* `nix-store --gc --print-roots': also print the path of the actual

root symlink, not just its target.  E.g.:

  /nix/var/nix/profiles/system-99-link -> /nix/store/76kwf88657nq7wgk1hx3l1z5q91zb9wd-system

src/libstore/gc.cc

@@ -614,11 +614,6 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
     if (!options.ignoreLiveness)
         addAdditionalRoots(state.roots);
 
-    if (options.action == GCOptions::gcReturnRoots) {
-        results.paths = state.roots;
-        return;
-    }
-
     /* Read the temporary roots.  This acquires read locks on all
        per-process temporary root files.  So after this point no paths
        can be added to the set of temporary roots. */

src/libstore/store-api.hh

@@ -22,10 +22,6 @@ struct GCOptions
 {
     /* Garbage collector operation:
 
-       - `gcReturnRoots': find and return the set of roots for the
-         garbage collector.  These are the store paths symlinked to in
-         the `gcroots' directory.
-
        - `gcReturnLive': return the set of paths reachable from
          (i.e. in the closure of) the roots.
 
@@ -38,7 +34,6 @@ struct GCOptions
           `pathsToDelete', insofar as they are not reachable.
     */
     typedef enum {
-        gcReturnRoots,
         gcReturnLive,
         gcReturnDead,
         gcDeleteDead,

src/nix-store/nix-store.cc

@@ -520,6 +520,7 @@ struct PrintFreed
 
 static void opGC(Strings opFlags, Strings opArgs)
 {
+    bool printRoots = false;
     GCOptions options;
     options.action = GCOptions::gcDeleteDead;
     
@@ -527,7 +528,7 @@ static void opGC(Strings opFlags, Strings opArgs)
     
     /* Do what? */
     foreach (Strings::iterator, i, opFlags)
-        if (*i == "--print-roots") options.action = GCOptions::gcReturnRoots;
+        if (*i == "--print-roots") printRoots = true;
         else if (*i == "--print-live") options.action = GCOptions::gcReturnLive;
         else if (*i == "--print-dead") options.action = GCOptions::gcReturnDead;
         else if (*i == "--delete") options.action = GCOptions::gcDeleteDead;
@@ -539,13 +540,21 @@ static void opGC(Strings opFlags, Strings opArgs)
         else throw UsageError(format("bad sub-operation `%1%' in GC") % *i);
 
     if (!opArgs.empty()) throw UsageError("no arguments expected");
-    
-    PrintFreed freed(options.action == GCOptions::gcDeleteDead, results);
-    store->collectGarbage(options, results);
 
-    if (options.action != GCOptions::gcDeleteDead)
-        foreach (PathSet::iterator, i, results.paths)
-            cout << *i << std::endl;
+    if (printRoots) {
+        Roots roots = store->findRoots();
+        foreach (Roots::iterator, i, roots)
+            cout << i->first << " -> " << i->second << std::endl;
+    }
+
+    else {
+        PrintFreed freed(options.action == GCOptions::gcDeleteDead, results);
+        store->collectGarbage(options, results);
+
+        if (options.action != GCOptions::gcDeleteDead)
+            foreach (PathSet::iterator, i, results.paths)
+                cout << *i << std::endl;
+    }
 }