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

See #27069 for a discussion of this

2 files changed, 39 insertions, 24 deletions

diff --git a/pkgs/stdenv/generic/default.nix b/pkgs/stdenv/generic/default.nix
index d7b736a12e56..a5d3c5a8ff5c 100644
--- a/pkgs/stdenv/generic/default.nix
+++ b/pkgs/stdenv/generic/default.nix
@@ -15,18 +15,32 @@ let lib = import ../../../lib; in lib.makeOverridable (
 , 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
@@ -49,7 +63,11 @@ let
     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;
 
@@ -59,7 +77,7 @@ let
 
       inherit preHook initialPath shell defaultNativeBuildInputs;
     }
-    // lib.optionalAttrs hostPlatform.isDarwin {
+    // lib.optionalAttrs buildPlatform.isDarwin {
       __sandboxProfile = stdenvSandboxProfile;
       __impureHostDeps = __stdenvImpureHostDeps;
     })
@@ -71,6 +89,8 @@ let
         platforms = lib.platforms.all;
       };
 
+      inherit buildPlatform hostPlatform targetPlatform;
+
       inherit extraBuildInputs __extraImpureHostDeps extraSandboxProfile;
 
       # Utility flags to test the type of platform.
@@ -85,9 +105,6 @@ let
 
       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
diff --git a/pkgs/stdenv/generic/make-derivation.nix b/pkgs/stdenv/generic/make-derivation.nix
index ec48e5374139..31b0428eeb2b 100644
--- a/pkgs/stdenv/generic/make-derivation.nix
+++ b/pkgs/stdenv/generic/make-derivation.nix
@@ -1,8 +1,4 @@
-{ lib, config, stdenv
-
-# TODO(@Ericson2314): get off stdenv
-, hostPlatform, targetPlatform
-}:
+{ lib, config, stdenv }:
 
 rec {
   # `mkDerivation` wraps the builtin `derivation` function to
@@ -49,12 +45,12 @@ rec {
 
       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;
@@ -82,7 +78,7 @@ rec {
           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;
 
@@ -91,7 +87,7 @@ rec {
 
           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 ];
@@ -139,7 +135,9 @@ rec {
           {
             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));