SSL rust.py   Interaktion und
PortierbarkeitPython

"""Emit code and parser tables in Rust."""

import json
import re
import unicodedata
import sys
import itertools
import collections
from contextlib import contextmanager

from ..runtime import (ERROR, ErrorToken, SPECIAL_CASE_TAG)
from ..ordered import OrderedSet

from ..grammar import (Some, Nt, InitNt, End, ErrorSymbol)
from ..actions import (Accept, Action, Replay, Unwind, Reduce, CheckNotOnNewLine, FilterStates,
                       PushFlag, PopFlag, FunCall, Seq)

from .. import types


TERMINAL_NAMES = {
    '&&=': 'LogicalAndAssign',
    '||=': 'LogicalOrAssign',
    '??=': 'CoalesceAssign',
    '{': 'OpenBrace',
    '}': 'CloseBrace',
    '(': 'OpenParenthesis',
    ')': 'CloseParenthesis',
    '[': 'OpenBracket',
    ']': 'CloseBracket',
    '+': 'Plus',
    '-': 'Minus',
    '~': 'BitwiseNot',
    '!': 'LogicalNot',
    '++': 'Increment',
    '--': 'Decrement',
    ':': 'Colon',
    '=>': 'Arrow',
    '=': 'EqualSign',
    '*=': 'MultiplyAssign',
    '/=': 'DivideAssign',
    '%=': 'RemainderAssign',
    '+=': 'AddAssign',
    '-=': 'SubtractAssign',
    '<<=': 'LeftShiftAssign',
    '>>=': 'SignedRightShiftAssign',
    '>>>=': 'UnsignedRightShiftAssign',
    '&=': 'BitwiseAndAssign',
    '^=': 'BitwiseXorAssign',
    '|=': 'BitwiseOrAssign',
    '**=': 'ExponentiateAssign',
    '.': 'Dot',
    '**': 'Exponentiate',
    '?.': 'OptionalChain',
    '?': 'QuestionMark',
    '??': 'Coalesce',
    '*': 'Star',
    '/': 'Divide',
    '%': 'Remainder',
    '<<': 'LeftShift',
    '>>': 'SignedRightShift',
    '>>>': 'UnsignedRightShift',
    '<': 'LessThan',
    '>': 'GreaterThan',
    '<=': 'LessThanOrEqualTo',
    '>=': 'GreaterThanOrEqualTo',
    '==': 'LaxEqual',
    '!=': 'LaxNotEqual',
    '===': 'StrictEqual',
    '!==': 'StrictNotEqual',
    '&': 'BitwiseAnd',
    '^': 'BitwiseXor',
    '|': 'BitwiseOr',
    '&&': 'LogicalAnd',
    '||': 'LogicalOr',
    ',': 'Comma',
    '...': 'Ellipsis',
}


@contextmanager
def indent(writer):
    """This function is meant to be used with the `with` keyword of python, and
    allow the user of it to add an indentation level to the code which is
    enclosed in the `with` statement.

    This has the advantage that the indentation of the python code is reflected
    to the generated code when `with indent(self):` is used. """
    writer.indent += 1
    yield None
    writer.indent -= 1

def extract_ranges(iterator):
    """Given a sorted iterator of integer, yield the contiguous ranges"""
    # Identify contiguous ranges of states.
    ranges = collections.defaultdict(list)
    # A sorted list of contiguous integers implies that elements are separated
    # by 1, as well as their indexes. Thus we can categorize them into buckets
    # of contiguous integers using the base, which is the value v from which we
    # remove the index i.
    for i, v in enumerate(iterator):
        ranges[v - i].append(v)
    for l in ranges.values():
        yield (l[0], l[-1])

def rust_range(riter):
    """Prettify a list of tuple of (min, max) of matched ranges into Rust
    syntax."""
    def minmax_join(rmin, rmax):
        if rmin == rmax:
            return str(rmin)
        else:
            return "{}..={}".format(rmin, rmax)
    return " | ".join(minmax_join(rmin, rmax) for rmin, rmax in riter)

class RustActionWriter:
    """Write epsilon state transitions for a given action function."""
    ast_builder = types.Type("AstBuilderDelegate", (types.Lifetime("alloc"),))

