build_meta.get_requires_for_build_sdist does not include wheel

the wheel package is not required to build a source distribution

Resolves #1474.

changelog.d/1474.change.rst

+``build_meta.get_requires_for_build_sdist`` now does not include the ``wheel`` package anymore

setuptools/build_meta.py

@@ -91,9 +91,8 @@ def _fix_config(config_settings):
     return config_settings
 
 
-def _get_build_requires(config_settings):
+def _get_build_requires(config_settings, requirements):
     config_settings = _fix_config(config_settings)
-    requirements = ['setuptools', 'wheel']
 
     sys.argv = sys.argv[:1] + ['egg_info'] + \
         config_settings["--global-option"]
@@ -113,20 +112,20 @@ def _get_immediate_subdirectories(a_dir):
 
 def get_requires_for_build_wheel(config_settings=None):
     config_settings = _fix_config(config_settings)
-    return _get_build_requires(config_settings)
+    return _get_build_requires(config_settings, requirements=['setuptools', 'wheel'])
 
 
 def get_requires_for_build_sdist(config_settings=None):
     config_settings = _fix_config(config_settings)
-    return _get_build_requires(config_settings)
+    return _get_build_requires(config_settings, requirements=['setuptools'])
 
 
 def prepare_metadata_for_build_wheel(metadata_directory, config_settings=None):
     sys.argv = sys.argv[:1] + ['dist_info', '--egg-base', _to_str(metadata_directory)]
     _run_setup()
-    
+
     dist_info_directory = metadata_directory
-    while True:    
+    while True:
         dist_infos = [f for f in os.listdir(dist_info_directory)
                       if f.endswith('.dist-info')]
 

setuptools/tests/test_build_meta.py

@@ -107,6 +107,12 @@ def test_get_requires_for_build_wheel(build_backend):
     assert sorted(actual) == sorted(expected)
 
 
+def test_get_requires_for_build_sdist(build_backend):
+    actual = build_backend.get_requires_for_build_sdist()
+    expected = ['six', 'setuptools']
+    assert sorted(actual) == sorted(expected)
+
+
 def test_build_wheel(build_backend):
     dist_dir = os.path.abspath('pip-wheel')
     os.makedirs(dist_dir)