Retire the setup_requires hack in cases where it isn't needed (and can cause build problems). refs #2286

Signed-off-by: Daira Hopwood <daira@jacaranda.org>

setup.py

@@ -64,6 +64,7 @@ else:
 adglobals = {}
 execfile('src/allmydata/_auto_deps.py', adglobals)
 install_requires = adglobals['install_requires']
+setup_requires = adglobals['setup_requires']
 
 if len(sys.argv) > 1 and sys.argv[1] == '--fakedependency':
     del sys.argv[1]
@@ -113,23 +114,6 @@ trove_classifiers=[
     ]
 
 
-setup_requires = []
-
-# Nevow imports itself when building, which causes Twisted and zope.interface
-# to be imported. We need to make sure that the versions of Twisted and
-# zope.interface used at build time satisfy Nevow's requirements. If not
-# then there are two problems:
-#  - prior to Nevow v0.9.33, Nevow didn't declare its dependency on Twisted
-#    in a way that enabled setuptools to satisfy that requirement at
-#    build time.
-#  - some versions of zope.interface, e.g. v3.6.4, are incompatible with
-#    Nevow, and we need to avoid those both at build and run-time.
-#
-# This only matters when compatible versions of Twisted and zope.interface
-# are not already installed. Retire this hack when
-# https://bugs.launchpad.net/nevow/+bug/812537 has been fixed.
-setup_requires += [req for req in install_requires if req.startswith('Twisted') or req.startswith('zope.interface')]
-
 # We no longer have any requirements specific to tests.
 tests_require=[]
 

src/allmydata/_auto_deps.py

@@ -121,12 +121,25 @@ if not hasattr(sys, 'frozen'):
 # already installed.
 # <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/2028>
 #
+# When the fallback is used we also need to work around the fact
+# that Nevow imports itself when building, which causes Twisted
+# and zope.interface to be imported; therefore, we need to set
+# setup_requires to make sure that the versions of Twisted and
+# zope.interface used at build time satisfy Nevow's requirements.
+#
 # In cases where this fallback isn't needed, we prefer Nevow >= 0.11.1
 # which can be installed using pip, and Twisted >= 13.0.0 which
-# Nevow 0.11.1 depends on.
+# Nevow 0.11.1 depends on. In this case we should *not* use the
+# setup_requires hack, because if we do then the build will break
+# when Twisted < 13.0.0 is already installed (even though it could
+# have succeeded by building a later version under support/ ).
+#
 # <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/2032>
 # <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/2249>
 # <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/2291>
+# <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/2286>
+
+setup_requires = []
 
 _use_old_Twisted_and_Nevow = False
 if sys.platform == "win32":
@@ -140,6 +153,8 @@ if _use_old_Twisted_and_Nevow:
         "Twisted >= 11.1.0, <= 12.1.0",
         "Nevow >= 0.9.33, <= 0.10",
     ]
+    setup_requires += [req for req in install_requires if req.startswith('Twisted')
+                                                       or req.startswith('zope.interface')]
 else:
     install_requires += [
         "Twisted >= 13.0.0",