top-level: {build,host,target}Platform are defined in the stdenv instead

See #27069 for a discussion of this

pkgs/build-support/cc-wrapper/default.nix

···
 , zlib ? null, extraPackages ? [], extraBuildCommands ? ""
 , dyld ? null # TODO: should this be a setup-hook on dyld?
 , isGNU ? false, isClang ? cc.isClang or false, gnugrep ? null
-, hostPlatform, targetPlatform
 , runCommand ? null
 }:
 
···
 assert !(nativeLibc && noLibc);
 assert (noLibc || nativeLibc) == (libc == null);
 
-assert targetPlatform != hostPlatform -> runCommand != null;
+assert stdenv.targetPlatform != stdenv.hostPlatform -> runCommand != null;
 
 # For ghdl (the vhdl language provider to gcc) we need zlib in the wrapper.
 assert cc.langVhdl or false -> zlib != null;
 
 let
+  inherit (stdenv) hostPlatform targetPlatform;
+
   # Prefix for binaries. Customarily ends with a dash separator.
   #
   # TODO(@Ericson2314) Make unconditional, or optional but always true by

pkgs/stdenv/adapters.nix

···
                     , buildPlatform, hostPlatform, targetPlatform
                     } @ overrideArgs: let
     stdenv = overrideArgs.stdenv.override {
-      # TODO(@Ericson2314): Cannot do this for now because then Nix thinks the
-      # resulting derivation should be built on the host platform.
-      #hostPlatform = buildPlatform;
-      #targetPlatform = hostPlatform;
-      inherit cc;
+      inherit
+        buildPlatform hostPlatform targetPlatform
+        cc;
 
       allowedRequisites = null;
 

pkgs/stdenv/cross/default.nix

···
 
   # Build Packages
   (vanillaPackages: {
-    buildPlatform = localSystem;
-    hostPlatform = localSystem;
-    targetPlatform = crossSystem;
     inherit config overlays;
     selfBuild = false;
+    stdenv =
+      assert vanillaPackages.hostPlatform == localSystem;
+      assert vanillaPackages.targetPlatform == localSystem;
+      vanillaPackages.stdenv.override { targetPlatform = crossSystem; };
     # It's OK to change the built-time dependencies
     allowCustomOverrides = true;
-    inherit (vanillaPackages) stdenv;
   })
 
   # Run Packages
   (buildPackages: {
-    buildPlatform = localSystem;
-    hostPlatform = crossSystem;
-    targetPlatform = crossSystem;
     inherit config overlays;
     selfBuild = false;
     stdenv = buildPackages.makeStdenvCross {

pkgs/stdenv/custom/default.nix

···
 
   # Additional stage, built using custom stdenv
   (vanillaPackages: {
-    buildPlatform = localSystem;
-    hostPlatform = localSystem;
-    targetPlatform = localSystem;
     inherit config overlays;
-    stdenv = config.replaceStdenv { pkgs = vanillaPackages; };
+    stdenv =
+      assert vanillaPackages.hostPlatform == localSystem;
+      assert vanillaPackages.targetPlatform == localSystem;
+      config.replaceStdenv { pkgs = vanillaPackages; };
   })
 
 ]

pkgs/stdenv/darwin/default.nix

···
 
         name = "stdenv-darwin-boot-${toString step}";
 
+        buildPlatform = localSystem;
+        hostPlatform = localSystem;
+        targetPlatform = localSystem;
+
         cc = if isNull last then "/dev/null" else import ../../build-support/cc-wrapper {
           inherit shell;
           inherit (last) stdenv;
···
           nativeTools  = true;
           nativePrefix = bootstrapTools;
           nativeLibc   = false;
-          hostPlatform = localSystem;
-          targetPlatform = localSystem;
           libc         = last.pkgs.darwin.Libsystem;
           isClang      = true;
           cc           = { name = "clang-9.9.9"; outPath = bootstrapTools; };
···
         '';
         initialPath  = [ bootstrapTools ];
 
