npins: enhance import-from-flake capabilities

We still chose this implementation because `getFlake' is "broken".
c.f. https://github.com/andir/npins/issues/159#issuecomment-3201185411

Also this avoids the double fetch problem.
c.f. https://github.com/andir/npins/issues/159#issuecomment-3148532945

npins/default.nix

@@ -64,7 +64,17 @@ let
         then mkTarballSource spec
         else builtins.throw "Unknown source type ${spec.type}";
     in
-      spec // {outPath = mayOverride name path;};
+      spec
+      // rec {
+        outPath = mayOverride name path;
+
+        # Waiting for discussion upstream
+        # https://github.com/andir/npins/issues/159
+        asFlake =
+          if sources ? flake-compat
+          then (import sources.flake-compat {src = outPath;}).outputs
+          else throw ".asFlake needs flake-compat as a source";
+      };
 
   mkGitSource = {
     repository,
@@ -146,7 +156,10 @@ let
       url = locked_url;
       sha256 = hash;
     };
+
+  sources =
+    if version == 5
+    then builtins.mapAttrs mkSource data.pins
+    else throw "Unsupported format version ${toString version} in sources.json. Try running `npins upgrade`";
 in
-  if version == 5
-  then builtins.mapAttrs mkSource data.pins
-  else throw "Unsupported format version ${toString version} in sources.json. Try running `npins upgrade`"
+  sources

npins/sources.json

@@ -75,6 +75,23 @@
       "url": null,
       "hash": "07d2mzjnggbxlpqarcj65xdndkqxcab38lkbbqh65cyfqzqahdg0"
     },
+    "flake-compat": {
+      "type": "GitRelease",
+      "repository": {
+        "type": "GitHub",
+        "owner": "edolstra",
+        "repo": "flake-compat"
+      },
+      "pre_releases": false,
+      "version_upper_bound": null,
+      "release_prefix": null,
+      "submodules": false,
+      "version": "v1.1.0",
+      "revision": "ff81ac966bb2cae68946d5ed5fc4994f96d0ffec",
+      "url": "https://api.github.com/repos/edolstra/flake-compat/tarball/v1.1.0",
+      "hash": "19d2z6xsvpxm184m41qrpi1bplilwipgnzv9jy17fgw421785q1m",
+      "frozen": true
+    },
     "home-manager": {
       "type": "Git",
       "repository": {