Fix `nix print-dev-env` & `nix develop` with drv paths

Fixes #8309

This regression was because both `CmdDevelop` and `CmdPrintDevEnv` were
switched to be `InstallableValueCommand` subclasses, but actually
neither should have been.

The `nixpkgsFlakeRef` method should indeed not be on the base
installable class, because "flake refs" and "nixpkgs" are not
installable-wide notions, but that doesn't mean these commands should
only accept installable values.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/libcmd/installable-flake.cc b/src/libcmd/installable-flake.cc
index f0d322e6d..37e59cfdf 100644
--- a/src/libcmd/installable-flake.cc
+++ b/src/libcmd/installable-flake.cc
@@ -234,7 +234,7 @@ FlakeRef InstallableFlake::nixpkgsFlakeRef() const
         }
     }
 
-    return InstallableValue::nixpkgsFlakeRef();
+    return defaultNixpkgsFlakeRef();
 }
 
 }