Support lorri

From what I currently understand, lorri is a tool (sponsored by Target) that
uses nix and direnv to build and switch between environments quickly and
easily.

When you run `lorri init` inside of a directory, lorri creates a shell.nix and
an .envrc file. The .envrc file calls `eval "$(lorri direnv)"` and the shell.nix
calls `<nixpkgs>.mkShell`, which creates a shell environment exposing
dependencies on $PATH and environment variables. lorri uses direnv to ensure
that $PATH and the environment variables are available depending on your CWD.

lorri becomes especially powerful because of Emacs's `direnv-mode`, which
ensures that Emacs buffers can access anything exposed by direnv as well.

I still need to learn more about how lorri works and how it will affect my
workflow, but I'm enjoying what I've seen thus far, and I'm optimistic about the
road ahead.

.envrc

@@ -1,7 +1 @@
-export BRIEFCASE=~/briefcase
+eval "$(lorri direnv)"
-export DEPOT=~/depot
-export NIXPKGS=$HOME/nixpkgs
-export DESKTOP=zeno.lon.corp.google.com
-export LAPTOP=seneca
-export CLOUDTOP=wpcarro.c.googlers.com
-NIX_PATH=nixpkgs=$NIXPKGS:depot=$DEPOT:briefcase=$BRIEFCASE

monzo_ynab/.envrc

@@ -1,5 +1,10 @@
 # source_up traversing up directories until it finds the nearest .envrc file,
 # which it uses to extend the environment in this .envrc.
+#
+# Since ../.envrc calls `eval "$(lorri direnv)"`, the buildInputs and variables
+# definitions inside of the attribute set passed to pkgs.mkShell become
+# available here as well.
 source_up
 export client_id="$(pass show finance/monzo/client-id)"
 export client_secret="$(pass show finance/monzo/client-secret)"
+eval "$(lorri direnv)"

monzo_ynab/shell.nix

@@ -0,0 +1,9 @@
+{ pkgs ? import <nixpkgs> {}, ... }:
+
+pkgs.mkShell {
+  buildInputs = [
+    pkgs.go
+    pkgs.goimports
+    pkgs.godef
+  ];
+}

shell.nix

@@ -0,0 +1,14 @@
+{ pkgs ? import <nixpkgs> {}, ... }:
+
+pkgs.mkShell rec {
+  buildInputs = [];
+  # TODO(wpcarro): How does pkgs.mkShell handle exported and non-exported
+  # variable definitions?
+  BRIEFCASE = builtins.toPath ~/briefcase;
+  DEPOT = builtins.toPath ~/depot;
+  NIXPKGS = builtins.toPath ~/nixpkgs;
+  NIX_PATH="nixpkgs=${NIXPKGS}:depot=${DEPOT}:briefcase=${BRIEFCASE}";
+  DESKTOP = "zeno.lon.corp.google.com";
+  LAPTOP = "seneca";
+  CLOUDTOP = "wpcarro.c.googlers.com";
+}