README.md

@@ -18,7 +18,8 @@ Afterwards, create a `default.nix` file containing the following:
   (
     let lock = builtins.fromJSON (builtins.readFile ./flake.lock); in
     fetchTarball {
-      url = "https://github.com/edolstra/flake-compat/archive/${lock.nodes.flake-compat.locked.rev}.tar.gz";
+      url = with lock.nodes.flake-compat.locked;
+        "https://github.com/${owner}/${repo}/archive/${rev}.tar.gz";
       sha256 = lock.nodes.flake-compat.locked.narHash;
     }
   )

default.nix

@@ -8,7 +8,11 @@
 { src, system ? builtins.currentSystem or "unknown-system" }:
 
 let
-
+  id = x: x;
+  overrideWrap' = fn: set: set // { overrideInputs = ov: fn (makeFlakeCompat ov); };
+  overrideWrap = overrideWrap' id;
+  makeFlakeCompat = impureOverrides:
+  let
     lockFilePath = src + "/flake.lock";
 
     lockFile = builtins.fromJSON (builtins.readFile lockFilePath);
@@ -104,6 +108,16 @@ let
       { lastModified = 0; lastModifiedDate = formatSecondsSinceEpoch 0; }
         // (if src ? outPath then src else tryFetchGit src);
 
+
+    nameValuePair = name: value:
+      { inherit name value; };
+    mapAttrs' =
+      # A function, given an attribute's name and value, returns a new `nameValuePair`.
+      f:
+      # Attribute set to map over.
+      set:
+      builtins.listToAttrs (map (attr: f attr set.${attr}) (builtins.attrNames set));
+
     # Format number of seconds in the Unix epoch as %Y%m%d%H%M%S.
     formatSecondsSinceEpoch = t:
       let
@@ -129,6 +143,11 @@ let
         pad = s: if builtins.stringLength s < 2 then "0" + s else s;
       in "${toString y'}${pad (toString m)}${pad (toString d)}${pad (toString hours)}${pad (toString minutes)}${pad (toString seconds)}";
 
+    rootOverrides =
+      mapAttrs'
+        (input: lockKey: nameValuePair lockKey (impureOverrides.${input} or null))
+        lockFile.nodes.${lockFile.root}.inputs;
+
     allNodes =
       builtins.mapAttrs
         (key: node:
@@ -136,7 +155,14 @@ let
             sourceInfo =
               if key == lockFile.root
               then rootSrc
-            else fetchTree (node.info or {} // removeAttrs node.locked ["dir"]);
+              else
+                if rootOverrides.${key} != null then
+                  { type = "path";
+                    outPath = rootOverrides.${key};
+                    narHash = throw "narHash unimplemented for impureOverride";
+                  }
+                else
+                fetchTree (node.info or {} // removeAttrs node.locked ["dir"]);
 
             subdir = if key == lockFile.root then "" else node.locked.dir or "";
 
@@ -187,14 +213,16 @@ let
       else throw "lock file '${lockFilePath}' has unsupported version ${toString lockFile.version}";
 
   in
-  rec {
+    builtins.mapAttrs (key: attr: overrideWrap' (res: res.${key}) attr)
+      (rec {
         defaultNix =
           (builtins.removeAttrs result ["__functor"])
           // (if result ? defaultPackage.${system} then { default = result.defaultPackage.${system}; } else {})
           // (if result ? packages.${system}.default then { default = result.packages.${system}.default; } else {});
-
         shellNix =
           defaultNix
           // (if result ? devShell.${system} then { default = result.devShell.${system}; } else {})
           // (if result ? devShells.${system}.default then { default = result.devShells.${system}.default; } else {});
-  }
+      });
+
+in makeFlakeCompat {}