gdb: Modernize and simplify derivation

- `isGNU` to `isHurd`, my sedding did not catch
- Simplify cross compilation in general
- Be more careful about python
- no more `gdbCross` in all-packages

pkgs/development/tools/misc/gdb/default.nix

···
 { fetchurl, stdenv, ncurses, readline, gmp, mpfr, expat, texinfo, zlib
 , dejagnu, perl, pkgconfig
-, python ? null
+
+, buildPlatform, hostPlatform, targetPlatform
+
+, pythonSupport ? hostPlatform == buildPlatform && !hostPlatform.isCygwin, python ? null
 , guile ? null
-, target ? null
+
 # Support all known targets in one gdb binary.
 , multitarget ? false
+
 # Additional dependencies for GNU/Hurd.
 , mig ? null, hurd ? null
-
 }:
 
 let
-
-  basename = "gdb-7.12.1";
-
-  # Whether (cross-)building for GNU/Hurd.  This is an approximation since
-  # having `stdenv ? cross' doesn't tell us if we're building `crossDrv' and
-  # `nativeDrv'.
-  isGNU =
-      stdenv.system == "i686-gnu"
-      || (stdenv ? cross && stdenv.cross.config == "i586-pc-gnu");
-
+  basename = "gdb-${version}";
+  version = "7.12.1";
 in
 
-assert isGNU -> mig != null && hurd != null;
+assert targetPlatform.isHurd -> mig != null && hurd != null;
+assert pythonSupport -> python != null;
 
 stdenv.mkDerivation rec {
-  name = basename + stdenv.lib.optionalString (target != null)
-      ("-" + target.config);
+  name =
+    stdenv.lib.optionalString (targetPlatform != hostPlatform)
+                              (targetPlatform.config + "-")
+    + basename;
 
   src = fetchurl {
     url = "mirror://gnu/gdb/${basename}.tar.xz";
···
   };
 
   nativeBuildInputs = [ pkgconfig texinfo perl ]
-    ++ stdenv.lib.optional isGNU mig;
+    # TODO(@Ericson2314) not sure if should be host or target
+    ++ stdenv.lib.optional targetPlatform.isHurd mig;
 
-  buildInputs = [ ncurses readline gmp mpfr expat zlib python guile ]
-    ++ stdenv.lib.optional isGNU hurd
+  buildInputs = [ ncurses readline gmp mpfr expat zlib guile ]
+    ++ stdenv.lib.optional pythonSupport python
+    ++ stdenv.lib.optional targetPlatform.isHurd hurd
     ++ stdenv.lib.optional doCheck dejagnu;
 
   enableParallelBuilding = true;
···
   # darwin build fails with format hardening since v7.12
   hardeningDisable = stdenv.lib.optionals stdenv.isDarwin [ "format" ];
 
-  configureFlags = with stdenv.lib;
-    [ "--with-gmp=${gmp.dev}" "--with-mpfr=${mpfr.dev}" "--with-system-readline"
-      "--with-system-zlib" "--with-expat" "--with-libexpat-prefix=${expat.dev}"
+  configureFlags = with stdenv.lib; [
+    "--with-gmp=${gmp.dev}" "--with-mpfr=${mpfr.dev}" "--with-system-readline"
+    "--with-system-zlib" "--with-expat" "--with-libexpat-prefix=${expat.dev}"
+  ] ++ stdenv.lib.optional hostPlatform.isLinux
+      # TODO(@Ericson2314): make this conditional on whether host platform is NixOS
       "--with-separate-debug-dir=/run/current-system/sw/lib/debug"
-    ]
-    ++ optional (target != null) "--target=${target.config}"
-    ++ optional multitarget "--enable-targets=all"
-    ++ optional (elem stdenv.system platforms.cygwin) "--without-python";
-
-  crossAttrs = {
-    # Do not add --with-python here to avoid cross building it.
-    configureFlags = with stdenv.lib;
-      [ "--with-gmp=${gmp.crossDrv}" "--with-mpfr=${mpfr.crossDrv}" "--with-system-readline"
-        "--with-system-zlib" "--with-expat" "--with-libexpat-prefix=${expat.crossDrv}" "--without-python"
-      ]
-      ++ optional (target != null) "--target=${target.config}"
-      ++ optional multitarget "--enable-targets=all";
-  };
+    ++ stdenv.lib.optional (!pythonSupport) "--without-python"
+    # TODO(@Ericson2314): This should be done in stdenv, not per-package
+    ++ stdenv.lib.optional (targetPlatform != hostPlatform) "--target=${target.config}"
+    ++ stdenv.lib.optional multitarget "--enable-targets=all";
 
   postInstall =
     '' # Remove Info files already provided by Binutils and other packages.

pkgs/top-level/all-packages.nix

···
 
   gdbGuile = lowPrio (gdb.override { inherit guile; });
 
-  gdbCross = lowPrio (callPackage ../development/tools/misc/gdb {
-    target = if targetPlatform != buildPlatform then targetPlatform else null;
-  });
-
   gdb-multitarget = lowPrio (gdb.override { multitarget = true; });
 
   valgrind = callPackage ../development/tools/analysis/valgrind {

pkgs/top-level/release-cross.nix

···
   };
 
   linuxCommon = lib.recursiveUpdate gnuCommon {
-    buildPackages.gdbCross = nativePlatforms;
+    buildPackages.gdb = nativePlatforms;
 
     bison = nativePlatforms;
     busybox = nativePlatforms;