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#include "error.hh"
namespace nix {
template<typename T>
std::vector<T> topoSort(std::set<T> items,
std::function<std::set<T>(const T &)> getChildren,
std::function<Error(const T &, const T &)> makeCycleError)
{
std::vector<T> sorted;
std::set<T> visited, parents;
std::function<void(const T & path, const T * parent)> dfsVisit;
dfsVisit = [&](const T & path, const T * parent) {
if (parents.count(path)) throw makeCycleError(path, *parent);
if (!visited.insert(path).second) return;
parents.insert(path);
std::set<T> references = getChildren(path);
for (auto & i : references)
/* Don't traverse into items that don't exist in our starting set. */
if (i != path && items.count(i))
dfsVisit(i, &path);
sorted.push_back(path);
parents.erase(path);
};
for (auto & i : items)
dfsVisit(i, nullptr);
std::reverse(sorted.begin(), sorted.end());
return sorted;
}
}
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