linux: parse configfile at eval-time if possible (#434608)

  lib,

  stdenv,

  buildPackages,

  runCommand,

  bc,

  bison,

  flex,

  readConfig =

    configfile:

    import

      (runCommand "config.nix" { } ''

        echo "{" > "$out"

        while IFS='=' read key val; do

          [ "x''${key#CONFIG_}" != "x$key" ] || continue

          no_firstquote="''${val#\"}";

          echo '  "'"$key"'" = "'"''${no_firstquote%\"}"'";' >> "$out"

        done < "${configfile}"

        echo "}" >> $out

      '').outPath;

    lib.listToAttrs (

      map

        (

          line:

          let

            match = lib.match "(.*)=\"?(.*)\"?" line;

          in

          {

            name = lib.elemAt match 0;

            value = lib.elemAt match 1;

          }

        )

        (

          lib.filter (line: !(lib.hasPrefix "#" line || line == "")) (

            lib.splitString "\n" (builtins.readFile configfile)

          )

        )

    );

in

lib.makeOverridable (

  {

    configfile,

    # Manually specified nixexpr representing the config

    # If unspecified, this will be autodetected from the .config

    config ? lib.optionalAttrs allowImportFromDerivation (readConfig configfile),

    config ? lib.optionalAttrs (builtins.isPath configfile || allowImportFromDerivation) (

      readConfig configfile

    ),

    # Custom seed used for CONFIG_GCC_PLUGIN_RANDSTRUCT if enabled. This is

    # automatically extended with extra per-version and per-config values.

    randstructSeed ? "",