cc-wrapper, bintools-wrapper: support MACOSX_DEPLOYMENT_TARGET with roles

In a typical build environment the toolchain will use the value of the
MACOSX_DEPLOYMENT_TARGET environment variable to determine the version
of macOS to support. When cross compiling there are two distinct
toolchains, but they will look at this single environment variable. To
avoid contamination, we always set the equivalent command line flag
which effectively disables the toolchain's internal handling.

Prior to this change, the MACOSX_DEPLOYMENT_TARGET variable was
ignored, and the toolchains always used the Nix platform
definition (`darwinMinVersion`) unless overridden with command line
arguments.

This change restores support for MACOSX_DEPLOYMENT_TARGET, and adds
nix-specific MACOSX_DEPLOYMENT_TARGET_FOR_BUILD and
MACOSX_DEPLOYMENT_TARGET_FOR_TARGET for cross compilation.

4 files changed, 55 insertions, 12 deletions

diff --git a/pkgs/build-support/bintools-wrapper/add-darwin-ldflags-before.sh b/pkgs/build-support/bintools-wrapper/add-darwin-ldflags-before.sh
index 37c6881810d..318311e1be9 100644
--- a/pkgs/build-support/bintools-wrapper/add-darwin-ldflags-before.sh
+++ b/pkgs/build-support/bintools-wrapper/add-darwin-ldflags-before.sh
@@ -21,6 +21,8 @@ havePlatformVersionFlag=
 haveDarwinSDKVersion=
 haveDarwinPlatformVersion=
 
+mangleVarSingle MACOSX_DEPLOYMENT_TARGET ${role_suffixes[@]+"${role_suffixes[@]}"}
+
 n=0
 nParams=${#params[@]}
 while (( n < nParams )); do
@@ -59,12 +61,12 @@ done
 if [ ! "$havePlatformVersionFlag" ]; then
     if [ ! "$haveDarwinSDKVersion" ] && [ ! "$haveDarwinPlatformVersion" ]; then
         # Nothing provided. Use the modern "-platform_version" to set both.
-        extraBefore+=(-platform_version @darwinPlatform@ @darwinMinVersion@ @darwinSdkVersion@)
+        extraBefore+=(-platform_version @darwinPlatform@ "${MACOSX_DEPLOYMENT_TARGET_@suffixSalt@:-@darwinMinVersion@}" @darwinSdkVersion@)
     elif [ ! "$haveDarwinSDKVersion" ]; then
         # Add missing sdk version
         extraBefore+=(-sdk_version @darwinSdkVersion@)
     elif [ ! "$haveDarwinPlatformVersion" ]; then
         # Add missing platform version
-        extraBefore+=(-@darwinPlatform@_version_min @darwinMinVersion@)
+        extraBefore+=(-@darwinPlatform@_version_min "${MACOSX_DEPLOYMENT_TARGET_@suffixSalt@:-@darwinMinVersion@}")
     fi
 fi
diff --git a/pkgs/build-support/cc-wrapper/add-flags.sh b/pkgs/build-support/cc-wrapper/add-flags.sh
index 94589131b70..f7276b04e54 100644
--- a/pkgs/build-support/cc-wrapper/add-flags.sh
+++ b/pkgs/build-support/cc-wrapper/add-flags.sh
@@ -65,5 +65,13 @@ if [ -e @out@/nix-support/cc-cflags-before ]; then
     NIX_CFLAGS_COMPILE_BEFORE_@suffixSalt@="$(< @out@/nix-support/cc-cflags-before) $NIX_CFLAGS_COMPILE_BEFORE_@suffixSalt@"
 fi
 
