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tamer: parse::state::transition: Extract module into own file 

That's it.  Just preparing for changes that will change how lookahaeds and
dead state transitions will work.

DEV-7145
main
Mike Gerwitz 2022-07-07 12:47:31 -04:00
parent e54f93b30f
commit 61ce7d3fc7
2 changed files with 251 additions and 238 deletions
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240
tamer/src/parse/state.rs
View File

@ -19,6 +19,8 @@
//! Parsing automaton.
mod transition;
use super::{Object, ParseError, Parser, Token, TokenStream};
use crate::diagnose::Diagnostic;
use std::{
@ -363,244 +365,6 @@ impl<O: Object, T: Token> Display for Aggregate<O, T> {
}
}
mod transition {
use super::{ParseState, ParseStateResult, ParseStatus};
use std::{
convert::Infallible,
hint::unreachable_unchecked,
ops::{ControlFlow, FromResidual, Try},
};
#[cfg(doc)]
use super::Token;
/// A state transition with associated data.
///
/// Conceptually,
/// imagine the act of a state transition producing data.
/// See [`Transition`] for convenience methods for producing this tuple.
///
/// Sometimes a parser is not able to complete the operation requested
/// based on the provided input token.
/// Since TAMER uses a streaming parsing framework that places strict
/// limits on control flow,
/// a single token can be returned as lookahead to indicate that the
/// token could not be parsed yet and should be provided once again
/// in place of the next token from the input stream.
/// This allows,
/// for example,
/// for multiple data to be emitted in response to a single token.
///
/// This struct is opaque to ensure that critical invariants involving
/// transitions and lookahead are properly upheld;
/// callers must use the appropriate parsing APIs.
#[derive(Debug, PartialEq)]
pub struct TransitionResult<S: ParseState>(
/// New parser state.
pub(in super::super) Transition<S>,
/// Result of the parsing operation.
pub(in super::super) ParseStateResult<S>,
/// Optional unused token to use as a lookahead token in place of
/// the next token from the input stream.
pub(in super::super) Option<S::Token>,
);
impl<S: ParseState> TransitionResult<S> {
/// Indicate that this transition include a single token of lookahead,
/// which should be provided back to the parser in place of the
/// next token from the input stream.
pub fn with_lookahead(self, lookahead: S::Token) -> Self {
match self {
Self(transition, result, None) => {
Self(transition, result, Some(lookahead))
}
// This represents a problem with the parser;
// we should never specify a lookahead token more than once.
// This could be enforced statically with the type system if
// ever such a thing is deemed to be worth doing.
Self(.., Some(prev)) => panic!(
"internal error: lookahead token overwrite: {prev:?}"
),
}
}
}
/// Denotes a state transition.
///
/// This newtype was created to produce clear, self-documenting code;
/// parsers can get confusing to read with all of the types involved,
/// so this provides a mental synchronization point.
///
/// This also provides some convenience methods to help remove boilerplate
/// and further improve code clarity.
#[derive(Debug, PartialEq, Eq)]
pub struct Transition<S: ParseState>(pub S);
impl<S: ParseState> Transition<S> {
/// A state transition with corresponding data.
///
/// This allows [`ParseState::parse_token`] to emit a parsed object and
/// corresponds to [`ParseStatus::Object`].
pub fn ok<T>(self, obj: T) -> TransitionResult<S>
where
T: Into<ParseStatus<S>>,
{
TransitionResult(self, Ok(obj.into()), None)
}
/// A transition with corresponding error.
///
/// This indicates a parsing failure.
/// The state ought to be suitable for error recovery.
pub fn err<E: Into<S::Error>>(self, err: E) -> TransitionResult<S> {
TransitionResult(self, Err(err.into()), None)
}
/// A state transition with corresponding [`Result`].
