Support "macosx_10_9_universal2" wheels (#380)

packaging/tags.py

@@ -458,14 +458,28 @@ def mac_platforms(version=None, arch=None):
                     major=major_version, minor=0, binary_format=binary_format
                 )
 
-    if version >= (11, 0) and arch == "x86_64":
+    if version >= (11, 0):
         # Mac OS 11 on x86_64 is compatible with binaries from previous releases.
         # Arm64 support was introduced in 11.0, so no Arm binaries from previous
         # releases exist.
-        for minor_version in range(16, 3, -1):
-            compat_version = 10, minor_version
-            binary_formats = _mac_binary_formats(compat_version, arch)
-            for binary_format in binary_formats:
+        #
+        # However, the "universal2" binary format can have a
+        # macOS version earlier than 11.0 when the x86_64 part of the binary supports
+        # that version of macOS.
+        if arch == "x86_64":
+            for minor_version in range(16, 3, -1):
+                compat_version = 10, minor_version
+                binary_formats = _mac_binary_formats(compat_version, arch)
+                for binary_format in binary_formats:
+                    yield "macosx_{major}_{minor}_{binary_format}".format(
+                        major=compat_version[0],
+                        minor=compat_version[1],
+                        binary_format=binary_format,
+                    )
+        else:
+            for minor_version in range(16, 3, -1):
+                compat_version = 10, minor_version
+                binary_format = "universal2"
                 yield "macosx_{major}_{minor}_{binary_format}".format(
                     major=compat_version[0],
                     minor=compat_version[1],

tests/test_tags.py

@@ -264,8 +264,14 @@ def test_version_detection(self, monkeypatch):
                 platform, "mac_ver", lambda: ("10.14", ("", "", ""), "x86_64")
             )
         version = platform.mac_ver()[0].split(".")
-        expected = "macosx_{major}_{minor}".format(major=version[0], minor=version[1])
+        if version[0] == "10":
+            expected = "macosx_{major}_{minor}".format(
+                major=version[0], minor=version[1]
+            )
+        else:
+            expected = "macosx_{major}_{minor}".format(major=version[0], minor=0)
         platforms = list(tags.mac_platforms(arch="x86_64"))
+        print(platforms, expected)
         assert platforms[0].startswith(expected)
 
     @pytest.mark.parametrize("arch", ["x86_64", "i386"])
@@ -311,6 +317,7 @@ def test_macos_11(self, major, minor):
         # with the environment variable SYSTEM_VERSION_COMPAT=1.
         assert "macosx_10_16_x86_64" in platforms
         assert "macosx_10_15_x86_64" in platforms
+        assert "macosx_10_15_universal2" in platforms
         assert "macosx_10_4_x86_64" in platforms
         assert "macosx_10_3_x86_64" not in platforms
         if major >= 12:
@@ -323,6 +330,7 @@ def test_macos_11(self, major, minor):
         assert "macosx_11_3_arm64" not in platforms
         assert "macosx_11_0_universal" not in platforms
         assert "macosx_11_0_universal2" in platforms
+        assert "macosx_10_15_universal2" in platforms
         assert "macosx_10_15_x86_64" not in platforms
         assert "macosx_10_4_x86_64" not in platforms
         assert "macosx_10_3_x86_64" not in platforms