Ensure that --root continues to work with Wheels

pip/locations.py

@@ -153,4 +153,10 @@ def distutils_scheme(dist_name, user=False, home=None, root=None):
                                     'python' + sys.version[:3],
                                     dist_name)
 
+        if root is not None:
+            scheme["headers"] = os.path.join(
+                root,
+                os.path.abspath(scheme["headers"])[1:],
+            )
+
     return scheme

tests/functional/test_install_wheel.py

@@ -57,6 +57,16 @@ def test_install_wheel_with_target(script, data):
     assert Path('scratch')/'target'/'simpledist' in result.files_created, str(result)
 
 
+def test_install_wheel_with_root(script, data):
+    """
+    Test installing a wheel using pip install --root
+    """
+    root_dir = script.scratch_path/'root'
+    result = script.pip('install', 'simple.dist==0.1', '--root', root_dir, '--use-wheel',
+                     '--no-index', '--find-links='+data.find_links)
+    assert Path('scratch')/'root' in result.files_created
+
+
 def test_install_from_wheel_installs_deps(script, data):
     """
     Test can install dependencies of wheels

tests/unit/test_locations.py

@@ -13,6 +13,8 @@ import pytest
 from mock import Mock
 import pip
 
+from pip.locations import distutils_scheme
+
 if sys.platform == 'win32':
    pwd = Mock()
 else:
@@ -120,3 +122,14 @@ class TestLocations:
         from pip import locations
         os.mkdir(self.get_build_dir_location())
         locations._get_build_prefix()
+
+
+class TestDisutilsScheme:
+
+    def test_root_modifies_appropiately(self):
+        norm_scheme = distutils_scheme("example")
+        root_scheme = distutils_scheme("example", root="/test/root/")
+
+        for key, value in norm_scheme.items():
+            expected = os.path.join("/test/root/", os.path.abspath(value)[1:])
+            assert root_scheme[key] == expected