///
/// This translates the provided [`Result`] in a manner equivalent to
/// [`Transition::ok`] and [`Transition::err`].
pub fn result<T, E>(self, result: Result<T, E>) -> TransitionResult<S>
where
T: Into<ParseStatus<S>>,
E: Into<S::Error>,
{
TransitionResult(
self,
result.map(Into::into).map_err(Into::into),
None,
)
}
/// A state transition indicating that more data is needed before an
/// object can be emitted.
///
/// This corresponds to [`ParseStatus::Incomplete`].
pub fn incomplete(self) -> TransitionResult<S> {
TransitionResult(self, Ok(ParseStatus::Incomplete), None)
}
/// A dead state transition.
///
/// This corresponds to [`ParseStatus::Dead`],
/// and a calling parser should use the provided [`Token`] as
/// lookahead.
pub fn dead(self, tok: S::DeadToken) -> TransitionResult<S> {
TransitionResult(self, Ok(ParseStatus::Dead(tok)), None)
}
}
impl<S: ParseState> Into<(Transition<S>, ParseStateResult<S>)>
for TransitionResult<S>
{
fn into(self) -> (Transition<S>, ParseStateResult<S>) {
(self.0, self.1)
}
}
impl<S: ParseState> Try for TransitionResult<S> {
type Output = (Transition<S>, ParseStateResult<S>);
type Residual = (Transition<S>, ParseStateResult<S>);
fn from_output(output: Self::Output) -> Self {
match output {
(st, result) => Self(st, result, None),
}
}
fn branch(self) -> ControlFlow<Self::Residual, Self::Output> {
match self.into() {
(st, Ok(x)) => ControlFlow::Continue((st, Ok(x))),
(st, Err(e)) => ControlFlow::Break((st, Err(e))),
}
}
}
impl<S: ParseState> FromResidual<(Transition<S>, ParseStateResult<S>)>
for TransitionResult<S>
{
fn from_residual(
residual: (Transition<S>, ParseStateResult<S>),
) -> Self {
match residual {
(st, result) => Self(st, result, None),
}
}
}
impl<S: ParseState> FromResidual<Result<Infallible, TransitionResult<S>>>
for TransitionResult<S>
{
fn from_residual(
residual: Result<Infallible, TransitionResult<S>>,
) -> Self {
match residual {
Err(e) => e,
// SAFETY: This match arm doesn't seem to be required in
// core::result::Result's FromResidual implementation,
// but as of 1.61 nightly it is here.
// Since this is Infallable,
// it cannot occur.
Ok(_) => unsafe { unreachable_unchecked() },
}
}
}
impl<S: ParseState>
FromResidual<ControlFlow<TransitionResult<S>, Infallible>>
for TransitionResult<S>
{
fn from_residual(
residual: ControlFlow<TransitionResult<S>, Infallible>,
) -> Self {
match residual {
ControlFlow::Break(result) => result,
// SAFETY: Infallible, so cannot hit.
ControlFlow::Continue(_) => unsafe { unreachable_unchecked() },
}
}
}
/// An object able to be used as data for a state [`Transition`].
///
/// This flips the usual order of things:
/// rather than using a method of [`Transition`] to provide data,
/// this starts with the data and produces a transition from it.
/// This is sometimes necessary to satisfy ownership/borrowing rules.
///
/// This trait simply removes boilerplate associated with storing
/// intermediate values and translating into the resulting type.
pub trait Transitionable<S: ParseState> {
/// Perform a state transition to `S` using [`Self`] as the associated
/// data.
///
/// This may be necessary to satisfy ownership/borrowing rules when
/// state data from `S` is used to compute [`Self`].
fn transition(self, to: S) -> TransitionResult<S>;
}
impl<S, E> Transitionable<S> for Result<ParseStatus<S>, E>
where
S: ParseState,
<S as ParseState>::Error: From<E>,
{
fn transition(self, to: S) -> TransitionResult<S> {
Transition(to).result(self)
}
}
impl<S, E> Transitionable<S> for Result<(), E>
where
S: ParseState,
<S as ParseState>::Error: From<E>,
{
fn transition(self, to: S) -> TransitionResult<S> {
Transition(to).result(self.map(|_| ParseStatus::Incomplete))
}
}
}
pub mod context {
use super::Debug;
use std::ops::{Deref, DerefMut};

249
tamer/src/parse/state/transition.rs 100644
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@ -0,0 +1,249 @@
// Parsing automaton
//
// Copyright (C) 2014-2022 Ryan Specialty Group, LLC.
