vendored parslet, deemed stable enough and better without dependency

lib/parslet/graphviz.rb

@@ -0,0 +1,97 @@
+
+# Paints a graphviz graph of your parser.
+
+begin
+  require 'ruby-graphviz'
+rescue LoadError
+  puts "Please install the 'ruby-graphviz' gem first."
+  fail
+end
+
+require 'set'
+require 'parslet/atoms/visitor'
+
+module Parslet
+  class GraphvizVisitor
+    def initialize g
+      @graph = g
+      @known_links = Set.new
+      @visited = Set.new
+    end
+
+    attr_reader :parent
+
+    def visit_parser(root)
+      recurse root, node('parser')
+    end
+    def visit_entity(name, block)
+      s = node(name)
+
+      downwards s
+
+      return if @visited.include?(name)
+      @visited << name
+
+      recurse block.call, s
+    end
+    def visit_named(name, atom)
+      recurse atom, parent
+    end
+    def visit_repetition(tag, min, max, atom)
+      recurse atom, parent
+    end
+    def visit_alternative(alternatives)
+      p = parent
+      alternatives.each do |atom|
+        recurse atom, p
+      end
+    end
+    def visit_sequence(sequence)
+      p = parent
+      sequence.each do |atom|
+        recurse atom, p
+      end
+    end
+    def visit_lookahead(positive, atom)
+      recurse atom, parent
+    end
+    def visit_re(regexp)
+      # downwards node(regexp.object_id, label: escape("re(#{regexp.inspect})"))
+    end
+    def visit_str(str)
+      # downwards node(str.object_id, label: escape("#{str.inspect}"))
+    end
+
+    def escape str
+      str.gsub('"', "'")
+    end
+    def node name, opts={}
+      @graph.add_nodes name.to_s, opts
+    end
+    def downwards child
+      if @parent && !@known_links.include?([@parent, child])
+        @graph.add_edges(@parent, child)
+        @known_links << [@parent, child]
+      end
+    end
+    def recurse node, current
+      @parent = current
+      node.accept(self)
+    end
+  end
+
+  module Graphable
+    def graph opts
+      g = GraphViz.new(:G, type: :digraph)
+      visitor = GraphvizVisitor.new(g)
+
+      new.accept(visitor)
+
+      g.output opts
+    end
+  end
+
+  class Parser # reopen for introducing the .graph method
+    extend Graphable
+  end
+end