gh-122931 Allow stable API extensions to include a multiarch tuple in the filename

Doc/whatsnew/3.16.rst

@@ -75,6 +75,14 @@ New features
 Other language changes
 ======================
 
+* Stable ABI extensions may now include a multiarch tuple in the
+  filename, e.g. ``foo.abi3-x86-64-linux-gnu.so``.
+  This permits stable ABI extensions for multiple architectures to be
+  co-installed into the same directory, without clashing with each
+  other, as regular dynamic extensions do. Build may tools will generate
+  these multiarch tagged filenames, by default, when targeting
+  compatibility with at least Python 3.15.
+  (Contributed by Stefano Rivera in :gh:`122931`.)
 
 
 New modules

Lib/test/test_importlib/extension/test_finder.py

@@ -5,6 +5,7 @@
 
 import unittest
 import sys
+import sysconfig
 
 
 class FinderTests(abc.FinderTests):
@@ -68,11 +69,22 @@ def test_abi3_extension_suffixes(self):
             pass
         else:
             if Py_GIL_DISABLED:
-                self.assertNotIn(".abi3.so", suffixes)
+                self.assertFalse(any(".abi3" in suffix) for suffix in suffixes)
             else:
                 self.assertIn(".abi3.so", suffixes)
             self.assertIn(".abi3t.so", suffixes)
 
+    @unittest.skipIf(
+        not sysconfig.get_config_var("SOABI_PLATFORM").strip('"'),
+        "Linux-only test"
+    )
+    def test_multiarch_abi3_extension_suffixes(self):
+        suffixes = self.machinery.EXTENSION_SUFFIXES
+        platform = sysconfig.get_config_var("SOABI_PLATFORM").strip('"')
+        if Py_GIL_DISABLED:
+            self.assertIn(f".abi3-{platform}.so", suffixes)
+        self.assertIn(f".abi3t-{platform}.so", suffixes)
+
 
 (Frozen_FinderTests,
  Source_FinderTests

Misc/NEWS.d/next/C_API/2024-08-12-09-48-04.gh-issue-122931.QwHc2l.rst

@@ -0,0 +1,2 @@
+Allow importing stable ABI C extensions that include a multiarch tuple
+in their filename, e.g. ``foo.abi3-x86-64-linux-gnu.so``.

Python/dynload_shlib.c

@@ -46,8 +46,14 @@ const char *_PyImport_DynLoadFiletab[] = {
     "." ALT_SOABI ".so",
 #endif
 #ifndef Py_GIL_DISABLED
+#ifdef SOABI_PLATFORM
+    ".abi" PYTHON_ABI_STRING "-" SOABI_PLATFORM ".so",
+#endif  /* SOABI_PLATFORM */
     ".abi" PYTHON_ABI_STRING ".so",
 #endif  /* Py_GIL_DISABLED */
+#ifdef SOABI_PLATFORM
+    ".abi" PYTHON_ABI_STRING "t-" SOABI_PLATFORM ".so",
+#endif  /* SOABI_PLATFORM */
     ".abi" PYTHON_ABI_STRING "t.so",
     ".so",
 #endif  /* __CYGWIN__ */

configure.ac

@@ -1212,6 +1212,8 @@ AS_CASE([$ac_sys_system],
   [SOABI_PLATFORM=$PLATFORM_TRIPLET]
 )
 
+AC_DEFINE_UNQUOTED([SOABI_PLATFORM], ["${SOABI_PLATFORM}"], [Platform tag, used in binary module extension filenames.])
+
 if test x$MULTIARCH != x; then
   MULTIARCH_CPPFLAGS="-DMULTIARCH=\\\"$MULTIARCH\\\""
 fi

pyconfig.h.in

@@ -1851,6 +1851,9 @@
 /* The size of '_Bool', as computed by sizeof. */
 #undef SIZEOF__BOOL
 
+/* Platform tag, used in binary module extension filenames. */
+#undef SOABI_PLATFORM
+
 /* Define to 1 if you have the ANSI C header files. */
 #undef STDC_HEADERS