[Afloat16]

Problem

PRM roadmap construction rejection-samples coordinates until it finds an unoccupied point. When the occupancy grid has no free cells, that loop never terminates. This can also occur after obstacle inflation removes the last free cell.

Change

Before sampling a nonempty roadmap, check whether the effective occupancy grid contains any free cells and raise NoPathError if it does not. Document the error on plan. Empty roadmap requests retain their existing behaviour.

The regression covers both an initially full grid and a grid made full by inflation, plus a free-space control that builds a real roadmap. The impossible cases use the project's timeout plugin to detect the former infinite loop.

Validation

• Original source: both impossible-map cases time out after 2 seconds; the free-space control passes.
• PYTHONPATH=src python -m pytest tests/test_prm_free_space.py tests/test_mobile_planners_a.py tests/test_mobile_performance.py -k 'PRM or prm or free_cells' -q: 14 passed, 22 deselected.
• Ruff passes for the changed source and new test file; the new file passes formatting.
• git diff --check passed.

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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🟢 Metrics 4 complexity · 0 duplication

Metric	Results
Complexity	4
Duplication	0

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