mkDerivation: Don't pass buildInputs to stdenv builder in nativeBuildInputs

When not cross compiling, nativeBuildInputs and buildInputs have
identical behaviour. Currently that is implemented by having
mkDerivation do a concatenation of those variables in Nix code and pass
that to the builder via the nativeBuildInputs attribute.

However, that has some annoying side effects, like `foo.buildInputs`
evaluating to `[ ]` even if buildInputs were specified in the nix
expression for foo.

Instead, pass buildInputs and nativeBuildInputs in separate variables as
usual, and move the logic of cross compilation vs. native compilation to
the stdenv builder script. This is probably a tiny bit uglier but
fixes the previous problem.

Issue #4855.

pkgs/stdenv/generic/default.nix

@@ -264,18 +264,16 @@ let
           __ignoreNulls = true;
 
           # Inputs built by the cross compiler.
-          buildInputs = if crossConfig != null then buildInputs' else [];
-          propagatedBuildInputs = if crossConfig != null then propagatedBuildInputs' else [];
+          buildInputs = buildInputs';
+          propagatedBuildInputs = propagatedBuildInputs';
           # Inputs built by the usual native compiler.
           nativeBuildInputs = nativeBuildInputs'
-            ++ lib.optionals (crossConfig == null) buildInputs'
             ++ lib.optional
                 (result.isCygwin
                   || (crossConfig != null && lib.hasSuffix "mingw32" crossConfig))
                 ../../build-support/setup-hooks/win-dll-link.sh
             ;
-          propagatedNativeBuildInputs = propagatedNativeBuildInputs' ++
-            (if crossConfig == null then propagatedBuildInputs' else []);
+          propagatedNativeBuildInputs = propagatedNativeBuildInputs';
         } // ifDarwin {
           # TODO: remove lib.unique once nix has a list canonicalization primitive
           __sandboxProfile =

pkgs/stdenv/generic/setup.sh

@@ -290,6 +290,16 @@ findInputs() {
     fi
 }
 
+if [ -z "$crossConfig" ]; then
+    # Not cross-compiling - both buildInputs (and variants like propagatedBuildInputs)
+    # are handled identically to nativeBuildInputs
+    nativePkgs=""
+    for i in $nativeBuildInputs $buildInputs \
+             $defaultNativeBuildInputs $defaultBuildInputs \
+             $propagatedNativeBuildInputs $propagatedBuildInputs; do
+        findInputs $i nativePkgs propagated-native-build-inputs
+    done
+else
     crossPkgs=""
     for i in $buildInputs $defaultBuildInputs $propagatedBuildInputs; do
         findInputs $i crossPkgs propagated-build-inputs
@@ -299,6 +309,7 @@ nativePkgs=""
     for i in $nativeBuildInputs $defaultNativeBuildInputs $propagatedNativeBuildInputs; do
         findInputs $i nativePkgs propagated-native-build-inputs
     done
+fi
 
 
 # Set the relevant environment variables to point to the build inputs
@@ -759,6 +770,17 @@ fixupPhase() {
 
     # Propagate build inputs and setup hook into the development output.
 
+    if [ -z "$crossConfig" ]; then
+        # Not cross-compiling - propagatedBuildInputs are handled identically to propagatedNativeBuildInputs
+        local propagated="$propagatedNativeBuildInputs"
+        if [ -n "$propagatedBuildInputs" ]; then
+            propagated+="${propagated:+ }$propagatedBuildInputs"
+        fi
+        if [ -n "$propagated" ]; then
+            mkdir -p "${!outputDev}/nix-support"
+            echo "$propagated" > "${!outputDev}/nix-support/propagated-native-build-inputs"
+        fi
+    else
         if [ -n "$propagatedBuildInputs" ]; then
             mkdir -p "${!outputDev}/nix-support"
             echo "$propagatedBuildInputs" > "${!outputDev}/nix-support/propagated-build-inputs"
@@ -768,6 +790,7 @@ fixupPhase() {
             mkdir -p "${!outputDev}/nix-support"
             echo "$propagatedNativeBuildInputs" > "${!outputDev}/nix-support/propagated-native-build-inputs"
         fi
+    fi
 
     if [ -n "$setupHook" ]; then
         mkdir -p "${!outputDev}/nix-support"