gh-136267: Use the target configuration in build-details.json

Lib/test/test_build_details.py

@@ -142,6 +142,17 @@ def contents(self):
     def test_location(self):
         self.assertTrue(os.path.isfile(self.location))
 
+    def test_abi(self):
+        self.assertEqual(self.key('abi.flags'), list(sys.abiflags))
+        self.assertEqual(self.key('abi.extension_suffix'),
+                         sysconfig.get_config_var('EXT_SUFFIX'))
+        self.assertIn(self.key('abi.stable_abi_suffix'),
+                      importlib.machinery.EXTENSION_SUFFIXES)
+
+    def test_extension_suffixes(self):
+        self.assertEqual(self.key('suffixes.extensions'),
+                         importlib.machinery.EXTENSION_SUFFIXES)
+
     # Override generic format tests with tests for our specific implemenation.
 
     @needs_installed_python
@@ -289,6 +300,62 @@ def check_relative_paths(self, data_abs_path, data_rel_path):
             self.assertEqual(data_abs_path[part][key], abs_rel_path)
 
 
+def generate_data(**config_vars):
+    """Generate build-details data with overridden config vars."""
+    get_config_var = sysconfig.get_config_var
+    def patched_get_config_var(name):
+        if name in config_vars:
+            return config_vars[name]
+        return get_config_var(name)
+    with mock.patch('sysconfig.get_config_var', patched_get_config_var):
+        data = generate_build_details.generate_data(schema_version='1.0')
+    return json.loads(json.dumps(data))
+
+
+@unittest.skipIf(
+    generate_build_details is None,
+    "Failed to import generate-build-details"
+)
+@unittest.skipIf(os.name != 'posix', 'Feature only implemented on POSIX')
+class BuildDetailsTargetTests(unittest.TestCase):
+    """Values that must come from the target configuration (gh-136267)."""
+
+    def test_native_extension_suffixes(self):
+        self.assertEqual(generate_build_details.get_extension_suffixes(),
+                         importlib.machinery.EXTENSION_SUFFIXES)
+
+    def test_free_threaded_debug(self):
+        # A GIL-enabled release build Python generating for this target
+        # used to report its own flags and suffixes.
+        data = generate_data(
+            ABIFLAGS='td', MACHDEP='linux', DYNLOADFILE='dynload_shlib.o',
+            SOABI_PLATFORM='aarch64-linux-gnu',
+            SOABI='cpython-3XXtd-aarch64-linux-gnu',
+            ALT_SOABI='cpython-3XXt-aarch64-linux-gnu',
+            EXT_SUFFIX='.cpython-3XXtd-aarch64-linux-gnu.so',
+            Py_GIL_DISABLED=1)
+        self.assertEqual(data['abi']['flags'], ['t', 'd'])
+        self.assertEqual(data['abi']['extension_suffix'],
+                         '.cpython-3XXtd-aarch64-linux-gnu.so')
+        self.assertEqual(data['abi']['stable_abi_suffix'],
+                         '.abi3t-aarch64-linux-gnu.so')
+        self.assertEqual(data['suffixes']['extensions'], [
+            '.cpython-3XXtd-aarch64-linux-gnu.so',
+            '.cpython-3XXt-aarch64-linux-gnu.so',
+            '.abi3t-aarch64-linux-gnu.so',
+            '.abi3t.so',
+            '.so',
+        ])
+
+    def test_no_dynamic_loading(self):
+        data = generate_data(MACHDEP='wasi', DYNLOADFILE='dynload_stub.o')
+        self.assertEqual(data['suffixes']['extensions'], [])
+        self.assertNotIn('extension_suffix', data['abi'])
+        self.assertNotIn('stable_abi_suffix', data['abi'])
+        self.assertFalse(
+            data['implementation']['supports_isolated_interpreters'])
+
+
 @unittest.skipIf(
     generate_build_details is None,
     "Failed to import generate-build-details"
@@ -299,26 +366,25 @@ class BuildDetailsLibpythonTests(unittest.TestCase):
     LIBDIR = '/prefix/lib'
     LIBPL = '/prefix/lib/python3.X/config-3.X'
 
+    def generate(self, **config_vars):
+        return generate_data(LIBDIR=self.LIBDIR, LIBPL=self.LIBPL,
+                             LIBRARY='libpython3.X.a', **config_vars)
+
     def generate_libpython(self, **config_vars):
         """Generate the libpython section with overridden config vars."""
-        config_vars = dict(LIBDIR=self.LIBDIR, LIBPL=self.LIBPL,
-                           LIBRARY='libpython3.X.a', **config_vars)
-        get_config_var = sysconfig.get_config_var
-        def patched_get_config_var(name):
-            if name in config_vars:
-                return config_vars[name]
-            return get_config_var(name)
-        with mock.patch('sysconfig.get_config_var', patched_get_config_var):
-            data = generate_build_details.generate_data(schema_version='1.0')
-        return json.loads(json.dumps(data)).get('libpython', {})
+        return self.generate(**config_vars).get('libpython', {})
 
     def test_static_only(self):
-        libpython = self.generate_libpython(
+        data = self.generate(
             LDLIBRARY='libpython3.X.a', STATIC_LIBPYTHON=1,
             PYTHONFRAMEWORK='')
+        libpython = data['libpython']
         self.assertNotIn('dynamic', libpython)
         self.assertEqual(libpython['static'],
                          os.path.join(self.LIBDIR, 'libpython3.X.a'))
+        # Extension modules are supported without a shared libpython.
+        self.assertIn('extension_suffix', data['abi'])
+        self.assertIn('stable_abi_suffix', data['abi'])
 
     def test_shared_and_static(self):
         # The static library is only installed into LIBPL, not LIBDIR.

