nix edit: Support non-derivation attributes

E.g.

  $ nix edit .#nixosConfigurations.bla

now works.

2 files changed, 2 insertions, 1 deletions

diff --git a/src/libexpr/attr-path.cc b/src/libexpr/attr-path.cc
index 1e22f5708..4545bfd72 100644
--- a/src/libexpr/attr-path.cc
+++ b/src/libexpr/attr-path.cc
@@ -103,7 +103,7 @@ Pos findDerivationFilename(EvalState & state, Value & v, std::string what)
         auto dummyArgs = state.allocBindings(0);
         v2 = findAlongAttrPath(state, "meta.position", *dummyArgs, v).first;
     } catch (Error &) {
-        throw Error("package '%s' has no source location information", what);
+        throw NoPositionInfo("package '%s' has no source location information", what);
     }
 
     // FIXME: is it possible to extract the Pos object instead of doing this
diff --git a/src/libexpr/attr-path.hh b/src/libexpr/attr-path.hh
index 3e78e2899..fce160da7 100644
--- a/src/libexpr/attr-path.hh
+++ b/src/libexpr/attr-path.hh
@@ -8,6 +8,7 @@
 namespace nix {
 
 MakeError(AttrPathNotFound, Error);
+MakeError(NoPositionInfo, Error);
 
 std::pair<Value *, Pos> findAlongAttrPath(EvalState & state, const string & attrPath,
     Bindings & autoArgs, Value & vIn);