1  #!/usr/bin/env python3.8
       2  
       3  """ Convert a grammar into a dot-file suitable for use with GraphViz
       4  
       5      For example:
       6          Generate the GraphViz file:
       7          # scripts/grammar_grapher.py data/python.gram > python.gv
       8  
       9          Then generate the graph...
      10  
      11          # twopi python.gv -Tpng > python_twopi.png
      12  
      13          or
      14  
      15          # dot python.gv -Tpng > python_dot.png
      16  
      17          NOTE: The _dot_ and _twopi_ tools seem to produce the most useful results.
      18                The _circo_ tool is the worst of the bunch. Don't even bother.
      19  """
      20  
      21  import argparse
      22  import sys
      23  
      24  from typing import Any, List
      25  
      26  sys.path.insert(0, ".")
      27  
      28  from pegen.build import build_parser
      29  from pegen.grammar import (
      30      Alt,
      31      Cut,
      32      Forced,
      33      Grammar,
      34      Group,
      35      Leaf,
      36      Lookahead,
      37      Rule,
      38      NameLeaf,
      39      NamedItem,
      40      Opt,
      41      Repeat,
      42      Rhs,
      43  )
      44  
      45  argparser = argparse.ArgumentParser(
      46      prog="graph_grammar",
      47      description="Graph a grammar tree",
      48  )
      49  argparser.add_argument(
      50      "-s",
      51      "--start",
      52      choices=["exec", "eval", "single"],
      53      default="exec",
      54      help="Choose the grammar's start rule (exec, eval or single)",
      55  )
      56  argparser.add_argument("grammar_file", help="The grammar file to graph")
      57  
      58  
      59  def references_for_item(item: Any) -> List[Any]:
      60      if isinstance(item, Alt):
      61          return [_ref for _item in item.items for _ref in references_for_item(_item)]
      62      elif isinstance(item, Cut):
      63          return []
      64      elif isinstance(item, Forced):
      65          return references_for_item(item.node)
      66      elif isinstance(item, Group):
      67          return references_for_item(item.rhs)
      68      elif isinstance(item, Lookahead):
      69          return references_for_item(item.node)
      70      elif isinstance(item, NamedItem):
      71          return references_for_item(item.item)
      72  
      73      # NOTE NameLeaf must be before Leaf
      74      elif isinstance(item, NameLeaf):
      75          if item.value == "ENDMARKER":
      76              return []
      77          return [item.value]
      78      elif isinstance(item, Leaf):
      79          return []
      80  
      81      elif isinstance(item, Opt):
      82          return references_for_item(item.node)
      83      elif isinstance(item, Repeat):
      84          return references_for_item(item.node)
      85      elif isinstance(item, Rhs):
      86          return [_ref for alt in item.alts for _ref in references_for_item(alt)]
      87      elif isinstance(item, Rule):
      88          return references_for_item(item.rhs)
      89      else:
      90          raise RuntimeError(f"Unknown item: {type(item)}")
      91  
      92  
      93  def main() -> None:
      94      args = argparser.parse_args()
      95  
      96      try:
      97          grammar, parser, tokenizer = build_parser(args.grammar_file)
      98      except Exception as err:
      99          print("ERROR: Failed to parse grammar file", file=sys.stderr)
     100          sys.exit(1)
     101  
     102      references = {}
     103      for name, rule in grammar.rules.items():
     104          references[name] = set(references_for_item(rule))
     105  
     106      # Flatten the start node if has only a single reference
     107      root_node = {"exec": "file", "eval": "eval", "single": "interactive"}[args.start]
     108  
     109      print("digraph g1 {")
     110      print('\toverlap="scale";')  # Force twopi to scale the graph to avoid overlaps
     111      print(f'\troot="{root_node}";')
     112      print(f"\t{root_node} [color=green, shape=circle];")
     113      for name, refs in references.items():
     114          for ref in refs:
     115              print(f"\t{name} -> {ref};")
     116      print("}")
     117  
     118  
     119  if __name__ == "__main__":
     120      main()