python · ned-deily · May 24, 2021
diff --git a/Lib/distutils/command/install.py b/Lib/distutils/command/install.py
@@ -316,6 +316,9 @@ def finalize_options(self):
             self.config_vars['userbase'] = self.install_userbase
             self.config_vars['usersite'] = self.install_usersite
 
+        if sysconfig.is_python_build(True):
+            self.config_vars['srcdir'] = sysconfig.get_config_var('srcdir')
+
         self.expand_basedirs()
 
         self.dump_dirs("post-expand_basedirs()")

@@ -182,6 +182,12 @@ def is_python_build(check_home=False):
 
 _PYTHON_BUILD = is_python_build(True)
 
+if _PYTHON_BUILD:
+    for scheme in ('posix_prefix', 'posix_home'):
+        _INSTALL_SCHEMES[scheme]['include'] = '{srcdir}/Include'
+        _INSTALL_SCHEMES[scheme]['platinclude'] = '{projectbase}/.'
+
+
 def _subst_vars(s, local_vars):
     try:
         return s.format(**local_vars)

diff --git a/Misc/NEWS.d/next/Build/2021-05-24-03-31-17.bpo-41282.L8nP44.rst b/Misc/NEWS.d/next/Build/2021-05-24-03-31-17.bpo-41282.L8nP44.rst
@@ -0,0 +1,3 @@
+Fix broken ``make install`` that caused standard library extension modules
+to be unnecessarily and incorrectly rebuilt during the install phase of
+cpython.