Misc/NEWS.d/next/Build/2026-11-06-12-00-01.gh-issue-136267.Qv7mRs.rst

@@ -0,0 +1,8 @@
+``build-details.json`` now describes the interpreter being built rather than
+the interpreter running :program:`generate-build-details.py`: ``abi.flags``,
+``suffixes.extensions``, ``abi.stable_abi_suffix`` and
+``implementation.supports_isolated_interpreters`` are derived from the
+target's configuration, which fixes cross builds and builds that use
+:option:`--with-build-python`. ``abi.extension_suffix`` and
+``abi.stable_abi_suffix`` are now also present when libpython is only built
+as a static library.

Tools/build/generate-build-details.py

@@ -29,6 +29,46 @@ def get_dict_key(container: dict[str, Any], key: str) -> dict[str, Any]:
     return container
 
 
+def get_extension_suffixes() -> list[str]:
+    """Return the extension module suffixes of the target interpreter.
+
+    importlib.machinery.EXTENSION_SUFFIXES describes the running interpreter,
+    which is not the target under --with-build-python. On POSIX, rebuild the
+    list from the target configuration instead, following
+    _PyImport_DynLoadFiletab in Python/dynload_*.c. The two are kept in sync
+    by test_build_details.BuildDetailsTargetTests.test_native_extension_suffixes.
+    """
+    if os.name != 'posix':
+        return importlib.machinery.EXTENSION_SUFFIXES
+
+    dynloadfile = sysconfig.get_config_var('DYNLOADFILE')
+    if dynloadfile == 'dynload_stub.o':
+        return []
+    if dynloadfile == 'dynload_hpux.o':
+        return [sysconfig.get_config_var('EXT_SUFFIX'), '.sl']
+    if dynloadfile != 'dynload_shlib.o':
+        raise ValueError(f'Unsupported DYNLOADFILE: {dynloadfile!r}')
+
+    soabi = sysconfig.get_config_var('SOABI')
+    if sysconfig.get_config_var('MACHDEP') == 'cygwin':
+        return [f'.{soabi}.dll', '.dll']
+
+    suffixes = [f'.{soabi}.so']
+    alt_soabi = sysconfig.get_config_var('ALT_SOABI')
+    if alt_soabi:
+        suffixes.append(f'.{alt_soabi}.so')
+    platform = sysconfig.get_config_var('SOABI_PLATFORM')
+    if not sysconfig.get_config_var('Py_GIL_DISABLED'):
+        if platform:
+            suffixes.append(f'.abi3-{platform}.so')
+        suffixes.append('.abi3.so')
+    if platform:
+        suffixes.append(f'.abi3t-{platform}.so')
+    suffixes.append('.abi3t.so')
+    suffixes.append('.so')
+    return suffixes
+
+
 def generate_data(schema_version: str) -> collections.defaultdict[str, Any]:
     """Generate the build-details.json data (PEP 739).
 
@@ -62,14 +102,20 @@ def generate_data(schema_version: str) -> collections.defaultdict[str, Any]:
     # Fix cross-compilation
     if '_multiarch' in data['implementation']:
         data['implementation']['_multiarch'] = sysconfig.get_config_var('MULTIARCH')
+    if 'supports_isolated_interpreters' in data['implementation']:
+        # Mirrors Python/sysmodule.c.
+        data['implementation']['supports_isolated_interpreters'] = (
+            sysconfig.get_config_var('MACHDEP') not in ('wasi', 'emscripten')
+        )
 
-    data['abi']['flags'] = list(sys.abiflags)
+    data['abi']['flags'] = list(sysconfig.get_config_var('ABIFLAGS'))
 
     data['suffixes']['source'] = importlib.machinery.SOURCE_SUFFIXES
     data['suffixes']['bytecode'] = importlib.machinery.BYTECODE_SUFFIXES
     #data['suffixes']['optimized_bytecode'] = importlib.machinery.OPTIMIZED_BYTECODE_SUFFIXES
     #data['suffixes']['debug_bytecode'] = importlib.machinery.DEBUG_BYTECODE_SUFFIXES
-    data['suffixes']['extensions'] = importlib.machinery.EXTENSION_SUFFIXES
+    extension_suffixes = get_extension_suffixes()
+    data['suffixes']['extensions'] = extension_suffixes
 
     LIBDIR = sysconfig.get_config_var('LIBDIR')
     LIBPL = sysconfig.get_config_var('LIBPL')
@@ -118,17 +164,16 @@ def generate_data(schema_version: str) -> collections.defaultdict[str, Any]:
     # regardless.
     #
     # We only want to set abi.extension_suffix and stable_abi_suffix if
-    # extension modules are supported.
-    if has_dynamic_library:
+    # extension modules are supported, regardless of how libpython is built.
+    if extension_suffixes:
         data['abi']['extension_suffix'] = sysconfig.get_config_var('EXT_SUFFIX')
 
-        # EXTENSION_SUFFIXES has been constant for a long time, and currently we
-        # don't have a better information source to find the stable ABI suffix.
-        for suffix in importlib.machinery.EXTENSION_SUFFIXES:
+        for suffix in extension_suffixes:
             if suffix.startswith('.abi'):
                 data['abi']['stable_abi_suffix'] = suffix
                 break
 
+    if has_dynamic_library:
         data['libpython']['dynamic'] = os.path.join(dynamic_library_dir, LDLIBRARY)
         # FIXME: Not sure if windows has a different dll for the stable ABI, and
         #        even if it does, currently we don't have a way to get its name.