Merge pull request #3238 from puckipedia/attrset-overrides-dynamic

Ensure enough space in attrset bindings

src/libexpr/eval.cc

@@ -875,7 +875,7 @@ void ExprAttrs::eval(EvalState & state, Env & env, Value & v)
         if (hasOverrides) {
             Value * vOverrides = (*v.attrs)[overrides->second.displ].value;
             state.forceAttrs(*vOverrides);
-            Bindings * newBnds = state.allocBindings(v.attrs->size() + vOverrides->attrs->size());
+            Bindings * newBnds = state.allocBindings(v.attrs->capacity() + vOverrides->attrs->size());
             for (auto & i : *v.attrs)
                 newBnds->push_back(i);
             for (auto & i : *vOverrides->attrs) {

tests/lang/eval-okay-attrs6.exp

@@ -0,0 +1 @@
+{ __overrides = { bar = "qux"; }; bar = "qux"; foo = "bar"; }

tests/lang/eval-okay-attrs6.nix

@@ -0,0 +1,4 @@
+rec {
+  "${"foo"}" = "bar";
+   __overrides = { bar = "qux"; };
+}