Fixes #2722: Adds an environment variable SETUPTOOLS_EXT_SUFFIX to override the suffix inferred from the host Python runtime.

3 files changed, 36 insertions, 3 deletions

diff --git a/changelog.d/2722.change.rst b/changelog.d/2722.change.rst
new file mode 100644
index 00000000..20bbb66f
--- /dev/null
+++ b/changelog.d/2722.change.rst
@@ -0,0 +1 @@
+Added support for ``SETUPTOOLS_EXT_SUFFIX`` environment variable to override the suffix normally detected from the ``sysconfig`` module.
diff --git a/setuptools/command/build_ext.py b/setuptools/command/build_ext.py
index 03a72b4f..c59eff8b 100644
--- a/setuptools/command/build_ext.py
+++ b/setuptools/command/build_ext.py
@@ -104,14 +104,20 @@ class build_ext(_build_ext):
                 self.write_stub(package_dir or os.curdir, ext, True)
 
     def get_ext_filename(self, fullname):
-        filename = _build_ext.get_ext_filename(self, fullname)
+        so_ext = os.getenv('SETUPTOOLS_EXT_SUFFIX')
+        if so_ext:
+            filename = os.path.join(*fullname.split('.')) + so_ext
+        else:
+            filename = _build_ext.get_ext_filename(self, fullname)
+            so_ext = get_config_var('EXT_SUFFIX')
+
         if fullname in self.ext_map:
             ext = self.ext_map[fullname]
             use_abi3 = getattr(ext, 'py_limited_api') and get_abi3_suffix()
             if use_abi3:
-                so_ext = get_config_var('EXT_SUFFIX')
                 filename = filename[:-len(so_ext)]
-                filename = filename + get_abi3_suffix()
+                so_ext = get_abi3_suffix()
+                filename = filename + so_ext
             if isinstance(ext, Library):
                 fn, ext = os.path.splitext(filename)
                 return self.shlib_compiler.library_filename(fn, libtype)
diff --git a/setuptools/tests/test_build_ext.py b/setuptools/tests/test_build_ext.py
index b6deebe4..5286358e 100644
--- a/setuptools/tests/test_build_ext.py
+++ b/setuptools/tests/test_build_ext.py
@@ -1,3 +1,4 @@
+import os
 import sys
 import distutils.command.build_ext as orig
 from distutils.sysconfig import get_config_var
@@ -47,6 +48,31 @@ class TestBuildExt:
         else:
             assert 'abi3' in res
 
+    def test_ext_suffix_override(self):
+        """
+        SETUPTOOLS_EXT_SUFFIX variable always overrides
+        default extension options.
+        """
+        dist = Distribution()
+        cmd = build_ext(dist)
+        cmd.ext_map['for_abi3'] = ext = Extension(
+            'for_abi3',
+            ['s.c'],
+            # Override shouldn't affect abi3 modules
+            py_limited_api=True,
+        )
+        # Mock value needed to pass tests
+        ext._links_to_dynamic = False
+        expect = cmd.get_ext_filename('for_abi3')
+        try:
+            os.environ['SETUPTOOLS_EXT_SUFFIX'] = '.test-suffix'
+            res = cmd.get_ext_filename('normal')
+            assert 'normal.test-suffix' == res
+            res = cmd.get_ext_filename('for_abi3')
+            assert expect == res
+        finally:
+            del os.environ['SETUPTOOLS_EXT_SUFFIX']
+
 
 def test_build_ext_config_handling(tmpdir_cwd):
     files = {