//
// This file is part of TAME.
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program. If not, see <http://www.gnu.org/licenses/>.
//! State transitions for parser automata.
use super::{ParseState, ParseStateResult, ParseStatus};
use std::{
convert::Infallible,
hint::unreachable_unchecked,
ops::{ControlFlow, FromResidual, Try},
};
#[cfg(doc)]
use super::Token;
/// A state transition with associated data.
///
/// Conceptually,
/// imagine the act of a state transition producing data.
/// See [`Transition`] for convenience methods for producing this tuple.
///
/// Sometimes a parser is not able to complete the operation requested
/// based on the provided input token.
/// Since TAMER uses a streaming parsing framework that places strict
/// limits on control flow,
/// a single token can be returned as lookahead to indicate that the
/// token could not be parsed yet and should be provided once again
/// in place of the next token from the input stream.
/// This allows,
/// for example,
/// for multiple data to be emitted in response to a single token.
///
/// This struct is opaque to ensure that critical invariants involving
/// transitions and lookahead are properly upheld;
/// callers must use the appropriate parsing APIs.
#[derive(Debug, PartialEq)]
pub struct TransitionResult<S: ParseState>(
/// New parser state.
pub(in super::super) Transition<S>,
/// Result of the parsing operation.
pub(in super::super) ParseStateResult<S>,
/// Optional unused token to use as a lookahead token in place of
/// the next token from the input stream.
pub(in super::super) Option<S::Token>,
);
impl<S: ParseState> TransitionResult<S> {
/// Indicate that this transition include a single token of lookahead,
/// which should be provided back to the parser in place of the
/// next token from the input stream.
pub fn with_lookahead(self, lookahead: S::Token) -> Self {
match self {
Self(transition, result, None) => {
Self(transition, result, Some(lookahead))
}
// This represents a problem with the parser;
// we should never specify a lookahead token more than once.
// This could be enforced statically with the type system if
// ever such a thing is deemed to be worth doing.
Self(.., Some(prev)) => {
panic!("internal error: lookahead token overwrite: {prev:?}")
}
}
}
}
/// Denotes a state transition.
///
/// This newtype was created to produce clear, self-documenting code;
/// parsers can get confusing to read with all of the types involved,
/// so this provides a mental synchronization point.
///
/// This also provides some convenience methods to help remove boilerplate
/// and further improve code clarity.
#[derive(Debug, PartialEq, Eq)]
pub struct Transition<S: ParseState>(pub S);
impl<S: ParseState> Transition<S> {
/// A state transition with corresponding data.
///
/// This allows [`ParseState::parse_token`] to emit a parsed object and
/// corresponds to [`ParseStatus::Object`].
pub fn ok<T>(self, obj: T) -> TransitionResult<S>
where
T: Into<ParseStatus<S>>,
{
TransitionResult(self, Ok(obj.into()), None)
}
/// A transition with corresponding error.
///
/// This indicates a parsing failure.
/// The state ought to be suitable for error recovery.
pub fn err<E: Into<S::Error>>(self, err: E) -> TransitionResult<S> {
TransitionResult(self, Err(err.into()), None)
}
/// A state transition with corresponding [`Result`].
///
/// This translates the provided [`Result`] in a manner equivalent to
/// [`Transition::ok`] and [`Transition::err`].
pub fn result<T, E>(self, result: Result<T, E>) -> TransitionResult<S>
where
T: Into<ParseStatus<S>>,
E: Into<S::Error>,
{
TransitionResult(self, result.map(Into::into).map_err(Into::into), None)
}
/// A state transition indicating that more data is needed before an
/// object can be emitted.
