* When obtaining derivations from Nix expressions, ignore all

  expressions that cause an assertion failure (like `assert system ==
  "i686-linux"').  This allows all-packages.nix in Nixpkgs to be used
  on all platforms, even if some Nix expressions don't work on all
  platforms.

  Not sure if this is a good idea; it's a bit hacky.  In particular,
  due to laziness some derivations might appear in `nix-env -qa' but
  disappear in `nix-env -qas' or `nix-env -i'.

  Commit 5000!

1 files changed, 7 insertions, 1 deletions

diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 045e5f632ff6..eac13c3fd980 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -383,7 +383,13 @@ Expr evalExpr(EvalState & state, Expr e)
 
     /* Otherwise, evaluate and memoize. */
     state.normalForms.set(e, state.blackHole);
-    nf = evalExpr2(state, e);
+    try {
+        nf = evalExpr2(state, e);
+    } catch (Error & err) {
+        debug("removing black hole");
+        state.normalForms.remove(e);
+        throw;
+    }
     state.normalForms.set(e, nf);
     return nf;
 }