functional-programming - 尼克斯药丸 14 : How to make callPackage overridable?

Question

我在理解时遇到问题 Nix Pill 14 .作者提供makeOverridable ，然后挑战用户将其与 callPackage 集成. makeOverridable和 default.nix提供如下，其中makeOverridable在文件中 lib.nix , 和 callPackage在文件中 default.nix :

# file: lib.nix

rec {
  makeOverridable = f: origArgs:
    let
      origRes = f origArgs;
    in
      origRes // { override = newArgs: makeOverridable f (origArgs // newArgs); };
}

# file: default.nix

let
  nixpkgs = import <nixpkgs> {};
  allPkgs = nixpkgs // pkgs;
  callPackage = path: overrides:
    let f = import path;
    in f ((builtins.intersectAttrs (builtins.functionArgs f) allPkgs) // overrides);
  pkgs = with nixpkgs; {
    mkDerivation = import ./autotools.nix nixpkgs;
    hello = callPackage ./hello.nix { };
    graphviz = callPackage ./graphviz.nix { };
    graphvizCore = callPackage ./graphviz.nix { gdSupport = false; };
  };
in pkgs

这是我想出的:

# file: default.nix (my implementation)

let
  nixpkgs = import <nixpkgs> {};
  allPkgs = nixpkgs // pkgs;
  callPackage = path: overrides:
    let
      f = import path;
      origRes = f ((builtins.intersectAttrs (builtins.functionArgs f) allPkgs) // overrides);
    in
      origRes // { override = newArgs: callPackage f (overrides // newArgs); };
  pkgs = with nixpkgs; {
    mkDerivation = import ./autotools.nix nixpkgs;
    hello = import ./hello.nix {};
    graphviz = import ./graphviz.nix {};
    graphvizCore = graphviz.override { gdSupport = false; };
  };
in pkgs

我想我对这里发生的事情有一个根本的误解。您能否提供正确的实现并解释我做错了什么？

编辑:我设法让它工作，但是，它仍然不是递归的。

# file: default.nix

let
  nixpkgs = import <nixpkgs> {};
  allPkgs = nixpkgs // pkgs;
  callPackage = path: overrides:
  let
    f = import path;
    origArgs = f ((builtins.intersectAttrs (builtins.functionArgs f) allPkgs) // overrides);
    makeOverridable = { override = newArgs: (origArgs // newArgs); };
  in
    origArgs // makeOverridable;
pkgs = with nixpkgs; rec {
  mkDerivation = import ./autotools.nix nixpkgs;
  hello = callPackage ./hello.nix { };
  graphviz = callPackage ./graphviz.nix { };
  graphvizCore = graphviz.override { gdSupport = false; };
};
in pkgs

编辑2:

# file: default.nix

let
  nixpkgs = import <nixpkgs> {};
  allPkgs = nixpkgs // pkgs;
  makeOverridable = f: origArgs:
    let origRes = f origArgs;
    in origRes // { override = newArgs: makeOverridable f (origArgs // newArgs); };
  callPackage1 = path: overrides:
    let f = import path;
    in f ((builtins.intersectAttrs (builtins.functionArgs f) allPkgs) // overrides);
  callPackage = makeOverridable callPackage1;
  pkgs = with nixpkgs; {
    mkDerivation = import ./autotools.nix nixpkgs;
    hello = callPackage ./hello.nix { };
    graphviz = callPackage ./graphviz.nix { };
    graphvizCore = graphviz.override { gdSupport = false; };
  };
in pkgs

解决方案:

# file: default.nix

let
  nixpkgs = import <nixpkgs> {};
  allPkgs = nixpkgs // pkgs;
  makeOverridable = f: origArgs:
    let origRes = f origArgs;
    in origRes // { override = newArgs: makeOverridable f (origArgs // newArgs); };
  callPackage1 = path: overrides:
    let f = import path;
    in f ((builtins.intersectAttrs (builtins.functionArgs f) allPkgs) // overrides);
  callPackage = path: makeOverridable (callPackage1 path);
  pkgs = with nixpkgs; rec {
    mkDerivation = import ./autotools.nix nixpkgs;
    hello = callPackage ./hello.nix { };
    local_graphviz = callPackage ./graphviz.nix { };
    graphvizCore = local_graphviz.override { gdSupport = false; };
    graphvizCore2 = graphvizCore.override { gdSupport = false; };
  };
in pkgs

Answer 1

如 makeOverridable使用 Nix Pills 中的定义之一正确定义，您可以将其视为高阶函数:它采用名为 f 的普通函数，并将其更改为一个新函数，其结果可以被覆盖。

假设您已经有一个名为 callPackage1 的函数，你可以像这样制作一个可覆盖的版本:

rec {
  callPackage1 = ...;
  callPackage = makeOverridable callPackage1;
}

编辑 1:

其实， callPackage1需要一个路径来返回 makeOverridable 期望的函数类型(一个接受集合并返回一个对象的函数，我们可以向其添加覆盖 attribute )。所以让我们试试 callPackage 的这个定义:

callPackage = path: makeOverridable (callPackage1 path);