all-packages.nix: Provide a shorter way to specify packages

There are zillions of lines of the form

  foo = callPackage ../bla/foo { };

in all-packages.nix. To get rid of this verbosity, you can now list
such packages in pkgs/auto-packages.nix. This is just a list of
package file names, e.g.

  development/libraries/libogg
  development/libraries/libvorbis
  tools/archivers/gnutar

If the package needs non-default function arguments, or if its
intended attribute name is different from its file name, then you
cannot put it in auto-packages.nix and instead need to specify it in
all-packages.nix.

If Nix had a glob function (NixOS/nix#235), we
could even get rid of auto-packages.nix and have package expressions
be discovered automatically. However, that might not be desirable
because of the need to traverse the file system to find packages we
may not even use.

pkgs/auto-packages.nix

@@ -0,0 +1,16 @@
+/* A list of file names of package Nix expressions, whose base names
+   match the intended attribute names, and that do not need to be
+   called with any overrides. Thus, listing ‘./foo.nix’ here is
+   equivalent to defining the attribute
+
+     foo = callPackage ./foo.nix { };
+
+   in all-packages.nix. */
+
+[
+  build-support/libredirect
+  development/libraries/libogg
+  development/libraries/libvorbis
+  tools/archivers/gnutar
+  tools/system/acct
+]

pkgs/top-level/all-packages.nix

@@ -130,11 +130,19 @@ let
     in pkgs;
 
 
-  # The package compositions.  Yes, this isn't properly indented.
+  # The package compositions.
   pkgsFun = pkgs: overrides:
-    with helperFunctions;
-    let defaultScope = pkgs // pkgs.xorg; self = self_ // overrides;
-    self_ = with self; helperFunctions // {
+    let
+      defaultScope = pkgs // pkgs.xorg;
+      autoPackages = lib.listToAttrs
+        (map (fn: { name = baseNameOf (toString fn); value = pkgs.callPackage fn { }; })
+        (import ../auto-packages.nix));
+      self = self_ // autoPackages // overrides;
+      self_ = with self; helperFunctions //
+
+
+# Yes, this isn't properly indented.
+{
 
   # Make some arguments passed to all-packages.nix available
   inherit system stdenvType platform;
@@ -361,8 +369,6 @@ let
     inherit url;
   };
 
-  libredirect = callPackage ../build-support/libredirect { };
-
   makeDesktopItem = import ../build-support/make-desktopitem {
     inherit stdenv;
   };
@@ -427,8 +433,6 @@ let
 
   ### TOOLS
 
-  acct = callPackage ../tools/system/acct { };
-
   acoustidFingerprinter = callPackage ../tools/audio/acoustid-fingerprinter {
     ffmpeg = ffmpeg_1;
   };
@@ -1159,8 +1163,6 @@ let
 
   gnused = callPackage ../tools/text/gnused { };
 
-  gnutar = callPackage ../tools/archivers/gnutar { };
-
   gnuvd = callPackage ../tools/misc/gnuvd { };
 
   goaccess = callPackage ../tools/misc/goaccess { };
@@ -5366,8 +5368,6 @@ let
 
   libofx = callPackage ../development/libraries/libofx { };
 
-  libogg = callPackage ../development/libraries/libogg { };
-
   liboggz = callPackage ../development/libraries/liboggz { };
 
   liboil = callPackage ../development/libraries/liboil { };
@@ -5534,8 +5534,6 @@ let
 
   libvterm = callPackage ../development/libraries/libvterm { };
 
-  libvorbis = callPackage ../development/libraries/libvorbis { };
-
   libwebp = callPackage ../development/libraries/libwebp { };
 
   libwmf = callPackage ../development/libraries/libwmf { };
@@ -10417,13 +10415,13 @@ let
     callPackage = newScope pkgs.cinnamon;
     inherit (gnome3) gnome_common libgnomekbd gnome-menus zenity;
 
-    muffin = callPackage ../desktops/cinnamon/muffin.nix { } ;
+    muffin = callPackage ../desktops/cinnamon/muffin.nix { };
 
-    cinnamon-control-center = callPackage ../desktops/cinnamon/cinnamon-control-center.nix{ };
+    cinnamon-control-center = callPackage ../desktops/cinnamon/cinnamon-control-center.nix { };
 
-    cinnamon-settings-daemon = callPackage ../desktops/cinnamon/cinnamon-settings-daemon.nix{ };
+    cinnamon-settings-daemon = callPackage ../desktops/cinnamon/cinnamon-settings-daemon.nix { };
 
-    cinnamon-session = callPackage ../desktops/cinnamon/cinnamon-session.nix{ } ;
+    cinnamon-session = callPackage ../desktops/cinnamon/cinnamon-session.nix { };
 
     cinnamon-desktop = callPackage ../desktops/cinnamon/cinnamon-desktop.nix { };