New experimental "graph" command

Produce a graphviz compatible graph of the parts dependencies.
fdp layout option seems to produce more readable graphs in this case.
Example invocation:
  buildout graph | fdp -t svg -o buildout.svg

src/zc/buildout/buildout.py

@@ -1271,6 +1271,69 @@ class Buildout(DictMixin):
     def annotate(self, args=None):
         _print_annotate(self._annotated)
 
+    def graph(self, args=None):
+        nodes = set([])
+        edges = set([])
+
+        def getRecipe(part):
+            recipe = self._raw[part].get('recipe')
+            if recipe:
+                return recipe
+            macro = self._raw[part].get('<')
+            if macro:
+                return getRecipe(macro)
+
+        _template_split = re.compile('([$]{[^}]*})').split
+
+        print_("digraph {")
+        for part in self._raw['buildout']['parts'].splitlines():
+            if part:
+                nodes.add(part)
+                print_('  buildout -> "%s"' % part)
+                for option, value in self._raw[part].items():
+                    if value == '<': # XXX macro
+                        nodes.add(option)
+                        edges.add((part, option))
+
+                    if "${" in value:
+                        for sub in _template_split(value):
+                            if sub.startswith("${"):
+                                dependency = sub[2:].split(":")[0]
+                                if dependency and dependency != 'buildout':
+                                    nodes.add(dependency)
+                                    edges.add((part, dependency))
+
+        for (part, dependency) in edges:
+            print_(
+                '  "%s" -> "%s"' % (
+                    part,
+                    dependency))
+
+        recipe_colors = {
+            'slapos.recipe.cmmi': '#00AA00',
+            'slapos.recipe.build': '#FF0000',
+            'slapos.recipe.build:gitclone': '#996666',
+            'slapos.recipe.build:download-unpacked': '#FF00FF',
+            'zc.recipe.egg': '#333399',
+            'zc.recipe.egg:custom': '#444499',
+            'zc.recipe.egg:scripts': '#666699',
+        }
+
+        for node in nodes:
+            recipe = getRecipe(node) or ''
+            print_(
+'''"{part_name}" [
+    shape=record
+    label="{{{part_name}|{recipe}}}"
+    style=filled
+    fillcolor="{color}"
+]
+'''.format(part_name=node,
+           recipe=recipe,
+           color=recipe_colors.get(recipe, "#FFFFFF")))
+
+        print_("}")
+
     def print_options(self):
         for section in sorted(self._data):
             if section == 'buildout' or section == self['buildout']['versions']:
@@ -2122,6 +2185,13 @@ Commands:
     The script can be given either as a script path or a path to a
     directory containing a setup.py script.
 
+  graph
+
+    Produce a graphviz compatible graph of the parts dependencies.
+    fdp layout option seems to produce more readable graphs in this case.
+    Example invocation:
+      buildout graph | fdp -t svg -o buildout.svg
+
   annotate
 
     Display annotated sections. All sections are displayed, sorted
@@ -2229,7 +2299,7 @@ def main(args=None):
         command = args.pop(0)
         if command not in (
             'install', 'bootstrap', 'runsetup', 'setup', 'init',
-            'annotate',
+            'annotate', 'graph'
             ):
             _error('invalid command:', command)
     else: