Merge pull request #213 from reinout/reinout-versionconflict-args-fix

Our VersionConflict handling could result in an UnpackError when rendering

CHANGES.rst

@@ -8,10 +8,16 @@ Unreleased
   ``site-packages`` directory:  don't remove it from ``sys.path``.  See
   https://github.com/buildout/buildout/issues/217
 
-- Remove assumption that ``pkg_resources`` is a module (untrue since 
+- Remove assumption that ``pkg_resources`` is a module (untrue since
   release of `setuptools 8.3``).  See
   https://github.com/buildout/buildout/issues/227
 
+- Fix for #212. For certain kinds of conflict errors you'd get an UnpackError
+  when rendering the error message. Instead of a nicely formatted version
+  conflict message.
+  [reinout]
+
+
 2.3.1 (2014-12-16)
 ==================
 

src/zc/buildout/easy_install.py

@@ -1350,17 +1350,16 @@ class VersionConflict(zc.buildout.UserError):
         self.err, self.ws = err, ws
 
     def __str__(self):
-        existing_dist, req = self.err.args
-        result = ["There is a version conflict.",
-                  "We already have: %s" % existing_dist,
-                  ]
-        stated = False
-        for dist in self.ws:
-            if req in dist.requires():
-                result.append("but %s requires %r." % (dist, str(req)))
-                stated = True
-        if not stated:
-            result.append("We require %s" % req)
+        result = ["There is a version conflict."]
+        if len(self.err.args) == 2:
+            existing_dist, req = self.err.args
+            result.append("We already have: %s" % existing_dist)
+            for dist in self.ws:
+                if req in dist.requires():
+                    result.append("but %s requires %r." % (dist, str(req)))
+        else:
+            # The error argument is already a nice error string.
+            result.append(self.err.args[0])
         return '\n'.join(result)
 
 

src/zc/buildout/tests.py

@@ -361,6 +361,30 @@ If we use the verbose switch, we can see where requirements are coming from:
     but sampley 1 requires 'demoneeded==1.0'.
     """
 
+def version_conflict_rendering():
+    """
+
+We use the arguments passed by pkg_resources.VersionConflict to construct a
+nice error message:
+
+    >>> error = pkg_resources.VersionConflict('pkg1 2.1', 'pkg1 1.0')
+    >>> ws = []  # Not relevant for this test
+    >>> print_(zc.buildout.easy_install.VersionConflict(
+    ...     error, ws)) # doctest: +ELLIPSIS
+    There is a version conflict...
+
+But sometimes pkg_resources passes a nicely formatted string itself already.
+Extracting the original arguments fails in that case, so we just show the string.
+
+    >>> error = pkg_resources.VersionConflict('pkg1 2.1 is simply wrong')
+    >>> ws = []  # Not relevant for this test
+    >>> print_(zc.buildout.easy_install.VersionConflict(
+    ...     error, ws)) # doctest: +ELLIPSIS
+    There is a version conflict.
+    pkg1 2.1 is simply wrong
+
+    """
+
 def show_who_requires_missing_distributions():
     """