* `nix-env (-i|-u) --dry-run' now shows exactly which missing paths

will be built or substituted.

src/libstore/misc.hh

@@ -0,0 +1,32 @@
+#ifndef __MISC_H
+#define __MISC_H
+
+#include "derivations.hh"
+
+
+/* Read a derivation, after ensuring its existence through
+   ensurePath(). */
+Derivation derivationFromPath(const Path & drvPath);
+
+/* Place in `paths' the set of all store paths in the file system
+   closure of `storePath'; that is, all paths than can be directly or
+   indirectly reached from it.  `paths' is not cleared.  If
+   `flipDirection' is true, the set of paths that can reach
+   `storePath' is returned; that is, the closures under the
+   `referrers' relation instead of the `references' relation is
+   returned. */
+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);
+
+/* Given a set of paths that are to be built, return the set of
+   derivations that will be built, and the set of output paths that
+   will be substituted. */
+void queryMissing(const PathSet & targets,
+    PathSet & willBuild, PathSet & willSubstitute);
+
+
+#endif /* !__MISC_H */