-        hostPlatform = localSystem;
-        targetPlatform = localSystem;
-
         fetchurlBoot = import ../../build-support/fetchurl {
           stdenv = stage0.stdenv;
           curl   = bootstrapTools;
···
       };
 
     in {
-      buildPlatform = localSystem;
-      hostPlatform = localSystem;
-      targetPlatform = localSystem;
       inherit config overlays;
       stdenv = thisStdenv;
     };
···
 
     name = "stdenv-darwin";
 
+    buildPlatform = localSystem;
+    hostPlatform = localSystem;
+    targetPlatform = localSystem;
+
     preHook = commonPreHook + ''
       export PATH_LOCALE=${pkgs.darwin.locale}/share/locale
     '';
···
     stdenvSandboxProfile = binShClosure + libSystemProfile;
     extraSandboxProfile  = binShClosure + libSystemProfile;
 
-    hostPlatform = localSystem;
-    targetPlatform = localSystem;
-
     initialPath = import ../common-path.nix { inherit pkgs; };
     shell       = "${pkgs.bash}/bin/bash";
 
···
       inherit shell;
       nativeTools = false;
       nativeLibc  = false;
-      hostPlatform = localSystem;
-      targetPlatform = localSystem;
       inherit (pkgs) coreutils binutils gnugrep;
       inherit (pkgs.darwin) dyld;
       cc   = pkgs.llvmPackages.clang-unwrapped;
···
     stage3
     stage4
     (prevStage: {
-      buildPlatform = localSystem;
-      hostPlatform = localSystem;
-      targetPlatform = localSystem;
       inherit config overlays;
       stdenv = stdenvDarwin prevStage;
     })

pkgs/stdenv/freebsd/default.nix

···
 
     stdenv = import ../generic {
       name = "stdenv-freebsd-boot-1";
+      buildPlatform = localSystem;
+      hostPlatform = localSystem;
+      targetPlatform = localSystem;
       inherit config;
       initialPath = [ "/" "/usr" ];
       hostPlatform = localSystem;
···
 
     stdenv = import ../generic {
       name = "stdenv-freebsd-boot-0";
+      buildPlatform = localSystem;
+      hostPlatform = localSystem;
+      targetPlatform = localSystem;
       inherit config;
       initialPath = [ prevStage.bootstrapTools ];
       inherit (prevStage.stdenv)
···
   })
 
   (prevStage: {
-    buildPlatform = localSystem;
-    hostPlatform = localSystem;
-    targetPlatform = localSystem;
     inherit config overlays;
     stdenv = import ../generic {
       name = "stdenv-freebsd-boot-3";
+      buildPlatform = localSystem;
+      hostPlatform = localSystem;
+      targetPlatform = localSystem;
       inherit config;
 
       inherit (prevStage.stdenv)
···
         nativeTools  = true;
         nativePrefix = "/usr";
         nativeLibc   = true;
-        hostPlatform = localSystem;
-        targetPlatform = localSystem;
         inherit (prevStage) stdenv;
         cc           = {
           name    = "clang-9.9.9";

pkgs/stdenv/generic/default.nix

···
 , stdenvSandboxProfile ? ""
 , extraSandboxProfile ? ""
 
-, # The platforms here do *not* correspond to the stage the stdenv is
-  # used in, but rather the previous one, in which it was built. We
-  # use the latter two platforms, like a cross compiler, because the
-  # stand environment is a build tool if you squint at it, and because
-  # neither of these are used when building stdenv so we know the
-  # build platform is irrelevant.
-  hostPlatform, targetPlatform
+  ## Platform parameters
+  ##
+  ## The "build" "host" "target" terminology below comes from GNU Autotools. See
+  ## its documentation for more information on what those words mean. Note that
+  ## each should always be defined, even when not cross compiling.
+  ##
+  ## For purposes of bootstrapping, think of each stage as a "sliding window"
+  ## over a list of platforms. Specifically, the host platform of the previous
+  ## stage becomes the build platform of the current one, and likewise the
+  ## target platform of the previous stage becomes the host platform of the
+  ## current one.
+  ##
+
+, # The platform on which packages are built. Consists of `system`, a
+  # string (e.g.,`i686-linux') identifying the most import attributes of the
+  # build platform, and `platform` a set of other details.
+  buildPlatform
+
+, # The platform on which packages run.
+  hostPlatform
+
+, # The platform which build tools (especially compilers) build for in this stage,
+  targetPlatform
 }:
 