    def __init__(self, writer, mode, traits, indent):
        self.states = writer.states
        self.writer = writer
        self.mode = mode
        self.traits = traits
        self.indent = indent
        self.has_ast_builder = self.ast_builder in traits
        self.used_variables = set()
        self.replay_args = []

    def implement_trait(self, funcall):
        "Returns True if this function call should be encoded"
        ty = funcall.trait
        if ty.name == "AstBuilder":
            return "AstBuilderDelegate<'alloc>" in map(str, self.traits)
        if ty in self.traits:
            return True
        if len(ty.args) == 0:
            return ty.name in map(lambda t: t.name, self.traits)
        return False

    def reset(self, act):
        "Traverse all action to collect preliminary information."
        self.used_variables = set(self.collect_uses(act))

    def collect_uses(self, act):
        "Generator which visit all used variables."
        assert isinstance(act, Action)
        if isinstance(act, (Reduce, Unwind)):
            yield "value"
        elif isinstance(act, FunCall):
            arg_offset = act.offset
            if arg_offset < 0:
                # See write_funcall.
                arg_offset = 0
            def map_with_offset(args):
                for a in args:
                    if isinstance(a, int):
                        yield a + arg_offset
                    if isinstance(a, str):
                        yield a
                    elif isinstance(a, Some):
                        for offset in map_with_offset([a.inner]):
                            yield offset
            if self.implement_trait(act):
                for var in map_with_offset(act.args):
                    yield var
        elif isinstance(act, Seq):
            for a in act.actions:
                for var in self.collect_uses(a):
                    yield var

    def write(self, string, *format_args):
        "Delegate to the RustParserWriter.write function"
        self.writer.write(self.indent, string, *format_args)

    def write_state_transitions(self, state, replay_args):
        "Given a state, generate the code corresponding to all outgoing epsilon edges."
        try:
            self.replay_args = replay_args
            assert not state.is_inconsistent()
            assert len(list(state.shifted_edges())) == 0
            for ctx in self.writer.parse_table.debug_context(state.index, None):
                self.write("// {}", ctx)
            first, dest = next(state.edges(), (None, None))
            if first is None:
                return
            self.reset(first)
            if first.is_condition():
                self.write_condition(state, first)
            else:
                assert len(list(state.edges())) == 1
                self.write_action(first, dest)
        except Exception as exc:
            print("Error while writing code for {}\n\n".format(state))
            self.writer.parse_table.debug_info = True
            print(self.writer.parse_table.debug_context(state.index, "\n", "# "))
            raise exc

    def write_replay_args(self, n):
        rp_args = self.replay_args[:n]
        rp_stck = self.replay_args[n:]
        for tv in rp_stck:
            self.write("parser.replay({});", tv)
        return rp_args


    def write_epsilon_transition(self, dest):
        # Replay arguments which are not accepted as input of the next state.
        dest = self.states[dest]
        rp_args = self.write_replay_args(dest.arguments)
        self.write("// --> {}", dest.index)
        if dest.index >= self.writer.shift_count:
            self.write("{}_{}(parser{})", self.mode, dest.index, "".join(map(lambda v: ", " + v, rp_args)))
        else:
            assert dest.arguments == 0
            self.write("parser.epsilon({});", dest.index)
            self.write("Ok(false)")

