python_generator.py

import os.path
import token
from typing import IO, Any, Dict, Optional, Sequence, Set, Text, Tuple

from pegen import grammar
from pegen.grammar import (
    Alt,
    Cut,
    Forced,
    Gather,
    GrammarVisitor,
    Group,
    Lookahead,
    NamedItem,
    NameLeaf,
    NegativeLookahead,
    Opt,
    PositiveLookahead,
    Repeat0,
    Repeat1,
    Rhs,
    Rule,
    StringLeaf,
)
from pegen.parser_generator import ParserGenerator

MODULE_PREFIX = """\
#!/usr/bin/env python3.8
# @generated by pegen from {filename}

import ast
import sys
import tokenize

from typing import Any, Optional

from pegen.parser import memoize, memoize_left_rec, logger, Parser

"""
MODULE_SUFFIX = """

if __name__ == '__main__':
    from pegen.parser import simple_parser_main
    simple_parser_main({class_name})
"""


class InvalidNodeVisitor(GrammarVisitor):
    def visit_NameLeaf(self, node: NameLeaf) -> bool:
        name = node.value
        return name.startswith("invalid")

    def visit_StringLeaf(self, node: StringLeaf) -> bool:
        return False

    def visit_NamedItem(self, node: NamedItem) -> bool:
        return self.visit(node.item)

    def visit_Rhs(self, node: Rhs) -> bool:
        return any(self.visit(alt) for alt in node.alts)

    def visit_Alt(self, node: Alt) -> bool:
        return any(self.visit(item) for item in node.items)

    def lookahead_call_helper(self, node: Lookahead) -> bool:
        return self.visit(node.node)

    def visit_PositiveLookahead(self, node: PositiveLookahead) -> bool:
        return self.lookahead_call_helper(node)

    def visit_NegativeLookahead(self, node: NegativeLookahead) -> bool:
        return self.lookahead_call_helper(node)

    def visit_Opt(self, node: Opt) -> bool:
        return self.visit(node.node)

    def visit_Repeat(self, node: Repeat0) -> Tuple[str, str]:
        return self.visit(node.node)

    def visit_Gather(self, node: Gather) -> Tuple[str, str]:
        return self.visit(node.node)

    def visit_Group(self, node: Group) -> bool:
        return self.visit(node.rhs)

    def visit_Cut(self, node: Cut) -> bool:
        return False

    def visit_Forced(self, node: Forced) -> bool:
        return self.visit(node.node)


class PythonCallMakerVisitor(GrammarVisitor):
    def __init__(self, parser_generator: ParserGenerator):
        self.gen = parser_generator
        self.cache: Dict[Any, Any] = {}

    def visit_NameLeaf(self, node: NameLeaf) -> Tuple[Optional[str], str]:
        name = node.value
        if name == "SOFT_KEYWORD":
            return "soft_keyword", "self.soft_keyword()"
        if name in ("NAME", "NUMBER", "STRING", "OP", "TYPE_COMMENT"):
            name = name.lower()
            return name, f"self.{name}()"
        if name in ("NEWLINE", "DEDENT", "INDENT", "ENDMARKER", "ASYNC", "AWAIT"):
            # Avoid using names that can be Python keywords
            return "_" + name.lower(), f"self.expect({name!r})"
        return name, f"self.{name}()"

    def visit_StringLeaf(self, node: StringLeaf) -> Tuple[str, str]:
        return "literal", f"self.expect({node.value})"

    def visit_Rhs(self, node: Rhs) -> Tuple[Optional[str], str]:
        if node in self.cache:
            return self.cache[node]
        if len(node.alts) == 1 and len(node.alts[0].items) == 1:
            self.cache[node] = self.visit(node.alts[0].items[0])
        else:
            name = self.gen.artifical_rule_from_rhs(node)
            self.cache[node] = name, f"self.{name}()"
        return self.cache[node]

    def visit_NamedItem(self, node: NamedItem) -> Tuple[Optional[str], str]:
        name, call = self.visit(node.item)
        if node.name:
            name = node.name
        return name, call

