vendored parslet, deemed stable enough and better without dependency

lib/parslet/cause.rb

@@ -0,0 +1,94 @@
+module Parslet
+  # Represents a cause why a parse did fail. A lot of these objects are
+  # constructed - not all of the causes turn out to be failures for the whole
+  # parse. 
+  #
+  class Cause
+    def initialize(message, source, pos, children)
+      @message, @source, @pos, @children = 
+        message, source, pos, children
+    end
+    
+    # @return [String, Array] A string or an array of message pieces that 
+    #   provide failure information. Use #to_s to get a formatted string.
+    attr_reader :message
+    
+    # @return [Parslet::Source] Source that was parsed when this error 
+    #   happend. Mainly used for line number information.
+    attr_reader :source
+    
+    # Location of the error. 
+    #
+    # @return [Fixnum] Position where the error happened. (character offset)
+    attr_reader :pos 
+    
+    # When this cause is part of a tree of error causes: child nodes for this
+    # node. Very often carries the reasons for this cause. 
+    #
+    # @return [Array<Parslet::Cause>] A list of reasons for this cause. 
+    def children
+      @children ||= []
+    end
+    
+    # Appends 'at line LINE char CHAR' to the string given. Use +pos+ to
+    # override the position of the +source+. This method returns an object
+    # that can be turned into a string using #to_s.
+    #
+    # @param source [Parslet::Source] source that was parsed when this error
+    #   happened 
+    # @param pos [Fixnum] position of error
+    # @param str [String, Array<String>] message parts
+    # @param children [Array<Parslet::Cause>] child nodes for this error tree
+    # @return [Parslet::Cause] a new instance of {Parslet::Cause}
+    #
+    def self.format(source, pos, str, children=[])
+      self.new(str, source, pos, children)
+    end
+    
+    def to_s
+      line, column = source.line_and_column(pos)
+      # Allow message to be a list of objects. Join them here, since we now
+      # really need it. 
+      Array(message).map { |o| 
+        o.respond_to?(:to_slice) ? 
+          o.str.inspect : 
+          o.to_s }.join + " at line #{line} char #{column}."
+    end
+    
+    # Signals to the outside that the parse has failed. Use this in
+    # conjunction with .format for nice error messages. 
+    #
+    def raise(exception_klass=Parslet::ParseFailed)
+      exception = exception_klass.new(self.to_s, self)
+      Kernel.raise exception
+    end
+
+    # Returns an ascii tree representation of the causes of this node and its
+    # children. 
+    #
+    def ascii_tree
+      StringIO.new.tap { |io| 
+        recursive_ascii_tree(self, io, [true]) }.
+        string
+    end
+
+  private
+    def recursive_ascii_tree(node, stream, curved)
+      append_prefix(stream, curved)
+      stream.puts node.to_s
+
+      node.children.each do |child|
+        last_child = (node.children.last == child)
+
+        recursive_ascii_tree(child, stream, curved + [last_child])
+      end
+    end
+    def append_prefix(stream, curved)
+      return if curved.size < 2
+      curved[1..-2].each do |c|
+        stream.print c ? "   " : "|  "
+      end
+      stream.print curved.last ? "`- " : "|- "
+    end
+  end
+end