    def write_condition(self, state, first_act):
        "Write code to test a conditions, and dispatch to the matching destination"
        # NOTE: we already asserted that this state is consistent, this implies
        # that the first state check the same variables as all remaining
        # states. Thus we use the first action to produce the match statement.
        assert isinstance(first_act, Action)
        assert first_act.is_condition()
        if isinstance(first_act, CheckNotOnNewLine):
            # TODO: At the moment this is Action is implemented as a single
            # operation with a single destination. However, we should implement
            # it in the future as 2 branches, one which is verifying the lack
            # of new lines, and one which is shifting an extra error token.
            # This might help remove the overhead of backtracking in addition
            # to make this backtracking visible through APS.
            assert len(list(state.edges())) == 1
            act, dest = next(state.edges())
            assert len(self.replay_args) == 0
            assert -act.offset > 0
            self.write("// {}", str(act))
            self.write("if !parser.check_not_on_new_line({})? {{", -act.offset)
            with indent(self):
                self.write("return Ok(false);")
            self.write("}")
            self.write_epsilon_transition(dest)
        elif isinstance(first_act, FilterStates):
            if len(state.epsilon) == 1:
                # This is an attempt to avoid huge unending compilations.
                _, dest = next(iter(state.epsilon), (None, None))
                pattern = rust_range(extract_ranges(first_act.states))
                self.write("// parser.top_state() in ({})", pattern)
                self.write_epsilon_transition(dest)
            else:
                self.write("match parser.top_state() {")
                with indent(self):
                    # Consider the branch which has the largest number of
                    # potential top-states to be most likely, and therefore the
                    # default branch to go to if all other fail to match.
                    default_weight = max(len(act.states) for act, dest in state.edges())
                    default_states = []
                    default_dest = None
                    for act, dest in state.edges():
                        assert first_act.check_same_variable(act)
                        if default_dest is None and default_weight == len(act.states):
                            # This range has the same weight as the default
                            # branch. Ignore it and use it as the default
                            # branch which would be generated at the end.
                            default_states = act.states
                            default_dest = dest
                            continue
                        pattern = rust_range(extract_ranges(act.states))
                        self.write("{} => {{", pattern)
                        with indent(self):
                            self.write_epsilon_transition(dest)
                        self.write("}")
                    # Generate code for the default branch, which got skipped
                    # while producing the loop.
                    self.write("_ => {")
                    with indent(self):
                        pattern = rust_range(extract_ranges(default_states))
                        self.write("// {}", pattern)
                        self.write_epsilon_transition(default_dest)
                    self.write("}")
                self.write("}")
        else:
            raise ValueError("Unexpected action type")

    def write_action(self, act, dest):
        assert isinstance(act, Action)
        assert not act.is_condition()
        is_packed = {}

        # Do not pop any of the stack elements if the reduce action has an
        # accept function call. Ideally we should be returning the result
        # instead of keeping it on the parser stack.
        if act.update_stack() and not act.contains_accept():
            stack_diff = act.update_stack_with()
            start = 0
            depth = stack_diff.pop
            args = len(self.replay_args)
            replay = stack_diff.replay
            if replay < 0:
                # At the moment, we do not handle having more arguments than
                # what is being popped and replay, thus write back the extra
                # arguments and continue.
                if stack_diff.pop + replay < 0:
                    self.replay_args = self.write_replay_args(replay)
                replay = 0
            if replay + stack_diff.pop - args > 0:
                assert (replay >= 0 and args == 0) or \
                    (replay == 0 and args >= 0)
            if replay > 0:
                # At the moment, assume that arguments are only added once we
                # consumed all replayed terms. Thus the replay_args can only be
                # non-empty once replay is 0. Otherwise some of the replay_args
                # would have to be replayed.
                assert args == 0
                self.write("parser.rewind({});", replay)
                start = replay
                depth += start

            inputs = []
            for i in range(start, depth):
                name = 's{}'.format(i + 1)
                if i + 1 not in self.used_variables:
                    name = '_' + name
                inputs.append(name)
            if stack_diff.pop > 0:
                args_pop = min(len(self.replay_args), stack_diff.pop)
                # Pop by moving arguments of the action function.
                for i, name in enumerate(inputs[:args_pop]):
                    self.write("let {} = {};", name, self.replay_args[-i - 1])
                # Pop by removing elements from the parser stack.
                for name in inputs[args_pop:]:
                    self.write("let {} = parser.pop();", name)
                if args_pop > 0:
                    del self.replay_args[-args_pop:]

        if isinstance(act, Seq):
            for a in act.actions:
                self.write_single_action(a, is_packed)
                if a.contains_accept():
                    break
        else:
            self.write_single_action(act, is_packed)

