cache: init (#7)

### 🐟 What?

- Adds a default package, that includes a script that builds and deploys
all other packages;
- Adds the cache URL to README.
- Adds the cache to the flake's `nixConf`.

### 🎣 Why?

- My laptop can't build the stuff my desktop builds.

### 🍥 Extra

- Needs bot to feed it;
- Usage:
  1. Set `CACHIX_SIGNING_KEY`;
  2. Run `nix shell -c build-chaotic-nyx`.
- We'll have both ours and cachix urls as trusted keys, I plan to keep
some stuff in cachix even when we have our cache running

README.md

@@ -70,4 +70,16 @@ nix run github:chaotic-aur/nyx#input-leap-git
 
 ## Cache
 
-Soon...
+```nix
+{
+  nix.settings = {
+    extra-substituters = [
+      "https://nyx.chaotic.cx"
+    ];
+    extra-trusted-public-keys = [
+      "nyx.chaotic.cx-1:HfnXSw4pj95iI/n17rIDy40agHj12WfF+Gqk6SonIT8="
+      "chaotic-nyx.cachix.org-1:HfnXSw4pj95iI/n17rIDy40agHj12WfF+Gqk6SonIT8="
+    ];
+  };
+}
+```

flake.nix

@@ -38,7 +38,7 @@
     };
   };
 
-  outputs = { nixpkgs, ... }@inputs: rec {
+  outputs = { nixpkgs, self, ... }@inputs: rec {
     # I would prefer if we had something stricter, with attribute alphabetical
     # sorting, and optimized for git's diffing. But this is the closer we have.
     formatter.x86_64-linux = nixpkgs.legacyPackages.x86_64-linux.nixpkgs-fmt;
@@ -54,8 +54,9 @@
           let
             overlayFinal = prev // final // { callPackage = prev.newScope final; };
             final = overlays.default overlayFinal prev;
+            builder = overlayFinal.callPackage ./shared/builder.nix { all-packages = final; flakeSelf = self; };
           in
-          final;
+          final // { default = builder; };
       in
       {
         x86_64-linux = applyOverlay nixpkgs.legacyPackages.x86_64-linux;
@@ -64,4 +65,12 @@
 
     hydraJobs.default = packages;
   };
+
+  nixConfig = {
+    extra-substituters = [ "https://nyx.chaotic.cx" ];
+    extra-trusted-public-keys = [
+      "nyx.chaotic.cx-1:HfnXSw4pj95iI/n17rIDy40agHj12WfF+Gqk6SonIT8="
+      "chaotic-nyx.cachix.org-1:HfnXSw4pj95iI/n17rIDy40agHj12WfF+Gqk6SonIT8="
+    ];
+  };
 }

shared/builder.nix

@@ -0,0 +1,54 @@
+{ all-packages
+, cachix
+, jq
+, lib
+, nix
+, flakeSelf
+, writeShellScriptBin
+}:
+let
+  evalCommand = where: drvOutputs:
+    let
+      derivation = "${flakeSelf}#${where}";
+      outputs = map (guide derivation) drvOutputs;
+    in
+    ''
+      echo "Building ${derivation}"
+      ${nix}/bin/nix build --json \
+        ${lib.strings.concatStringsSep " \\\n  " outputs} |\
+        ${jq}/bin/jq -r '.[].outputs[]' |\
+        ${cachix}/bin/cachix push chaotic-nyx --compression-method zstd
+    '';
+
+  guide = namespace: n:
+    if namespace != "" then
+      "${namespace}.${n}"
+    else
+      n
+  ;
+  packagesEval = namespace: n: v:
+    (if (builtins.tryEval v).success then
+      (if lib.attrsets.isDerivation v then
+        (if (v.meta.broken or true) then
+          "# broken: ${n}"
+        else if (v.meta.unfree or true) then
+          "# unfree: ${n}"
+        else
+          evalCommand (guide namespace n) v.outputs
+        )
+      else if builtins.isAttrs v then
+        lib.strings.concatStringsSep "\n"
+          (lib.attrsets.mapAttrsToList (packagesEval (guide namespace n)) v)
+      else
+        "# unrelated: ${n}"
+      )
+    else
+      "# not evaluating: ${n}"
+    )
+  ;
+in
+writeShellScriptBin "build-chaotic-nyx" ''
+  cd "$(mktemp -d)"
+
+  ${packagesEval "" "" all-packages}
+''