Merge pull request #8553 from uranusjr/header-location-prefix

Header location prefix

news/8521.bugfix

@@ -0,0 +1,3 @@
+Headers provided by wheels in .data directories are now correctly installed
+into the user-provided locations, such as ``--prefix``, instead of the virtual
+environment pip is running in.

src/pip/_internal/locations.py

@@ -138,7 +138,7 @@ def distutils_scheme(
 
     if running_under_virtualenv():
         scheme['headers'] = os.path.join(
-            sys.prefix,
+            i.prefix,
             'include',
             'site',
             'python{}'.format(get_major_minor_version()),

tests/unit/test_locations.py

@@ -130,3 +130,19 @@ class TestDistutilsScheme:
         scheme = distutils_scheme('example')
         assert scheme['platlib'] == install_lib + os.path.sep
         assert scheme['purelib'] == install_lib + os.path.sep
+
+    def test_prefix_modifies_appropriately(self):
+        prefix = os.path.abspath(os.path.join('somewhere', 'else'))
+
+        normal_scheme = distutils_scheme("example")
+        prefix_scheme = distutils_scheme("example", prefix=prefix)
+
+        def _calculate_expected(value):
+            path = os.path.join(prefix, os.path.relpath(value, sys.prefix))
+            return os.path.normpath(path)
+
+        expected = {
+            k: _calculate_expected(v)
+            for k, v in normal_scheme.items()
+        }
+        assert prefix_scheme == expected