top-level: Introduce `buildPackages` for resolving build-time deps

[N.B., this package also applies to the commits that follow it in the same
PR.]

In most cases, buildPackages = pkgs so things work just as before. For
cross compiling, however, buildPackages is resolved as the previous
bootstrapping stage. This allows us to avoid the mkDerivation hacks cross
compiling currently uses today.

To avoid a massive refactor, callPackage will splice together both package
sets. Again to avoid churn, it uses the old `nativeDrv` vs `crossDrv` to do
so. So now, whether cross compiling or not, packages with get a `nativeDrv`
and `crossDrv`---in the non-cross-compiling case they are simply the same
derivation. This is good because it reduces the divergence between the
cross and non-cross dataflow. See `pkgs/top-level/splice.nix` for a comment
along the lines of the preceding paragraph, and the code that does this
splicing.

Also, `forceNativeDrv` is replaced with `forceNativePackages`. The latter
resolves `pkgs` unless the host platform is different from the build
platform, in which case it resolves to `buildPackages`. Note that the
target platform is not important here---it will not prevent
`forcedNativePackages` from resolving to `pkgs`.

--------

Temporarily, we make preserve some dubious decisions in the name of preserving
hashes:

Most importantly, we don't distinguish between "host" and "target" in the
autoconf sense. This leads to the proliferation of *Cross derivations
currently used. What we ought to is resolve native deps of the cross "build
packages" (build = host != target) package set against the "vanilla
packages" (build = host = target) package set. Instead, "build packages"
uses itself, with (informally) target != build in all cases.

This is wrong because it violates the "sliding window" principle of
bootstrapping stages that shifting the platform triple of one stage to the
left coincides with the next stage's platform triple. Only because we don't
explicitly distinguish between "host" and "target" does it appear that the
"sliding window" principle is preserved--indeed it is over the reductionary
"platform double" of just "build" and "host/target".

Additionally, we build libc, libgcc, etc in the same stage as the compilers
themselves, which is wrong because they are used at runtime, not build
time. Fixing this is somewhat subtle, and the solution and problem will be
better explained in the commit that does fix it.

Commits after this will solve both these issues, at the expense of breaking
cross hashes. Native hashes won't be broken, thankfully.

--------

Did the temporary ugliness pan out? Of the packages that currently build in
`release-cross.nix`, the only ones that have their hash changed are
`*.gcc.crossDrv` and `bootstrapTools.*.coreutilsMinimal`. In both cases I
think it doesn't matter.

 1. GCC when doing a `build = host = target = foreign` build (maximally
    cross), still defines environment variables like `CPATH`[1] with
    packages.  This seems assuredly wrong because whether gcc dynamically
    links those, or the programs built by gcc dynamically link those---I
    have no idea which case is reality---they should be foreign. Therefore,
    in all likelihood, I just made the gcc less broken.

 2. Coreutils (ab)used the old cross-compiling infrastructure to depend on
    a native version of itself. When coreutils was overwritten to be built
    with fewer features, the native version it used would also be
    overwritten because the binding was tight. Now it uses the much looser
    `BuildPackages.coreutils` which is just fine as a richer build dep
    doesn't cause any problems and avoids a rebuild.

So, in conclusion I'd say the conservatism payed off. Onward to actually
raking the muck in the next PR!

[1]: https://gcc.gnu.org/onlinedocs/gcc/Environment-Variables.html

5 files changed, 46 insertions, 36 deletions

diff --git a/pkgs/stdenv/adapters.nix b/pkgs/stdenv/adapters.nix
index 11f9a43c035e..daa180c644fa 100644
--- a/pkgs/stdenv/adapters.nix
+++ b/pkgs/stdenv/adapters.nix
@@ -66,12 +66,10 @@ rec {
 