    def lookahead_call_helper(self, node: Lookahead) -> Tuple[str, str]:
        name, call = self.visit(node.node)
        head, tail = call.split("(", 1)
        assert tail[-1] == ")"
        tail = tail[:-1]
        return head, tail

    def visit_PositiveLookahead(self, node: PositiveLookahead) -> Tuple[None, str]:
        head, tail = self.lookahead_call_helper(node)
        return None, f"self.positive_lookahead({head}, {tail})"

    def visit_NegativeLookahead(self, node: NegativeLookahead) -> Tuple[None, str]:
        head, tail = self.lookahead_call_helper(node)
        return None, f"self.negative_lookahead({head}, {tail})"

    def visit_Opt(self, node: Opt) -> Tuple[str, str]:
        name, call = self.visit(node.node)
        # Note trailing comma (the call may already have one comma
        # at the end, for example when rules have both repeat0 and optional
        # markers, e.g: [rule*])
        if call.endswith(","):
            return "opt", call
        else:
            return "opt", f"{call},"

    def visit_Repeat0(self, node: Repeat0) -> Tuple[str, str]:
        if node in self.cache:
            return self.cache[node]
        name = self.gen.artificial_rule_from_repeat(node.node, False)
        self.cache[node] = name, f"self.{name}(),"  # Also a trailing comma!
        return self.cache[node]

    def visit_Repeat1(self, node: Repeat1) -> Tuple[str, str]:
        if node in self.cache:
            return self.cache[node]
        name = self.gen.artificial_rule_from_repeat(node.node, True)
        self.cache[node] = name, f"self.{name}()"  # But no trailing comma here!
        return self.cache[node]

    def visit_Gather(self, node: Gather) -> Tuple[str, str]:
        if node in self.cache:
            return self.cache[node]
        name = self.gen.artifical_rule_from_gather(node)
        self.cache[node] = name, f"self.{name}()"  # No trailing comma here either!
        return self.cache[node]

    def visit_Group(self, node: Group) -> Tuple[Optional[str], str]:
        return self.visit(node.rhs)

    def visit_Cut(self, node: Cut) -> Tuple[str, str]:
        return "cut", "True"

    def visit_Forced(self, node: Forced) -> Tuple[str, str]:
        if isinstance(node.node, Group):
            _, val = self.visit(node.node.rhs)
            return "forced", f"self.expect_forced({val}, '''({node.node.rhs!s})''')"
        else:
            return (
                "forced",
                f"self.expect_forced(self.expect({node.node.value}), {node.node.value!r})",
            )


class PythonParserGenerator(ParserGenerator, GrammarVisitor):
    def __init__(
        self,
        grammar: grammar.Grammar,
        file: Optional[IO[Text]],
        tokens: Set[str] = set(token.tok_name.values()),
        location_formatting: Optional[str] = None,
        unreachable_formatting: Optional[str] = None,
    ):
        tokens.add("SOFT_KEYWORD")
        super().__init__(grammar, tokens, file)
        self.callmakervisitor: PythonCallMakerVisitor = PythonCallMakerVisitor(self)
        self.invalidvisitor: InvalidNodeVisitor = InvalidNodeVisitor()
        self.unreachable_formatting = unreachable_formatting or "None  # pragma: no cover"
        self.location_formatting = (
            location_formatting
            or "lineno=start_lineno, col_offset=start_col_offset, "
            "end_lineno=end_lineno, end_col_offset=end_col_offset"
        )

    def generate(self, filename: str) -> None:
        self.collect_rules()
        header = self.grammar.metas.get("header", MODULE_PREFIX)
        if header is not None:
            basename = os.path.basename(filename)
            self.print(header.rstrip("\n").format(filename=basename))
        subheader = self.grammar.metas.get("subheader", "")
        if subheader:
            self.print(subheader)
        cls_name = self.grammar.metas.get("class", "GeneratedParser")
        self.print("# Keywords and soft keywords are listed at the end of the parser definition.")
        self.print(f"class {cls_name}(Parser):")
        for rule in self.all_rules.values():
            self.print()
            with self.indent():
                self.visit(rule)

