core/pkgs/build-support/make-pkgconfigitem/default.nix

{ lib, writeTextFile, buildPackages }:

# See https://people.freedesktop.org/~dbn/pkg-config-guide.html#concepts
{ name # The name of the pc file
# keywords
# provide a default description for convenience. it's not important but still required by pkg-config.
, description ? "A pkg-config file for ${name}", url ? "", version ? ""
, requires ? [ ], requiresPrivate ? [ ], conflicts ? [ ], cflags ? [ ]
, libs ? [ ], libsPrivate ? [ ], variables ? { } }:

let
  # only 'out' has to be changed, otherwise it would be replaced by the out of the writeTextFile
  placeholderToSubstVar =
    builtins.replaceStrings [ "${placeholder "out"}" ] [ "@out@" ];

  replacePlaceholderAndListToString = x:
    if builtins.isList x then
      placeholderToSubstVar (builtins.concatStringsSep " " x)
    else
      placeholderToSubstVar x;

  keywordsSection = let
    mustBeAList = attr: attrName:
      lib.throwIfNot (lib.isList attr) "'${attrName}' must be a list" attr;
  in {
    "Name" = name;
    "Description" = description;
    "URL" = url;
    "Version" = version;
    "Requires" = mustBeAList requires "requires";
    "Requires.private" = mustBeAList requiresPrivate "requiresPrivate";
    "Conflicts" = mustBeAList conflicts "conflicts";
    "Cflags" = mustBeAList cflags "cflags";
    "Libs" = mustBeAList libs "libs";
    "Libs.private" = mustBeAList libsPrivate "libsPrivate";
  };

  renderVariable = name: value:
    lib.optionalString (value != "" && value != [ ])
    "${name}=${replacePlaceholderAndListToString value}";
  renderKeyword = name: value:
    lib.optionalString (value != "" && value != [ ])
    "${name}: ${replacePlaceholderAndListToString value}";

  renderSomething = renderFunc: attrs:
    lib.pipe attrs [
      (lib.mapAttrsToList renderFunc)
      (builtins.filter (v: v != ""))
      (builtins.concatStringsSep "\n")
      (section: ''
        ${section}
      '')
    ];

  variablesSectionRendered = renderSomething renderVariable variables;
  keywordsSectionRendered = renderSomething renderKeyword keywordsSection;

  content = [ variablesSectionRendered keywordsSectionRendered ];
in writeTextFile {
  name = "${name}.pc";
  destination = "/lib/pkgconfig/${name}.pc";
  text = builtins.concatStringsSep "\n" content;
  checkPhase = ''
    ${buildPackages.pkg-config}/bin/${buildPackages.pkg-config.targetPrefix}pkg-config --validate "$target"'';
}