nix-instantiate: Add a --no-readonly-mode flag

This allows running nix-instantiate --eval-only without performing the
evaluation in readonly mode, letting features like import from
derivation and automatic substitution of builtins.storePath paths work.

Signed-off-by: Shea Levy <shea@shealevy.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/src/nix-instantiate/nix-instantiate.cc b/src/nix-instantiate/nix-instantiate.cc
index b7f944062c..1f4d1ffab8 100644
--- a/src/nix-instantiate/nix-instantiate.cc
+++ b/src/nix-instantiate/nix-instantiate.cc
@@ -107,6 +107,9 @@ void run(Strings args)
             settings.readOnlyMode = true;
             evalOnly = true;
         }
+        else if (arg == "--no-readonly-mode") {
+            settings.readOnlyMode = false;
+        }
         else if (arg == "--parse-only") {
             settings.readOnlyMode = true;
             parseOnly = evalOnly = true;