+# Only add darwin min version flag if a default darwin min version is set,
+# which is a signal that we're targetting darwin.
+if [ "@darwinMinVersion@" ]; then
+    mangleVarSingle MACOSX_DEPLOYMENT_TARGET ${role_suffixes[@]+"${role_suffixes[@]}"}
+
+    NIX_CFLAGS_COMPILE_BEFORE_@suffixSalt@="-m@darwinPlatformForCC@-version-min=${MACOSX_DEPLOYMENT_TARGET_@suffixSalt@:-@darwinMinVersion@} $NIX_CFLAGS_COMPILE_BEFORE_@suffixSalt@"
+fi
+
 # That way forked processes will not extend these environment variables again.
 export NIX_CC_WRAPPER_FLAGS_SET_@suffixSalt@=1
diff --git a/pkgs/build-support/cc-wrapper/default.nix b/pkgs/build-support/cc-wrapper/default.nix
index 3d2a142c36d..834c4e6d46a 100644
--- a/pkgs/build-support/cc-wrapper/default.nix
+++ b/pkgs/build-support/cc-wrapper/default.nix
@@ -100,6 +100,15 @@ let
     else
       false;
 
+
+  darwinPlatformForCC = optionalString stdenv.targetPlatform.isDarwin (
+    if (targetPlatform.darwinPlatform == "macos" && isGNU) then "macosx"
+    else targetPlatform.darwinPlatform
+  );
+
+  darwinMinVersion = optionalString stdenv.targetPlatform.isDarwin (
+    stdenv.targetPlatform.darwinMinVersion
+  );
 in
 
 # Ensure bintools matches
@@ -122,6 +131,7 @@ stdenv.mkDerivation {
   gnugrep_bin = if nativeTools then "" else gnugrep;
 
   inherit targetPrefix suffixSalt;
+  inherit darwinPlatformForCC darwinMinVersion;
 
   outputs = [ "out" ] ++ optionals propagateDoc [ "man" "info" ];
 
@@ -473,6 +483,10 @@ stdenv.mkDerivation {
       done
     ''
 
+    + optionalString stdenv.targetPlatform.isDarwin ''
+        echo "-arch ${targetPlatform.darwinArch}" >> $out/nix-support/cc-cflags
+    ''
+
     # There are a few tools (to name one libstdcxx5) which do not work
     # well with multi line flags, so make the flags single line again
     + ''
@@ -485,16 +499,6 @@ stdenv.mkDerivation {
       substituteAll ${../wrapper-common/utils.bash} $out/nix-support/utils.bash
     ''
 
-    + optionalString stdenv.targetPlatform.isDarwin (
-      let darwinPlatformForCC =
-        if (targetPlatform.darwinPlatform == "macos" && isGNU) then "macosx"
-        else targetPlatform.darwinPlatform;
-      in ''
-        echo "-arch ${targetPlatform.darwinArch}" >> $out/nix-support/cc-cflags
-        echo "-m${darwinPlatformForCC}-version-min=${targetPlatform.darwinMinVersion}" >> $out/nix-support/cc-cflags-before
-      ''
-    )
-
     ##
     ## Extra custom steps
     ##
diff --git a/pkgs/build-support/wrapper-common/utils.bash b/pkgs/build-support/wrapper-common/utils.bash
index d164982b434..66b7c3f3e83 100644
--- a/pkgs/build-support/wrapper-common/utils.bash
+++ b/pkgs/build-support/wrapper-common/utils.bash
@@ -49,6 +49,35 @@ mangleVarBool() {
     done
 }
 
+# Combine a singular value from all roles. If multiple roles are being served,
+# and the value differs in these roles then the request is impossible to
+# satisfy and we abort immediately.
+mangleVarSingle() {
+    local var="$1"
+    shift
+    local -a role_suffixes=("$@")
+
+    local outputVar="${var}_@suffixSalt@"
+    for suffix in "${role_suffixes[@]}"; do
+        local inputVar="${var}${suffix}"
+        if [ -v "$inputVar" ]; then
+            if [ -v "$outputVar" ]; then
+                if [ "${!outputVar}" != "${!inputVar}" ]; then
+                    {
+                        echo "Multiple conflicting values defined for $outputVar"
+                        echo "Existing value is ${!outputVar}"
+                        echo "Attempting to set to ${!inputVar} via $inputVar"
+                    } >&2
+
+                    exit 1
+                fi
+            else
+                declare -gx ${outputVar}="${!inputVar}"
+            fi
+        fi
+    done
+}
+
 skip () {
     if (( "${NIX_DEBUG:-0}" >= 1 )); then
         echo "skipping impure path $1" >&2