Make warning about chroot store location more accurate

While trying to use an alternate directory for my Nix installation, I
noticed that nix's output didn't reflect the updated state
directory. This patch corrects that and now prints the warning before
attempting to create the directory (if the directory creation fails,
it wouldn't have been obvious why nix was attempting to create the
directory in the first place).

With this patch, I now get the following warning:

    warning: '/home/deck/.var/app/org.nixos.nix/var/nix' does not
    exist, so Nix will use '/home/deck/.local/share/nix/root' as a
    chroot store

1 files changed, 2 insertions, 2 deletions

diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index 86b12257a..06a9758fc 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -1363,9 +1363,9 @@ std::shared_ptr<Store> openFromNonUri(const std::string & uri, const Store::Para
                 } catch (Error & e) {
                     return std::make_shared<LocalStore>(params);
                 }
-                warn("'/nix' does not exist, so Nix will use '%s' as a chroot store", chrootStore);
+                warn("'%s' does not exist, so Nix will use '%s' as a chroot store", stateDir, chrootStore);
             } else
-                debug("'/nix' does not exist, so Nix will use '%s' as a chroot store", chrootStore);
+                debug("'%s' does not exist, so Nix will use '%s' as a chroot store", stateDir, chrootStore);
             Store::Params params2;
             params2["root"] = chrootStore;
             return std::make_shared<LocalStore>(params2);