Fix topological sort order#14688
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Moved out of draft after a final pass over the diff and the current CI state. Validation visible on the PR is green for build, ruff, Sphinx docs, and pre-commit.ci. The change stays scoped to returning a topological order with each source before its reachable targets. |
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Fixes #12192.
The DFS implementation appended nodes after visiting their descendants and returned that postorder directly, which placed dependents before their prerequisites. This keeps the existing implementation shape but inserts each completed node at the front of the output so every edge source appears before its targets.
I also added a doctest for the module sample graph.
Validation:
python -m doctest -v sorts/topological_sort.pypython sorts/topological_sort.pypython - <<'PY'\nfrom sorts.topological_sort import edges, topological_sort\norder = topological_sort('a', [], [])\nposition = {node: index for index, node in enumerate(order)}\nprint(order)\nprint(all(position[src] < position[dst] for src, neighbors in edges.items() for dst in neighbors))\nPY\n-uv run --no-project --with pytest python -m pytest sorts/topological_sort.py -q\n-uv run --no-project --with ruff ruff check sorts/topological_sort.py