From 1c226cc8c6562379ffd0ac36ca095396250d94d7 Mon Sep 17 00:00:00 2001
From: Jonas Chevalier <zimbatm@zimbatm.com>
Date: Sun, 9 Apr 2023 12:34:52 +0200
Subject: [PATCH] introduce externally extensible systems (#93)

This PR is a back-compatible subset of #84.

By adding a new flake input here, it makes it possible to override the
list of systems using flake overrides.

See <https://github.com/nix-systems/nix-systems> for the full
explanation.
---
 default.nix | 230 +---------------------------------------------------
 flake.lock  |  26 ++++++
 flake.nix   |  10 ++-
 lib.nix     | 229 +++++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 265 insertions(+), 230 deletions(-)
 create mode 100644 flake.lock
 create mode 100644 lib.nix

diff --git a/default.nix b/default.nix
index 2b01461..0c00fb0 100644
--- a/default.nix
+++ b/default.nix
@@ -1,228 +1,2 @@
-let
-  # The list of systems supported by nixpkgs and hydra
-  defaultSystems = [
-    "aarch64-linux"
-    "aarch64-darwin"
-    "x86_64-darwin"
-    "x86_64-linux"
-  ];
-
-  # List of all systems defined in nixpkgs
-  # Keep in sync with nixpkgs wit the following command:
-  # $ nix-instantiate --json --eval --expr "with import <nixpkgs> {}; lib.platforms.all" | jq 'sort' | sed 's!,!!'
-
-  allSystems = [
-    "aarch64-darwin"
-    "aarch64-genode"
-    "aarch64-linux"
-    "aarch64-netbsd"
-    "aarch64-none"
-    "aarch64_be-none"
-    "arm-none"
-    "armv5tel-linux"
-    "armv6l-linux"
-    "armv6l-netbsd"
-    "armv6l-none"
-    "armv7a-darwin"
-    "armv7a-linux"
-    "armv7a-netbsd"
-    "armv7l-linux"
-    "armv7l-netbsd"
-    "avr-none"
-    "i686-cygwin"
-    "i686-darwin"
-    "i686-freebsd"
-    "i686-genode"
-    "i686-linux"
-    "i686-netbsd"
-    "i686-none"
-    "i686-openbsd"
-    "i686-windows"
-    "js-ghcjs"
-    "m68k-linux"
-    "m68k-netbsd"
-    "m68k-none"
-    "mips64el-linux"
-    "mipsel-linux"
-    "mipsel-netbsd"
-    "mmix-mmixware"
-    "msp430-none"
-    "or1k-none"
-    "powerpc-netbsd"
-    "powerpc-none"
-    "powerpc64-linux"
-    "powerpc64le-linux"
-    "powerpcle-none"
-    "riscv32-linux"
-    "riscv32-netbsd"
-    "riscv32-none"
-    "riscv64-linux"
-    "riscv64-netbsd"
-    "riscv64-none"
-    "s390-linux"
-    "s390-none"
-    "s390x-linux"
-    "s390x-none"
-    "vc4-none"
-    "wasm32-wasi"
-    "wasm64-wasi"
-    "x86_64-cygwin"
-    "x86_64-darwin"
-    "x86_64-freebsd"
-    "x86_64-genode"
-    "x86_64-linux"
-    "x86_64-netbsd"
-    "x86_64-none"
-    "x86_64-openbsd"
-    "x86_64-redox"
-    "x86_64-solaris"
-    "x86_64-windows"
-  ];
-
-  # A map from system to system. It's useful to detect typos.
-  #
-  # Instead of typing `"x86_64-linux"`, type `flake-utils.lib.system.x86_64-linux`
-  # and get an error back if you used a dash instead of an underscore.
-  system =
-    builtins.listToAttrs
-      (map (system: { name = system; value = system; }) allSystems);
-
-  # eachSystem using defaultSystems
-  eachDefaultSystem = eachSystem defaultSystems;
-
-  # Builds a map from <attr>=value to <attr>.<system>=value for each system,
-  # except for the `hydraJobs` attribute, where it maps the inner attributes,
-  # from hydraJobs.<attr>=value to hydraJobs.<attr>.<system>=value.
