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Translate expr scanner to table driven
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@dtolnay
dtolnay committed Nov 2, 2024
1 parent 8039cb3 commit ca97c7d
Showing 1 changed file with 254 additions and 66 deletions.
320 changes: 254 additions & 66 deletions src/scan_expr.rs
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Original file line number Diff line number Diff line change
@@ -1,76 +1,264 @@
use proc_macro2::Delimiter::{self, Brace, Bracket, Parenthesis};
use self::{Action::*, Input::*};
use proc_macro2::{Delimiter, Ident, Spacing, TokenTree};
use syn::parse::{ParseStream, Result};
use syn::{
token, AngleBracketedGenericArguments, BinOp, ExprPath, Lifetime, Lit, LitFloat, Member, Token,
Type, UnOp,
};
use syn::{AngleBracketedGenericArguments, BinOp, Expr, ExprPath, Lifetime, Lit, Token, Type};

pub(crate) fn scan_expr(input: ParseStream) -> Result<()> {
let consume = |delimiter: Delimiter| {
Result::unwrap(input.step(|cursor| match cursor.group(delimiter) {
Some((_inside, _span, rest)) => Ok((true, rest)),
None => Ok((false, *cursor)),
}))
};

macro_rules! consume {
[$token:tt] => {
input.parse::<Option<Token![$token]>>().unwrap().is_some()
};
}
enum Input {
Keyword(&'static str),
Punct(&'static str),
ConsumeAny,
ConsumeBinOp,
ConsumeBrace,
ConsumeDelimiter,
ConsumeIdent,
ConsumeLifetime,
ConsumeLiteral,
ConsumeNestedBrace,
ExpectPath,
ExpectTurbofish,
ExpectType,
CanBeginExpr,
Otherwise,
Empty,
}

enum Action {
SetState(&'static [(Input, Action)]),
IncDepth,
DecDepth,
Finish,
}

static INIT: [(Input, Action); 28] = [
(ConsumeDelimiter, SetState(&POSTFIX)),
(Keyword("async"), SetState(&ASYNC)),
(Keyword("break"), SetState(&BREAK_LABEL)),
(Keyword("const"), SetState(&CONST)),
(Keyword("continue"), SetState(&CONTINUE)),
(Keyword("for"), SetState(&FOR)),
(Keyword("if"), IncDepth),
(Keyword("let"), SetState(&PATTERN)),
(Keyword("loop"), SetState(&BLOCK)),
(Keyword("match"), IncDepth),
(Keyword("move"), SetState(&CLOSURE)),
(Keyword("return"), SetState(&RETURN)),
(Keyword("static"), SetState(&CLOSURE)),
(Keyword("unsafe"), SetState(&BLOCK)),
(Keyword("while"), IncDepth),
(Keyword("yield"), SetState(&RETURN)),
(Keyword("_"), SetState(&POSTFIX)),
(Punct("!"), SetState(&INIT)),
(Punct("#"), SetState(&[(ConsumeDelimiter, SetState(&INIT))])),
(Punct("&"), SetState(&REFERENCE)),
(Punct("*"), SetState(&INIT)),
(Punct("-"), SetState(&INIT)),
(Punct("..="), SetState(&INIT)),
(Punct(".."), SetState(&RANGE)),
(Punct("|"), SetState(&CLOSURE_ARGS)),
(ConsumeLifetime, SetState(&[(Punct(":"), SetState(&INIT))])),
(ConsumeLiteral, SetState(&POSTFIX)),
(ExpectPath, SetState(&PATH)),
];

static POSTFIX: [(Input, Action); 10] = [
(Keyword("as"), SetState(&[(ExpectType, SetState(&POSTFIX))])),
(Punct("..="), SetState(&INIT)),
(Punct(".."), SetState(&RANGE)),
(Punct("."), SetState(&DOT)),
(Punct("?"), SetState(&POSTFIX)),
(ConsumeBinOp, SetState(&INIT)),
(Punct("="), SetState(&INIT)),
(ConsumeNestedBrace, SetState(&IF_THEN)),
(ConsumeDelimiter, SetState(&POSTFIX)),
(Empty, Finish),
];

static ASYNC: [(Input, Action); 3] = [
(Keyword("move"), SetState(&ASYNC)),
(Punct("|"), SetState(&CLOSURE_ARGS)),
(ConsumeBrace, SetState(&POSTFIX)),
];

static BLOCK: [(Input, Action); 1] = [(ConsumeBrace, SetState(&POSTFIX))];

