unix: set MACOSX_DEPLOYMENT_TARGET when building Python

See the inline comment. Python's configure isn't smart enough to
pick up the value from cflags and we regressed the platform tag when
we switched to cflags for minimum version targeting.

Author: indygreg

cpython-unix/build-cpython.sh

@@ -535,6 +535,15 @@ if [ "${PYBUILD_PLATFORM}" = "macos" ]; then
             exit 1
         fi
     fi
+
+    # Python's configure looks exclusively at MACOSX_DEPLOYMENT_TARGET for
+    # determining the platform tag. We specify the minimum target via cflags
+    # like -mmacosx-version-min but configure doesn't pick up on those. In
+    # addition, configure isn't smart enough to look at environment variables
+    # for other SDK targets to determine the OS version. So our hack here is
+    # to expose MACOSX_DEPLOYMENT_TARGET everywhere so the value percolates
+    # into platform tag.
+    export MACOSX_DEPLOYMENT_TARGET="${APPLE_MIN_DEPLOYMENT_TARGET}"
 fi
 
 if [ "${BUILD_TRIPLE}" != "${TARGET_TRIPLE}" ]; then

cpython-unix/build.py

@@ -123,51 +123,59 @@ def add_target_env(env, build_platform, target_triple, build_env):
             min_version_flags = [
                 "-mmacosx-version-min=%s" % MACOSX_DEPLOYMENT_TARGET_ARM
             ]
+            env["APPLE_MIN_DEPLOYMENT_TARGET"] = MACOSX_DEPLOYMENT_TARGET_ARM
         elif target_triple == "aarch64-apple-ios":
             env["TARGET_TRIPLE"] = "aarch64-apple-ios"
             # TODO arm64e not supported by open source Clang.
             # TODO add arm7 / arm7s?
             arches = ["arm64"]
             sdk_platform = "iphoneos"
             min_version_flags = ["-mios-version-min=%s" % IPHONEOS_DEPLOYMENT_TARGET]
+            env["APPLE_MIN_DEPLOYMENT_TARGET"] = IPHONEOS_DEPLOYMENT_TARGET
         elif target_triple == "arm64-apple-tvos":
             env["TARGET_TRIPLE"] = "arm64-apple-tvos"
             arches = ["arm64"]
             sdk_platform = "appletvos"
             min_version_flags = ["-mappletvos-version-min=%s" % TVOS_DEPLOYMENT_TARGET]
+            env["APPLE_MIN_DEPLOYMENT_TARGET"] = TVOS_DEPLOYMENT_TARGET
         elif target_triple == "thumbv7k-apple-watchos":
             env["TARGET_TRIPLE"] = "thumbv7k-apple-watchos"
             arches = ["armv7k"]
             sdk_platform = "watchos"
             min_version_flags = ["-mwatchos-version-min=%s" % WATCHOS_DEPLOYMENT_TARGET]
+            env["APPLE_MIN_DEPLOYMENT_TARGET"] = WATCHOS_DEPLOYMENT_TARGET
         elif target_triple == "x86_64-apple-darwin":
             env["TARGET_TRIPLE"] = "x86_64-apple-darwin"
             arches = ["x86_64"]
             sdk_platform = "macosx"
             min_version_flags = [
                 "-mmacosx-version-min=%s" % MACOSX_DEPLOYMENT_TARGET_X86
             ]
+            env["APPLE_MIN_DEPLOYMENT_TARGET"] = MACOSX_DEPLOYMENT_TARGET_X86
         elif target_triple == "x86_64-apple-ios":
             env["TARGET_TRIPLE"] = "x86_64-apple-ios"
             arches = ["x86_64"]
             sdk_platform = "iphonesimulator"
             min_version_flags = [
                 "-mios-simulator-version-min=%s" % IPHONEOS_DEPLOYMENT_TARGET,
             ]
+            env["APPLE_MIN_DEPLOYMENT_TARGET"] = IPHONEOS_DEPLOYMENT_TARGET
         elif target_triple == "x86_64-apple-tvos":
             env["TARGET_TRIPLE"] = "x86_64-apple-tvos"
             arches = ["x86_64"]
             sdk_platform = "appletvsimulator"
             min_version_flags = [
                 "-mappletvsimulator-version-min=%s" % TVOS_DEPLOYMENT_TARGET
             ]
+            env["APPLE_MIN_DEPLOYMENT_TARGET"] = TVOS_DEPLOYMENT_TARGET
         elif target_triple == "x86_64-apple-watchos":
             env["TARGET_TRIPLE"] = "x86_64-apple-watchos"
             arches = ["x86_64"]
             sdk_platform = "watchsimulator"
             min_version_flags = [
                 "-mwatchsimulator-version-min=%s" % WATCHOS_DEPLOYMENT_TARGET
             ]
+            env["APPLE_MIN_DEPLOYMENT_TARGET"] = WATCHOS_DEPLOYMENT_TARGET
         else:
             raise ValueError("unhandled target triple: %s" % target_triple)