-  #
-  eachSystem = systems: f:
-    let
-      # Taken from <nixpkgs/lib/attrsets.nix>
-      isDerivation = x: builtins.isAttrs x && x ? type && x.type == "derivation";
-
-      # Used to match Hydra's convention of how to define jobs. Basically transforms
-      #
-      #     hydraJobs = {
-      #       hello = <derivation>;
-      #       haskellPackages.aeson = <derivation>;
-      #     }
-      #
-      # to
-      #
-      #     hydraJobs = {
-      #       hello.x86_64-linux = <derivation>;
-      #       haskellPackages.aeson.x86_64-linux = <derivation>;
-      #     }
-      #
-      # if the given flake does `eachSystem [ "x86_64-linux" ] { ... }`.
-      pushDownSystem = system: merged:
-        builtins.mapAttrs
-          (name: value:
-            if ! (builtins.isAttrs value) then value
-            else if isDerivation value then (merged.${name} or {}) // { ${system} = value; }
-            else pushDownSystem system (merged.${name} or {}) value);
-
-      # Merge together the outputs for all systems.
-      op = attrs: system:
-        let
-          ret = f system;
-          op = attrs: key:
-            let
-              appendSystem = key: system: ret:
-                if key == "hydraJobs"
-                  then (pushDownSystem system (attrs.hydraJobs or {}) ret.hydraJobs)
-                  else { ${system} = ret.${key}; };
-            in attrs //
-              {
-                ${key} = (attrs.${key} or { })
-                  // (appendSystem key system ret);
-              }
-          ;
-        in
-        builtins.foldl' op attrs (builtins.attrNames ret);
-    in
-    builtins.foldl' op { } systems
-  ;
-
-  # eachSystemMap using defaultSystems
-  eachDefaultSystemMap = eachSystemMap defaultSystems;
-  
-  # Builds a map from <attr>=value to <system>.<attr> = value.
-  eachSystemMap = systems: f: builtins.listToAttrs (builtins.map (system: { name = system; value = f system; }) systems);
-
-  # Nix flakes insists on having a flat attribute set of derivations in
-  # various places like the `packages` and `checks` attributes.
-  #
-  # This function traverses a tree of attributes (by respecting
-  # recurseIntoAttrs) and only returns their derivations, with a flattened
-  # key-space.
-  #
-  # Eg:
-  #
-  #   flattenTree { hello = pkgs.hello; gitAndTools = pkgs.gitAndTools };
-  #
-  # Returns:
-  #
-  #   {
-  #      hello = «derivation»;
-  #      "gitAndTools/git" = «derivation»;
-  #      "gitAndTools/hub" = «derivation»;
-  #      # ...
-  #   }
-  flattenTree = tree: import ./flattenTree.nix tree;
-
-  # Nix check functionality validates packages for various conditions, like if
-  # they build for any given platform or if they are marked broken.
-  #
-  # This function filters a flattend package set for conditinos that
-  # would *trivially* break `nix flake check`. It does not flatten a tree and it
-  # does not implement advanced package validation checks.
-  #
-  # Eg:
-  #
-  #   filterPackages "x86_64-linux" {
-  #     hello = pkgs.hello;
-  #     "gitAndTools/git" = pkgs.gitAndTools // {meta.broken = true;};
-  #    };
-  #
-  # Returns:
-  #
-  #   {
-  #      hello = «derivation»;
-  #   }
-  filterPackages = import ./filterPackages.nix { inherit allSystems; };
-
-  # Returns the structure used by `nix app`
-  mkApp =
-    { drv
-    , name ? drv.pname or drv.name
-    , exePath ? drv.passthru.exePath or "/bin/${name}"
-    }:
-    {
-      type = "app";
-      program = "${drv}${exePath}";
-    };
-
-  # This function tries to capture a common flake pattern.
