nix: support legacy nix using 'flake-compat'

default.nix

@@ -0,0 +1,13 @@
+(import
+  (
+    let
+      lock = builtins.fromJSON (builtins.readFile ./flake.lock);
+    in
+    fetchTarball {
+      url = "https://github.com/edolstra/flake-compat/archive/${lock.nodes.flake-compat.locked.rev}.tar.gz";
+      sha256 = lock.nodes.flake-compat.locked.narHash;
+    }
+  )
+  {
+    src = ./.;
+  }).defaultNix

flake.lock

@@ -1,5 +1,21 @@
 {
   "nodes": {
+    "flake-compat": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1606424373,
+        "narHash": "sha256-oq8d4//CJOrVj+EcOaSXvMebvuTkmBJuT5tzlfewUnQ=",
+        "owner": "edolstra",
+        "repo": "flake-compat",
+        "rev": "99f1c2157fba4bfe6211a321fd0ee43199025dbf",
+        "type": "github"
+      },
+      "original": {
+        "owner": "edolstra",
+        "repo": "flake-compat",
+        "type": "github"
+      }
+    },
     "flake-utils": {
       "locked": {
         "lastModified": 1614513358,
@@ -82,6 +98,7 @@
     },
     "root": {
       "inputs": {
+        "flake-compat": "flake-compat",
         "flake-utils": "flake-utils",
         "mozillapkgs": "mozillapkgs",
         "naersk": "naersk",

flake.nix

@@ -7,6 +7,10 @@
     };
     nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
     flake-utils.url = "github:numtide/flake-utils";
+    flake-compat = {
+      url = "github:edolstra/flake-compat";
+      flake = false;
+    };
   };
 
   outputs = { self, naersk, mozillapkgs, nixpkgs, flake-utils, ... }:

shell.nix

@@ -0,0 +1,13 @@
+(import
+  (
+    let
+      lock = builtins.fromJSON (builtins.readFile ./flake.lock);
+    in
+    fetchTarball {
+      url = "https://github.com/edolstra/flake-compat/archive/${lock.nodes.flake-compat.locked.rev}.tar.gz";
+      sha256 = lock.nodes.flake-compat.locked.narHash;
+    }
+  )
+  {
+    src = ./.;
+  }).shellNix