        self.print()
        with self.indent():
            self.print(f"KEYWORDS = {tuple(self.keywords)}")
            self.print(f"SOFT_KEYWORDS = {tuple(self.soft_keywords)}")

        trailer = self.grammar.metas.get("trailer", MODULE_SUFFIX.format(class_name=cls_name))
        if trailer is not None:
            self.print(trailer.rstrip("\n"))

    def alts_uses_locations(self, alts: Sequence[Alt]) -> bool:
        for alt in alts:
            if alt.action and "LOCATIONS" in alt.action:
                return True
            for n in alt.items:
                if isinstance(n.item, Group) and self.alts_uses_locations(n.item.rhs.alts):
                    return True
        return False

    def visit_Rule(self, node: Rule) -> None:
        is_loop = node.is_loop()
        is_gather = node.is_gather()
        rhs = node.flatten()
        if node.left_recursive:
            if node.leader:
                self.print("@memoize_left_rec")
            else:
                # Non-leader rules in a cycle are not memoized,
                # but they must still be logged.
                self.print("@logger")
        else:
            self.print("@memoize")
        node_type = node.type or "Any"
        self.print(f"def {node.name}(self) -> Optional[{node_type}]:")
        with self.indent():
            self.print(f"# {node.name}: {rhs}")
            self.print("mark = self._mark()")
            if self.alts_uses_locations(node.rhs.alts):
                self.print("tok = self._tokenizer.peek()")
                self.print("start_lineno, start_col_offset = tok.start")
            if is_loop:
                self.print("children = []")
            self.visit(rhs, is_loop=is_loop, is_gather=is_gather)
            if is_loop:
                self.print("return children")
            else:
                self.print("return None")

    def visit_NamedItem(self, node: NamedItem) -> None:
        name, call = self.callmakervisitor.visit(node.item)
        if node.name:
            name = node.name
        if not name:
            self.print(call)
        else:
            if name != "cut":
                name = self.dedupe(name)
            self.print(f"({name} := {call})")

    def visit_Rhs(self, node: Rhs, is_loop: bool = False, is_gather: bool = False) -> None:
        if is_loop:
            assert len(node.alts) == 1
        for alt in node.alts:
            self.visit(alt, is_loop=is_loop, is_gather=is_gather)

    def visit_Alt(self, node: Alt, is_loop: bool, is_gather: bool) -> None:
        has_cut = any(isinstance(item.item, Cut) for item in node.items)
        with self.local_variable_context():
            if has_cut:
                self.print("cut = False")
            if is_loop:
                self.print("while (")
            else:
                self.print("if (")
            with self.indent():
                first = True
                for item in node.items:
                    if first:
                        first = False
                    else:
                        self.print("and")
                    self.visit(item)
                    if is_gather:
                        self.print("is not None")

            self.print("):")
            with self.indent():
                action = node.action
                if not action:
                    if is_gather:
                        assert len(self.local_variable_names) == 2
                        action = (
                            f"[{self.local_variable_names[0]}] + {self.local_variable_names[1]}"
                        )
                    else:
                        if self.invalidvisitor.visit(node):
                            action = "UNREACHABLE"
                        elif len(self.local_variable_names) == 1:
                            action = f"{self.local_variable_names[0]}"
                        else:
                            action = f"[{', '.join(self.local_variable_names)}]"
                elif "LOCATIONS" in action:
                    self.print("tok = self._tokenizer.get_last_non_whitespace_token()")
                    self.print("end_lineno, end_col_offset = tok.end")
                    action = action.replace("LOCATIONS", self.location_formatting)

                if is_loop:
                    self.print(f"children.append({action})")
                    self.print(f"mark = self._mark()")
                else:
                    if "UNREACHABLE" in action:
                        action = action.replace("UNREACHABLE", self.unreachable_formatting)
                    self.print(f"return {action}")

            self.print("self._reset(mark)")
            # Skip remaining alternatives if a cut was reached.
            if has_cut:
                self.print("if cut: return None")