top-level: Lay the groundwork for `{build,host,target}Platform`

The long term goal is a big replace:
  { inherit system platform; } => buildPlatform
  crossSystem => hostPlatform
  stdenv.cross => targetPlatform
And additionally making sure each is defined even when not cross compiling.

This commit refactors the bootstrapping code along that vision, but leaves
the old identifiers with their null semantics in place so packages can be
modernized incrementally.

1 files changed, 20 insertions, 12 deletions

diff --git a/pkgs/stdenv/linux/default.nix b/pkgs/stdenv/linux/default.nix
index 12da007f2a76..611628b35aba 100644
--- a/pkgs/stdenv/linux/default.nix
+++ b/pkgs/stdenv/linux/default.nix
@@ -4,21 +4,23 @@
 # compiler and linker that do not search in default locations,
 # ensuring purity of components produced by it.
 { lib
-, system, platform, crossSystem, config, overlays
-
-, bootstrapFiles ?
-    if system == "i686-linux" then import ./bootstrap-files/i686.nix
-    else if system == "x86_64-linux" then import ./bootstrap-files/x86_64.nix
-    else if system == "armv5tel-linux" then import ./bootstrap-files/armv5tel.nix
-    else if system == "armv6l-linux" then import ./bootstrap-files/armv6l.nix
-    else if system == "armv7l-linux" then import ./bootstrap-files/armv7l.nix
-    else if system == "mips64el-linux" then import ./bootstrap-files/loongson2f.nix
-    else abort "unsupported platform for the pure Linux stdenv"
+, localSystem, crossSystem, config, overlays
+
+, bootstrapFiles ? { # switch
+    "i686-linux" = import ./bootstrap-files/i686.nix;
+    "x86_64-linux" = import ./bootstrap-files/x86_64.nix;
+    "armv5tel-linux" = import ./bootstrap-files/armv5tel.nix;
+    "armv6l-linux" = import ./bootstrap-files/armv6l.nix;
+    "armv7l-linux" = import ./bootstrap-files/armv7l.nix;
+    "mips64el-linux" = import ./bootstrap-files/loongson2f.nix;
+  }.${localSystem.system}
+    or (abort "unsupported platform for the pure Linux stdenv")
 }:
 
 assert crossSystem == null;
 
 let
+  inherit (localSystem) system platform;
 
   commonPreHook =
     ''
@@ -91,7 +93,10 @@ let
       };
 
     in {
-      inherit system platform crossSystem config overlays;
+      buildPlatform = localSystem;
+      hostPlatform = localSystem;
+      targetPlatform = localSystem;
+      inherit config overlays;
       stdenv = thisStdenv;
     };
 
@@ -246,7 +251,10 @@ in
   # dependency (`nix-store -qR') on bootstrapTools or the first
   # binutils built.
   (prevStage: {
-    inherit system crossSystem platform config overlays;
+    buildPlatform = localSystem;
+    hostPlatform = localSystem;
+    targetPlatform = localSystem;
+    inherit config overlays;
     stdenv = import ../generic rec {
       inherit system config;