* It is now possible to add store derivations or paths directly to a

user environment, e.g.,

    $ nix-env -i /nix/store/z58v41v21xd3ywrqk1vmvdwlagjx7f10-aterm-2.3.1.drv

  or 

    $ nix-env -i /nix/store/hsyj5pbn0d9iz7q0aj0fga7cpaadvp1l-aterm-2.3.1

  This is useful because it allows Nix expressions to be bypassed
  entirely.  For instance, if only a nix-pull manifest is provided,
  plus the top-level path of some component, it can be installed
  without having to supply the Nix expression (e.g., for obfuscation,
  or to be independent of Nix expression language changes or context
  dependencies).

src/libstore/build.hh

@@ -28,4 +28,9 @@ Derivation derivationFromPath(const Path & drvPath);
 void computeFSClosure(const Path & storePath,
     PathSet & paths, bool flipDirection = false);
 
+/* Return the path corresponding to the output identifier `id' in the
+   given derivation. */
+Path findOutput(const Derivation & drv, string id);
+    
+
 #endif /* !__BUILD_H */

src/libstore/misc.cc

@@ -27,3 +27,12 @@ void computeFSClosure(const Path & storePath,
          i != references.end(); ++i)
         computeFSClosure(*i, paths, flipDirection);
 }
+
+
+ Path findOutput(const Derivation & drv, string id)
+{
+    for (DerivationOutputs::const_iterator i = drv.outputs.begin();
+         i != drv.outputs.end(); ++i)
+        if (i->first == id) return i->second.path;
+    throw Error(format("derivation has no output `%1%'") % id);
+}