///
/// This corresponds to [`ParseStatus::Incomplete`].
pub fn incomplete(self) -> TransitionResult<S> {
TransitionResult(self, Ok(ParseStatus::Incomplete), None)
}
/// A dead state transition.
///
/// This corresponds to [`ParseStatus::Dead`],
/// and a calling parser should use the provided [`Token`] as
/// lookahead.
pub fn dead(self, tok: S::DeadToken) -> TransitionResult<S> {
TransitionResult(self, Ok(ParseStatus::Dead(tok)), None)
}
}
impl<S: ParseState> Into<(Transition<S>, ParseStateResult<S>)>
for TransitionResult<S>
{
fn into(self) -> (Transition<S>, ParseStateResult<S>) {
(self.0, self.1)
}
}
impl<S: ParseState> Try for TransitionResult<S> {
type Output = (Transition<S>, ParseStateResult<S>);
type Residual = (Transition<S>, ParseStateResult<S>);
fn from_output(output: Self::Output) -> Self {
match output {
(st, result) => Self(st, result, None),
}
}
fn branch(self) -> ControlFlow<Self::Residual, Self::Output> {
match self.into() {
(st, Ok(x)) => ControlFlow::Continue((st, Ok(x))),
(st, Err(e)) => ControlFlow::Break((st, Err(e))),
}
}
}
impl<S: ParseState> FromResidual<(Transition<S>, ParseStateResult<S>)>
for TransitionResult<S>
{
fn from_residual(residual: (Transition<S>, ParseStateResult<S>)) -> Self {
match residual {
(st, result) => Self(st, result, None),
}
}
}
impl<S: ParseState> FromResidual<Result<Infallible, TransitionResult<S>>>
for TransitionResult<S>
{
fn from_residual(
residual: Result<Infallible, TransitionResult<S>>,
) -> Self {
match residual {
Err(e) => e,
// SAFETY: This match arm doesn't seem to be required in
// core::result::Result's FromResidual implementation,
// but as of 1.61 nightly it is here.
// Since this is Infallable,
// it cannot occur.
Ok(_) => unsafe { unreachable_unchecked() },
}
}
}
impl<S: ParseState> FromResidual<ControlFlow<TransitionResult<S>, Infallible>>
for TransitionResult<S>
{
fn from_residual(
residual: ControlFlow<TransitionResult<S>, Infallible>,
) -> Self {
match residual {
ControlFlow::Break(result) => result,
// SAFETY: Infallible, so cannot hit.
ControlFlow::Continue(_) => unsafe { unreachable_unchecked() },
}
}
}
/// An object able to be used as data for a state [`Transition`].
///
/// This flips the usual order of things:
/// rather than using a method of [`Transition`] to provide data,
/// this starts with the data and produces a transition from it.
/// This is sometimes necessary to satisfy ownership/borrowing rules.
///
/// This trait simply removes boilerplate associated with storing
/// intermediate values and translating into the resulting type.
pub trait Transitionable<S: ParseState> {
/// Perform a state transition to `S` using [`Self`] as the associated
/// data.
///
/// This may be necessary to satisfy ownership/borrowing rules when
/// state data from `S` is used to compute [`Self`].
fn transition(self, to: S) -> TransitionResult<S>;
}
impl<S, E> Transitionable<S> for Result<ParseStatus<S>, E>
where
S: ParseState,
<S as ParseState>::Error: From<E>,
{
fn transition(self, to: S) -> TransitionResult<S> {
Transition(to).result(self)
}
}
impl<S, E> Transitionable<S> for Result<(), E>
where
S: ParseState,
<S as ParseState>::Error: From<E>,
{
fn transition(self, to: S) -> TransitionResult<S> {
Transition(to).result(self.map(|_| ParseStatus::Incomplete))
}
}