        # If we fallthrough the execution of the action, then generate an
        # epsilon transition.
        if act.follow_edge() and not act.contains_accept():
            assert 0 <= dest < self.writer.shift_count + self.writer.action_count
            self.write_epsilon_transition(dest)

    def write_single_action(self, act, is_packed):
        self.write("// {}", str(act))
        if isinstance(act, Replay):
            self.write_replay(act)
        elif isinstance(act, (Reduce, Unwind)):
            self.write_reduce(act, is_packed)
        elif isinstance(act, Accept):
            self.write_accept()
        elif isinstance(act, PushFlag):
            raise ValueError("NYI: PushFlag action")
        elif isinstance(act, PopFlag):
            raise ValueError("NYI: PopFlag action")
        elif isinstance(act, FunCall):
            self.write_funcall(act, is_packed)
        else:
            raise ValueError("Unexpected action type")

    def write_replay(self, act):
        assert len(self.replay_args) == 0
        for shift_state in act.replay_steps:
            self.write("parser.shift_replayed({});", shift_state)

    def write_reduce(self, act, is_packed):
        value = "value"
        if value in is_packed:
            packed = is_packed[value]
        else:
            packed = False
            value = "None"

        if packed:
            # Extract the StackValue from the packed TermValue
            value = "{}.value".format(value)
        elif self.has_ast_builder:
            # Convert into a StackValue
            value = "TryIntoStack::try_into_stack({})?".format(value)
        else:
            # Convert into a StackValue (when no ast-builder)
            value = "value"

        stack_diff = act.update_stack_with()
        assert stack_diff.nt is not None
        self.write("let term = NonterminalId::{}.into();",
                   self.writer.nonterminal_to_camel(stack_diff.nt))
        if value != "value":
            self.write("let value = {};", value)
        self.write("let reduced = TermValue { term, value };")
        self.replay_args.append("reduced")

    def write_accept(self):
        self.write("return Ok(true);")

    def write_funcall(self, act, is_packed):
        arg_offset = act.offset
        if arg_offset < 0:
            # NOTE: When replacing replayed stack elements by arguments, the
            # offset is reduced by -1, and can become negative for cases where
            # we read the value associated with an argument instead of the
            # value read from the stack. However, write_action shift everything
            # as-if we had replayed all the necessary terms, and therefore
            # variables are named as-if the offset were 0.
            arg_offset = 0

        def no_unpack(val):
            return val

        def unpack(val):
            if val in is_packed:
                packed = is_packed[val]
            else:
                packed = True
            if packed:
                return "{}.value.to_ast()?".format(val)
            return val

        def map_with_offset(args, unpack):
            get_value = "s{}"
            for a in args:
                if isinstance(a, int):
                    yield unpack(get_value.format(a + arg_offset))
                elif isinstance(a, str):
                    yield unpack(a)
                elif isinstance(a, Some):
                    yield "Some({})".format(next(map_with_offset([a.inner], unpack)))
                elif a is None:
                    yield "None"
                else:
                    raise ValueError(a)

        packed = False
        # If the variable is used, then generate the let binding.
        set_var = ""
        if act.set_to in self.used_variables:
            set_var = "let {} = ".format(act.set_to)

        # If the function cannot be call as the generated action function does
        # not use the trait on which this function is implemented, then replace
        # the value by `()`.
        if not self.implement_trait(act):
            self.write("{}();", set_var)
            return

        # NOTE: Currently "AstBuilder" is implemented through the
        # AstBuilderDelegate which returns a mutable reference to the
        # AstBuilder. This would call the specific special case method to get
        # the actual AstBuilder.
        delegate = ""
        if str(act.trait) == "AstBuilder":
            delegate = "ast_builder_refmut()."

        # NOTE: Currently "AstBuilder" functions are made fallible
        # using the fallible_methods taken from some Rust code
        # which extract this information to produce a JSON file.
        forward_errors = ""
        if act.fallible or act.method in self.writer.fallible_methods:
            forward_errors = "?"

        # By default generate a method call, with the method name. However,
        # there is a special case for the "id" function which is an artifact,
        # which does not have to unpack the content of its argument.
        value = "parser.{}{}({})".format(
            delegate, act.method,
            ", ".join(map_with_offset(act.args, unpack)))
        packed = False
        if act.method == "id":
            assert len(act.args) == 1
            value = next(map_with_offset(act.args, no_unpack))
            if isinstance(act.args[0], str):
                packed = is_packed[act.args[0]]
            else:
                assert isinstance(act.args[0], int)
                packed = True

        self.write("{}{}{};", set_var, value, forward_errors)
        is_packed[act.set_to] = packed


