From 3f98ee42509679a5bfd53899c9b6127d6f52e44d Mon Sep 17 00:00:00 2001
From: Adam Tse <adam.tse@me.com>
Date: Sun, 28 Oct 2018 11:44:03 +0000
Subject: [PATCH] Explicit support and tests for `hg+file` scheme for `pip
 install`.

---
 docs/html/reference/pip_install.rst | 2 +-
 news/4358.bugfix                    | 2 ++
 src/pip/_internal/vcs/mercurial.py  | 4 +++-
 tests/functional/test_install.py    | 4 +++-
 4 files changed, 9 insertions(+), 3 deletions(-)
 create mode 100644 news/4358.bugfix

diff --git a/docs/html/reference/pip_install.rst b/docs/html/reference/pip_install.rst
index fa475c462..9fcf94676 100644
--- a/docs/html/reference/pip_install.rst
+++ b/docs/html/reference/pip_install.rst
@@ -418,7 +418,7 @@ Mercurial
 ~~~~~~~~~
 
 The supported schemes are: ``hg+http``, ``hg+https``,
-``hg+static-http`` and ``hg+ssh``.
+``hg+static-http``, ``hg+ssh`` and ``hg+file``.
 
 Here are the supported forms::
 
diff --git a/news/4358.bugfix b/news/4358.bugfix
new file mode 100644
index 000000000..891d819de
--- /dev/null
+++ b/news/4358.bugfix
@@ -0,0 +1,2 @@
+Not a feature because the ``hg+file`` scheme was already functioning implicitly but inconsistently documented.
+This change is to make the scheme support explicit, including tests and docs.
\ No newline at end of file
diff --git a/src/pip/_internal/vcs/mercurial.py b/src/pip/_internal/vcs/mercurial.py
index 21697ff15..e9906632d 100644
--- a/src/pip/_internal/vcs/mercurial.py
+++ b/src/pip/_internal/vcs/mercurial.py
@@ -22,7 +22,9 @@ class Mercurial(VersionControl):
     name = 'hg'
     dirname = '.hg'
     repo_name = 'clone'
-    schemes = ('hg', 'hg+http', 'hg+https', 'hg+ssh', 'hg+static-http')
+    schemes = (
+        'hg', 'hg+http', 'hg+https', 'hg+ssh', 'hg+static-http', 'hg+file'
+    )
 
     @staticmethod
     def get_base_rev_args(rev):
diff --git a/tests/functional/test_install.py b/tests/functional/test_install.py
index 7a0e4a9cb..d11368b11 100644
--- a/tests/functional/test_install.py
+++ b/tests/functional/test_install.py
@@ -334,11 +334,13 @@ def test_install_editable_uninstalls_existing_from_path(script, data):
 
 @need_mercurial
 def test_basic_install_editable_from_hg(script, tmpdir):
-    """Test cloning from Mercurial."""
+    """Test cloning and hg+file install from Mercurial."""
     pkg_path = _create_test_package(script, name='testpackage', vcs='hg')
     args = ['install', '-e', 'hg+%s#egg=testpackage' % path_to_url(pkg_path)]
     result = script.pip(*args)
     result.assert_installed('testpackage', with_files=['.hg'])
+    assert path_to_url(pkg_path).startswith("file://")
+
 
 
 @need_mercurial