-  simpleFlake = import ./simpleFlake.nix { inherit lib defaultSystems; };
-
-  # Helper functions for Nix evaluation
-  check-utils = import ./check-utils.nix;
-
-  lib = {
-    inherit
-      allSystems
-      check-utils
-      defaultSystems
-      eachDefaultSystem
-      eachSystem
-      eachDefaultSystemMap
-      eachSystemMap
-      filterPackages
-      flattenTree
-      mkApp
-      simpleFlake
-      system
-      ;
-  };
-in
-lib
+# Used for back-compat
+import ./lib.nix { }
diff --git a/flake.lock b/flake.lock
new file mode 100644
index 0000000..c90a2bf
--- /dev/null
+++ b/flake.lock
@@ -0,0 +1,26 @@
+{
+  "nodes": {
+    "root": {
+      "inputs": {
+        "systems": "systems"
+      }
+    },
+    "systems": {
+      "locked": {
+        "lastModified": 1681028828,
+        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
+        "owner": "nix-systems",
+        "repo": "default",
+        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-systems",
+        "repo": "default",
+        "type": "github"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}
diff --git a/flake.nix b/flake.nix
index ae76102..34afb1a 100644
--- a/flake.nix
+++ b/flake.nix
@@ -1,7 +1,13 @@
 {
   description = "Pure Nix flake utility functions";
-  outputs = { self }: {
-    lib = import ./.;
+
+  # Externally extensible flake systems. See <https://github.com/nix-systems/nix-systems>.
+  inputs.systems.url = "github:nix-systems/default";
+
+  outputs = { self, systems }: {
+    lib = import ./lib.nix {
+      defaultSystems = import systems;
+    };
     templates = {
       simple-flake = {
         path = ./examples/simple-flake;
diff --git a/lib.nix b/lib.nix
new file mode 100644
index 0000000..17f3569
--- /dev/null
+++ b/lib.nix
@@ -0,0 +1,229 @@
+{
+  # The list of systems supported by nixpkgs and hydra
+  defaultSystems ? [
+    "aarch64-linux"
+    "aarch64-darwin"
+    "x86_64-darwin"
+    "x86_64-linux"
+  ]
+}:
+let
+  # List of all systems defined in nixpkgs
+  # Keep in sync with nixpkgs wit the following command:
+  # $ nix-instantiate --json --eval --expr "with import <nixpkgs> {}; lib.platforms.all" | jq 'sort' | sed 's!,!!'
+
+  allSystems = [
+    "aarch64-darwin"
+    "aarch64-genode"
+    "aarch64-linux"
+    "aarch64-netbsd"
+    "aarch64-none"
+    "aarch64_be-none"
+    "arm-none"
+    "armv5tel-linux"
+    "armv6l-linux"
+    "armv6l-netbsd"
+    "armv6l-none"
+    "armv7a-darwin"
+    "armv7a-linux"
+    "armv7a-netbsd"
+    "armv7l-linux"
+    "armv7l-netbsd"
+    "avr-none"
+    "i686-cygwin"
+    "i686-darwin"
+    "i686-freebsd"
+    "i686-genode"
+    "i686-linux"
+    "i686-netbsd"
+    "i686-none"
+    "i686-openbsd"
+    "i686-windows"
+    "js-ghcjs"
+    "m68k-linux"
+    "m68k-netbsd"
+    "m68k-none"
+    "mips64el-linux"
+    "mipsel-linux"
+    "mipsel-netbsd"
+    "mmix-mmixware"
+    "msp430-none"
+    "or1k-none"
+    "powerpc-netbsd"
+    "powerpc-none"
+    "powerpc64-linux"
+    "powerpc64le-linux"
+    "powerpcle-none"
+    "riscv32-linux"
+    "riscv32-netbsd"
+    "riscv32-none"
+    "riscv64-linux"
+    "riscv64-netbsd"
+    "riscv64-none"
+    "s390-linux"
+    "s390-none"
+    "s390x-linux"
+    "s390x-none"
+    "vc4-none"
+    "wasm32-wasi"
+    "wasm64-wasi"
+    "x86_64-cygwin"
+    "x86_64-darwin"
+    "x86_64-freebsd"
+    "x86_64-genode"
+    "x86_64-linux"
+    "x86_64-netbsd"
+    "x86_64-none"
+    "x86_64-openbsd"
+    "x86_64-redox"
+    "x86_64-solaris"
+    "x86_64-windows"
+  ];
+
+  # A map from system to system. It's useful to detect typos.
+  #
+  # Instead of typing `"x86_64-linux"`, type `flake-utils.lib.system.x86_64-linux`
+  # and get an error back if you used a dash instead of an underscore.
+  system =
+    builtins.listToAttrs
+      (map (system: { name = system; value = system; }) allSystems);
+
+  # eachSystem using defaultSystems
+  eachDefaultSystem = eachSystem defaultSystems;
+
+  # Builds a map from <attr>=value to <attr>.<system>=value for each system,
+  # except for the `hydraJobs` attribute, where it maps the inner attributes,
+  # from hydraJobs.<attr>=value to hydraJobs.<attr>.<system>=value.
