fix macro "inheritance" bug.

src/zc/buildout/buildout.py

@@ -1117,7 +1117,7 @@ class Options(DictMixin):
             raise zc.buildout.UserError("Infinite extending loop %r" % name)
         doing.append(name)
         try:
-            to_do = data.pop('<', None)
+            to_do = data.get('<', None)
             if to_do is None:
                 return data
             __doing__ = 'Loading input sections for %r', name
@@ -1133,6 +1133,7 @@ class Options(DictMixin):
                 result.update(self._do_extend_raw(iname, raw, doing))
 
             result.update(data)
+            result.pop('<')
             return result
         finally:
             assert doing.pop() == name

src/zc/buildout/tests.py

@@ -2715,6 +2715,40 @@ def want_new_zcrecipeegg():
     Error: Bad constraint >=2.0.0a3 zc.recipe.egg<2dev
     """
 
+def macro_inheritance_bug():
+    """
+
+There was a bug preventing a section from using another section as a macro
+if that section was extended with macros, and both sections were listed as
+parts (phew!).  The following contrived example demonstrates that this
+now works.
+
+    >>> write('buildout.cfg',
+    ... '''
+    ... [buildout]
+    ... parts = foo bar
+    ... [base]
+    ... recipe = zc.recipe.egg
+    ... [foo]
+    ... <=base
+    ... eggs = zc.buildout
+    ... interpreter = python
+    ... [bar]
+    ... <=foo
+    ... interpreter = py
+    ... ''')
+    >>> print_(system(join('bin', 'buildout')), end='') # doctest: +ELLIPSIS
+    Installing foo.
+    ...
+    Installing bar.
+    ...
+    >>> ls("./bin")
+    -  buildout
+    -  py
+    -  python
+    """
+
+
 
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