 let
-  inherit (targetPlatform) system;
-
   defaultNativeBuildInputs = extraBuildInputs ++
     [ ../../build-support/setup-hooks/move-docs.sh
       ../../build-support/setup-hooks/compress-man-pages.sh
···
     derivation (
     (if isNull allowedRequisites then {} else { allowedRequisites = allowedRequisites ++ defaultNativeBuildInputs; }) //
     {
-      inherit system name;
+      inherit name;
+
+      # Nix itself uses the `system` field of a derivation to decide where to
+      # build it. This is a bit confusing for cross compilation.
+      inherit (buildPlatform) system;
 
       builder = shell;
 
···
 
       inherit preHook initialPath shell defaultNativeBuildInputs;
     }
-    // lib.optionalAttrs hostPlatform.isDarwin {
+    // lib.optionalAttrs buildPlatform.isDarwin {
       __sandboxProfile = stdenvSandboxProfile;
       __impureHostDeps = __stdenvImpureHostDeps;
     })
···
         platforms = lib.platforms.all;
       };
 
+      inherit buildPlatform hostPlatform targetPlatform;
+
       inherit extraBuildInputs __extraImpureHostDeps extraSandboxProfile;
 
       # Utility flags to test the type of platform.
···
 
       inherit (import ./make-derivation.nix {
         inherit lib config stdenv;
-        # TODO(@Ericson2314): Remove
-        inherit
-          hostPlatform targetPlatform;
       }) mkDerivation;
 
       # For convenience, bring in the library functions in lib/ so

pkgs/stdenv/generic/make-derivation.nix

···
-{ lib, config, stdenv
-
-# TODO(@Ericson2314): get off stdenv
-, hostPlatform, targetPlatform
-}:
+{ lib, config, stdenv }:
 
 rec {
   # `mkDerivation` wraps the builtin `derivation` function to
···
 
       outputs' =
         outputs ++
-        (if separateDebugInfo then assert targetPlatform.isLinux; [ "debug" ] else []);
+        (if separateDebugInfo then assert stdenv.hostPlatform.isLinux; [ "debug" ] else []);
 
       dependencies' = let
           justMap = map lib.chooseDevOutputs dependencies;
           nativeBuildInputs = lib.elemAt justMap 0
-            ++ lib.optional targetPlatform.isWindows ../../build-support/setup-hooks/win-dll-link.sh;
+            ++ lib.optional stdenv.hostPlatform.isWindows ../../build-support/setup-hooks/win-dll-link.sh;
           buildInputs = lib.elemAt justMap 1
                # TODO(@Ericson2314): Should instead also be appended to `nativeBuildInputs`.
             ++ lib.optional separateDebugInfo ../../build-support/setup-hooks/separate-debug-info.sh;
···
           builder = attrs.realBuilder or stdenv.shell;
           args = attrs.args or ["-e" (attrs.builder or ./default-builder.sh)];
           inherit stdenv;
-          system = stdenv.system; # TODO(@Ericson2314): be correct about cross compilation
+          inherit (stdenv) system;
           userHook = config.stdenv.userHook or null;
           __ignoreNulls = true;
 
