/* This file contains various functions that take a stdenv and return
   a new stdenv with different behaviour, e.g. using a different C
   compiler. */

pkgs:

rec {


  # Override the compiler in stdenv for specific packages.
  overrideCC = stdenv: cc: stdenv.override { allowedRequisites = null; cc = cc; };


  # Add some arbitrary packages to buildInputs for specific packages.
  # Used to override packages in stdenv like Make.  Should not be used
  # for other dependencies.
  overrideInStdenv = stdenv: pkgs:
    stdenv.override (prev: { allowedRequisites = null; extraBuildInputs = prev.extraBuildInputs or [] ++ pkgs; });


  # Override the setup script of stdenv.  Useful for testing new
  # versions of the setup script without causing a rebuild of
  # everything.
  #
  # Example:
  #   randomPkg = import ../bla { ...
  #     stdenv = overrideSetup stdenv ../stdenv/generic/setup-latest.sh;
  #   };
  overrideSetup = stdenv: setupScript: stdenv.override { inherit setupScript; };


  # Return a modified stdenv that tries to build statically linked
  # binaries.
  makeStaticBinaries = stdenv:
    let stdenv' = if stdenv.hostPlatform.libc != "glibc" then stdenv else
      stdenv.override (prev: {
          extraBuildInputs = prev.extraBuildInputs or [] ++ [
              stdenv.glibc.static
            ];
        });
    in stdenv' //
    { mkDerivation = args:
      if stdenv'.hostPlatform.isDarwin
      then throw "Cannot build fully static binaries on Darwin/macOS"
      else stdenv'.mkDerivation (args // {
        NIX_CFLAGS_LINK = toString (args.NIX_CFLAGS_LINK or "") + " -static";
        configureFlags = (args.configureFlags or []) ++ [
            "--disable-shared" # brrr...
          ];
      });
    };


  # Return a modified stdenv that builds static libraries instead of
  # shared libraries.
  makeStaticLibraries = stdenv: stdenv //
    { mkDerivation = args: stdenv.mkDerivation (args // {
        dontDisableStatic = true;
        configureFlags = (args.configureFlags or []) ++ [
          "--enable-static"
          "--disable-shared"
        ];
        mesonFlags = (args.mesonFlags or []) ++ [ "-Ddefault_library=static" ];
      });
    };

  /* Modify a stdenv so that the specified attributes are added to
     every derivation returned by its mkDerivation function.

     Example:
       stdenvNoOptimise =
         addAttrsToDerivation
           { NIX_CFLAGS_COMPILE = "-O0"; }
           stdenv;
  */
  addAttrsToDerivation = extraAttrs: stdenv: stdenv //
    { mkDerivation = args: stdenv.mkDerivation (args // extraAttrs); };


  /* Return a modified stdenv that builds packages with GCC's coverage
     instrumentation.  The coverage note files (*.gcno) are stored in
     $out/.build, along with the source code of the package, to enable
     programs like lcov to produce pretty-printed reports.
  */
  addCoverageInstrumentation = stdenv:
    overrideInStdenv stdenv [ pkgs.enableGCOVInstrumentation pkgs.keepBuildTree ];


  /* Replace the meta.maintainers field of a derivation.  This is useful
     when you want to fork to update some packages without disturbing other
     developers.

     e.g.:  in all-packages.nix:

     # remove all maintainers.
     defaultStdenv = replaceMaintainersField allStdenvs.stdenv pkgs [];
  */
  replaceMaintainersField = stdenv: pkgs: maintainers: stdenv //
    { mkDerivation = args:
        stdenv.lib.recursiveUpdate
          (stdenv.mkDerivation args)
          { meta.maintainers = maintainers; };
    };


  /* Use the trace output to report all processed derivations with their
     license name.
  */
  traceDrvLicenses = stdenv: stdenv //
    { mkDerivation = args:
        let
          pkg = stdenv.mkDerivation args;
          printDrvPath = val: let
            drvPath = builtins.unsafeDiscardStringContext pkg.drvPath;
            license = pkg.meta.license or null;
          in
            builtins.trace "@:drv:${toString drvPath}:${builtins.toString license}:@" val;
        in pkg // {
          outPath = printDrvPath pkg.outPath;
          drvPath = printDrvPath pkg.drvPath;
        };
    };


  /* Abort if the license predicate is not verified for a derivation
     declared with mkDerivation.

     One possible predicate to avoid all non-free packages can be achieved
     with the following function:

     isFree = license: with builtins;
       if isNull license then true
       else if isList license then lib.all isFree license
       else license != "non-free" && license != "unfree";

     This adapter can be defined on the defaultStdenv definition.  You can
     use it by patching the all-packages.nix file or by using the override
     feature of ~/.config/nixpkgs/config.nix .
  */
  validateLicenses = licensePred: stdenv: stdenv //
    { mkDerivation = args:
        let
          pkg = stdenv.mkDerivation args;
          drv = builtins.unsafeDiscardStringContext pkg.drvPath;
          license =
            pkg.meta.license or
              # Fixed-output derivations such as source tarballs usually
              # don't have licensing information, but that's OK.
              (pkg.outputHash or
                (builtins.trace
                  "warning: ${drv} lacks licensing information" null));

          validate = arg:
            if licensePred license then arg
            else abort ''
              while building ${drv}:
              license `${builtins.toString license}' does not pass the predicate.
            '';

        in pkg // {
          outPath = validate pkg.outPath;
          drvPath = validate pkg.drvPath;
        };
    };


  /* Modify a stdenv so that it produces debug builds; that is,
     binaries have debug info, and compiler optimisations are
     disabled. */
  keepDebugInfo = stdenv: stdenv //
    { mkDerivation = args: stdenv.mkDerivation (args // {
        dontStrip = true;
        NIX_CFLAGS_COMPILE = toString (args.NIX_CFLAGS_COMPILE or "") + " -ggdb -Og";
      });
    };


  /* Modify a stdenv so that it uses the Gold linker. */
  useGoldLinker = stdenv: stdenv //
    { mkDerivation = args: stdenv.mkDerivation (args // {
        NIX_CFLAGS_LINK = toString (args.NIX_CFLAGS_LINK or "") + " -fuse-ld=gold";
      });
    };


  /* Modify a stdenv so that it builds binaries optimized specifically
     for the machine they are built on.

     WARNING: this breaks purity! */
  impureUseNativeOptimizations = stdenv: stdenv //
    { mkDerivation = args: stdenv.mkDerivation (args // {
        NIX_CFLAGS_COMPILE = toString (args.NIX_CFLAGS_COMPILE or "") + " -march=native";
        NIX_ENFORCE_NO_NATIVE = false;

        preferLocalBuild = true;
        allowSubstitutes = false;
      });
    };
}