fix(vasp): collect OUTCAR files from multiple directories

[njzjz-bot]

Fixes #894.

Recursively discover and deterministically parse standard-named OUTCAR files for MultiSystems conversion.

Tests: Relevant VASP/MultiSystems tests plus CLI deepmd/npy conversion.

Why existing tests missed it: Tests covered single-file LabeledSystem parsing and other multi-mode backends, never VASP default multi-directory discovery.

Coding agent: Codex
Codex version: codex-cli 0.144.4
Model: gpt-5.6-sol
Reasoning effort: xhigh

Summary by CodeRabbit

• New Features
  • Added support for loading multiple VASP OUTCAR calculations from a directory, including nested subdirectories.
  • Discovered OUTCAR files are processed in a consistent order.
• Tests
  • Added coverage confirming that multiple nested calculations are loaded correctly, with each calculation represented as a separate system.

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Review details

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 8899d238-040f-4305-a676-421f3c8ba3bf

📥 Commits

Reviewing files that changed from the base of the PR and between 12f6f2e and 42450f9.

📒 Files selected for processing (1)

• tests/test_vasp_outcar.py

📝 Walkthrough

Walkthrough

VASP OUTCAR format loading now recursively discovers and sorts nested OUTCAR paths for MultiSystems. A test creates two nested calculations, loads both files, and verifies that two one-frame systems are returned.

Changes

VASP multi-system loading

Layer / File(s)	Summary
Recursive OUTCAR discovery dpdata/plugins/vasp.py	VASPOutcarFormat.from_multi_systems recursively finds files named OUTCAR and returns their sorted paths.
Multi-system loading validation tests/test_vasp_outcar.py	The test loads two nested OUTCAR files and verifies that both resulting systems contain one frame.

Estimated code review effort: 2 (Simple) | ~10 minutes

Sequence Diagram(s)

sequenceDiagram
  participant MultiSystems
  participant VASPOutcarFormat
  participant Filesystem
  MultiSystems->>VASPOutcarFormat: from_multi_systems(directory)
  VASPOutcarFormat->>Filesystem: os.walk(directory)
  Filesystem-->>VASPOutcarFormat: nested OUTCAR paths
  VASPOutcarFormat-->>MultiSystems: sorted OUTCAR paths

Loading

Suggested labels: bug

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly states the main change: collecting OUTCAR files from multiple directories.
Linked Issues check	✅ Passed	The recursive OUTCAR discovery and regression test directly address [#894]'s MultiSystems conversion failure.
Out of Scope Changes check	✅ Passed	All changes are directly related to recursive OUTCAR discovery and its regression coverage.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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[codspeed-hq]

Merging this PR will improve performance by 33.1%

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⚡ 2 improved benchmarks

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	WallTime	test_cli	378.2 ms	277.1 ms	+36.49%
⚡	WallTime	test_import	11.2 ms	8.6 ms	+29.81%

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---

_{Comparing njzjz-bot:fix/issue-894 (42450f9) with master (d2105f6)}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.95%. Comparing base (d2105f6) to head (42450f9).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1034   +/-   ##
=======================================
  Coverage   86.94%   86.95%           
=======================================
  Files          90       90           
  Lines        9178     9185    +7     
=======================================
+ Hits         7980     7987    +7     
  Misses       1198     1198           

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[wanghan-iapcm]

Approving: correct fix for #894. VASPOutcarFormat.from_multi_systems recursively walks the directory and returns sorted OUTCAR file paths, which is exactly the type MultiSystems.from_fmt_obj feeds into from_labeled_system(file_name=...); it mirrors the established os.walk pattern in the deepmd/npy loader (returning file paths rather than directories because VASP loads a file, and adding sorted() for determinism). The new test is a genuine regression test -- verified to raise NotImplementedError (format.py:317) on pre-fix code and pass after, exercising the public MultiSystems.from_file path over a nested layout. Build and codecov/patch green (docs/readthedocs red is the unrelated emscripten-forge outage, #1035). Optional follow-up: the test asserts only counts (len/nframes); asserting the two discovered systems' formulas match the sources would harden it (per the same guidance on #1015).

[njzjz]

Addressed the optional composition assertion in commit 42450f9. The regression test now compares the two discovered systems' non-zero element compositions with the source OUTCAR systems, while normalizing the shared zero-count type entries introduced by MultiSystems. Focused VASP OUTCAR tests pass.

Coding agent: Codex
Codex version: codex-cli 0.144.6
Model: gpt-5.6-sol
Reasoning effort: xhigh