Add devenv-up into the shell environment

[judofyr]

This brings devenv-up as a package which is brought into the shell environment. devenv-up is now present in the $PATH and runs it immediately and devenv up execs.

The main motivation here is when using a Flake directly. Previously devenv up would run nix build on demand which is (1) fragile since it makes assumptions around what the flake is actually called and (2) doesn't register it as root.

By bringing the devenv-up into shell we solve both of these problems. Be aware that we're not able to bring it into the profile since this leads to a infinite recursion: The devenv-up script is designed to run "outside" of the devenv environment (since the process-compose.yaml file sets the environment variables for you).

This commit doesn't change behavior in the Rust implementation, but I believe we could now also tweak this to invoke devenv-up directly instead of adding it as a root.

[judofyr]

While pondering more about this, I think this would have been pretty neat if …

• processes.nix contains packages = [ config.procfileBin ]. This is what brings devenv-up into the environment.
• process-compose.yaml will not include the environment variables, but instead the assumption is that devenv-up is executed under the right environment.
• devenv exec makes it possible to run an arbitrary command under the environment. It's a no-op if you're already inside the environment.
• devenv shell is basically an alias to devenv exec $SHELL
• devenv up is basically an alias to devenv exec devenv-up

Not sure if this is actually possible to implement in a backwards compatible way, or if there are other problems here…

[judofyr]

The following diff (on top of this branch) works fine for my setup (where I call devenv-up under nix-direnv), but I'm not sure if this breaks other scenarios?

diff --git i/src/modules/process-managers/process-compose.nix w/src/modules/process-managers/process-compose.nix
index d8acb4a..13df529 100644
--- i/src/modules/process-managers/process-compose.nix
+++ w/src/modules/process-managers/process-compose.nix
@@ -53,9 +53,6 @@ in
         is_strict = true;
         port = lib.mkDefault 9999;
         tui = lib.mkDefault true;
-        environment = lib.mapAttrsToList
-          (name: value: "${name}=${toString value}")
-          config.env;
         processes = lib.mapAttrs
           (name: value: { command = "exec ${pkgs.writeShellScript name value.exec}"; } // value.process-compose)
           config.processes;
diff --git i/src/modules/processes.nix w/src/modules/processes.nix
index bbfe61b..d590ca6 100644
--- i/src/modules/processes.nix
+++ w/src/modules/processes.nix
@@ -153,6 +153,8 @@ in
       wait
     '';
 
+    packages = [ config.procfileBin ];
+
     ci = [ config.procfileScript ];
 
     infoSections."processes" = lib.mapAttrsToList (name: process: "${name}: exec ${pkgs.writeShellScript name process.exec}") config.processes;
diff --git i/src/modules/top-level.nix w/src/modules/top-level.nix
index a8ac7b2..9df3fdc 100644
--- i/src/modules/top-level.nix
+++ w/src/modules/top-level.nix
@@ -281,7 +281,7 @@ in
     shell = performAssertions (
       (pkgs.mkShell.override { stdenv = config.stdenv; }) ({
         name = "devenv-shell";
-        packages = config.packages ++ [config.procfileBin];
+        packages = config.packages;
         shellHook = ''
           ${lib.optionalString config.devenv.debug "set -x"}
           ${config.enterShell}