             # In nixpkgs, sometimes 'null' gets in as a buildInputs element,
             # and we handle that through isAttrs.
-            getNativeDrv = drv: drv.nativeDrv or drv;
-            getCrossDrv = drv: drv.crossDrv or drv;
-            nativeBuildInputsDrvs = map getNativeDrv nativeBuildInputs;
-            buildInputsDrvs = map getCrossDrv buildInputs;
-            propagatedBuildInputsDrvs = map getCrossDrv propagatedBuildInputs;
-            propagatedNativeBuildInputsDrvs = map getNativeDrv propagatedNativeBuildInputs;
+            nativeBuildInputsDrvs = nativeBuildInputs;
+            buildInputsDrvs = buildInputs;
+            propagatedBuildInputsDrvs = propagatedBuildInputs;
+            propagatedNativeBuildInputsDrvs = propagatedNativeBuildInputs;
 
             # The base stdenv already knows that nativeBuildInputs and
             # buildInputs should be built with the usual gcc-wrapper
@@ -88,10 +86,7 @@ rec {
                 (drv: builtins.isAttrs drv && drv ? nativeDrv) buildInputs;
             nativeInputsFromBuildInputs = stdenv.lib.filter hostAsNativeDrv buildInputsNotNull;
 
-            # We should overwrite the input attributes in crossDrv, to overwrite
-            # the defaults for only-native builds in the base stdenv
-            crossDrv = if cross == null then nativeDrv else
-                stdenv.mkDerivation (args // {
+        in      stdenv.mkDerivation (args // {
                     name = name + "-" + cross.config;
                     nativeBuildInputs = nativeBuildInputsDrvs
                       ++ nativeInputsFromBuildInputs
@@ -112,9 +107,6 @@ rec {
 
                     crossConfig = cross.config;
                 } // args.crossAttrs or {});
-        in nativeDrv // {
-          inherit crossDrv nativeDrv;
-        };
     } // {
       inherit cross gccCross binutilsCross;
       ccCross = gccCross;
diff --git a/pkgs/stdenv/booter.nix b/pkgs/stdenv/booter.nix
index 11ca8e1440e1..6e5d073e55a7 100644
--- a/pkgs/stdenv/booter.nix
+++ b/pkgs/stdenv/booter.nix
@@ -57,12 +57,18 @@ stageFuns: let
   # debugging purposes.
   folder = stageFun: finalSoFar: let
     args = stageFun finalSoFar;
-    stdenv = args.stdenv // {
-      # For debugging
-      __bootPackages = finalSoFar;
+    args' = args // {
+      stdenv = args.stdenv // {
+        # For debugging
+        __bootPackages = finalSoFar;
+      };
     };
-    args' = args // { inherit stdenv; };
-  in
-    (if args.__raw or false then lib.id else allPackages) args';
+    self =
+      if args.__raw or false
+      then args'
+      else allPackages ((builtins.removeAttrs args' ["selfBuild"]) // {
+        buildPackages = if args.selfBuild or true then self else finalSoFar;
+      });
+  in self;
 
 in lib.lists.fold folder {} withAllowCustomOverrides
diff --git a/pkgs/stdenv/cross/default.nix b/pkgs/stdenv/cross/default.nix
index 16f41671b768..e684c14da4a5 100644
--- a/pkgs/stdenv/cross/default.nix
+++ b/pkgs/stdenv/cross/default.nix
@@ -12,13 +12,11 @@ let
 
 in bootStages ++ [
 
-  # Build Packages.
-  #
-  # For now, this is just used to build the native stdenv. Eventually, it
-  # should be used to build compilers and other such tools targeting the cross
-  # platform. Then, `forceNativeDrv` can be removed.
+  # Build Packages
   (vanillaPackages: {
     inherit system platform crossSystem config overlays;
+    # Should be false, but we're trying to preserve hashes for now
+    selfBuild = true;
     # It's OK to change the built-time dependencies
     allowCustomOverrides = true;
     stdenv = vanillaPackages.stdenv // {
@@ -28,9 +26,10 @@ in bootStages ++ [
     };
   })
 
