Switch lib to an overlay (#207)

* switch lib to an overlay

* update README.md

* cleanup README

* format

README.md

@@ -77,26 +77,32 @@ latest development environment you should run:
 nix develop github:informalsystems/cosmos.nix#cosmos-shell --refresh
 ```
 
-## Library
+## Overlays
 
-There are a few nix utilities provided as a nix library. You can use these in your own flake like so:
+There are a few nix utilities provided as a nix library. There is also an
+overlay for all the cosmos packages exported by this flake, so you can fold
+them into your nixpkgs package set.
 
 ```nix
 {
-
   inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs";
     cosmos-nix.url = "github:informalsystems/cosmos.nix";
   };
-  outputs = { cosmos-nix }: {
-        cosmosLib = cosmos-nix.lib "x86_64-linux";
+  outputs = { cosmos-nix, nixpkgs }: {
+    let pkgs = import nixpkgs { 
+            system = "x86_64-linux"; # Or whatever system you are on
+            overlays = [
+                cosmos-nix.overlays.cosmosNixLib # Provides just the nix utility lib
+                cosmos-nix.overlays.cosmosNix    # Provides all the cosmos packages provided by cosmos.nix
+                cosmos-nix.overlay               # The default overlay gives you everything in the previous two combined
+            ];
+        }
     in ...
   };
 }
 ```
 
-> NOTE: you need to pass `cosmosLib` a "system" argument because it uses system specific pkgs internally. It is 
-> slightly unfortunate that it isn't pure nix (without derivations), and needs to be `system` aware.
-
 ## Development
 
 #### Formatting

modules/lib.nix

@@ -1,10 +1,6 @@
 # This module provides the lib argument to all other modules as 'cosmosLib'.
 # This provides utility functions for packaging cosmos sdk and cosmwasm packages
-{
-  withSystem,
-  inputs,
-  ...
-}: let
+{inputs, ...}: let
   lib = import ../lib;
   std = inputs.nix-std;
 in {
@@ -19,14 +15,4 @@ in {
       inherit (self'.packages) cosmwasm-check;
     };
   };
-  flake.lib = system:
-    withSystem system ({
-      pkgs,
-      self',
-      ...
-    }:
-      lib std {
-        inherit pkgs;
-        inherit (self'.packages) cosmwasm-check;
-      });
 }

modules/overlay.nix

@@ -1,6 +1,35 @@
 # Provides an overlay for other flakes to consume and get all the cosmos packages in their pkgs
 # https://flake.parts/overlays.html?highlight=overlay#defining-an-overlay
-{withSystem, ...}: {
-  flake.overlays.default = final: prev:
+{
+  withSystem,
+  inputs,
+  self,
+  ...
+}: {
+  # Overlay with everything
+  flake.overlays.default = with self.overlays;
+    inputs.nixpkgs.lib.fixedPoints.composeExtensions
+    cosmosNix
+    cosmosNixLib;
+
+  # Overlay with all the cosmos.nix cosmos packages
+  flake.overlays.cosmosNixPackages = final: prev:
     withSystem prev.stdenv.hostPlatform.system ({self', ...}: self'.packages);
+
+  # Overlay with the cosmos.nix nix lib (comes with a bunch of utility functions for packaging cosmos packages)
+  flake.overlays.cosmosNixLib = final: prev:
+    withSystem prev.stdenv.hostPlatform.system ({
+      self',
+      pkgs,
+      ...
+    }: {
+      cosmosLib = let
+        lib = import ../lib;
+        std = inputs.nix-std;
+      in
+        lib std {
+          inherit pkgs;
+          inherit (self'.packages) cosmwasm-check;
+        };
+    });
 }