{ stdenv, fetchurl, unzip, ant, gcj }:

let
  version = "3.6.1";
  date    = "201009090800";
  isGCJ   = stdenv.lib.strings.substring 0 3 gcj.name == "gcj";
  javaExec  = if isGCJ then "gij" else "java";
  javaFlags = if isGCJ then "--cp" else "-cp";
in
  stdenv.mkDerivation rec {
    name = "ecj-${version}";

    src = fetchurl {
      url = "http://eclipse.ialto.org/eclipse/downloads/drops/R-${version}-${date}/ecjsrc-${version}.zip";
      sha256 = "0xfsig2pzd9wy524wp11s7pc7cj81s28g1485995b44d9qbi17h8";
    };

    buildInputs = [ unzip ant gcj ];

    unpackPhase = ''
      mkdir "${name}"
      cd "${name}"
      unzip "$src"
    '';

    # Use whatever compiler Ant knows.
    buildPhase = "ant build";

    installPhase = ''
      mkdir -pv "$out/lib/java"
      cp -v *.jar "$out/lib/java"

      mkdir -pv "$out/bin"
      cat > "$out/bin/ecj" <<EOF
#! /bin/sh
exec "$(type -P ${javaExec})" ${javaFlags} "$out/lib/java/ecj.jar" org.eclipse.jdt.internal.compiler.batch.Main \$@
EOF

      chmod u+x "$out/bin/ecj"
    '';

    meta = {
      description = "The Eclipse Compiler for Java (ECJ)";

      longDescription = ''
        ECJ is an incremental Java compiler.  Implemented as an Eclipse
        builder, it is based on technology evolved from VisualAge for Java
        compiler.  In particular, it allows users to run and debug code which
        still contains unresolved errors.
      '';

      homepage = http://www.eclipse.org/jdt/core/index.php;

      # http://www.eclipse.org/legal/epl-v10.html (free software, copyleft)
      license = "EPLv1.0";

      maintainers = [ stdenv.lib.maintainers.ludo ];
    };
  }