···
 
           propagatedNativeBuildInputs = lib.elemAt propagatedDependencies' 0;
           propagatedBuildInputs = lib.elemAt propagatedDependencies' 1;
-        } // lib.optionalAttrs (hostPlatform.isDarwin) {
+        } // lib.optionalAttrs (stdenv.buildPlatform.isDarwin) {
           # TODO: remove lib.unique once nix has a list canonicalization primitive
           __sandboxProfile =
           let profiles = [ stdenv.extraSandboxProfile ] ++ computedSandboxProfile ++ computedPropagatedSandboxProfile ++ [ propagatedSandboxProfile sandboxProfile ];
···
           {
             inherit lib config meta derivationArg;
             mkDerivationArg = attrs;
-            inherit (stdenv) system; # TODO: cross-compilation?
+            # Nix itself uses the `system` field of a derivation to decide where
+            # to build it. This is a bit confusing for cross compilation.
+            inherit (stdenv) system;
           }))
         ( {
             overrideAttrs = f: mkDerivation (attrs // (f attrs));

pkgs/stdenv/linux/default.nix

···
     let
 
       thisStdenv = import ../generic {
+        name = "stdenv-linux-boot";
+        buildPlatform = localSystem;
+        hostPlatform = localSystem;
+        targetPlatform = localSystem;
         inherit config extraBuildInputs;
-        name = "stdenv-linux-boot";
         preHook =
           ''
             # Don't patch #!/interpreter because it leads to retained
···
         shell = "${bootstrapTools}/bin/bash";
         initialPath = [bootstrapTools];
 
-        hostPlatform = localSystem;
-        targetPlatform = localSystem;
-
         fetchurlBoot = import ../../build-support/fetchurl/boot.nix {
           inherit system;
         };
···
              else lib.makeOverridable (import ../../build-support/cc-wrapper) {
           nativeTools = false;
           nativeLibc = false;
-          hostPlatform = localSystem;
-          targetPlatform = localSystem;
           cc = prevStage.gcc-unwrapped;
           isGNU = true;
           libc = prevStage.glibc;
···
       };
 
     in {
-      buildPlatform = localSystem;
-      hostPlatform = localSystem;
-      targetPlatform = localSystem;
       inherit config overlays;
       stdenv = thisStdenv;
     };
···
         nativeTools = false;
         nativeLibc = false;
         isGNU = true;
-        hostPlatform = localSystem;
-        targetPlatform = localSystem;
         cc = prevStage.gcc-unwrapped;
         libc = self.glibc;
         inherit (self) stdenv binutils coreutils gnugrep;
···
   # dependency (`nix-store -qR') on bootstrapTools or the first
   # binutils built.
   (prevStage: {
-    buildPlatform = localSystem;
-    hostPlatform = localSystem;
-    targetPlatform = localSystem;
     inherit config overlays;
     stdenv = import ../generic rec {
+      buildPlatform = localSystem;
+      hostPlatform = localSystem;
+      targetPlatform = localSystem;
       inherit config;
 
       preHook = ''
···
 
       initialPath =
         ((import ../common-path.nix) {pkgs = prevStage;});
-
-      hostPlatform = localSystem;
-      targetPlatform = localSystem;
 
       extraBuildInputs = [ prevStage.patchelf prevStage.paxctl ] ++
         # Many tarballs come with obsolete config.sub/config.guess that don't recognize aarch64.

pkgs/stdenv/native/default.nix

···
     { cc, fetchurl, extraPath ? [], overrides ? (self: super: { }) }:
 
     import ../generic {
+      buildPlatform = localSystem;
       hostPlatform = localSystem;
       targetPlatform = localSystem;
 
···
         "i686-solaris" = "/usr/gnu";
         "x86_64-solaris" = "/opt/local/gcc47";
       }.${system} or "/usr";
-      hostPlatform = localSystem;
-      targetPlatform = localSystem;
       inherit stdenv;
     };
 
