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why-depends: refactor Node struct

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* Better name for refs
* Use std::optional<T> for distance

Suggested-by: eldritch horrors <pennae@lix.systems>
Change-Id: Ie35c3f2a7ea1a90ce3a9807025d0af9ea73e2403
This commit is contained in:
Maximilian Bosch
2025-07-07 11:44:17 +00:00
parent 57e071e815
commit 353a87727b
1 changed files with 23 additions and 21 deletions
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lix/nix/why-depends.cc
+23 -21
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@@ -100,13 +100,12 @@ try {
co_return result::current_exception();
}
auto const inf = std::numeric_limits<size_t>::max();
struct Node
{
StorePath path;
StorePathSet refs;
StorePathSet rrefs;
size_t dist = inf;
StorePathSet dependencies;
StorePathSet dependents;
std::optional<size_t> dist = std::nullopt;
Node * prev = nullptr;
bool queued = false;
bool visited = false;
@@ -130,7 +129,7 @@ static kj::Promise<Result<void>> printNode(
try {
auto pathS = store.printStorePath(node.path);
assert(node.dist != inf);
assert(node.dist.has_value());
if (precise) {
output.push_back(
fmt("%s%s%s%s" ANSI_NORMAL,
@@ -158,16 +157,15 @@ try {
std::multimap<size_t, Node *> refs;
std::set<std::string> hashes;
for (auto & ref : node.refs) {
for (auto & ref : node.dependencies) {
if (ref == node.path && packagePath != dependencyPath) {
continue;
}
auto & node2 = graph.at(ref);
if (node2.dist == inf) {
continue;
if (auto dist = node2.dist) {
refs.emplace(*node2.dist, &node2);
hashes.insert(std::string(node2.path.hashPart()));
}
refs.emplace(node2.dist, &node2);
hashes.insert(std::string(node2.path.hashPart()));
}
/* For each reference, find the files and symlinks that
@@ -321,31 +319,36 @@ struct CmdWhyDepends : SourceExprCommand, MixOperateOnOptions
std::map<StorePath, Node> graph;
for (auto & path : closure)
graph.emplace(path, Node {
.path = path,
.refs = aio().blockOn(store->queryPathInfo(path))->references,
.dist = path == dependencyPath ? 0 : inf
});
graph.emplace(
path,
Node{
.path = path,
.dependencies = aio().blockOn(store->queryPathInfo(path))->references,
.dist = path == dependencyPath ? std::optional(0) : std::nullopt
}
);
// Transpose the graph.
for (auto & node : graph)
for (auto & ref : node.second.refs)
graph.find(ref)->second.rrefs.insert(node.first);
for (auto & ref : node.second.dependencies) {
graph.find(ref)->second.dependents.insert(node.first);
}
/* Run Dijkstra's shortest path algorithm to get the distance
of every path in the closure to 'dependency'. */
std::priority_queue<Node *> queue;
queue.push(&graph.at(dependencyPath));
auto const inf = std::numeric_limits<size_t>::max();
while (!queue.empty()) {
auto & node = *queue.top();
queue.pop();
for (auto & rref : node.rrefs) {
for (auto & rref : node.dependents) {
auto & node2 = graph.at(rref);
auto dist = node.dist + 1;
if (dist < node2.dist) {
auto dist = node.dist.transform([](auto n) { return n + 1; });
if (dist.value_or(inf) < node2.dist.value_or(inf)) {
node2.dist = dist;
node2.prev = &node;
if (!node2.queued) {
@@ -353,7 +356,6 @@ struct CmdWhyDepends : SourceExprCommand, MixOperateOnOptions
queue.push(&node2);
}
}
}
}