Support platform-specific requirements files

This patch adds support for choosing a requirements file, based on the
current OS, with the format 'requirements-{osname}'. This can be combined
with the current approach of choosing a requirement file based on the
Python version. The motivation for this is to replace conditional
choosing of packages inside setup.py.

Change-Id: I30c56082bb9b9bcd80128eedcef17b6beb793cf8

doc/source/index.rst

@@ -107,11 +107,21 @@ You can also have a requirement file for each specific major version of
 Python. If you want to have a different package list for Python 3, just drop
 a requirements-py3.txt, and it will be used instead.
 
-The requirement files are tried in that order (N being the Python major
-version number used to install the package):
+It's also possible to select a requirement file specific for an OS. The format
+is requirements-{osname}.txt, where ``{osname}`` is the equivalent of
+``platform.system()``. The two approaches, Python version and OS version, can
+be combined.
 
+The requirement files are tried in that order (N being the Python major
+version number used to install the package and OS being the current
+platform's name in lowercase, retrieved with ``platform.system()``):
+
+* requirements-OS-pyN.txt
+* tools/pip-requires-OS-pyN
+* requirements-OS.txt
+* tools/pip-requires-OS
 * requirements-pyN.txt
-* tools/pip-requires-py3
+* tools/pip-requires-pyN
 * requirements.txt
 * tools/pip-requires
 

pbr/packaging.py

@@ -24,8 +24,11 @@ from distutils.command import install as du_install
 import distutils.errors
 from distutils import log
 import email
+import functools
 import io
+import itertools
 import os
+import platform
 import re
 import subprocess
 import sys
@@ -56,10 +59,26 @@ def get_requirements_files():
     # Returns a list composed of:
     # - REQUIREMENTS_FILES with -py2 or -py3 in the name
     #   (e.g. requirements-py3.txt)
+    # - REQUIREMENTS_FILES with -{platform.system} in the name
+    #   (e.g. requirements-windows.txt)
+    # - REQUIREMENTS_FILES with both Python version and platform's
+    #   system in the name
+    #   (e.g. requirements-freebsd-py2.txt)
     # - REQUIREMENTS_FILES
-    return (list(map(('-py' + str(sys.version_info[0])).join,
-                     map(os.path.splitext, REQUIREMENTS_FILES)))
-            + list(REQUIREMENTS_FILES))
+    pyversion = sys.version_info[0]
+    system = platform.system().lower()
+    parts = list(map(os.path.splitext, REQUIREMENTS_FILES))
+
+    version_cb = functools.partial("{1}-py{0}{2}".format, pyversion)
+    platform_cb = functools.partial("{1}-{0}{2}".format, system)
+    both_cb = functools.partial("{2}-{0}-py{1}{3}".format, system, pyversion)
+
+    return list(itertools.chain(
+        itertools.starmap(both_cb, parts),
+        itertools.starmap(platform_cb, parts),
+        itertools.starmap(version_cb, parts),
+        REQUIREMENTS_FILES,
+    ))
 
 
 def append_text_list(config, key, text_list):

pbr/tests/test_packaging.py

@@ -39,6 +39,7 @@
 # BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 
 import os
+import sys
 import tempfile
 
 import fixtures
@@ -214,6 +215,32 @@ class TestNestedRequirements(base.BaseTestCase):
         self.assertEqual(result, ['pbr'])
 
 
+class TestGetRequirements(base.BaseTestCase):
+
+    def test_get_requirements_file(self):
+        platforms = ['Windows', 'Freebsd', 'Darwin', 'Linux']
+        version = sys.version_info[0]
+
+        with mock.patch('platform.system') as platform_system:
+            platform_system.side_effect = platforms
+
+            for platform in map(str.lower, platforms):
+                expected = [
+                    'requirements-{plat}-py{ver}.txt'.format(
+                        plat=platform, ver=version),
+                    'tools/pip-requires-{plat}-py{ver}'.format(
+                        plat=platform, ver=version),
+                    'requirements-{0}.txt'.format(platform),
+                    'tools/pip-requires-{0}'.format(platform),
+                    'requirements-py{0}.txt'.format(version),
+                    'tools/pip-requires-py{0}'.format(version),
+                    'requirements.txt',
+                    'tools/pip-requires',
+                ]
+                files = packaging.get_requirements_files()
+                self.assertEqual(expected, files)
+
+
 class TestVersions(base.BaseTestCase):
 
     scenarios = [