+  #
+  eachSystem = systems: f:
+    let
+      # Taken from <nixpkgs/lib/attrsets.nix>
+      isDerivation = x: builtins.isAttrs x && x ? type && x.type == "derivation";
+
+      # Used to match Hydra's convention of how to define jobs. Basically transforms
+      #
+      #     hydraJobs = {
+      #       hello = <derivation>;
+      #       haskellPackages.aeson = <derivation>;
+      #     }
+      #
+      # to
+      #
+      #     hydraJobs = {
+      #       hello.x86_64-linux = <derivation>;
+      #       haskellPackages.aeson.x86_64-linux = <derivation>;
+      #     }
+      #
+      # if the given flake does `eachSystem [ "x86_64-linux" ] { ... }`.
+      pushDownSystem = system: merged:
+        builtins.mapAttrs
+          (name: value:
+            if ! (builtins.isAttrs value) then value
+            else if isDerivation value then (merged.${name} or {}) // { ${system} = value; }
+            else pushDownSystem system (merged.${name} or {}) value);
+
+      # Merge together the outputs for all systems.
+      op = attrs: system:
+        let
+          ret = f system;
+          op = attrs: key:
+            let
+              appendSystem = key: system: ret:
+                if key == "hydraJobs"
+                  then (pushDownSystem system (attrs.hydraJobs or {}) ret.hydraJobs)
+                  else { ${system} = ret.${key}; };
+            in attrs //
+              {
+                ${key} = (attrs.${key} or { })
+                  // (appendSystem key system ret);
+              }
+          ;
+        in
+        builtins.foldl' op attrs (builtins.attrNames ret);
+    in
+    builtins.foldl' op { } systems
+  ;
+
+  # eachSystemMap using defaultSystems
+  eachDefaultSystemMap = eachSystemMap defaultSystems;
+  
+  # Builds a map from <attr>=value to <system>.<attr> = value.
+  eachSystemMap = systems: f: builtins.listToAttrs (builtins.map (system: { name = system; value = f system; }) systems);
+
+  # Nix flakes insists on having a flat attribute set of derivations in
+  # various places like the `packages` and `checks` attributes.
+  #
+  # This function traverses a tree of attributes (by respecting
+  # recurseIntoAttrs) and only returns their derivations, with a flattened
+  # key-space.
+  #
+  # Eg:
+  #
+  #   flattenTree { hello = pkgs.hello; gitAndTools = pkgs.gitAndTools };
+  #
+  # Returns:
+  #
+  #   {
+  #      hello = «derivation»;
+  #      "gitAndTools/git" = «derivation»;
+  #      "gitAndTools/hub" = «derivation»;
+  #      # ...
+  #   }
+  flattenTree = tree: import ./flattenTree.nix tree;
+
+  # Nix check functionality validates packages for various conditions, like if
+  # they build for any given platform or if they are marked broken.
+  #
+  # This function filters a flattend package set for conditinos that
+  # would *trivially* break `nix flake check`. It does not flatten a tree and it
+  # does not implement advanced package validation checks.
+  #
+  # Eg:
+  #
+  #   filterPackages "x86_64-linux" {
+  #     hello = pkgs.hello;
+  #     "gitAndTools/git" = pkgs.gitAndTools // {meta.broken = true;};
+  #    };
+  #
+  # Returns:
+  #
+  #   {
+  #      hello = «derivation»;
+  #   }
+  filterPackages = import ./filterPackages.nix { inherit allSystems; };
+
+  # Returns the structure used by `nix app`
+  mkApp =
+    { drv
+    , name ? drv.pname or drv.name
+    , exePath ? drv.passthru.exePath or "/bin/${name}"
+    }:
+    {
+      type = "app";
+      program = "${drv}${exePath}";
+    };
+
+  # This function tries to capture a common flake pattern.
+  simpleFlake = import ./simpleFlake.nix { inherit lib defaultSystems; };
+
+  # Helper functions for Nix evaluation
+  check-utils = import ./check-utils.nix;
+
+  lib = {
+    inherit
+      allSystems
+      check-utils
+      defaultSystems
+      eachDefaultSystem
+      eachSystem
+      eachDefaultSystemMap
+      eachSystemMap
+      filterPackages
+      flattenTree
+      mkApp
+      simpleFlake
+      system
+      ;
+  };
+in
+lib