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-rw-r--r--third_party/nix/src/nix/why-depends.cc267
1 files changed, 267 insertions, 0 deletions
diff --git a/third_party/nix/src/nix/why-depends.cc b/third_party/nix/src/nix/why-depends.cc
new file mode 100644
index 000000000000..325a2be0a793
--- /dev/null
+++ b/third_party/nix/src/nix/why-depends.cc
@@ -0,0 +1,267 @@
+#include "command.hh"
+#include "store-api.hh"
+#include "progress-bar.hh"
+#include "fs-accessor.hh"
+#include "shared.hh"
+
+#include <queue>
+
+using namespace nix;
+
+static std::string hilite(const std::string & s, size_t pos, size_t len,
+    const std::string & colour = ANSI_RED)
+{
+    return
+        std::string(s, 0, pos)
+        + colour
+        + std::string(s, pos, len)
+        + ANSI_NORMAL
+        + std::string(s, pos + len);
+}
+
+static std::string filterPrintable(const std::string & s)
+{
+    std::string res;
+    for (char c : s)
+        res += isprint(c) ? c : '.';
+    return res;
+}
+
+struct CmdWhyDepends : SourceExprCommand
+{
+    std::string _package, _dependency;
+    bool all = false;
+
+    CmdWhyDepends()
+    {
+        expectArg("package", &_package);
+        expectArg("dependency", &_dependency);
+
+        mkFlag()
+            .longName("all")
+            .shortName('a')
+            .description("show all edges in the dependency graph leading from 'package' to 'dependency', rather than just a shortest path")
+            .set(&all, true);
+    }
+
+    std::string name() override
+    {
+        return "why-depends";
+    }
+
+    std::string description() override
+    {
+        return "show why a package has another package in its closure";
+    }
+
+    Examples examples() override
+    {
+        return {
+            Example{
+                "To show one path through the dependency graph leading from Hello to Glibc:",
+                "nix why-depends nixpkgs.hello nixpkgs.glibc"
+            },
+            Example{
+                "To show all files and paths in the dependency graph leading from Thunderbird to libX11:",
+                "nix why-depends --all nixpkgs.thunderbird nixpkgs.xorg.libX11"
+            },
+            Example{
+                "To show why Glibc depends on itself:",
+                "nix why-depends nixpkgs.glibc nixpkgs.glibc"
+            },
+        };
+    }
+
+    void run(ref<Store> store) override
+    {
+        auto package = parseInstallable(*this, store, _package, false);
+        auto packagePath = toStorePath(store, Build, package);
+        auto dependency = parseInstallable(*this, store, _dependency, false);
+        auto dependencyPath = toStorePath(store, NoBuild, dependency);
+        auto dependencyPathHash = storePathToHash(dependencyPath);
+
+        PathSet closure;
+        store->computeFSClosure({packagePath}, closure, false, false);
+
+        if (!closure.count(dependencyPath)) {
+            printError("'%s' does not depend on '%s'", package->what(), dependency->what());
+            return;
+        }
+
+        stopProgressBar(); // FIXME
+
+        auto accessor = store->getFSAccessor();
+
+        auto const inf = std::numeric_limits<size_t>::max();
+
+        struct Node
+        {
+            Path path;
+            PathSet refs;
+            PathSet rrefs;
+            size_t dist = inf;
+            Node * prev = nullptr;
+            bool queued = false;
+            bool visited = false;
+        };
+
+        std::map<Path, Node> graph;
+
+        for (auto & path : closure)
+            graph.emplace(path, Node{path, store->queryPathInfo(path)->references});
+
+        // Transpose the graph.