static BREAK_LABEL: [(Input, Action); 2] = [
(ConsumeLifetime, SetState(&BREAK_VALUE)),
(Otherwise, SetState(&BREAK_VALUE)),
];

static BREAK_VALUE: [(Input, Action); 3] = [
(ConsumeNestedBrace, SetState(&IF_THEN)),
(CanBeginExpr, SetState(&INIT)),
(Otherwise, SetState(&POSTFIX)),
];

static CLOSURE: [(Input, Action); 6] = [
(Keyword("async"), SetState(&CLOSURE)),
(Keyword("move"), SetState(&CLOSURE)),
(Punct(","), SetState(&CLOSURE)),
(Punct(">"), SetState(&CLOSURE)),
(Punct("|"), SetState(&CLOSURE_ARGS)),
(ConsumeLifetime, SetState(&CLOSURE)),
];

static CLOSURE_ARGS: [(Input, Action); 2] = [
(Punct("|"), SetState(&CLOSURE_RET)),
(ConsumeAny, SetState(&CLOSURE_ARGS)),
];

static CLOSURE_RET: [(Input, Action); 2] = [
(Punct("->"), SetState(&[(ExpectType, SetState(&BLOCK))])),
(Otherwise, SetState(&INIT)),
];

static CONST: [(Input, Action); 2] = [
(Punct("|"), SetState(&CLOSURE_ARGS)),
(ConsumeBrace, SetState(&POSTFIX)),
];

static CONTINUE: [(Input, Action); 2] = [
(ConsumeLifetime, SetState(&POSTFIX)),
(Otherwise, SetState(&POSTFIX)),
];

static DOT: [(Input, Action); 3] = [
(Keyword("await"), SetState(&POSTFIX)),
(ConsumeIdent, SetState(&METHOD)),
(ConsumeLiteral, SetState(&POSTFIX)),
];

let mut initial = true;
static FOR: [(Input, Action); 2] = [
(Punct("<"), SetState(&CLOSURE)),
(Otherwise, SetState(&PATTERN)),
];

static IF_ELSE: [(Input, Action); 2] = [(Keyword("if"), SetState(&INIT)), (ConsumeBrace, DecDepth)];
static IF_THEN: [(Input, Action); 2] =
[(Keyword("else"), SetState(&IF_ELSE)), (Otherwise, DecDepth)];

static METHOD: [(Input, Action); 1] = [(ExpectTurbofish, SetState(&POSTFIX))];

static PATH: [(Input, Action); 4] = [
(Punct("!="), SetState(&INIT)),
(Punct("!"), SetState(&INIT)),
(ConsumeNestedBrace, SetState(&IF_THEN)),
(Otherwise, SetState(&POSTFIX)),
];

static PATTERN: [(Input, Action); 15] = [
(ConsumeDelimiter, SetState(&PATTERN)),
(Keyword("box"), SetState(&PATTERN)),
(Keyword("in"), IncDepth),
(Keyword("mut"), SetState(&PATTERN)),
(Keyword("ref"), SetState(&PATTERN)),
(Keyword("_"), SetState(&PATTERN)),
(Punct("!"), SetState(&PATTERN)),
(Punct("&"), SetState(&PATTERN)),
(Punct("..="), SetState(&PATTERN)),
(Punct(".."), SetState(&PATTERN)),
(Punct("="), SetState(&INIT)),
(Punct("@"), SetState(&PATTERN)),
(Punct("|"), SetState(&PATTERN)),
(ConsumeLiteral, SetState(&PATTERN)),
(ExpectPath, SetState(&PATTERN)),
];

static RANGE: [(Input, Action); 6] = [
(Punct("..="), SetState(&INIT)),
(Punct(".."), SetState(&RANGE)),
(Punct("."), SetState(&DOT)),
(ConsumeNestedBrace, SetState(&IF_THEN)),
(Empty, Finish),
(Otherwise, SetState(&INIT)),
];

static RAW: [(Input, Action); 3] = [
(Keyword("const"), SetState(&INIT)),
(Keyword("mut"), SetState(&INIT)),
(Otherwise, SetState(&POSTFIX)),
];

static REFERENCE: [(Input, Action); 3] = [
(Keyword("mut"), SetState(&INIT)),
(Keyword("raw"), SetState(&RAW)),
(Otherwise, SetState(&INIT)),
];

static RETURN: [(Input, Action); 2] = [
(CanBeginExpr, SetState(&INIT)),
(Otherwise, SetState(&POSTFIX)),
];

