stdenv: implement crossOverlays

crossOverlays only apply to the packages being built, not the build
packages. It is useful when you don’t care what is used to build your
packages, just what is being built. The idea relies heavily on the
cross compiling infrastructure. Using this implies that we need to
create a cross stdenv.

(cherry picked from commit a3a6ad7a01e943a4097c87cb144d331910693d82)

9 files changed, 28 insertions, 20 deletions

diff --git a/pkgs/stdenv/cross/default.nix b/pkgs/stdenv/cross/default.nix
index daa9f66615c..a6063049a3a 100644
--- a/pkgs/stdenv/cross/default.nix
+++ b/pkgs/stdenv/cross/default.nix
@@ -1,11 +1,14 @@
 { lib
-, localSystem, crossSystem, config, overlays
+, localSystem, crossSystem, config, overlays, crossOverlays ? []
 }:
 
 let
   bootStages = import ../. {
     inherit lib localSystem overlays;
-    crossSystem = null;
+
+    crossSystem = localSystem;
+    crossOverlays = [];
+
     # Ignore custom stdenvs when cross compiling for compatability
     config = builtins.removeAttrs config [ "replaceStdenv" ];
   };
@@ -33,7 +36,8 @@ in lib.init bootStages ++ [
 
   # Run Packages
   (buildPackages: {
-    inherit config overlays;
+    inherit config;
+    overlays = overlays ++ crossOverlays;
     selfBuild = false;
     stdenv = buildPackages.stdenv.override (old: rec {
       buildPlatform = localSystem;
@@ -48,7 +52,7 @@ in lib.init bootStages ++ [
 
       cc = if crossSystem.useiOSPrebuilt or false
              then buildPackages.darwin.iosSdkPkgs.clang
-           else if crossSystem.useAndroidPrebuilt
+           else if crossSystem.useAndroidPrebuilt or false
              then buildPackages.androidenv."androidndkPkgs_${crossSystem.ndkVer}".gcc
            else buildPackages.gcc;
 
@@ -56,6 +60,7 @@ in lib.init bootStages ++ [
         ++ lib.optionals
              (hostPlatform.isLinux && !buildPlatform.isLinux)
              [ buildPackages.patchelf buildPackages.paxctl ]
+        ++ lib.optional hostPlatform.isDarwin buildPackages.clang
         ++ lib.optional
              (let f = p: !p.isx86 || p.libc == "musl"; in f hostPlatform && !(f buildPlatform))
              buildPackages.updateAutotoolsGnuConfigScriptsHook
diff --git a/pkgs/stdenv/custom/default.nix b/pkgs/stdenv/custom/default.nix
index b6ea8685f8e..e86face9519 100644
--- a/pkgs/stdenv/custom/default.nix
+++ b/pkgs/stdenv/custom/default.nix
@@ -2,7 +2,7 @@
 , localSystem, crossSystem, config, overlays
 }:
 
-assert crossSystem == null;
+assert crossSystem == localSystem;
 
 let
   bootStages = import ../. {
diff --git a/pkgs/stdenv/darwin/default.nix b/pkgs/stdenv/darwin/default.nix
index cda643c42fe..4c693f3e5d6 100644
--- a/pkgs/stdenv/darwin/default.nix
+++ b/pkgs/stdenv/darwin/default.nix
@@ -1,5 +1,5 @@
 { lib
-, localSystem, crossSystem, config, overlays
+, localSystem, crossSystem, config, overlays, crossOverlays ? []
 
 # Allow passing in bootstrap files directly so we can test the stdenv bootstrap process when changing the bootstrap tools
 , bootstrapFiles ? let
@@ -16,7 +16,7 @@
   }
 }:
 
-assert crossSystem == null;
+assert crossSystem == localSystem;
 
 let
   inherit (localSystem) system platform;
diff --git a/pkgs/stdenv/default.nix b/pkgs/stdenv/default.nix
index 210e0439c0b..c0bbe24e521 100644
--- a/pkgs/stdenv/default.nix
+++ b/pkgs/stdenv/default.nix
@@ -7,7 +7,7 @@
 { # Args just for stdenvs' usage
   lib
   # Args to pass on to the pkgset builder, too
-, localSystem, crossSystem, config, overlays
+, localSystem, crossSystem, config, overlays, crossOverlays ? []
 } @ args:
 