+        for (auto & node : graph)
+            for (auto & ref : node.second.refs)
+                graph[ref].rrefs.insert(node.first);
+
+        /* Run Dijkstra's shortest path algorithm to get the distance
+           of every path in the closure to 'dependency'. */
+        graph[dependencyPath].dist = 0;
+
+        std::priority_queue<Node *> queue;
+
+        queue.push(&graph.at(dependencyPath));
+
+        while (!queue.empty()) {
+            auto & node = *queue.top();
+            queue.pop();
+
+            for (auto & rref : node.rrefs) {
+                auto & node2 = graph.at(rref);
+                auto dist = node.dist + 1;
+                if (dist < node2.dist) {
+                    node2.dist = dist;
+                    node2.prev = &node;
+                    if (!node2.queued) {
+                        node2.queued = true;
+                        queue.push(&node2);
+                    }
+                }
+
+            }
+        }
+
+        /* Print the subgraph of nodes that have 'dependency' in their
+           closure (i.e., that have a non-infinite distance to
+           'dependency'). Print every edge on a path between `package`
+           and `dependency`. */
+        std::function<void(Node &, const string &, const string &)> printNode;
+
+        const string treeConn = "╠═══";
+        const string treeLast = "╚═══";
+        const string treeLine = "║   ";
+        const string treeNull = "    ";
+
+        struct BailOut { };
+
+        printNode = [&](Node & node, const string & firstPad, const string & tailPad) {
+            assert(node.dist != inf);
+            std::cout << fmt("%s%s%s%s" ANSI_NORMAL "\n",
+                firstPad,
+                node.visited ? "\e[38;5;244m" : "",
+                firstPad != "" ? "=> " : "",
+                node.path);
+
+            if (node.path == dependencyPath && !all
+                && packagePath != dependencyPath)
+                throw BailOut();
+
+            if (node.visited) return;
+            node.visited = true;
+
+            /* Sort the references by distance to `dependency` to
+               ensure that the shortest path is printed first. */
+            std::multimap<size_t, Node *> refs;
+            std::set<std::string> hashes;
+
+            for (auto & ref : node.refs) {
+                if (ref == node.path && packagePath != dependencyPath) continue;
+                auto & node2 = graph.at(ref);
+                if (node2.dist == inf) continue;
+                refs.emplace(node2.dist, &node2);
+                hashes.insert(storePathToHash(node2.path));
+            }
+
+            /* For each reference, find the files and symlinks that
+               contain the reference. */
+            std::map<std::string, Strings> hits;
+
+            std::function<void(const Path &)> visitPath;
+
+            visitPath = [&](const Path & p) {
+                auto st = accessor->stat(p);
+
+                auto p2 = p == node.path ? "/" : std::string(p, node.path.size() + 1);
+
+                auto getColour = [&](const std::string & hash) {
+                    return hash == dependencyPathHash ? ANSI_GREEN : ANSI_BLUE;
+                };
+
+                if (st.type == FSAccessor::Type::tDirectory) {
+                    auto names = accessor->readDirectory(p);
+                    for (auto & name : names)
+                        visitPath(p + "/" + name);
+                }
+
+                else if (st.type == FSAccessor::Type::tRegular) {
+                    auto contents = accessor->readFile(p);
+
+                    for (auto & hash : hashes) {
+                        auto pos = contents.find(hash);
+                        if (pos != std::string::npos) {
+                            size_t margin = 32;
+                            auto pos2 = pos >= margin ? pos - margin : 0;
+                            hits[hash].emplace_back(fmt("%s: …%s…\n",
+                                    p2,
+                                    hilite(filterPrintable(
+                                            std::string(contents, pos2, pos - pos2 + hash.size() + margin)),
+                                        pos - pos2, storePathHashLen,
+                                        getColour(hash))));
+                        }
+                    }
+                }
+
+                else if (st.type == FSAccessor::Type::tSymlink) {
+                    auto target = accessor->readLink(p);
+
+                    for (auto & hash : hashes) {
+                        auto pos = target.find(hash);
+                        if (pos != std::string::npos)
+                            hits[hash].emplace_back(fmt("%s -> %s\n", p2,
+                                    hilite(target, pos, storePathHashLen, getColour(hash))));
+                    }
+                }
+            };
+
+            // FIXME: should use scanForReferences().
+
+            visitPath(node.path);
+
+            RunPager pager;
+            for (auto & ref : refs) {
+                auto hash = storePathToHash(ref.second->path);
+
+                bool last = all ? ref == *refs.rbegin() : true;
+
+                for (auto & hit : hits[hash]) {
+                    bool first = hit == *hits[hash].begin();
+                    std::cout << tailPad
+                              << (first ? (last ? treeLast : treeConn) : (last ? treeNull : treeLine))
+                              << hit;
+                    if (!all) break;
+                }
+
+                printNode(*ref.second,
+                    tailPad + (last ? treeNull : treeLine),
+                    tailPad + (last ? treeNull : treeLine));
+            }
+        };
+
+        try {
+            printNode(graph.at(packagePath), "", "");
+        } catch (BailOut & ) { }
+    }
+};
+
+static RegisterCommand r1(make_ref<CmdWhyDepends>());