pub(crate) fn scan_expr(input: ParseStream) -> Result<()> {
let mut state = INIT.as_slice();
let mut depth = 0usize;
loop {
if initial {
if consume![&] {
initial = consume![mut] || !consume![raw] || consume![const] || consume![mut];
} else if consume![if] || consume![match] || consume![while] {
depth += 1;
} else if input.parse::<Option<Lit>>()?.is_some()
|| (consume(Brace) || consume(Bracket) || consume(Parenthesis))
|| (consume![async] || consume![const] || consume![loop] || consume![unsafe])
&& (consume(Brace) || break)
{
initial = false;
} else if consume![let] {
while !consume![=] {
if !((consume![|] || consume![ref] || consume![mut] || consume![@])
|| (consume![!] || input.parse::<Option<Lit>>()?.is_some())
|| (consume![..=] || consume![..] || consume![&] || consume![_])
|| (consume(Brace) || consume(Bracket) || consume(Parenthesis)))
{
input.parse::<ExprPath>()?;
'table: loop {
for rule in state {
if match rule.0 {
Input::Keyword(expected) => input.step(|cursor| match cursor.ident() {
Some((ident, rest)) if ident == expected => Ok((true, rest)),
_ => Ok((false, *cursor)),
})?,
Input::Punct(expected) => input.step(|cursor| {
let begin = *cursor;
let mut cursor = begin;
for (i, ch) in expected.chars().enumerate() {
match cursor.punct() {
Some((punct, _)) if punct.as_char() != ch => break,
Some((_, rest)) if i == expected.len() - 1 => {
return Ok((true, rest));
}
Some((punct, rest)) if punct.spacing() == Spacing::Joint => {
cursor = rest;
}
_ => break,
}
}
Ok((false, begin))
})?,
Input::ConsumeAny => input.parse::<Option<TokenTree>>()?.is_some(),
Input::ConsumeBinOp => input.parse::<BinOp>().is_ok(),
Input::ConsumeBrace | Input::ConsumeNestedBrace => {
(matches!(rule.0, Input::ConsumeBrace) || depth > 0)
&& input.step(|cursor| match cursor.group(Delimiter::Brace) {
Some((_inside, _span, rest)) => Ok((true, rest)),
None => Ok((false, *cursor)),
})?
}
} else if input.parse::<Option<Lifetime>>()?.is_some() && !consume![:] {
break;
} else if input.parse::<UnOp>().is_err() {
input.parse::<ExprPath>()?;
initial = consume![!] || depth == 0 && input.peek(token::Brace);
}
} else if input.is_empty() || input.peek(Token![,]) {
return Ok(());
} else if depth > 0 && consume(Brace) {
if consume![else] && !consume(Brace) {
initial = consume![if] || break;
} else {
depth -= 1;
}
} else if input.parse::<BinOp>().is_ok() || (consume![..] | consume![=]) {
initial = true;
} else if consume![.] {
if input.parse::<Option<LitFloat>>()?.is_none()
&& (matches!(input.parse()?, Member::Named(_)) && input.peek(Token![::]))
{
input.parse::<AngleBracketedGenericArguments>()?;
Input::ConsumeDelimiter => input.step(|cursor| match cursor.any_group() {
Some((_inside, _delimiter, _span, rest)) => Ok((true, rest)),
None => Ok((false, *cursor)),
})?,
Input::ConsumeIdent => input.parse::<Option<Ident>>()?.is_some(),
Input::ConsumeLifetime => input.parse::<Option<Lifetime>>()?.is_some(),
Input::ConsumeLiteral => input.parse::<Option<Lit>>()?.is_some(),
Input::ExpectPath => {
input.parse::<ExprPath>()?;
true
}
Input::ExpectTurbofish => {
if input.peek(Token![::]) {
input.parse::<AngleBracketedGenericArguments>()?;
}
true
}
Input::ExpectType => {
Type::without_plus(input)?;
true
}
Input::CanBeginExpr => Expr::peek(input),
Input::Otherwise => true,
Input::Empty => input.is_empty() || input.peek(Token![,]),
} {
state = match rule.1 {
Action::SetState(next) => next,
Action::IncDepth => (depth += 1, &INIT).1,
Action::DecDepth => (depth -= 1, &POSTFIX).1,
Action::Finish => return if depth == 0 { Ok(()) } else { break },
};
continue 'table;
}
} else if consume![as] {
input.parse::<Type>()?;
} else if !(consume(Brace) || consume(Bracket) || consume(Parenthesis)) {
break;
}
return Err(input.error("unsupported expression"));
}

Err(input.error("unsupported expression"))
}

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