get_requires_for_build* hooks rely on 'installing' setup_requires

setuptools/build_meta.py

@@ -155,7 +155,6 @@ class _BuildMetaBackend(object):
         with _open_setup_script(__file__) as f:
             code = f.read().replace(r'\r\n', r'\n')
 
-        with no_install_setup_requires():
         exec(compile(code, __file__, 'exec'), locals())
 
     def get_requires_for_build_wheel(self, config_settings=None):
@@ -171,6 +170,7 @@ class _BuildMetaBackend(object):
                                          config_settings=None):
         sys.argv = sys.argv[:1] + ['dist_info', '--egg-base',
                                    _to_str(metadata_directory)]
+        with no_install_setup_requires():
             self.run_setup()
 
         dist_info_directory = metadata_directory
@@ -211,6 +211,7 @@ class _BuildMetaBackend(object):
             sys.argv = (sys.argv[:1] + setup_command +
                         ['--dist-dir', tmp_dist_dir] +
                         config_settings["--global-option"])
+            with no_install_setup_requires():
                 self.run_setup()
 
             result_basename = _file_with_extension(