···
 
   # First build a stdenv based only on tools outside the store.
   (prevStage: {
-    buildPlatform = localSystem;
-    hostPlatform = localSystem;
-    targetPlatform = localSystem;
     inherit config overlays;
     stdenv = makeStdenv {
       inherit (prevStage) cc fetchurl;
···
   # Using that, build a stdenv that adds the ‘xz’ command (which most systems
   # don't have, so we mustn't rely on the native environment providing it).
   (prevStage: {
-    buildPlatform = localSystem;
-    hostPlatform = localSystem;
-    targetPlatform = localSystem;
     inherit config overlays;
     stdenv = makeStdenv {
       inherit (prevStage.stdenv) cc fetchurl;

pkgs/stdenv/nix/default.nix

···
   (prevStage: let
     inherit (prevStage) stdenv;
   in {
-    inherit (prevStage) buildPlatform hostPlatform targetPlatform;
     inherit config overlays;
 
     stdenv = import ../generic rec {
+      buildPlatform = localSystem;
+      hostPlatform = localSystem;
+      targetPlatform = localSystem;
+
       inherit config;
 
       preHook = ''
···
         nativeTools = false;
         nativePrefix = stdenv.lib.optionalString hostPlatform.isSunOS "/usr";
         nativeLibc = true;
-        hostPlatform = localSystem;
-        targetPlatform = localSystem;
         inherit stdenv;
         inherit (prevStage) binutils coreutils gnugrep;
         cc = prevStage.gcc.cc;

pkgs/top-level/stage.nix

···
 , # Use to reevaluate Nixpkgs; a dirty hack that should be removed
   nixpkgsFun
 
-  ## Platform parameters
-  ##
-  ## The "build" "host" "target" terminology below comes from GNU Autotools. See
-  ## its documentation for more information on what those words mean. Note that
-  ## each should always be defined, even when not cross compiling.
-  ##
-  ## For purposes of bootstrapping, think of each stage as a "sliding window"
-  ## over a list of platforms. Specifically, the host platform of the previous
-  ## stage becomes the build platform of the current one, and likewise the
-  ## target platform of the previous stage becomes the host platform of the
-  ## current one.
-  ##
-
-, # The platform on which packages are built. Consists of `system`, a
-  # string (e.g.,`i686-linux') identifying the most import attributes of the
-  # build platform, and `platform` a set of other details.
-  buildPlatform
-
-, # The platform on which packages run.
-  hostPlatform
-
-, # The platform which build tools (especially compilers) build for in this stage,
-  targetPlatform
-
   ## Other parameters
   ##
 
···
 , # Non-GNU/Linux OSes are currently "impure" platforms, with their libc
   # outside of the store.  Thus, GCC, GFortran, & co. must always look for files
   # in standard system directories (/usr/include, etc.)
-  noSysDirs ? buildPlatform.system != "x86_64-freebsd"
-           && buildPlatform.system != "i686-freebsd"
-           && buildPlatform.system != "x86_64-solaris"
-           && buildPlatform.system != "x86_64-kfreebsd-gnu"
+  noSysDirs ? stdenv.buildPlatform.system != "x86_64-freebsd"
+           && stdenv.buildPlatform.system != "i686-freebsd"
+           && stdenv.buildPlatform.system != "x86_64-solaris"
+           && stdenv.buildPlatform.system != "x86_64-kfreebsd-gnu"
 
 , # The configuration attribute set
   config
···
       // { recurseForDerivations = false; };
     __targetPackages = (if __targetPackages == null then self else __targetPackages)
       // { recurseForDerivations = false; };
-    inherit stdenv
-      buildPlatform hostPlatform targetPlatform;
+    inherit stdenv;
   };
 
   # The old identifiers for cross-compiling. These should eventually be removed,
   # and the packages that rely on them refactored accordingly.
   platformCompat = self: super: let
-    # TODO(@Ericson2314) this causes infinite recursion
-    #inherit (self) buildPlatform hostPlatform targetPlatform;
+    inherit (super.stdenv) buildPlatform hostPlatform targetPlatform;
   in {
     stdenv = super.stdenv // {
-      inherit (buildPlatform) platform;
+      inherit (super.stdenv.buildPlatform) platform;
     };
+    inherit buildPlatform hostPlatform targetPlatform;
     inherit (buildPlatform) system platform;
   };