5 files changed, 23 insertions, 14 deletions

diff --git a/src/libexpr/eval-inline.hh b/src/libexpr/eval-inline.hh
index c34e24d3da39..c275f7ba83e8 100644
--- a/src/libexpr/eval-inline.hh
+++ b/src/libexpr/eval-inline.hh
@@ -55,6 +55,14 @@ inline void EvalState::forceAttrs(Value & v)
 }
 
 
+inline void EvalState::forceAttrs(Value & v, const Pos & pos)
+{
+    forceValue(v);
+    if (v.type != tAttrs)
+        throwTypeError("value is %1% while a set was expected, at %2%", v, pos);
+}
+
+
 inline void EvalState::forceList(Value & v)
 {
     forceValue(v);
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index b74170ecb158..5c88a34a92ca 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -850,7 +850,7 @@ void EvalState::callFunction(Value & fun, Value & arg, Value & v, const Pos & po
         env2.values[displ++] = &arg;
 
     else {
-        forceAttrs(arg);
+        forceAttrs(arg, pos);
 
         if (!lambda.arg.empty())
             env2.values[displ++] = &arg;
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index decca9e40674..248805004c6b 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -161,6 +161,7 @@ public:
     NixInt forceInt(Value & v, const Pos & pos);
     bool forceBool(Value & v);
     inline void forceAttrs(Value & v);
+    inline void forceAttrs(Value & v, const Pos & pos);
     inline void forceList(Value & v);
     inline void forceList(Value & v, const Pos & pos);
     void forceFunction(Value & v, const Pos & pos); // either lambda or primop
diff --git a/src/libexpr/get-drvs.cc b/src/libexpr/get-drvs.cc
index 96298556d851..4e7690063a0b 100644
--- a/src/libexpr/get-drvs.cc
+++ b/src/libexpr/get-drvs.cc
@@ -75,7 +75,7 @@ Bindings * DrvInfo::getMeta()
     if (!attrs) return 0;
     Bindings::iterator a = attrs->find(state->sMeta);
     if (a == attrs->end()) return 0;
-    state->forceAttrs(*a->value);
+    state->forceAttrs(*a->value, *a->pos);
     meta = a->value->attrs;
     return meta;
 }
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 7028ddc907b9..2aa45525e6d5 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -86,7 +86,7 @@ static void prim_import(EvalState & state, const Pos & pos, Value * * args, Valu
         state.evalFile(state.findFile("nix/imported-drv-to-derivation.nix"), fun);
         state.forceFunction(fun, pos);
         mkApp(v, fun, w);
-        state.forceAttrs(v);
+        state.forceAttrs(v, pos);
     } else {
         state.evalFile(path, v);
     }
@@ -188,7 +188,7 @@ static void prim_genericClosure(EvalState & state, const Pos & pos, Value * * ar
 {
     startNest(nest, lvlDebug, "finding dependencies");
 
-    state.forceAttrs(*args[0]);
+    state.forceAttrs(*args[0], pos);
 
     /* Get the start set. */
     Bindings::iterator startSet =
@@ -219,7 +219,7 @@ static void prim_genericClosure(EvalState & state, const Pos & pos, Value * * ar
         Value * e = *(workSet.begin());
         workSet.pop_front();
 
-        state.forceAttrs(*e);
+        state.forceAttrs(*e, pos);
 
         Bindings::iterator key =
             e->attrs->find(state.symbols.create("key"));
@@ -334,7 +334,7 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
 {
     startNest(nest, lvlVomit, "evaluating derivation");
 
-    state.forceAttrs(*args[0]);
+    state.forceAttrs(*args[0], pos);
 
     /* Figure out the name first (for stack backtraces). */
     Bindings::iterator attr = args[0]->attrs->find(state.sName);
@@ -758,7 +758,7 @@ static void prim_filterSource(EvalState & state, const Pos & pos, Value * * args
    strings. */
 static void prim_attrNames(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    state.forceAttrs(*args[0]);
+    state.forceAttrs(*args[0], pos);
 
     state.mkList(v, args[0]->attrs->size());
 
@@ -776,7 +776,7 @@ static void prim_attrNames(EvalState & state, const Pos & pos, Value * * args, V
 void prim_getAttr(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     string attr = state.forceStringNoCtx(*args[0]);
-    state.forceAttrs(*args[1]);
+    state.forceAttrs(*args[1], pos);
     // !!! Should we create a symbol here or just do a lookup?
     Bindings::iterator i = args[1]->attrs->find(state.symbols.create(attr));
     if (i == args[1]->attrs->end())
@@ -792,7 +792,7 @@ void prim_getAttr(EvalState & state, const Pos & pos, Value * * args, Value & v)
 void prim_unsafeGetAttrPos(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     string attr = state.forceStringNoCtx(*args[0]);
-    state.forceAttrs(*args[1]);
+    state.forceAttrs(*args[1], pos);
     Bindings::iterator i = args[1]->attrs->find(state.symbols.create(attr));
     if (i == args[1]->attrs->end())
         mkNull(v);
@@ -805,7 +805,7 @@ void prim_unsafeGetAttrPos(EvalState & state, const Pos & pos, Value * * args, V
 static void prim_hasAttr(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     string attr = state.forceStringNoCtx(*args[0]);
-    state.forceAttrs(*args[1]);
+    state.forceAttrs(*args[1], pos);
     mkBool(v, args[1]->attrs->find(state.symbols.create(attr)) != args[1]->attrs->end());
 }
 
@@ -820,7 +820,7 @@ static void prim_isAttrs(EvalState & state, const Pos & pos, Value * * args, Val
 
 static void prim_removeAttrs(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    state.forceAttrs(*args[0]);
+    state.forceAttrs(*args[0], pos);
     state.forceList(*args[1], pos);
 
     /* Get the attribute names to be removed. */
@@ -856,7 +856,7 @@ static void prim_listToAttrs(EvalState & state, const Pos & pos, Value * * args,
 
     for (unsigned int i = 0; i < args[0]->list.length; ++i) {
         Value & v2(*args[0]->list.elems[i]);
-        state.forceAttrs(v2);
+        state.forceAttrs(v2, pos);
 
         Bindings::iterator j = v2.attrs->find(state.sName);
         if (j == v2.attrs->end())
@@ -883,8 +883,8 @@ static void prim_listToAttrs(EvalState & state, const Pos & pos, Value * * args,
    member of as1. */
 static void prim_intersectAttrs(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    state.forceAttrs(*args[0]);
-    state.forceAttrs(*args[1]);
+    state.forceAttrs(*args[0], pos);
+    state.forceAttrs(*args[1], pos);
 
     state.mkAttrs(v, std::min(args[0]->attrs->size(), args[1]->attrs->size()));