class RustParserWriter:
    def __init__(self, out, pt, fallible_methods):
        self.out = out
        self.fallible_methods = fallible_methods
        assert pt.exec_modes is not None
        self.parse_table = pt
        self.states = pt.states
        self.shift_count = pt.count_shift_states()
        self.action_count = pt.count_action_states()
        self.action_from_shift_count = pt.count_action_from_shift_states()
        self.init_state_map = pt.named_goals
        self.terminals = list(OrderedSet(pt.terminals))
        # This extra terminal is used to represent any ErrorySymbol transition,
        # knowing that we assert that there is only one ErrorSymbol kind per
        # state.
        self.terminals.append("ErrorToken")
        self.nonterminals = list(OrderedSet(pt.nonterminals))

    def emit(self):
        self.header()
        self.terms_id()
        self.shift()
        self.error_codes()
        self.check_camel_case()
        self.actions()
        self.entry()

    def write(self, indentation, string, *format_args):
        if len(format_args) == 0:
            formatted = string
        else:
            formatted = string.format(*format_args)
        self.out.write(" " * indentation + formatted + "\n")

    def header(self):
        self.write(0, "// WARNING: This file is autogenerated.")
        self.write(0, "")
        self.write(0, "use crate::ast_builder::AstBuilderDelegate;")
        self.write(0, "use crate::stack_value_generated::{StackValue, TryIntoStack};")
        self.write(0, "use crate::traits::{TermValue, ParserTrait};")
        self.write(0, "use crate::error::Result;")
        traits = OrderedSet()
        for mode_traits in self.parse_table.exec_modes.values():
            traits |= mode_traits
        traits = list(traits)
        traits = [ty for ty in traits if ty.name != "AstBuilderDelegate"]
        traits = [ty for ty in traits if ty.name != "ParserTrait"]
        if traits == []:
            pass
        elif len(traits) == 1:
            self.write(0, "use crate::traits::{};", traits[0].name)
        else:
            self.write(0, "use crate::traits::{{{}}};", ", ".join(ty.name for ty in traits))
        self.write(0, "")
        self.write(0, "const ERROR: i64 = {};", hex(ERROR))
        self.write(0, "")

    def terminal_name(self, value):
        if isinstance(value, End) or value is None:
            return "End"
        elif isinstance(value, ErrorSymbol) or value is ErrorToken:
            return "ErrorToken"
        elif value in TERMINAL_NAMES:
            return TERMINAL_NAMES[value]
        elif value.isalpha():
            if value.islower():
                return value.capitalize()
            else:
                return value
        else:
            raw_name = " ".join((unicodedata.name(c) for c in value))
            snake_case = raw_name.replace("-", " ").replace(" ", "_").lower()
            camel_case = self.to_camel_case(snake_case)
            return camel_case

    def terminal_name_camel(self, value):
        return self.to_camel_case(self.terminal_name(value))

