Add 'brew graph' external command.

This command generates a GraphViz dot file from the Hoembrew
dependency graph.

$ brew install graphviz
$ brew graph | dot -Tsvg -ohomebrew.svg
$ open homebrew.svg

Library/Contributions/examples/brew-graph

+#!/usr/bin/env python
+"""
+$ brew install graphviz
+$ brew graph | dot -Tsvg -ohomebrew.svg
+$ open homebrew.svg
+"""
+from __future__ import with_statement
+
+from contextlib import contextmanager
+import re
+from subprocess import Popen, PIPE
+import sys
+
+
+def run(command, print_command=False):
+    "Run a command, returning the exit code and output."
+    if print_command: print command
+    p = Popen(command, stdout=PIPE)
+    output, errput = p.communicate()
+    return p.returncode, output
+
+
+def _quote_id(id):
+    return '"' + id.replace('"', '\"') + '"'
+
+
+def format_attribs(attrib):
+    if len(attrib) == 0:
+        return ''
+
+    values = ['%s="%s"' % (k, attrib[k]) for k in attrib]
+    return '[' + ','.join(values) + ']'
+
+
+class Output(object):
+    def __init__(self, fd=sys.stdout, tabstyle="  "):
+        self.fd = fd
+        self.tabstyle = tabstyle
+        self.tablevel = 0
+
+    def close(self):
+        self.fd = None
+
+    def out(self, s):
+        self.tabout()
+        self.fd.write(s)
+
+    def outln(self, s=None):
+        if s is not None:
+            self.tabout()
+            self.fd.write(s)
+        self.fd.write('\n')
+
+    @contextmanager
+    def indented(self):
+        self.indent()
+        yield self
+        self.dedent()
+
+    def indent(self):
+        self.tablevel += 1
+
+    def dedent(self):
+        if self.tablevel == 0:
+            raise Exception('No existing indent level.')
+        self.tablevel -= 1
+
+    def tabout(self):
+        if self.tablevel:
+            self.fd.write(self.tabstyle * self.tablevel)
+
+
+class NodeContainer(object):
+    def __init__(self):
+        self.nodes = list()
+        self.node_defaults = dict()
+        # Stack of node attribs
+        self._node_styles = list()
+
+    def _node_style(self):
+        if (len(self._node_styles) > 0):
+            return self._node_styles[-1]
+        else:
+            return dict()
+
+    def _push_node_style(self, attrib):
+        self._node_styles.append(attrib)
+
+    def _pop_node_style(self):
+        return self._node_styles.pop()
+
+    @contextmanager
+    def node_styles(self, attrib):
+        self._push_node_style(attrib)
+        yield
+        self._pop_node_style()
+
+    def node(self, nodeid, label, attrib=None):
+        _attrib = dict(self._node_style())
+        if attrib is not None:
+            _attrib.update(attrib)
+
+        n = Node(nodeid, label, _attrib)
+        self.nodes.append(n)
+        return n
+
+    def nodes_to_dot(self, out):
+        if len(self.node_defaults) > 0:
+            out.outln("node " + format_attribs(self.node_defaults) + ";")
+
+        if len(self.nodes) == 0:
+            return
+
+        id_width = max([len(_quote_id(n.id)) for n in self.nodes])
+        for node in self.nodes:
+            node.to_dot(out, id_width)
+
+
+class Node(object):
+    def __init__(self, nodeid, label, attrib=None):
+        self.id = nodeid
+        self.label = label
+        self.attrib = attrib if attrib is not None else dict()
+
+    def as_dot(self, id_width=1):
+        _attribs = dict(self.attrib)
+        _attribs['label'] = self.label
+
+        return '%-*s %s' % (id_width, _quote_id(self.id), format_attribs(_attribs))
+
+
+    def to_dot(self, out, id_width=1):
+        out.outln(self.as_dot(id_width))
+
+
+class ClusterContainer(object):
+    def __init__(self):
+        self.clusters = list()
+
+    def cluster(self, clusterid, label, attrib=None):
+        c = Cluster(clusterid, label, self, attrib)
+        self.clusters.append(c)
+        return c
+
+
+class Cluster(NodeContainer, ClusterContainer):
+    def __init__(self, clusterid, label, parentcluster=None, attrib=None):
+        NodeContainer.__init__(self)
+        ClusterContainer.__init__(self)
+
+        self.id = clusterid
+        self.label = label
+        self.attrib = attrib if attrib is not None else dict()
