Make the Store API more type-safe

Most functions now take a StorePath argument rather than a Path (which
is just an alias for std::string). The StorePath constructor ensures
that the path is syntactically correct (i.e. it looks like
<store-dir>/<base32-hash>-<name>). Similarly, functions like
buildPaths() now take a StorePathWithOutputs, rather than abusing Path
by adding a '!<outputs>' suffix.

Note that the StorePath type is implemented in Rust. This involves
some hackery to allow Rust values to be used directly in C++, via a
helper type whose destructor calls the Rust type's drop()
function. The main issue is the dynamic nature of C++ move semantics:
after we have moved a Rust value, we should not call the drop function
on the original value. So when we move a value, we set the original
value to bitwise zero, and the destructor only calls drop() if the
value is not bitwise zero. This should be sufficient for most types.

Also lots of minor cleanups to the C++ API to make it more modern
(e.g. using std::optional and std::string_view in some places).

1 files changed, 16 insertions, 14 deletions

diff --git a/src/nix/why-depends.cc b/src/nix/why-depends.cc
index fa2a903a8..8566e5851 100644
--- a/src/nix/why-depends.cc
+++ b/src/nix/why-depends.cc
@@ -73,9 +73,9 @@ struct CmdWhyDepends : SourceExprCommand
         auto packagePath = toStorePath(store, Build, package);
         auto dependency = parseInstallable(*this, store, _dependency, false);
         auto dependencyPath = toStorePath(store, NoBuild, dependency);
-        auto dependencyPathHash = storePathToHash(dependencyPath);
+        auto dependencyPathHash = storePathToHash(store->printStorePath(dependencyPath));
 
-        PathSet closure;
+        StorePathSet closure;
         store->computeFSClosure({packagePath}, closure, false, false);
 
         if (!closure.count(dependencyPath)) {
@@ -91,28 +91,28 @@ struct CmdWhyDepends : SourceExprCommand
 
         struct Node
         {
-            Path path;
-            PathSet refs;
-            PathSet rrefs;
+            StorePath path;
+            StorePathSet refs;
+            StorePathSet rrefs;
             size_t dist = inf;
             Node * prev = nullptr;
             bool queued = false;
             bool visited = false;
         };
 
-        std::map<Path, Node> graph;
+        std::map<StorePath, Node> graph;
 
         for (auto & path : closure)
-            graph.emplace(path, Node{path, store->queryPathInfo(path)->references});
+            graph.emplace(path.clone(), Node{path.clone(), cloneStorePathSet(store->queryPathInfo(path)->references)});
 
         // Transpose the graph.
         for (auto & node : graph)
             for (auto & ref : node.second.refs)
-                graph[ref].rrefs.insert(node.first);
+                graph.find(ref)->second.rrefs.insert(node.first.clone());
 
         /* Run Dijkstra's shortest path algorithm to get the distance
            of every path in the closure to 'dependency'. */
-        graph[dependencyPath].dist = 0;
+        graph[dependencyPath.clone()].dist = 0;
 
         std::priority_queue<Node *> queue;
 
@@ -151,12 +151,14 @@ struct CmdWhyDepends : SourceExprCommand
         struct BailOut { };
 
         printNode = [&](Node & node, const string & firstPad, const string & tailPad) {
+            auto pathS = store->printStorePath(node.path);
+
             assert(node.dist != inf);
             std::cout << fmt("%s%s%s%s" ANSI_NORMAL "\n",
                 firstPad,
                 node.visited ? "\e[38;5;244m" : "",
                 firstPad != "" ? "=> " : "",
-                node.path);
+                pathS);
 
             if (node.path == dependencyPath && !all
                 && packagePath != dependencyPath)
@@ -175,7 +177,7 @@ struct CmdWhyDepends : SourceExprCommand
                 auto & node2 = graph.at(ref);
                 if (node2.dist == inf) continue;
                 refs.emplace(node2.dist, &node2);
-                hashes.insert(storePathToHash(node2.path));
+                hashes.insert(storePathToHash(store->printStorePath(node2.path)));
             }
 
             /* For each reference, find the files and symlinks that
@@ -187,7 +189,7 @@ struct CmdWhyDepends : SourceExprCommand
             visitPath = [&](const Path & p) {
                 auto st = accessor->stat(p);
 
-                auto p2 = p == node.path ? "/" : std::string(p, node.path.size() + 1);
+                auto p2 = p == pathS ? "/" : std::string(p, pathS.size() + 1);
 
                 auto getColour = [&](const std::string & hash) {
                     return hash == dependencyPathHash ? ANSI_GREEN : ANSI_BLUE;
@@ -231,11 +233,11 @@ struct CmdWhyDepends : SourceExprCommand
 
             // FIXME: should use scanForReferences().
 
-            visitPath(node.path);
+            visitPath(pathS);
 
             RunPager pager;
             for (auto & ref : refs) {
-                auto hash = storePathToHash(ref.second->path);
+                auto hash = storePathToHash(store->printStorePath(ref.second->path));
 
                 bool last = all ? ref == *refs.rbegin() : true;