    def terms_id(self):
        self.write(0, "#[derive(Copy, Clone, Debug, PartialEq)]")
        self.write(0, "#[repr(u32)]")
        self.write(0, "pub enum TerminalId {")
        for i, t in enumerate(self.terminals):
            name = self.terminal_name(t)
            self.write(1, "{} = {}, // {}", name, i, repr(t))
        self.write(0, "}")
        self.write(0, "")
        self.write(0, "#[derive(Clone, Copy, Debug, PartialEq)]")
        self.write(0, "#[repr(u32)]")
        self.write(0, "pub enum NonterminalId {")
        offset = len(self.terminals)
        for i, nt in enumerate(self.nonterminals):
            self.write(1, "{} = {},", self.nonterminal_to_camel(nt), i + offset)
        self.write(0, "}")
        self.write(0, "")
        self.write(0, "#[derive(Clone, Copy, Debug, PartialEq)]")
        self.write(0, "pub struct Term(u32);")
        self.write(0, "")
        self.write(0, "impl Term {")
        self.write(1, "pub fn is_terminal(&self) -> bool {")
        self.write(2, "self.0 < {}", offset)
        self.write(1, "}")
        self.write(1, "pub fn to_terminal(&self) -> TerminalId {")
        self.write(2, "assert!(self.is_terminal());")
        self.write(2, "unsafe { std::mem::transmute(self.0) }")
        self.write(1, "}")
        self.write(0, "}")
        self.write(0, "")
        self.write(0, "impl From for Term {")
        self.write(1, "fn from(t: TerminalId) -> Self {")
        self.write(2, "Term(t as _)")
        self.write(1, "}")
        self.write(0, "}")
        self.write(0, "")
        self.write(0, "impl From for Term {")
        self.write(1, "fn from(nt: NonterminalId) -> Self {")
        self.write(2, "Term(nt as _)")
        self.write(1, "}")
        self.write(0, "}")
        self.write(0, "")
        self.write(0, "impl From for usize {")
        self.write(1, "fn from(term: Term) -> Self {")
        self.write(2, "term.0 as _")
        self.write(1, "}")
        self.write(0, "}")
        self.write(0, "")
        self.write(0, "impl From for &'static str {")
        self.write(1, "fn from(term: Term) -> Self {")
        self.write(2, "match term.0 {")
        for i, t in enumerate(self.terminals):
            self.write(3, "{} => &\"{}\",", i, repr(t))
        for j, nt in enumerate(self.nonterminals):
            i = j + offset
            self.write(3, "{} => &\"{}\",", i, str(nt.name))
        self.write(3, "_ => panic!(\"unknown Term\")", i, str(nt.name))
        self.write(2, "}")
        self.write(1, "}")
        self.write(0, "}")
        self.write(0, "")

    def shift(self):
        self.write(0, "#[rustfmt::skip]")
        width = len(self.terminals) + len(self.nonterminals)
        num_shifted_edges = 0

        def state_get(state, t):
            nonlocal num_shifted_edges
            res = state.get(t, "ERROR")
            if res == "ERROR":
                error_symbol = state.get_error_symbol()
                if t == "ErrorToken" and error_symbol:
                    res = state[error_symbol]
                    num_shifted_edges += 1
            else:
                num_shifted_edges += 1
            return res

        self.write(0, "static SHIFT: [i64; {}] = [", self.shift_count * width)
        assert self.terminals[-1] == "ErrorToken"
        for i, state in enumerate(self.states[:self.shift_count]):
            num_shifted_edges = 0
            self.write(1, "// {}.", i)
            for ctx in self.parse_table.debug_context(state.index, None):
                self.write(1, "// {}", ctx)
            self.write(1, "{}",
                       ' '.join("{},".format(state_get(state, t)) for t in self.terminals))
            self.write(1, "{}",
                       ' '.join("{},".format(state_get(state, t)) for t in self.nonterminals))
            try:
                assert sum(1 for _ in state.shifted_edges()) == num_shifted_edges
            except Exception:
                print("Some edges are not encoded.")
                print("List of terminals: {}".format(', '.join(map(repr, self.terminals))))
                print("List of nonterminals: {}".format(', '.join(map(repr, self.nonterminals))))
                print("State having the issue: {}".format(str(state)))
                raise
        self.write(0, "];")
        self.write(0, "")

    def render_action(self, action):
        if isinstance(action, tuple):
            if action[0] == 'IfSameLine':
                _, a1, a2 = action
                if a1 is None:
                    a1 = 'ERROR'
                if a2 is None:
                    a2 = 'ERROR'
                index = self.add_special_case(
                    "if token.is_on_new_line { %s } else { %s }"
                    % (a2, a1))
            else:
                raise ValueError("unrecognized kind of special case: {!r}".format(action))
            return SPECIAL_CASE_TAG + index
        elif action == 'ERROR':
            return action
        else:
            assert isinstance(action, int)
            return action

    def emit_special_cases(self):
        self.write(0, "static SPECIAL_CASES: [fn(&Token) -> i64; {}] = [",
                   len(self.special_cases))
        for i, code in enumerate(self.special_cases):
            self.write(1, "|token| {{ {} }},", code)
        self.write(0, "];")
        self.write(0, "")

    def error_codes(self):
        self.write(0, "#[derive(Clone, Copy, Debug, PartialEq)]")
        self.write(0, "pub enum ErrorCode {")
        error_symbols = (s.get_error_symbol() for s in self.states[:self.shift_count])
        error_codes = (e.error_code for e in error_symbols if e is not None)
        for error_code in OrderedSet(error_codes):
            self.write(1, "{},", self.to_camel_case(error_code))
        self.write(0, "}")
        self.write(0, "")

