add fallback functionality using latest.json

Closes #12

latest.json

@@ -1 +1,26 @@
-{}
+{
+  "24.05": {
+    "name": "nixos-24.05pre552472.1b99d72c8b74",
+    "url": "/nixos/unstable-small/nixos-24.05pre552472.1b99d72c8b74/nixexprs.tar.xz",
+    "nixexprs_hash": "c05c48bf6c1a02e555ffb8a5703a423665b49e421fdbec57e685addae824e800",
+    "programs_sqlite_hash": "84721632459c8db1eb38064ccda6f89221543500d26ace5c3f78b582dd8970f5"
+  },
+  "22.11": {
+    "name": "nixos-22.11.4773.ea4c80b39be4",
+    "url": "/nixos/22.11/nixos-22.11.4773.ea4c80b39be4/nixexprs.tar.xz",
+    "nixexprs_hash": "c4828378407ebd3255ff9d51d31e942c4a9acd088540c6b83dbd8dc7d24283dd",
+    "programs_sqlite_hash": "fbb9c05caae92e51e1c4d14018656aeddb2d6222009f6d483dd38ddcbc1f2076"
+  },
+  "23.05": {
+    "name": "nixos-23.05.4970.cbd3f3722ac4",
+    "url": "/nixos/23.05-small/nixos-23.05.4970.cbd3f3722ac4/nixexprs.tar.xz",
+    "nixexprs_hash": "75e0ba7717bfab4d6abab3318c4ca8c4c646001f87a2ef6c8e3778a59d96848f",
+    "programs_sqlite_hash": "4b44b3b01dc11695193a24968d7dc035dba1592ba239c889dc9ad39f2bb0365a"
+  },
+  "23.11": {
+    "name": "nixos-23.11beta470.c9e054502e72",
+    "url": "/nixos/23.11-small/nixos-23.11beta470.c9e054502e72/nixexprs.tar.xz",
+    "nixexprs_hash": "866523a1b1ab37ba514320eea08350e92e4434a3f5236ca51b79b7aadc3a3941",
+    "programs_sqlite_hash": "b6237513b04693c2133675c10feef17a09603f5faae3e0d66047427150b219ee"
+  }
+}

programs-sqlite.nix

@@ -1,6 +1,6 @@
 { lib, fetchurl, pkgs, rev }:
 let
-  meta = (lib.importJSON ./sources.json)."${rev}";
+  meta = (lib.importJSON ./sources.json)."${rev}" or (lib.importJSON ./latest.json).${lib.trivial.release};
 in
 pkgs.stdenvNoCC.mkDerivation {
   pname = "programs-sqlite";

sources.json

@@ -196,5 +196,11 @@
     "url": "/nixos/22.11-small/nixos-22.11.1059.ba86945ee00/nixexprs.tar.xz",
     "nixexprs_hash": "6bda28ac8d6cc8cf71d444503d3b974c03b5bda1e58a850490188035975e044b",
     "programs_sqlite_hash": "d91745ce3aa0512d86c4fdc2dbc14e81227a5fa60c44a021068e77b69653aae5"
+  },
+  "53dad94e874c9586e71decf82d972dfb640ef044": {
+    "name": "nixos-23.05pre470275.53dad94e874",
+    "url": "/nixos/unstable/nixos-23.05pre470275.53dad94e874/nixexprs.tar.xz",
+    "nixexprs_hash": "9380965016f278231b12fcc323928ebfb389ce95d816c3e986a597d8883b9aa9",
+    "programs_sqlite_hash": "9e349c2bde7eb9f751785ed78dfb7723fc54b538ebf4d26286e62a533f577656"
   }
-}
+}

test.nix

@@ -20,7 +20,15 @@ let
   programs-sqlite-db = flake.packages.${system}.programs-sqlite;
   rev = flake.inputs.nixpkgs.rev;
 
-in pkgs.nixosTest {
+  programs-sqlite-db-for-fallback-test = pkgs.callPackage ./programs-sqlite.nix {
+    rev = "0000000000000000000000000000000000000000";
+  };
+
+in
+  # for the fallback test, we need a rev not in sources.json
+  assert (false == (pkgs.lib.importJSON ./sources.json) ? revForFallbackTest);
+
+  pkgs.nixosTest {
   name = "packages-sqlite-test";
   nodes = {
     directConfig = { config, pkgs, ... }: {
@@ -43,15 +51,26 @@ in pkgs.nixosTest {
         };
       };
     };
+
+    directConfigFallback = { config, pkgs, ... }: {
+      imports = [ sharedModule ];
+      users = {
+        mutableUsers = false;
+        users = {
+          root.password = "";
+        };
+      };
+      programs.command-not-found.dbPath = programs-sqlite-db-for-fallback-test;
+    };
   };
 
   testScript = ''
     import json;
 
-    with open("${flake.outPath}/sources.json") as f:
-      hashes = json.load(f)
+    def check(machine, expected_rev, db):
+        with open(f"${flake.outPath}/{db}", "r") as f:
+            hashes = json.load(f)
 
-    def check(machine):
         machine.start()
         machine.wait_for_unit("multi-user.target")
 
@@ -67,11 +86,12 @@ in pkgs.nixosTest {
           cnfsrc = machine.succeed("readlink $(which command-not-found)").strip()
           cnfdb = machine.succeed("grep -m 1 dbPath '" + cnfsrc + "' | cut -d '" + '"' + "' -f 2").strip()
           cnfdbhash = machine.succeed("sha256sum " + cnfdb + " | cut -d ' ' -f 1").strip()
-          assert hashes.get("${rev}").get("programs_sqlite_hash") == cnfdbhash, "incorrect programs.sqlite is used"
+          assert hashes.get(expected_rev).get("programs_sqlite_hash") == cnfdbhash, "incorrect programs.sqlite is used"
 
         machine.shutdown()
 
-    check(directConfig)
-    check(moduleConfig)
+    check(directConfig, "${rev}", "sources.json")
+    check(moduleConfig, "${rev}", "sources.json")
+    check(directConfigFallback, "${pkgs.lib.trivial.release}", "latest.json")
   '';
 }