setup.py: work with tox under py3

This allows a python3-based "tox" (as shipped with modern debian and
ubuntu systems) to run setup.py egg_info, update_version, and sdist
commands. It moves the main "tahoe requires py2" check out of setup.py
and into allmydata.scripts.runner.run, where it gets applied at runtime
rather than build time.

It also changes the execfile(_auto_deps.py) and Versioneer-like "ask git
what our version string should be" code to work under both py2 and py3.

fixes ticket:2747

setup.py

@@ -1,6 +1,6 @@
 #! /usr/bin/env python
 # -*- coding: utf-8 -*-
-import sys; assert sys.version_info < (3,), ur"Tahoe-LAFS does not run under Python 3. Please use Python 2.7.x."
+import sys
 
 # Tahoe-LAFS -- secure, distributed storage grid
 #
@@ -12,8 +12,6 @@ import sys; assert sys.version_info < (3,), ur"Tahoe-LAFS does not run under Pyt
 
 import os, subprocess, re
 
-##### sys.path management
-
 basedir = os.path.dirname(os.path.abspath(__file__))
 
 # locate our version number
@@ -49,7 +47,12 @@ else:
 # the _auto_deps.install_requires list, which is used in the call to setup()
 # below.
 adglobals = {}
-execfile('src/allmydata/_auto_deps.py', adglobals)
+auto_deps_fn = "src/allmydata/_auto_deps.py"
+if sys.version_info[0] >= 3:
+    exec(compile(open(auto_deps_fn, 'rb').read(), auto_deps_fn, "exec"),
+         adglobals, adglobals)
+else:
+    execfile(auto_deps_fn, adglobals)
 install_requires = adglobals['install_requires']
 setup_requires = adglobals['setup_requires']
 
@@ -98,11 +101,11 @@ trove_classifiers=[
 GIT_VERSION_BODY = '''
 # This _version.py is generated from git metadata by the tahoe setup.py.
 
-__pkgname__ = %(pkgname)r
-real_version = %(version)r
-full_version = %(full)r
-branch = %(branch)r
-verstr = %(normalized)r
+__pkgname__ = "%(pkgname)s"
+real_version = "%(version)s"
+full_version = "%(full)s"
+branch = "%(branch)s"
+verstr = "%(normalized)s"
 __version__ = verstr
 '''
 
@@ -153,6 +156,7 @@ def versions_from_git(tag_prefix):
     if stdout is None:
         # run_command already complained.
         return {}
+    stdout = stdout.decode("ascii")
     if not stdout.startswith(tag_prefix):
         print("Warning: tag %r doesn't start with prefix %r." % (stdout, tag_prefix))
         return {}
@@ -167,16 +171,18 @@ def versions_from_git(tag_prefix):
     if stdout is None:
         # run_command already complained.
         return {}
-    full = stdout.strip()
+    full = stdout.decode("ascii").strip()
     if version.endswith("-dirty"):
         full += "-dirty"
         normalized_version += ".dev0"
 
     # Thanks to Jistanidiot at <http://stackoverflow.com/questions/6245570/get-current-branch-name>.
     stdout = run_command(["git", "rev-parse", "--abbrev-ref", "HEAD"], cwd=source_dir)
-    branch = (stdout or "unknown").strip()
+    branch = (stdout or b"unknown").decode("ascii").strip()
 
-    return {"version": version, "normalized": normalized_version, "full": full, "branch": branch}
+    # this returns native strings (bytes on py2, unicode on py3)
+    return {"version": version, "normalized": normalized_version,
+            "full": full, "branch": branch}
 
 # setup.cfg has an [aliases] section which runs "update_version" before many
 # commands (like "build" and "sdist") that need to know our package version
@@ -210,15 +216,21 @@ Warning: no version information found. This may cause tests to fail.
     def try_from_git(self):
         # If we change APPNAME, the release tag names should also change from then on.
         versions = versions_from_git(APPNAME + '-')
+
+        # setup.py might be run by either py2 or py3 (when run by tox, which
+        # uses py3 on modern debian/ubuntu distros). We want this generated
+        # file to contain native strings on both (str=bytes in py2,
+        # str=unicode in py3)
         if versions:
+            body = GIT_VERSION_BODY % {
+                "pkgname": self.distribution.get_name(),
+                "version": versions["version"],
+                "normalized": versions["normalized"],
+                "full": versions["full"],
+                "branch": versions["branch"],
+                }
             f = open(VERSION_PY_FILENAME, "wb")
-            f.write(GIT_VERSION_BODY %
-                    { "pkgname": self.distribution.get_name(),
-                      "version": versions["version"],
-                      "normalized": versions["normalized"],
-                      "full": versions["full"],
-                      "branch": versions["branch"],
-                    })
+            f.write(body.encode("ascii"))
             f.close()
             print("Wrote normalized version %r into '%s'" % (versions["normalized"], VERSION_PY_FILENAME))
 

src/allmydata/scripts/runner.py

@@ -93,6 +93,8 @@ def runner(argv,
            stdin=None, stdout=None, stderr=None,
            install_node_control=True, additional_commands=None):
 
+    assert sys.version_info < (3,), ur"Tahoe-LAFS does not run under Python 3. Please use Python 2.7.x."
+
     stdin  = stdin  or sys.stdin
     stdout = stdout or sys.stdout
     stderr = stderr or sys.stderr