Add note

so that fetchurl outputs a real path instead of a source, and our
hashes match correctly between flake and non-flake.

also it looks like fetchTarball can support local files

README.md

@@ -2,25 +2,13 @@
 
 ## Usage
 
-> [!WARNING]
-> During the Lix private beta period during which Forgejo is private, this
-> requires configuring netrc in Lix for the tarball download to work.
->
-> Your netrc should look something like so:
-> ```
-> machine git.lix.systems login YOUR-USERNAME password SOME-PERSONAL-ACCESS-TOKEN-REPO-READ
-> ```
->
-> We are terribly sorry for the UX for this being very bad
-> ([issue](https://git.lix.systems/lix-project/lix/issues/254)).
-
 To use, add the following to your `flake.nix`:
 
-<!-- FIXME: this can use the standard non-api archive url when we are
-un-privated -->
-
 ```nix
-inputs.flake-compat.url = "https://git.lix.systems/api/v1/repos/lix-project/flake-compat/archive/main.tar.gz";
+inputs.flake-compat = {
+  url = "github:edolstra/flake-compat";
+  flake = false;
+};
 ```
 
 Afterwards, create a `default.nix` file containing the following:
@@ -30,7 +18,7 @@ Afterwards, create a `default.nix` file containing the following:
   (
     let lock = builtins.fromJSON (builtins.readFile ./flake.lock); in
     fetchTarball {
-      url = lock.nodes.flake-compat.locked.url;
+      url = "https://github.com/edolstra/flake-compat/archive/${lock.nodes.flake-compat.locked.rev}.tar.gz";
       sha256 = lock.nodes.flake-compat.locked.narHash;
     }
   )

default.nix

@@ -13,6 +13,42 @@ let
 
   lockFile = builtins.fromJSON (builtins.readFile lockFilePath);
 
+  # Using custom fetchurl function here so that we can specify outputHashMode.
+  # The hash we get from the lock file is using recursive ingestion even though
+  # it’s not unpacked. So builtins.fetchurl and import <nix/fetchurl.nix> are
+  # insufficient.
+  # Note that this will be a derivation and not a path as fetchTarball is,
+  # causing the hash of this input to be different on flake and non-flake evaluation.
+  fetchurl = { url, sha256 }:
+    derivation {
+      builder = "builtin:fetchurl";
+
+      name = "source";
+      inherit url;
+
+      outputHash = sha256;
+      outputHashAlgo = "sha256";
+      outputHashMode = "recursive";
+      executable = false;
+      unpack = false;
+
+      system = "builtin";
+
+      # No need to double the amount of network traffic
+      preferLocalBuild = true;
+
+      impureEnvVars = [
+        # We borrow these environment variables from the caller to allow
+        # easy proxy configuration.  This is impure, but a fixed-output
+        # derivation like fetchurl is allowed to do so since its result is
+        # by definition pure.
+        "http_proxy" "https_proxy" "ftp_proxy" "all_proxy" "no_proxy"
+      ];
+
+      # To make "nix-prefetch-url" work.
+      urls = [ url ];
+    };
+
   fetchTree =
     info:
     if info.type == "github" then
@@ -44,7 +80,10 @@ let
       } else {
       })
     else if info.type == "path" then
-      { outPath = builtins.path { path = info.path; };
+      { outPath = builtins.path
+          ({ path = info.path; }
+           // (if info ? narHash then { sha256 = info.narHash; } else {})
+          );
         narHash = info.narHash;
       }
     else if info.type == "tarball" then
@@ -53,6 +92,7 @@ let
             ({ inherit (info) url; }
              // (if info ? narHash then { sha256 = info.narHash; } else {})
             );
+        narHash = info.narHash;
       }
     else if info.type == "gitlab" then
       { inherit (info) rev narHash lastModified;
@@ -63,17 +103,23 @@ let
             );
         shortRev = builtins.substring 0 7 info.rev;
       }
-    else if info.type == "sourcehut" then
-      { inherit (info) rev narHash lastModified;
-        outPath =
-          fetchTarball
-            ({ url = "https://${info.host or "git.sr.ht"}/${info.owner}/${info.repo}/archive/${info.rev}.tar.gz"; }
-             // (if info ? narHash then { sha256 = info.narHash; } else {})
-            );
-        shortRev = builtins.substring 0 7 info.rev;
+    else if info.type == "file" then
+      { outPath =
+          if builtins.substring 0 7 info.url == "http://" || builtins.substring 0 8 info.url == "https://" then
+            fetchurl
+              ({ inherit (info) url; }
+               // (if info ? narHash then { sha256 = info.narHash; } else {})
+              )
+          else if builtins.substring 0 7 info.url == "file://" then
+            builtins.path
+              ({ path = builtins.substring 7 (-1) info.url; }
+               // (if info ? narHash then { sha256 = info.narHash; } else {})
+              )
+          else throw "can't support url scheme of flake input with url '${info.url}'";
+        narHash = info.narHash;
       }
     else
-      # FIXME: add Mercurial inputs.
+      # FIXME: add Mercurial input
       throw "flake input has unsupported input type '${info.type}'";
 
