Files
Maximilian Bosch f7871fcb57 libutil/topo-sort: return std::variant<std::vector<T>, Cycle>
The variant has on the left-hand side the topologically sorted vector
and the right-hand side is a pair showing the path and its parent that
represent a cycle in the graph making the sort impossible.

The goal is to implement #551 which needs to throw an error if the
topo-sort fails. However, the error-message is supposed to contain a
graph of store-paths and the API to generate this is inherently async.

Now, catching the exception and re-throwing another one is impossible
since `co_await` is forbidden in `catch`-blocks and adding another
topoSort variant that allows an async `makeError` also seems odd. Hence,
I decided to alter the data-structure in use a bit for this use-case.
One out of two uses of the function are affected after all.

Change-Id: I70a987f470437df8beb3b1cc203ff88701d0aa1b
2025-08-23 16:23:35 +02:00

46 lines
1.2 KiB
C++

#include "lix/libutil/topo-sort.hh"
#include <gtest/gtest.h>
namespace nix {
static auto testToposort(const std::map<std::string, std::set<std::string>> & data)
{
std::set<std::string> keys;
for (auto & [k, _] : data) {
keys.insert(k);
}
return topoSort(keys, {[&](const std::string & lib) { return data.at(lib); }});
}
TEST(toposort, trivial)
{
// The dependencies are incomplete on purpose here, this is just a test-case.
auto result = testToposort(
{{"openssh", {"glibc", "zlib", "polkit"}},
{"zlib", {"glibc"}},
{"polkit", {"glibc", "pam"}},
{"pam", {"glibc"}},
{"glibc", {}}}
);
auto ordered = std::get<std::vector<std::string>>(result);
ASSERT_EQ(5, ordered.size());
ASSERT_EQ("openssh", ordered[0]);
ASSERT_EQ("zlib", ordered[1]);
ASSERT_EQ("polkit", ordered[2]);
ASSERT_EQ("pam", ordered[3]);
ASSERT_EQ("glibc", ordered[4]);
}
TEST(toposort, cycle)
{
auto result = testToposort({{"foo", {"bar"}}, {"bar", {"baz"}}, {"baz", {"foo"}}});
auto cycle = std::get<Cycle<std::string>>(result);
ASSERT_EQ(cycle.path, "bar");
ASSERT_EQ(cycle.parent, "foo");
}
}