Support also pip install -e --prefix

pip/req/req_install.py

@@ -795,7 +795,8 @@ exec(compile(
     def install(self, install_options, global_options=[], root=None,
                 prefix=None):
         if self.editable:
-            self.install_editable(install_options, global_options)
+            self.install_editable(
+                install_options, global_options, prefix=prefix)
             return
         if self.is_wheel:
             version = pip.wheel.wheel_version(self.source_dir)
@@ -929,12 +930,17 @@ exec(compile(
             rmtree(self._temp_build_dir)
         self._temp_build_dir = None
 
-    def install_editable(self, install_options, global_options=()):
+    def install_editable(self, install_options,
+                         global_options=(), prefix=None):
         logger.info('Running setup.py develop for %s', self.name)
 
         if self.isolated:
             global_options = list(global_options) + ["--no-user-cfg"]
 
+        if prefix:
+            prefix_param = ['--prefix={0}'.format(prefix)]
+            install_options = list(install_options) + prefix_param
+
         with indent_log():
             # FIXME: should we do --install-headers here too?
             cwd = self.source_dir

tests/functional/test_install.py

@@ -494,7 +494,7 @@ def test_install_package_with_prefix(script, data):
     prefix_path = script.scratch_path / 'prefix'
     result = script.pip(
         'install', '--prefix', prefix_path, '-f', data.find_links,
-        '--no-index', 'simple==1.0',
+        '--no-binary', 'simple', '--no-index', 'simple==1.0',
     )
 
     if hasattr(sys, "pypy_version_info"):
@@ -507,6 +507,34 @@ def test_install_package_with_prefix(script, data):
     assert install_path in result.files_created, str(result)
 
 
+def test_install_editable_with_prefix(script):
+    # make a dummy project
+    pkga_path = script.scratch_path / 'pkga'
+    pkga_path.mkdir()
+    pkga_path.join("setup.py").write(textwrap.dedent("""
+        from setuptools import setup
+        setup(name='pkga',
+              version='0.1')
+    """))
+
+    site_packages = os.path.join(
+        'prefix', 'lib', 'python{0}'.format(pyversion), 'site-packages')
+
+    # make sure target path is in PYTHONPATH
+    pythonpath = script.scratch_path / site_packages
+    pythonpath.makedirs()
+    script.environ["PYTHONPATH"] = pythonpath
+
+    # install pkga package into the absolute prefix directory
+    prefix_path = script.scratch_path / 'prefix'
+    result = script.pip(
+        'install', '--editable', pkga_path, '--prefix', prefix_path)
+
+    # assert pkga is installed at correct location
+    install_path = script.scratch / site_packages / 'pkga.egg-link'
+    assert install_path in result.files_created, str(result)
+
+
 def test_install_package_conflict_prefix_and_user(script, data):
     """
     Test installing a package using pip install --prefix --user errors out