[Nix-dev] Infinite recursion with npm2nix

[Colin Putney]

Hi folks,

In my on-going quest to package up my node applications, I've run into a
noob-trap that has me completely stumped.

The app is a web app, so it has both client- and server-side code. One of
the dependencies is Yahoo's Pure CSS library. PureCSS, in turn relies on
Grunt for its build process. I've created the following nix expressions:

$ cat purecss.nix
{ pkgs ? import <nixpkgs> {} }:

with pkgs.stdenv.lib;

let

  name = "pure-css";
  version = "v0.5.0-rc-1";

  # pull in the code for building npm packages
  nodePackages = import ./purecss-npm-packages.nix {
    inherit pkgs;
    inherit (pkgs) stdenv nodejs fetchurl fetchgit;
    neededNatives = [ pkgs.python ] ++ pkgs.lib.optional
pkgs.stdenv.isLinux pkgs.utillinux;
    self = nodePackages;
  };

  buildModules = [
     nodePackages."bower"
     nodePackages."grunt"
     nodePackages."grunt-cli"
     nodePackages."grunt-contrib-cssmin"
     nodePackages."grunt-contrib-clean"
     nodePackages."grunt-contrib-copy"
     nodePackages."grunt-contrib-concat"
     nodePackages."grunt-contrib-compress"
     nodePackages."grunt-contrib-csslint"
     nodePackages."grunt-contrib-watch"
     nodePackages."grunt-css-selectors"
     nodePackages."grunt-pure-grids"
     nodePackages."grunt-stripmq"
  ];

in pkgs.stdenv.mkDerivation {

  name = "${name}-${version}";

  src = pkgs.fetchgit {
    url = https://github.com/yui/pure;
    rev = "refs/tags/v0.5.0-rc-1";
    sha256 =
"049ac2ef812771852978d11cd5aecac2dd561e97bb16ad89c79eb1e10aa57672";
  };

  buildInputs = buildModules;

  buildCommand = ''
    cp -r $src src
    chmod +w src
    cd src
    grunt
  '';

}


$ cat purecss-npm-packages.nix
{ pkgs, stdenv, nodejs, fetchurl, fetchgit, neededNatives, self }:

rec {

  nativeDeps = {};

  buildNodePackage = import
"${pkgs.path}/pkgs/development/web/nodejs/build-node-package.nix" {
    inherit stdenv nodejs neededNatives;
    inherit (pkgs) runCommand;
  };

  patchSource = fn: srcAttrs:
    let src = fn srcAttrs; in pkgs.runCommand src.name {} ''
      mkdir unpack
      cd unpack
      unpackFile ${src}
      chmod -R +w */
      mv */ package 2>/dev/null || true
      sed -i -e "s/:\s*\"latest\"/:  \"*\"/" -e
"s/:\s*\"\(https\?\|git\(\+\(ssh\|http\|https\)\)\?\):\/\/[^\"]*\"/:
\"*\"/" package/package.json
      mv */ $out
    '';

  # Backwards compat
  patchLatest = patchSource fetchurl;

} // import ./purecss-npm-generated.nix { inherit self fetchurl fetchgit;
inherit (pkgs) lib; }


The file purecss-npm-generated.nix is about 4000 lines of nix expressions
generated by npm2nix.



Now, the problem is this:

error: while evaluating the attribute `nativeBuildInputs' of the derivation
`pure-css-v0.5.0-rc-1' at
/Users/colin/Better/usul/edric/harah/purecss.nix:36:3:
while evaluating the attribute `deps' of the derivation
`node-grunt-css-selectors-1.0.0' at
/Users/colin/Better/usul/edric/harah/purecss-npm-generated.nix:1807:5:
while evaluating the attribute `deps' of the derivation
`node-rework-0.20.2' at
/Users/colin/Better/usul/edric/harah/purecss-npm-generated.nix:3389:5:
while evaluating the attribute `nativeBuildInputs' of the derivation
`node-rework-inherit-0.2.1' at
/Users/colin/Better/usul/edric/harah/purecss-npm-generated.nix:3426:5:
infinite recursion encountered


The relevant section of the generated code is here:


  by-spec."rework".">= 0.15.0" =
    self.by-version."rework"."0.20.2";
  by-version."rework"."0.20.2" = lib.makeOverridable self.buildNodePackage {
    name = "node-rework-0.20.2";
    src = [
      (fetchurl {
        url = "http://registry.npmjs.org/rework/-/rework-0.20.2.tgz";
        name = "rework-0.20.2.tgz";
        sha1 = "b64b082a1660cf33c874729353ead5341c100d23";
      })
    ];
    buildInputs =
      (self.nativeDeps."rework" or []);
    deps = [
      self.by-version."css"."1.6.0"
      self.by-version."commander"."1.0.4"
      self.by-version."color-parser"."0.1.0"
      self.by-version."hsb2rgb"."1.0.2"
      self.by-version."mime"."1.2.11"
      self.by-version."debug"."0.8.0"
      self.by-version."rework-inherit"."0.2.1"
      self.by-version."rework-visit"."1.0.0"
      self.by-version."convert-source-map"."0.3.3"
      self.by-version."rework"."0.20.2"
    ];
    peerDependencies = [
    ];
    passthru.names = [ "rework" ];
  };
  by-spec."rework".">=0.18.0" =
    self.by-version."rework"."0.20.2";
  by-spec."rework".">=0.20.2-0 <0.21.0-0" =
    self.by-version."rework"."0.20.2";
  by-spec."rework".">=0.20.2-0 >=0.20.2-0 <0.21.0-0" =
    self.by-version."rework"."0.20.2";
  by-spec."rework"."~0.20.2" =
    self.by-version."rework"."0.20.2";
  by-spec."rework-inherit"."0.2.1" =
    self.by-version."rework-inherit"."0.2.1";
  by-version."rework-inherit"."0.2.1" = lib.makeOverridable
self.buildNodePackage {
    name = "node-rework-inherit-0.2.1";
    src = [
      (fetchurl {
        url = "
http://registry.npmjs.org/rework-inherit/-/rework-inherit-0.2.1.tgz";
        name = "rework-inherit-0.2.1.tgz";
        sha1 = "fdd01a199b0a86ef909436fb373f7b343936f185";
      })
    ];
    buildInputs =
      (self.nativeDeps."rework-inherit" or []);
    deps = [
      self.by-version."debug"."0.8.0"
    ];
    peerDependencies = [
      self.by-version."rework"."0.20.2"
    ];
    passthru.names = [ "rework-inherit" ];
  };



And sure enough, we have circular dependencies: rework depends
rework-inherit via it's "deps" attribute, while rework-inherit depends on
rework via "peerDependencies". For confirmation, I commented out the
contents of rework-inherit's peerDependencies, and sure enough, the
infinite recursion goes away. (But then the build fails, because
rework-inherit is missing a dependency.)

What's puzzling to me is that clearly peerDependencies are an important
feature of npm. Both npm2nix and buildNodePackage explicitly support them
and npm packages can be correctly installed without them. But if they cause
infinite recursion in this trivial way, how could that code ever work? Is
there a way to avoid infinite recursion?

Thanks in advance,

Colin
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