* Added syntactic sugar to the construction of attribute sets to

  `inherit' variables from the surrounding lexical scope.

  E.g.,

    {stdenv, libfoo}: derivation {
      builder = ./bla;
      inherit stdenv libfoo;
      xyzzy = 1;
    }

  is equivalent to

    {stdenv, libfoo}: derivation {
      builder = ./bla;
      stdenv = stdenv;
      libfoo = libfoo;
      xyzzy = 1;
    }

  Note that for mutually recursive attribute set definitions (`rec
  {...}'), this also works, that is, `rec {inherit x;}' is equivalent
  to `let {fresh = x; body = rec {x = fresh;};}', *not*
  `rec {x = x}'.

1 files changed, 6 insertions, 4 deletions

diff --git a/src/libexpr/nixexpr.cc b/src/libexpr/nixexpr.cc
index 7de3e823c4f4..b0f506e65d6f 100644
--- a/src/libexpr/nixexpr.cc
+++ b/src/libexpr/nixexpr.cc
@@ -181,16 +181,18 @@ Expr substitute(const ATermMap & subs, Expr e)
     }
 
     /* Idem for a mutually recursive attribute set. */
-    ATermList bindings;
-    if (atMatch(m, e) >> "Rec" >> bindings) {
+    ATermList rbnds, nrbnds;
+    if (atMatch(m, e) >> "Rec" >> rbnds >> nrbnds) {
         ATermMap subs2(subs);
-        for (ATermIterator i(bindings); i; ++i) {
+        for (ATermIterator i(rbnds); i; ++i) {
             Expr e;
             if (!(atMatch(m, *i) >> "Bind" >> s >> e))
                 abort(); /* can't happen */
             subs2.remove(s);
         }
-        return ATmake("Rec(<term>)", substitute(subs2, (ATerm) bindings));
+        return ATmake("Rec(<term>, <term>)",
+            substitute(subs2, (ATerm) rbnds),
+            substitute(subs, (ATerm) nrbnds));
     }
 
     if (ATgetType(e) == AT_APPL) {