this is purely diagnostic.

Validation

• tests/test_vasp_outcar_interrupted.py, 4 new cases: a complete file stays silent, a file cut before the last TOTEN warns naming frame 3, the surviving frames keep their exact energies and coordinates, and the energies array stays float64 (a direct regression test for the dtype in the original traceback).
• python -m unittest discover — 2240 passed, 28 skipped.
• ruff format / ruff check clean.

On closing the issue

This PR says Ref rather than Fixes because #566 was filed against dpgen with awaiting response and the reporter never came back. The reported crash is gone as of #844 and this closes the silent-data-loss gap it left. Happy to switch to Fixes if you would rather close it out.

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📥 Commits

Reviewing files that changed from the base of the PR and between c77e038 and 5896cb1.

📒 Files selected for processing (2)

• dpdata/formats/vasp/outcar.py
• tests/test_vasp_outcar_interrupted.py

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[codspeed-hq]

Merging this PR will not alter performance

⚠️ Unknown Walltime execution environment detected

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✅ 2 untouched benchmarks

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_{Comparing njzjz:fix/issue-566 (5896cb1) with master (c77e038)}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.63%. Comparing base (c77e038) to head (5896cb1).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1047   +/-   ##
=======================================
  Coverage   87.63%   87.63%           
=======================================
  Files          90       90           
  Lines        9209     9211    +2     
=======================================
+ Hits         8070     8072    +2     
  Misses       1139     1139           

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[Copilot]

Pull request overview

This PR improves VASP OUTCAR robustness in dpdata by emitting a targeted warning when an OUTCAR ends with an ionic step that has started producing step data (coords/cell/forces) but never records a TOTEN energy, which would otherwise cause silent frame loss at the end of the trajectory.

Changes:

• Add a conditional UserWarning before breaking out of OUTCAR frame parsing when energy is None for a block that already contains step data, indicating the dropped frame number and that subsequent frames cannot be read.
• Add a focused unittest module covering both the “complete OUTCAR should not warn” case and the “truncated before final TOTEN should warn and preserve prior frames/dtypes” regressions.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
dpdata/formats/vasp/outcar.py	Adds a conditional warning when the final (or truncated) block contains step data but lacks an energy token, avoiding silent frame truncation.
tests/test_vasp_outcar_interrupted.py	Adds regression tests ensuring complete OUTCARs stay quiet and truncated OUTCARs warn while keeping earlier frames intact and energies float64.

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