        self.write(0, "static STATE_TO_ERROR_CODE: [Option; {}] = [",
                   self.shift_count)
        for i, state in enumerate(self.states[:self.shift_count]):
            error_symbol = state.get_error_symbol()
            if error_symbol is None:
                self.write(1, "None,")
            else:
                self.write(1, "// {}.", i)
                for ctx in self.parse_table.debug_context(state.index, None):
                    self.write(1, "// {}", ctx)
                self.write(1, "Some(ErrorCode::{}),",
                           self.to_camel_case(error_symbol.error_code))
        self.write(0, "];")
        self.write(0, "")

    def nonterminal_to_snake(self, ident):
        if isinstance(ident, Nt):
            if isinstance(ident.name, InitNt):
                name = "Start" + ident.name.goal.name
            else:
                name = ident.name
            base_name = self.to_snek_case(name)
            args = ''.join((("_" + self.to_snek_case(name))
                            for name, value in ident.args if value))
            return base_name + args
        else:
            assert isinstance(ident, str)
            return self.to_snek_case(ident)

    def nonterminal_to_camel(self, nt):
        return self.to_camel_case(self.nonterminal_to_snake(nt))

    def to_camel_case(self, ident):
        if '_' in ident:
            return ''.join(word.capitalize() for word in ident.split('_'))
        elif ident.islower():
            return ident.capitalize()
        else:
            return ident

    def check_camel_case(self):
        seen = {}
        for nt in self.nonterminals:
            cc = self.nonterminal_to_camel(nt)
            if cc in seen:
                raise ValueError("{} and {} have the same camel-case spelling ({})".format(
                    seen[cc], nt, cc))
            seen[cc] = nt

    def to_snek_case(self, ident):
        # https://stackoverflow.com/questions/1175208
        s1 = re.sub('(.)([A-Z][a-z]+)', r'\1_\2', ident)
        return re.sub('([a-z0-9])([A-Z])', r'\1_\2', s1).lower()

    def type_to_rust(self, ty, namespace="", boxed=False):
        """
        Convert a jsparagus type (see types.py) to Rust.

        Pass boxed=True if the type needs to be boxed.
        """
        if isinstance(ty, types.Lifetime):
            assert not boxed
            rty = "'" + ty.name
        elif ty == types.UnitType:
            assert not boxed
            rty = '()'
        elif ty == types.TokenType:
            rty = "Token"
        elif ty.name == 'Option' and len(ty.args) == 1:
            # We auto-translate `Box<Option<T>>` to `Option<Box<T>>` since
            # that's basically the same thing but more efficient.
            [arg] = ty.args
            return 'Option<{}>'.format(self.type_to_rust(arg, namespace, boxed))
        elif ty.name == 'Vec' and len(ty.args) == 1:
            [arg] = ty.args
            rty = "Vec<'alloc, {}>".format(self.type_to_rust(arg, namespace, boxed=False))
        else:
            if namespace == "":
                rty = ty.name
            else:
                rty = namespace + '::' + ty.name
            if ty.args:
                rty += '<{}>'.format(', '.join(self.type_to_rust(arg, namespace, boxed)
                                               for arg in ty.args))
        if boxed:
            return "Box<'alloc, {}>".format(rty)
        else:
            return rty

