Add 'nix upgrade-nix' command

This command upgrades Nix to the latest stable version by installing a
store path obtained from

  https://github.com/NixOS/nixpkgs/raw/master/nixos/modules/installer/tools/nix-fallback-paths.nix

which is the same store path that the installer at
https://nixos.org/nix/install.sh uses.

The upgrade fails if Nix is not installed in a profile (e.g. on NixOS,
or when installed outside of the Nix store).

1 files changed, 4 insertions, 1 deletions

diff --git a/src/nix/main.cc b/src/nix/main.cc
index 06bb8a1c3043..8f6bbe8f51ae 100644
--- a/src/nix/main.cc
+++ b/src/nix/main.cc
@@ -16,6 +16,8 @@ void chrootHelper(int argc, char * * argv);
 
 namespace nix {
 
+std::string programPath;
+
 struct NixArgs : virtual MultiCommand, virtual MixCommonArgs
 {
     NixArgs() : MultiCommand(*RegisterCommand::commands), MixCommonArgs("nix")
@@ -78,7 +80,8 @@ void mainWrapped(int argc, char * * argv)
     initNix();
     initGC();
 
-    string programName = baseNameOf(argv[0]);
+    programPath = argv[0];
+    string programName = baseNameOf(programPath);
 
     {
         auto legacy = (*RegisterLegacyCommand::commands)[programName];