nix-build nix-generate-from-cpan：表达式不计算为派生答案

【问题标题】：nix-build nix-generate-from-cpan: expression does not evaluate to a derivationnix-build nix-generate-from-cpan：表达式不计算为派生
【发布时间】：2017-11-28 00:49:26
【问题描述】：

我正在尝试使用nix-generate-from-cspan 安装sqitch

来自nix-generate-from-cpan App::Sqitch DBD::Pg，我制作了这个文件：

{buildPerlModule, fetchurl}:
buildPerlModule rec {
    name = "App-Sqitch-0.9995";
    src = fetchurl {
        url = "mirror://cpan/authors/id/D/DW/DWHEELER/${name}.tar.gz";
        sha256 = "c29b4610ce43bd43ecfa39188f4cbb00b38c390136fcdd9984142efd99eba292";
    };
    buildInputs = [ CaptureTiny ModuleBuild TestDeep TestDir TestException TestFile TestFileContents TestMockModule TestNoWarnings ];
    propagatedBuildInputs = [ Clone ConfigGitLike DBI DateTime DateTimeTimeZone DevelStackTrace EncodeLocale FileHomeDir HashMerge IOPager IPCRun3 IPCSystemSimple ListMoreUtils Moo PathClass PerlIOutf8_strict StringFormatter StringShellQuote SubExporter TemplateTiny Throwable TryTiny TypeTiny URI URIdb libintlperl namespaceautoclean self."if" ];
    meta = {
        homepage = http://sqitch.org/;
        description = "Sane database change management";
        license = stdenv.lib.licenses.mit;
    };
}

但运行 nix-build -E 'with import <nixpkgs> { }; callPackage ./sqitch.nix' 会出现此错误：

expression does not evaluate to a derivation (or a set or list of those)

为了调试，我尝试了nix-instantiate --eval --expr 'with import <nixpkgs> { }; callPackage ./sqitch.nix'，它给出了：

<LAMBDA>

所以我尝试了nix-build -E 'with import <nixpkgs> { }; callPackage callPackage ./sqitch.nix'，但它仍然给出同样的错误，而nix-instantiate --eval --expr 'with import <nixpkgs> { }; callPackage callPackage ./sqitch.nix' 给出：

{ __functor = <CODE>; override = <CODE>; overrideDerivation = <CODE>; }

这对我没有多大帮助。

【问题讨论】：

我忘了在callPackages 之后添加{}。这解释了很多事情

标签： nix nixpkgs

【解决方案1】：

简答

buildPerlModule 的结果将用作mkDerivation 参数中的src。

长答案

原来sqitch已经是nixpkgs的一部分了，它的定义是这样的：

https://github.com/NixOS/nixpkgs/blob/56904d7c423f2b13b37fbd29f39bbb4b52bc7824/pkgs/development/tools/misc/sqitch/default.nix

{ name, stdenv, perl, makeWrapper, sqitchModule, databaseModule }:

stdenv.mkDerivation {
  name = "${name}-${sqitchModule.version}";

  buildInputs = [ perl makeWrapper sqitchModule databaseModule ];

  src = sqitchModule;
  dontBuild = true;

  installPhase = ''
    mkdir -p $out/bin
    for d in bin/sqitch etc lib share ; do
      ln -s ${sqitchModule}/$d $out/$d
    done
  '';
  dontStrip = true;
  postFixup = "wrapProgram $out/bin/sqitch --prefix PERL5LIB : $PERL5LIB";

  meta = {
    platforms = stdenv.lib.platforms.unix;
  };
}

https://github.com/NixOS/nixpkgs/blob/56904d7c423f2b13b37fbd29f39bbb4b52bc7824/pkgs/top-level/all-packages.nix#L10116-L10120

  sqitchPg = callPackage ../development/tools/misc/sqitch {
    name = "sqitch-pg";
    databaseModule = perlPackages.DBDPg;
    sqitchModule = perlPackages.AppSqitch;
  };

https://github.com/NixOS/nixpkgs/blob/56904d7c423f2b13b37fbd29f39bbb4b52bc7824/pkgs/top-level/perl-packages.nix#L281-L305（这是nix-generate-from-cpan App::Sqitch的输出）

 AppSqitch = buildPerlModule rec {
    version = "0.9994";
    name = "App-Sqitch-${version}";
    src = fetchurl {
      url = "mirror://cpan/authors/id/D/DW/DWHEELER/${name}.tar.gz";
      sha256 = "0in602z40s50fdlmws4g0a1pb8p7yn0wx8jgsacz26a4i1q7gpi4";
    };
    buildInputs = [
      CaptureTiny PathClass TestDeep TestDir TestException
      TestFile TestFileContents TestMockModule TestNoWarnings
    ];
    propagatedBuildInputs = [
      Clone ConfigGitLike DBI DateTime
      DevelStackTrace EncodeLocale FileHomeDir HashMerge IOPager IPCRun3
      IPCSystemSimple ListMoreUtils Moo PathClass PerlIOutf8_strict StringFormatter
      StringShellQuote SubExporter TemplateTiny Throwable TryTiny TypeTiny URI
      URIdb libintlperl namespaceautoclean
    ];
    doCheck = false;  # Can't find home directory.
    meta = {
      homepage = http://sqitch.org/;
      description = "Sane database change management";
      license = stdenv.lib.licenses.mit;
    };
  };

https://github.com/NixOS/nixpkgs/blob/56904d7c423f2b13b37fbd29f39bbb4b52bc7824/pkgs/top-level/perl-packages.nix#L3555-L3558

  DBDPg = import ../development/perl-modules/DBD-Pg {
    inherit stdenv fetchurl buildPerlPackage DBI;
    inherit (pkgs) postgresql;
  };

https://github.com/NixOS/nixpkgs/blob/56904d7c423f2b13b37fbd29f39bbb4b52bc7824/pkgs/development/perl-modules/DBD-Pg/default.nix（看起来像 nix-generate-from-cpan DBD::Pg 的输出，但不完全一样）

{ stdenv, fetchurl, buildPerlPackage, DBI, postgresql }:

buildPerlPackage rec {
  name = "DBD-Pg-3.5.3";

  src = fetchurl {
    url = "mirror://cpan/authors/id/T/TU/TURNSTEP/${name}.tar.gz";
    sha256 = "03m9w1cd0yyrbqwkwcl92j1cpmasmm69f3hwvcrlfsi5fnwsk63y";
  };

  buildInputs = [ postgresql ];
  propagatedBuildInputs = [ DBI ];

  makeMakerFlags = "POSTGRES_HOME=${postgresql}";

  meta = {
    homepage = http://search.cpan.org/dist/DBD-Pg/;
    description = "DBI PostgreSQL interface";
    license = with stdenv.lib.licenses; [ artistic1 gpl1Plus ];
    platforms = stdenv.lib.platforms.unix;
  };
}

这就是它的用途。

注意：正如我刚刚在问题的 cmets 中指出的那样，我还忘记在 callPackages 之后添加 {}，这解释了我得到的奇怪类型。

【讨论】：