separate minimal-bootstrap-sources from make-minimal-bootstrap-sources

Ericson2314 observed that although FODs break the build-time cycle,
they don't break the eval-time cycle.  This cycle must be broken in
order to compute the derivation hash.

make-minimal-bootstrap-sources does and always has depended on the
full nixpkgs (including fetchFromGitHub).  This commit completely
separates minimal-bootstrap-sources from it, so that
minimal-bootstrap-sources now does not depend on
make-minimal-bootstrap-sources (or nixpkgs) in any way.

minimal-bootstrap-sources is now a "bare Nix" derivation.  It is an
FOD whose builder always fails with an error message.

pkgs/os-specific/linux/minimal-bootstrap/default.nix

@@ -4,7 +4,6 @@
 , hostPlatform
 , fetchurl
 , checkMeta
-, make-minimal-bootstrap-sources
 }:
 
 lib.makeScope
@@ -61,8 +60,6 @@ lib.makeScope
 
     ln-boot = callPackage ./ln-boot { };
 
-    inherit make-minimal-bootstrap-sources;
-
     mes = lib.recurseIntoAttrs (callPackage ./mes { });
     mes-libc = callPackage ./mes/libc.nix { };
 

pkgs/os-specific/linux/minimal-bootstrap/stage0-posix/bootstrap-sources.nix

@@ -1,11 +1,12 @@
-{ make-minimal-bootstrap-sources
+{
 }:
 
 rec {
   name = "stage0-posix-${version}-${rev}-source";
   # Pinned from https://github.com/oriansj/stage0-posix/commit/3189b5f325b7ef8b88e3edec7c1cde4fce73c76c
   version = "unstable-2023-05-02";
   rev = "3189b5f325b7ef8b88e3edec7c1cde4fce73c76c";
+  outputHashAlgo = "sha256";
 
   # This 256 byte seed is the only pre-compiled binary in the bootstrap chain.
   hex0-seed = import <nix/fetchurl.nix> {
@@ -69,9 +70,37 @@ rec {
   specifically designed for bit-exact reproducibility, none of the
   requirements above apply to `minimal-bootstrap-sources`.
   */
-  minimal-bootstrap-sources = make-minimal-bootstrap-sources.overrideAttrs(_: {
+  minimal-bootstrap-sources = derivation {
+    name = "${name}.nar.xz";
+    system = builtins.currentSystem;
     outputHashMode = "flat";
-    outputHashAlgo = "sha256";
+    inherit outputHashAlgo;
     outputHash = "sha256-ig988BiRTz92hhZZgKQW1tVPoV4aQ2D69Cq3wHvVgHg=";
-  });
+
+    # This builder always fails, but fortunately Nix will print the
+    # "builder", which is really the error message that we want the
+    # user to see.
+    builder = ''
+      #
+      #
+      # Neither your store nor your substituters seems to have:
+      #
+      #  ${name}.nar.xz
+      #
+      # Please obtain or create this file, give it exactly the name
+      # shown above, and then run the following command:
+      #
+      #   nix-store --add-fixed ${outputHashAlgo} ${name}.nar.xz
+      #
+      # You can create this file from an already-bootstrapped nixpkgs
+      # using the following command:
+      #
+      #   nix-build '<nixpkgs>' -A make-minimal-bootstrap-sources
+      #
+      # Or, if you prefer, you can create this file using only `git`,
+      # `nix`, and `xz`.  For the commands needed in order to do this,
+      # see `make-bootstrap-sources.nix`.
+      #
+    '';
+  };
 }

pkgs/os-specific/linux/minimal-bootstrap/stage0-posix/default.nix

@@ -3,7 +3,7 @@
 }:
 
 lib.makeScope newScope (self: with self; {
-  inherit (self.callPackage ./bootstrap-sources.nix)
+  inherit (self.callPackage ./bootstrap-sources.nix {})
     version hex0-seed minimal-bootstrap-sources;
 
   src = minimal-bootstrap-sources;

pkgs/os-specific/linux/minimal-bootstrap/stage0-posix/make-bootstrap-sources.nix

@@ -18,7 +18,7 @@
 , xz
 }:
 let
-  inherit (import ./bootstrap-sources.nix { make-minimal-bootstrap-sources = null; }) name rev;
+  inherit (import ./bootstrap-sources.nix { }) name rev;
 
   src = fetchFromGitHub {
     owner = "oriansj";

pkgs/top-level/all-packages.nix

@@ -27440,8 +27440,8 @@ with pkgs;
       inherit (stdenv.buildPlatform) system;
     };
     checkMeta = callPackage ../stdenv/generic/check-meta.nix { };
-    inherit make-minimal-bootstrap-sources;
   });
+  minimal-bootstrap-sources = callPackage ../os-specific/linux/minimal-bootstrap/stage0-posix/bootstrap-sources.nix { };
   make-minimal-bootstrap-sources = callPackage ../os-specific/linux/minimal-bootstrap/stage0-posix/make-bootstrap-sources.nix { };
 
   mingetty = callPackage ../os-specific/linux/mingetty { };