-  # Run packages
+  # Run Packages
   (buildPackages: {
     inherit system platform crossSystem config overlays;
+    selfBuild = false;
     stdenv = if crossSystem.useiOSCross or false
       then let
           inherit (buildPackages.darwin.ios-cross {
diff --git a/pkgs/stdenv/generic/default.nix b/pkgs/stdenv/generic/default.nix
index 32e0d8948188..269d7ef893a1 100644
--- a/pkgs/stdenv/generic/default.nix
+++ b/pkgs/stdenv/generic/default.nix
@@ -115,7 +115,19 @@ let
     , sandboxProfile ? ""
     , propagatedSandboxProfile ? ""
     , ... } @ attrs:
-    let
+    let # Rename argumemnts to avoid cycles
+      buildInputs__ = buildInputs;
+      nativeBuildInputs__ = nativeBuildInputs;
+      propagatedBuildInputs__ = propagatedBuildInputs;
+      propagatedNativeBuildInputs__ = propagatedNativeBuildInputs;
+    in let
+      getNativeDrv = drv: drv.nativeDrv or drv;
+      getCrossDrv = drv: drv.crossDrv or drv;
+      nativeBuildInputs = map getNativeDrv nativeBuildInputs__;
+      buildInputs = map getCrossDrv buildInputs__;
+      propagatedBuildInputs = map getCrossDrv propagatedBuildInputs__;
+      propagatedNativeBuildInputs = map getNativeDrv propagatedNativeBuildInputs__;
+    in let
       pos' =
         if pos != null then
           pos
diff --git a/pkgs/stdenv/linux/make-bootstrap-tools-cross.nix b/pkgs/stdenv/linux/make-bootstrap-tools-cross.nix
index 9f4a4517627e..a1b1f02d83d8 100644
--- a/pkgs/stdenv/linux/make-bootstrap-tools-cross.nix
+++ b/pkgs/stdenv/linux/make-bootstrap-tools-cross.nix
@@ -55,11 +55,12 @@ let
     if toolsArch == "armv6l" then raspberrypiCrossSystem else
     if toolsArch == "armv7l" then armv7l-hf-multiplatform-crossSystem else null;
 
-  pkgs = pkgsFun ({inherit system;} // selectedCrossSystem);
+  pkgsUnspliced = pkgsFun ({inherit system;} // selectedCrossSystem);
+  pkgs = pkgsUnspliced.splicedPackages;
 
-  inherit (pkgs) stdenv nukeReferences cpio binutilsCross;
+  inherit (pkgsUnspliced.buildPackages) stdenv nukeReferences cpio binutilsCross;
 
-  glibc = pkgs.libcCross;
+  glibc = pkgs.libcCross.nativeDrv;
   bash = pkgs.bash.crossDrv;
   findutils = pkgs.findutils.crossDrv;
   diffutils = pkgs.diffutils.crossDrv;
@@ -71,7 +72,7 @@ let
   gnumake = pkgs.gnumake.crossDrv;
   patch = pkgs.patch.crossDrv;
   patchelf = pkgs.patchelf.crossDrv;
-  gcc = pkgs.gcc.cc.crossDrv;
+  gcc = pkgs.gcc.crossDrv.cc;
   gmpxx = pkgs.gmpxx.crossDrv;
   mpfr = pkgs.mpfr.crossDrv;
   zlib = pkgs.zlib.crossDrv;
@@ -86,17 +87,17 @@ in
 rec {
 
 
-  coreutilsMinimal = (pkgs.coreutils.override (args: {
+  coreutilsMinimal = pkgs.coreutils.override (args: {
     # We want coreutils without ACL/attr support.
     aclSupport = false;
     attrSupport = false;
     # Our tooling currently can't handle scripts in bin/, only ELFs and symlinks.
     singleBinary = "symlinks";
-  })).crossDrv;
+  });
 
-  tarMinimal = (pkgs.gnutar.override { acl = null; }).crossDrv;
+  tarMinimal = pkgs.gnutar.override { acl = null; };
 
-  busyboxMinimal = (pkgs.busybox.override {
+  busyboxMinimal = pkgs.busybox.override {
     useMusl = true;
     enableStatic = true;
     enableMinimal = true;
@@ -109,13 +110,13 @@ rec {
       CONFIG_TAR y
       CONFIG_UNXZ y
     '';
-  }).crossDrv;
+  };
 
   build =
 
     stdenv.mkDerivation {
       name = "stdenv-bootstrap-tools-cross";
-      crossConfig = stdenv.cross.config;
+      crossConfig = pkgsUnspliced.crossSystem.config;
 
       buildInputs = [nukeReferences cpio binutilsCross];