Refactor OFDFT line-search status to std::string

[zzlinpku]

What's changed?

The OFDFT line-search status was stored in a manually allocated 60-character buffer. Use std::string for ESolver_OF::task_ and pass it by reference through Opt_DCsrch::dcSrch and the internal dcsrch function. Status writes now use string assignment; prefix checks use C++11-compatible compare. This removes manual allocation, fixed-capacity status storage, and raw character writes while preserving status text and numerical logic.

Update both existing CG/TN test callers. Add three focused line-search tests for convergence/restart, error-to-short-status replacement, and a maximum-step warning; register them as MODULE_BASE_opt_dcsrch.

Linked Issue

No linked issue: self-contained ownership and status-string cleanup.

Unit Tests and/or Case Tests for my changes

Verified on the branch based on 3d200fd47b67275d2a101ea036b2634d29c29fb9. Local submitted files were SHA-256 matched to the server files.

Server build configuration (unchanged): ENABLE_LCAO=OFF, ENABLE_LIBXC=OFF, ENABLE_LIBRI=OFF, ENABLE_ELPA=OFF.

Commands run:

git diff --cached --check
python3 tools/03_code_analysis/agent_governance_check.py --staged
cmake --build /home/zzl/build-ofdft-pr-latest -j4

# In a scratch copy of tests/07_OFDFT/03_OF_OP_TN,
# preserving its relative path to tests/PP_ORB:
OMP_NUM_THREADS=1 mpirun --bind-to none -n 2 \
  /home/zzl/build-ofdft-pr-latest/abacus_pw_para

Results:

• PW build succeeded after the string/interface changes.
• OFDFT case completed through TN7. Final energy -57.93385514279088 eV, identical to the prior array version; reference -57.93385514279199 eV; absolute difference about 1.108e-12 eV, below 1e-8 eV.
• MPI emitted the same hwloc PCI-domain/display-authorization warnings; calculation completed successfully.
• Diff check passed; governance check found no blocking errors.

Focused tests were also compiled locally with Clang, C++11 and GoogleTest 1.12.1:

clang++ -std=c++11 -pthread \
  -I/private/tmp/ofdft-googletest-1121/googletest/include \
  -I/private/tmp/ofdft-googletest-1121/googletest \
  source/source_base/test/test_opt_dcsrch.cpp \
  source/source_base/opt_dcsrch.cpp \
  /private/tmp/ofdft-googletest-1121/googletest/src/gtest-all.cc \
  /private/tmp/ofdft-googletest-1121/googletest/src/gtest_main.cc \
  -o /private/tmp/ofdft-test-opt-dcsrch
/private/tmp/ofdft-test-opt-dcsrch

All 3 tests passed.

Limits:

• Full regression suite and existing CG/TN test executables were not run locally; their callers were migrated and are left for CI.
• The new test passed as a standalone executable; its CTest registration has not been exercised locally.
• Full LCAO build was previously blocked by missing RI/global/Array_Operator.h; only the stated PW build is claimed.
• Upstream has advanced beyond the branch base. No fresh build of the merge with upstream was performed.

Governance Notes

• INPUT/docs changes: no INPUT or user-facing calculation behavior changes, so no INPUT documentation update is required. The internal status-parameter documentation is updated.
• Core module impact: Opt_DCsrch::dcSrch now requires std::string& rather than char*; all in-repository callers are migrated. Out-of-tree callers must adapt. Numerical line-search operations are unchanged.
• Headers: <string> is required for the owned member and the string-reference interface.
• Global dependencies: existing diagnostic output is retained; no net increase of global references.
• Exceptions requested: none.

Reminder

• Read repository governance.
• Explained issue linkage, test evidence and limitations.
• Listed verification commands and results.
• Described interface, core-module and INPUT impact.
• Explained header dependencies and remaining global usage.

[Copilot]

🟢 Approval recommended

No unresolved review issues remain, and existing behavior is preserved.

Pull request overview

Refactors the OFDFT line-search buffer to use RAII-managed std::array storage while preserving behavior.

Changes:

• Replaces manual allocation with std::array<char, 60>.
• Removes matching allocation and deallocation.
• Updates buffer usage to call .data().

File summaries

File	Description
source/source_esolver/esolver_of.h	Declares the fixed-size array buffer.
source/source_esolver/esolver_of.cpp	Removes manual buffer management.
source/source_esolver/esolver_of_interface.cpp	Uses the array buffer through .data().

Review details

• Files reviewed: 3/3 changed files
• Comments generated: 0
• Review effort level: Lite

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[mohanchen]

Nice try as a first PR, please keep going. @zzlinpku