 let
@@ -36,7 +36,7 @@ let
 
   # Select the appropriate stages for the platform `system'.
 in
-  if crossSystem != null then stagesCross
+  if crossSystem != localSystem || crossOverlays != [] then stagesCross
   else if config ? replaceStdenv then stagesCustom
   else { # switch
     "i686-linux" = stagesLinux;
diff --git a/pkgs/stdenv/freebsd/default.nix b/pkgs/stdenv/freebsd/default.nix
index b3a6cedad84..dbb4a056455 100644
--- a/pkgs/stdenv/freebsd/default.nix
+++ b/pkgs/stdenv/freebsd/default.nix
@@ -2,7 +2,7 @@
 , localSystem, crossSystem, config, overlays
 }:
 
-assert crossSystem == null;
+assert crossSystem == localSystem;
 let inherit (localSystem) system; in
 
 
diff --git a/pkgs/stdenv/linux/default.nix b/pkgs/stdenv/linux/default.nix
index 884730cfe90..3700211fa29 100644
--- a/pkgs/stdenv/linux/default.nix
+++ b/pkgs/stdenv/linux/default.nix
@@ -4,7 +4,7 @@
 # compiler and linker that do not search in default locations,
 # ensuring purity of components produced by it.
 { lib
-, localSystem, crossSystem, config, overlays
+, localSystem, crossSystem, config, overlays, crossOverlays ? []
 
 , bootstrapFiles ?
   let table = {
@@ -32,7 +32,7 @@
   in files
 }:
 
-assert crossSystem == null;
+assert crossSystem == localSystem;
 
 let
   inherit (localSystem) system platform;
diff --git a/pkgs/stdenv/native/default.nix b/pkgs/stdenv/native/default.nix
index 37795b11f6d..810cf16301f 100644
--- a/pkgs/stdenv/native/default.nix
+++ b/pkgs/stdenv/native/default.nix
@@ -2,7 +2,7 @@
 , localSystem, crossSystem, config, overlays
 }:
 
-assert crossSystem == null;
+assert crossSystem == localSystem;
 
 let
   inherit (localSystem) system;
diff --git a/pkgs/stdenv/nix/default.nix b/pkgs/stdenv/nix/default.nix
index ffff8bdf51d..a8311f49609 100644
--- a/pkgs/stdenv/nix/default.nix
+++ b/pkgs/stdenv/nix/default.nix
@@ -1,10 +1,10 @@
 { lib
-, crossSystem, config, overlays
+, crossSystem, localSystem, config, overlays
 , bootStages
 , ...
 }:
 
-assert crossSystem == null;
+assert crossSystem == localSystem;
 
 bootStages ++ [
   (prevStage: {
diff --git a/pkgs/top-level/default.nix b/pkgs/top-level/default.nix
index da7fc1bed34..dcd443a1c29 100644
--- a/pkgs/top-level/default.nix
+++ b/pkgs/top-level/default.nix
@@ -22,9 +22,8 @@
   # `*Platform`s.
   localSystem
 
-, # The system packages will ultimately be run on. Null if the two should be the
-  # same.
-  crossSystem ? null
+, # The system packages will ultimately be run on.
+  crossSystem ? localSystem
 
 , # Allow a configuration attribute set to be passed in as an argument.
   config ? {}
@@ -32,6 +31,9 @@
 , # List of overlays layers used to extend Nixpkgs.
   overlays ? []
 
+, # List of overlays to apply to target packages only.
+  crossOverlays ? []
+
 , # A function booting the final package set for a specific standard
   # environment. See below for the arguments given to that function, the type of
   # list it returns.
@@ -61,7 +63,8 @@ in let
     builtins.intersectAttrs { platform = null; } config
     // args.localSystem);
 
-  crossSystem = lib.mapNullable lib.systems.elaborate crossSystem0;
+  crossSystem = if crossSystem0 == null then localSystem
+                else lib.systems.elaborate crossSystem0;
 
   # A few packages make a new package set to draw their dependencies from.
   # (Currently to get a cross tool chain, or forced-i686 package.) Rather than
@@ -91,7 +94,7 @@ in let
   boot = import ../stdenv/booter.nix { inherit lib allPackages; };
 
   stages = stdenvStages {
-    inherit lib localSystem crossSystem config overlays;
+    inherit lib localSystem crossSystem config overlays crossOverlays;
   };
 
   pkgs = boot stages;