Make roots a map of store paths to pinning links

This new structure makes more sense as there may be many sources rooting
the same store path. Many profiles can reference the same path but this
is even more true with /proc/<pid>/maps where distinct pids can and
often do map the same store path.
This implementation is also more efficient as the `Roots` map contains
only one entry per rooted store path.

1 files changed, 7 insertions, 5 deletions

diff --git a/src/nix-store/nix-store.cc b/src/nix-store/nix-store.cc
index 33138baff388..b281ea2dd328 100644
--- a/src/nix-store/nix-store.cc
+++ b/src/nix-store/nix-store.cc
@@ -428,9 +428,10 @@ static void opQuery(Strings opFlags, Strings opArgs)
                     referrers, true, settings.gcKeepOutputs, settings.gcKeepDerivations);
             }
             Roots roots = store->findRoots();
-            for (auto & i : roots)
-                if (referrers.find(i.second) != referrers.end())
-                    cout << format("%1%\n") % i.first;
+            for (auto & [path, roots] : roots)
+                if (referrers.find(path) != referrers.end())
+                    for (auto & root : roots)
+                        cout << format("%1% -> %2%\n") % root % path;
             break;
         }
 
@@ -591,8 +592,9 @@ static void opGC(Strings opFlags, Strings opArgs)
 
     if (printRoots) {
         Roots roots = store->findRoots();
-        for (auto & i : roots)
-            cout << i.first << " -> " << i.second << std::endl;
+        for (auto & [path, roots] : roots)
+            for (auto & root : roots)
+                cout << root << " -> " << path << std::endl;
     }
 
     else {