    def actions(self):
        # For each execution mode, add a corresponding function which
        # implements various traits. The trait list is used for filtering which
        # function is added in the generated code.
        for mode, traits in self.parse_table.exec_modes.items():
            action_writer = RustActionWriter(self, mode, traits, 2)
            start_at = self.shift_count
            end_at = start_at + self.action_from_shift_count
            assert len(self.states[self.shift_count:]) == self.action_count
            traits_text = ' + '.join(map(self.type_to_rust, traits))
            table_holder_name = self.to_camel_case(mode)
            table_holder_type = table_holder_name + "<'alloc, Handler>"
            # As we do not have default associated types yet in Rust
            # (rust-lang#29661), we have to peak from the parameter of the
            # ParserTrait.
            assert list(traits)[0].name == "ParserTrait"
            arg_type = "TermValue<" + self.type_to_rust(list(traits)[0].args[1]) + ">"
            self.write(0, "struct {} {{", table_holder_type)
            self.write(1, "fns: [fn(&mut Handler) -> Result<'alloc, bool>; {}]",
                       self.action_from_shift_count)
            self.write(0, "}")
            self.write(0, "impl<'alloc, Handler> {}", table_holder_type)
            self.write(0, "where")
            self.write(1, "Handler: {}", traits_text)
            self.write(0, "{")
            self.write(1, "const TABLE : {} = {} {{", table_holder_type, table_holder_name)
            self.write(2, "fns: [")
            for state in self.states[start_at:end_at]:
                assert state.arguments == 0
                self.write(3, "{}_{},", mode, state.index)
            self.write(2, "],")
            self.write(1, "};")
            self.write(0, "}")
            self.write(0, "")
            self.write(0,
                       "pub fn {}<'alloc, Handler>(parser: &mut Handler, state: usize) "
                       "-> Result<'alloc, bool>",
                       mode)
            self.write(0, "where")
            self.write(1, "Handler: {}", traits_text)
            self.write(0, "{")
            self.write(1, "{}::<'alloc, Handler>::TABLE.fns[state - {}](parser)",
                       table_holder_name, start_at)
            self.write(0, "}")
            self.write(0, "")
            for state in self.states[self.shift_count:]:
                state_args = ""
                for i in range(state.arguments):
                    state_args += ", v{}: {}".format(i, arg_type)
                replay_args = ["v{}".format(i) for i in range(state.arguments)]
                self.write(0, "#[inline]")
                self.write(0, "#[allow(unused)]")
                self.write(0,
                           "pub fn {}_{}<'alloc, Handler>(parser: &mut Handler{}) "
                           "-> Result<'alloc, bool>",
                           mode, state.index, state_args)
                self.write(0, "where")
                self.write(1, "Handler: {}", ' + '.join(map(self.type_to_rust, traits)))
                self.write(0, "{")
                action_writer.write_state_transitions(state, replay_args)
                self.write(0, "}")

    def entry(self):
        self.write(0, "#[derive(Clone, Copy)]")
        self.write(0, "pub struct ParseTable<'a> {")
        self.write(1, "pub shift_count: usize,")
        self.write(1, "pub action_count: usize,")
        self.write(1, "pub action_from_shift_count: usize,")
        self.write(1, "pub shift_table: &'a [i64],")
        self.write(1, "pub shift_width: usize,")
        self.write(1, "pub error_codes: &'a [Option],")
        self.write(0, "}")
        self.write(0, "")

        self.write(0, "impl<'a> ParseTable<'a> {")
        self.write(1, "pub fn check(&self) {")
        self.write(2, "assert_eq!(")
        self.write(3, "self.shift_table.len(),")
        self.write(3, "(self.shift_count * self.shift_width) as usize")
        self.write(2, ");")
        self.write(1, "}")
        self.write(0, "}")
        self.write(0, "")

        self.write(0, "pub static TABLES: ParseTable<'static> = ParseTable {")
        self.write(1, "shift_count: {},", self.shift_count)
        self.write(1, "action_count: {},", self.action_count)
        self.write(1, "action_from_shift_count: {},", self.action_from_shift_count)
        self.write(1, "shift_table: &SHIFT,")
        self.write(1, "shift_width: {},", len(self.terminals) + len(self.nonterminals))
        self.write(1, "error_codes: &STATE_TO_ERROR_CODE,")
        self.write(0, "};")
        self.write(0, "")

        for init_nt, index in self.init_state_map:
            assert init_nt.args == ()
            self.write(0, "pub static START_STATE_{}: usize = {};",
                       self.nonterminal_to_snake(init_nt).upper(), index)
            self.write(0, "")


def write_rust_parse_table(out, parse_table, handler_info):
    if not handler_info:
        print("WARNING: info.json is not provided", file=sys.stderr)
        fallible_methods = []
    else:
        with open(handler_info, "r") as json_file:
            handler_info_json = json.load(json_file)
        fallible_methods = handler_info_json["fallible-methods"]

    RustParserWriter(out, parse_table, fallible_methods).emit()