* Use a 2-stage bootstrap for creating the standard build environment

(stdenv) on Linux.  The previous 1-stage bootstrap was insufficient,
  because the tools in stdenv where built by native tools.  For
  instance, the Nix bash had a reference to /lib/libncurses.  This
  doesn't happen with a 2-stage bootstrap, since the bash built in
  stage 2 will be built with the gcc built in stage 1, which doesn't
  search in the "standard" locations.

  Motto: "Disparaging the boot is a bootable offense."

svn path=/nixpkgs/trunk/; revision=809

pkgs/system/all-packages.nix

@@ -1,60 +1,17 @@
 # This file evaluates to a function that, when supplied with a system
 # identifier, returns the set of all packages provided by the Nix
 # Package Collection.  It does this by supplying
-# `all-packages-generic.nix' with a standard build environment.
-#
-# On Linux systems, the standard build environment consists of
-# Nix-built instances glibc and the `standard' Unix tools, i.e., the
-# Posix utilities, the GNU C compiler, and so on.  On other systems,
-# we use the native C library.
+# `all-packages-generic.nix' with one of the standard build
+# environments defined in `stdenvs.nix'.
 
 {system}: let {
   allPackages = import ./all-packages-generic.nix;
 
-
-  # The native (i.e., impure) build environment.  This one uses the
-  # tools installed on the system outside of the Nix environment,
-  # i.e., the stuff in /bin, /usr/bin, etc.  This environment should
-  # be used with care, since many Nix packages will not build properly
-  # with it (e.g., because they require GNU Make).
-  stdenvNative = (import ../stdenv/native) {system = system;};
-  stdenvNativePkgs = allPackages {system = system; stdenv = stdenvNative;};
-
-
-  # The Nix build environment.
-  stdenvNix = (import ../stdenv/nix) {
-    bootStdenv = stdenvNative;
-    pkgs = stdenvNativePkgs;
-  };
-  stdenvNixPkgs = allPackages {system = system; stdenv = stdenvNix;};
-
-
-  # The Linux build environment consists of the Nix build environment
-  # built against the GNU C Library.
-  stdenvLinuxGlibc = stdenvNativePkgs.glibc;
-  stdenvLinuxBoot = (import ../stdenv/nix-linux/boot.nix) {
-    system = system;
-    glibc = stdenvLinuxGlibc;
-  };
-  stdenvLinuxBootPkgs = allPackages {system = system; stdenv = stdenvLinuxBoot;};
-
-  stdenvLinux = (import ../stdenv/nix-linux) {
-    bootStdenv = stdenvLinuxBoot;
-    pkgs = stdenvLinuxBootPkgs;
-    glibc = stdenvLinuxGlibc;
-  };
-  stdenvLinuxPkgs =
-    allPackages {system = system; stdenv = stdenvLinux;} //
-    {inherit (stdenvLinuxBootPkgs)
-      gzip bzip2 /* bash */ binutils coreutils diffutils findutils gawk gcc
-      gnumake gnused gnutar gnugrep wget;
-    } //
-    {glibc = stdenvLinuxGlibc;};
-
+  stdenvs = import ./stdenvs.nix {inherit system allPackages;};
 
   # Select the right instantiation.
   body =
     if system == "i686-linux"
-    then stdenvLinuxPkgs
-    else stdenvNixPkgs;
+    then stdenvs.stdenvLinuxPkgs
+    else stdenvs.stdenvNixPkgs;
 }

pkgs/system/stdenvs.nix

@@ -0,0 +1,76 @@
+# This file defines the various standard build environments.
+#
+# On Linux systems, the standard build environment consists of
+# Nix-built instances glibc and the `standard' Unix tools, i.e., the
+# Posix utilities, the GNU C compiler, and so on.  On other systems,
+# we use the native C library.
+
+{system, allPackages}: rec {
+
+
+  # The native (i.e., impure) build environment.  This one uses the
+  # tools installed on the system outside of the Nix environment,
+  # i.e., the stuff in /bin, /usr/bin, etc.  This environment should
+  # be used with care, since many Nix packages will not build properly
+  # with it (e.g., because they require GNU Make).
+  stdenvNative = (import ../stdenv/native) {system = system;};
+
+  stdenvNativePkgs = allPackages {system = system; stdenv = stdenvNative;};
+
+
+  # The Nix build environment.
+  stdenvNix = (import ../stdenv/nix) {
+    bootStdenv = stdenvNative;
+    pkgs = stdenvNativePkgs;
+  };
+
+  stdenvNixPkgs = allPackages {system = system; stdenv = stdenvNix;};
+
+
+  # The Linux build environment is a fully bootstrapped Nix
+  # environment, that is, it should contain no external references.
+
+  # 1) Build glibc in the native build environment.  The result is
+  #    pure (I promise!).
+  stdenvLinuxGlibc = stdenvNativePkgs.glibc;
+
+  # 2) Construct a stdenv consisting of the native build environment,
+  #    plus the pure glibc.
+  stdenvLinuxBoot1 = (import ../stdenv/nix-linux/boot.nix) {
+    system = system;
+    glibc = stdenvLinuxGlibc;
+  };
+
+  # 3) Now we can build packages that will have the Nix glibc.
+  stdenvLinuxBoot1Pkgs = allPackages {system = system; stdenv = stdenvLinuxBoot1;};
+
+  # 4) However, since these packages are built by an native C compiler
+  #    and linker, they may well pick up impure references (e.g., bash
+  #    might end up linking against /lib/libncurses).  So repeat, but
+  #    now use the Nix-built tools from step 2/3.
+  stdenvLinuxBoot2 = (import ../stdenv/nix-linux) {
+    bootStdenv = stdenvLinuxBoot1;
+    pkgs = stdenvLinuxBoot1Pkgs;
+    glibc = stdenvLinuxGlibc;
+  };
+
+  # 5) These packages should be pure.
+  stdenvLinuxBoot2Pkgs = allPackages {system = system; stdenv = stdenvLinuxBoot2;};
+
+  # 6) So finally we can construct the Nix build environment.
+  stdenvLinux = (import ../stdenv/nix-linux) {
+    bootStdenv = stdenvLinuxBoot2;
+    pkgs = stdenvLinuxBoot2Pkgs;
+    glibc = stdenvLinuxGlibc;
+  };
+
+  # 7) And we can build all packages against that, but we don't
+  #    rebuild stuff from step 6.
+  stdenvLinuxPkgs =
+    allPackages {system = system; stdenv = stdenvLinux;} //
+    {inherit (stdenvLinuxBoot2Pkgs)
+      gzip bzip2 bash binutils coreutils diffutils findutils gawk gcc
+      gnumake gnused gnutar gnugrep wget;
+    } //
+    {glibc = stdenvLinuxGlibc;};
+}