   callFlake4 = flakeSrc: locks:
@@ -104,22 +150,7 @@ let
       then
         let res = builtins.fetchGit src;
         in if res.rev == "0000000000000000000000000000000000000000" then removeAttrs res ["rev" "shortRev"]  else res
-      else {
-        outPath =
-          # Massage `src` into a store path.
-          if builtins.isPath src
-          then
-            if dirOf (toString src) == builtins.storeDir
-              # `builtins.storePath` is not available in pure-eval mode.
-              && builtins ? currentSystem
-            then
-              # If it's already a store path, don't copy it again.
-              builtins.storePath src
-            else
-              "${src}"
-          else
-            src;
-      };
+      else { outPath = src; };
     # NB git worktrees have a file for .git, so we don't check the type of .git
     isGit = builtins.pathExists (src + "/.git");
     isShallow = builtins.pathExists (src + "/.git/shallow");
@@ -164,9 +195,7 @@ let
 
           subdir = if key == lockFile.root then "" else node.locked.dir or "";
 
-          outPath = sourceInfo + ((if subdir == "" then "" else "/") + subdir);
-
-          flake = import (outPath + "/flake.nix");
+          flake = import (sourceInfo + (if subdir != "" then "/" else "") + subdir + "/flake.nix");
 
           inputs = builtins.mapAttrs
             (inputName: inputSpec: allNodes.${resolveInput inputSpec})
@@ -193,21 +222,7 @@ let
 
           outputs = flake.outputs (inputs // { self = result; });
 
-          result =
-            outputs
-            # We add the sourceInfo attribute for its metadata, as they are
-            # relevant metadata for the flake. However, the outPath of the
-            # sourceInfo does not necessarily match the outPath of the flake,
-            # as the flake may be in a subdirectory of a source.
-            # This is shadowed in the next //
-            // sourceInfo
-            // {
-              # This shadows the sourceInfo.outPath
-              inherit outPath;
-
-              inherit inputs; inherit outputs; inherit sourceInfo; _type = "flake";
-            };
-
+          result = outputs // sourceInfo // { inherit inputs; inherit outputs; inherit sourceInfo; };
         in
           if node.flake or true then
             assert builtins.isFunction flake.outputs;
@@ -229,7 +244,7 @@ let
 in
   rec {
     defaultNix =
-      (builtins.removeAttrs result ["__functor"])
+      result
       // (if result ? defaultPackage.${system} then { default = result.defaultPackage.${system}; } else {})
       // (if result ? packages.${system}.default then { default = result.packages.${system}.default; } else {});
 

flake.nix

@@ -1,6 +0,0 @@
-{
-  description = "Allow flakes to be used with Nix < 2.4";
-
-  outputs = { self }: {
-  };
-}