From 6cd93c82f5c0a09bc0a3ccab214d87537c5e60c2 Mon Sep 17 00:00:00 2001
From: John Vandenberg <jayvdb@gmail.com>
Date: Fri, 22 Jul 2016 09:11:31 +0700
Subject: [PATCH] Monkeypatch pkg_resources to always use _markerlib

Prior to setuptools 20.10.0 there is patchy support for environment markers,
and setup.py fails while parsing them.
html5lib requires at least setuptools 18.5 for its environment markers.

However, @gsnedders developed a way to monkey patch pkg_resources
so that it always uses _markerlib, which allows all environment markers
to be used for any version of setuptools.  Some patching of _markerlib
is also required so that it works on Python 3 also.

On removing the dependency for setuptools>=18.5, pip partially fails on
Python 2.6 with an error `Double requirement given: ordereddict`
and does not install the requirements.txt.
Fixed by removing ordereddict from requirements-test.txt
---
 requirements-install.sh |  3 ---
 requirements-test.txt   |  1 -
 requirements.txt        |  1 -
 setup.py                | 53 +++++++++++++++++++++++++++++++++++++----
 4 files changed, 48 insertions(+), 10 deletions(-)

diff --git a/requirements-install.sh b/requirements-install.sh
index 9b28888a..cd693444 100755
--- a/requirements-install.sh
+++ b/requirements-install.sh
@@ -5,9 +5,6 @@ if [[ $USE_OPTIONAL != "true" && $USE_OPTIONAL != "false" ]]; then
   exit 1
 fi
 
-# Make sure we're running setuptools >= 18.5
-pip install -U pip setuptools>=18.5
-
 pip install -U -r requirements-test.txt
 
 if [[ $USE_OPTIONAL == "true" ]]; then
diff --git a/requirements-test.txt b/requirements-test.txt
index e24223ef..e1ad307d 100644
--- a/requirements-test.txt
+++ b/requirements-test.txt
@@ -4,4 +4,3 @@ flake8
 pytest
 pytest-expect>=1.1,<2.0
 mock
-ordereddict ; python_version < '2.7'
diff --git a/requirements.txt b/requirements.txt
index 92c09036..745993b9 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,4 +1,3 @@
 six
 webencodings
 ordereddict ; python_version < '2.7'
-setuptools>=18.5
diff --git a/setup.py b/setup.py
index 7c419e2c..00fee241 100644
--- a/setup.py
+++ b/setup.py
@@ -8,10 +8,54 @@
 from setuptools import setup, find_packages, __version__ as setuptools_version
 from pkg_resources import parse_version
 
-if parse_version(setuptools_version) < parse_version("18.5"):
-    print("html5lib requires setuptools version 18.5 or above; "
-          "please upgrade before installing (you have %s)" % setuptools_version)
-    sys.exit(1)
+import pkg_resources
+
+try:
+    import _markerlib.markers
+except ImportError:
+    _markerlib = None
+
+
+# _markerlib.default_environment() obtains its data from _VARS
+# and wraps it in another dict, but _markerlib_evaluate writes
+# to the dict while it is iterating the keys, causing an error
+# on Python 3 only.
+# Replace _markerlib.default_environment to return a custom dict
+# that has all the necessary markers, and ignores any writes.
+
+class Python3MarkerDict(dict):
+
+    def __setitem__(self, key, value):
+        pass
+
+    def pop(self, i=-1):
+        return self[i]
+
+
+if _markerlib and sys.version_info[0] == 3:
+    env = _markerlib.markers._VARS
+    for key in list(env.keys()):
+        new_key = key.replace('.', '_')
+        if new_key != key:
+            env[new_key] = env[key]
+
+    _markerlib.markers._VARS = Python3MarkerDict(env)
+
+    def default_environment():
+        return _markerlib.markers._VARS
+
+    _markerlib.default_environment = default_environment
+
+# Avoid the very buggy pkg_resources.parser, which doesnt consistently
+# recognise the markers needed by this setup.py
+# Change this to setuptools 20.10.0 to support all markers.
+if pkg_resources:
+    if parse_version(setuptools_version) < parse_version('18.5'):
+        MarkerEvaluation = pkg_resources.MarkerEvaluation
+
+        del pkg_resources.parser
+        pkg_resources.evaluate_marker = MarkerEvaluation._markerlib_evaluate
+        MarkerEvaluation.evaluate_marker = MarkerEvaluation._markerlib_evaluate
 
 classifiers = [
     'Development Status :: 5 - Production/Stable',
@@ -60,7 +104,6 @@
       install_requires=[
           'six',
           'webencodings',
-          'setuptools>=18.5'
       ],
       extras_require={
           # A empty extra that only has a conditional marker will be