1 files changed, 36 insertions, 12 deletions
diff --git a/src/libexpr/get-drvs.cc b/src/libexpr/get-drvs.cc
index 723d3a6bc744..eaab867a6f82 100644
--- a/src/libexpr/get-drvs.cc
+++ b/src/libexpr/get-drvs.cc
@@ -2,7 +2,11 @@
 #include "nixexpr-ast.hh"
 
 
-bool getDerivation(EvalState & state, Expr e, DrvInfo & drv)
+typedef set<Expr> Exprs;
+
+
+static bool getDerivation(EvalState & state, Expr e,
+    DrvInfos & drvs, Exprs & doneExprs)
 {
     ATermList es;
     e = evalExpr(state, e);
@@ -14,6 +18,13 @@ bool getDerivation(EvalState & state, Expr e, DrvInfo & drv)
     Expr a = attrs.get("type");
     if (!a || evalString(state, a) != "derivation") return false;
 
+    /* Remove spurious duplicates (e.g., an attribute set like `rec {
+       x = derivation {...}; y = x;}'. */
+    if (doneExprs.find(e) != doneExprs.end()) return true;
+    doneExprs.insert(e);
+
+    DrvInfo drv;
+    
     a = attrs.get("name");
     if (!a) throw badTerm("derivation name missing", e);
     drv.name = evalString(state, a);
@@ -26,11 +37,23 @@ bool getDerivation(EvalState & state, Expr e, DrvInfo & drv)
 
     drv.attrs = attrs;
 
+    drvs.push_back(drv);
     return true;
 }
 
 
-void getDerivations(EvalState & state, Expr e, DrvInfos & drvs)
+bool getDerivation(EvalState & state, Expr e, DrvInfo & drv)
+{
+    Exprs doneExprs;
+    DrvInfos drvs;
+    bool result = getDerivation(state, e, drvs, doneExprs);
+    if (result) drv = drvs.front();
+    return result;
+}
+
+
+static void getDerivations(EvalState & state, Expr e,
+    DrvInfos & drvs, Exprs & doneExprs)
 {
     ATermList es;
     DrvInfo drv;
@@ -47,11 +70,7 @@ void getDerivations(EvalState & state, Expr e, DrvInfos & drvs)
         queryAllAttrs(e, drvMap);
         for (ATermIterator i(drvMap.keys()); i; ++i) {
             debug(format("evaluating attribute `%1%'") % aterm2String(*i));
-            if (getDerivation(state, drvMap.get(*i), drv))
-                drvs.push_back(drv);
-            else
-                ;
-                //                parseDerivations(state, drvMap.get(*i), drvs);
+            getDerivation(state, drvMap.get(*i), drvs, doneExprs);
         }
         return;
     }
@@ -59,10 +78,8 @@ void getDerivations(EvalState & state, Expr e, DrvInfos & drvs)
     if (matchList(e, es)) {
         for (ATermIterator i(es); i; ++i) {
             debug(format("evaluating list element"));
-            if (getDerivation(state, *i, drv))
-                drvs.push_back(drv);
-            else
-                getDerivations(state, *i, drvs);
+            if (!getDerivation(state, *i, drvs, doneExprs))
+                getDerivations(state, *i, drvs, doneExprs);
         }
         return;
     }
@@ -78,9 +95,16 @@ void getDerivations(EvalState & state, Expr e, DrvInfos & drvs)
             else if (!matchDefFormal(*i, name, def))
                 abort(); /* can't happen */
         }
-        getDerivations(state, makeCall(e, makeAttrs(ATermMap())), drvs);
+        getDerivations(state, makeCall(e, makeAttrs(ATermMap())), drvs, doneExprs);
         return;
     }
 
     throw Error("expression does not evaluate to a derivation (or a set or list of those)");
 }
+
+
+void getDerivations(EvalState & state, Expr e, DrvInfos & drvs)
+{
+    Exprs doneExprs;
+    getDerivations(state, e, drvs, doneExprs);
+}