+        self.parentcluster = parentcluster
+
+    def cluster_id(self):
+        return _quote_id("cluster_" + self.id)
+
+    def to_dot(self, out):
+        out.outln("subgraph %s {" % self.cluster_id())
+        with out.indented():
+            out.outln('label = "%s"' % self.label)
+            for k in self.attrib:
+                out.outln('%s = "%s"' % (k, self.attrib[k]))
+
+            for cluster in self.clusters:
+                cluster.to_dot(out)
+
+            self.nodes_to_dot(out)
+        out.outln("}")
+
+
+class Edge(object):
+    def __init__(self, source, target, attrib=None):
+        if attrib is None:
+            attrib = dict()
+
+        self.source = source
+        self.target = target
+        self.attrib = attrib
+
+    def to_dot(self, out):
+        out.outln(self.as_dot())
+
+    def as_dot(self):
+        return " ".join((_quote_id(self.source), "->", _quote_id(self.target), format_attribs(self.attrib)))
+
+
+class EdgeContainer(object):
+    def __init__(self):
+        self.edges = list()
+        self.edge_defaults = dict()
+        # Stack of edge attribs
+        self._edge_styles = list()
+
+    def _edge_style(self):
+        if (len(self._edge_styles) > 0):
+            return self._edge_styles[-1]
+        else:
+            return dict()
+
+    def _push_edge_style(self, attrib):
+        self._edge_styles.append(attrib)
+
+    def _pop_edge_style(self):
+        return self._edge_styles.pop()
+
+    @contextmanager
+    def edge_styles(self, attrib):
+        self._push_edge_style(attrib)
+        yield
+        self._pop_edge_style()
+
+    def link(self, source, target, attrib=None):
+        _attrib = dict(self._edge_style())
+        if attrib is not None:
+            _attrib.update(attrib)
+
+        e = Edge(source, target, _attrib)
+        self.edges.append(e)
+        return e
+
+    def edges_to_dot(self, out):
+        if len(self.edge_defaults) > 0:
+            out.outln("edge " + format_attribs(self.edge_defaults) + ";")
+
+        if len(self.edges) == 0:
+            return
+
+        for edge in self.edges:
+            edge.to_dot(out)
+
+
+class Graph(NodeContainer, EdgeContainer, ClusterContainer):
+    """
+    Contains the nodes, edges, and subgraph definitions for a graph to be
+    turned into a Graphviz DOT file.
+    """
+
+    def __init__(self, label=None, attrib=None):
+        NodeContainer.__init__(self)
+        EdgeContainer.__init__(self)
+        ClusterContainer.__init__(self)
+
+        self.label = label if label is not None else "Default Label"
+        self.attrib = attrib if attrib is not None else dict()
+
+    def dot(self, fd=sys.stdout):
+        try:
+            self.o = Output(fd)
+            self._dot()
+        finally:
+            self.o.close()
+
+    def _dot(self):
+        self.o.outln("digraph G {")
+
+        with self.o.indented():
+            self.o.outln('label = "%s"' % self.label)
+            for k in self.attrib:
+                self.o.outln('%s = "%s"' % (k, self.attrib[k]))
+
+            self.nodes_to_dot(self.o)
+
+            for cluster in self.clusters:
+                self.o.outln()
+                cluster.to_dot(self.o)
+
+            self.o.outln()
+            self.edges_to_dot(self.o)
+
+        self.o.outln("}")
+
+
+def main():
+    code, output = run(["brew", "deps", "--all"])
+    output = output.strip()
+    depgraph = list()
+
+    for f in output.split("\n"):
+        stuff = f.split(":",2)
+        name = stuff[0]
+        deps = stuff[1].strip()
+        if not deps:
+            deps = list()
+        else:
+            deps = deps.split(" ")
+        depgraph.append((name, deps))
+
+    hb = Graph("Homebrew Dependencies", attrib={'labelloc':'b', 'rankdir':'LR', 'ranksep':'5'})
+
+    used = set()
+    for f in depgraph:
+        for d in f[1]:
+            used.add(f[0])
+            used.add(d)
+
+    for f in depgraph:
+        if f[0] not in used:
+            continue
+        n = hb.node(f[0], f[0])
+        for d in f[1]:
+            hb.link(d, f[0])
+
+    hb.dot()
+
+
+if __name__ == "__main__":
+    main()