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Merge pull request #1779 from dtolnay/scan
Translate expr scanner to table driven
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,264 @@ | ||
| use self::{Action::*, Input::*}; | ||
| use proc_macro2::{Delimiter, Ident, Spacing, TokenTree}; | ||
| use syn::parse::{ParseStream, Result}; | ||
| use syn::{AngleBracketedGenericArguments, BinOp, Expr, ExprPath, Lifetime, Lit, Token, Type}; | ||
|
|
||
| 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)), | ||
| ]; | ||
|
|
||
| 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; | ||
| '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)), | ||
| })? | ||
| } | ||
| 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; | ||
| } | ||
| } | ||
| return Err(input.error("unsupported expression")); | ||
| } | ||
| } |
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