[meld] build_helpers: Override install command to fix install layout issues

[Kai Willadsen <kaiw src gnome org>]

commit e82594a876811dada161aa3cf2dd72a0cb7f9f06
Author: Kai Willadsen <kai willadsen gmail com>
Date:   Wed Sep 10 07:17:58 2014 +1000

    build_helpers: Override install command to fix install layout issues
    
    Debian and Ubuntu need --install-layout=deb to be enabled by default
    for sane user behaviour, but that flag doesn't work for non-install
    commands, breaking `python setup.py build`.
    
    This commit stops hard-adding the layout argument to sys.argv for
    Debian and Ubuntu in favour of defaulting the argument to the deb
    layout if it's not otherwise specified, and only doing so on install.

 meld/build_helpers.py |   15 +++++++++++++++
 setup.py              |    7 +------
 2 files changed, 16 insertions(+), 6 deletions(-)
---
diff --git a/meld/build_helpers.py b/meld/build_helpers.py
index 7eb2fd1..385e3dc 100644
--- a/meld/build_helpers.py
+++ b/meld/build_helpers.py
@@ -23,11 +23,13 @@ from __future__ import print_function
 import distutils.cmd
 import distutils.command.build
 import distutils.command.build_py
+import distutils.command.install
 import distutils.command.install_data
 import distutils.dist
 import distutils.dir_util
 import glob
 import os.path
+import platform
 import sys
 
 from distutils.log import info
@@ -360,6 +362,19 @@ class build_py(distutils.command.build_py.build_py):
             self, module, module_file, package)
 
 
+class install(distutils.command.install.install):
+
+    def finalize_options(self):
+        special_cases = ('debian', 'ubuntu')
+        if (platform.system() == 'Linux' and
+                platform.linux_distribution()[0].lower() in special_cases):
+            # Maintain an explicit install-layout, but use deb by default
+            specified_layout = getattr(self, 'install_layout', None)
+            self.install_layout = specified_layout or 'deb'
+
+        distutils.command.install.install.finalize_options(self)
+
+
 class install_data(distutils.command.install_data.install_data):
 
     def run(self):
diff --git a/setup.py b/setup.py
index e1840af..8f3c333 100644
--- a/setup.py
+++ b/setup.py
@@ -2,17 +2,11 @@
 
 from distutils.core import setup
 import glob
-import platform
-import sys
 
 import meld.build_helpers
 import meld.conf
 
 
-if (platform.system() == 'Linux' and
-        platform.linux_distribution()[0].lower() in ('debian', 'ubuntu')):
-    sys.argv.append('--install-layout=deb')
-
 setup(
     name=meld.conf.__package__,
     version=meld.conf.__version__,
@@ -66,6 +60,7 @@ setup(
         "build_icons": meld.build_helpers.build_icons,
         "build_data": meld.build_helpers.build_data,
         "build_py": meld.build_helpers.build_py,
+        "install": meld.build_helpers.install,
         "install_data": meld.build_helpers.install_data,
     },
     distclass=meld.build_helpers.MeldDistribution,