913 lines
38 KiB
Rust
913 lines
38 KiB
Rust
// Copyright 2012-2017 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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//! This is an NFA-based parser, which calls out to the main rust parser for named nonterminals
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//! (which it commits to fully when it hits one in a grammar). There's a set of current NFA threads
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//! and a set of next ones. Instead of NTs, we have a special case for Kleene star. The big-O, in
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//! pathological cases, is worse than traditional use of NFA or Earley parsing, but it's an easier
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//! fit for Macro-by-Example-style rules.
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//!
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//! (In order to prevent the pathological case, we'd need to lazily construct the resulting
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//! `NamedMatch`es at the very end. It'd be a pain, and require more memory to keep around old
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//! items, but it would also save overhead)
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//!
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//! We don't say this parser uses the Earley algorithm, because it's unnecessarily inaccurate.
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//! The macro parser restricts itself to the features of finite state automata. Earley parsers
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//! can be described as an extension of NFAs with completion rules, prediction rules, and recursion.
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//!
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//! Quick intro to how the parser works:
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//!
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//! A 'position' is a dot in the middle of a matcher, usually represented as a
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//! dot. For example `· a $( a )* a b` is a position, as is `a $( · a )* a b`.
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//!
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//! The parser walks through the input a character at a time, maintaining a list
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//! of threads consistent with the current position in the input string: `cur_items`.
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//!
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//! As it processes them, it fills up `eof_items` with threads that would be valid if
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//! the macro invocation is now over, `bb_items` with threads that are waiting on
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//! a Rust nonterminal like `$e:expr`, and `next_items` with threads that are waiting
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//! on a particular token. Most of the logic concerns moving the · through the
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//! repetitions indicated by Kleene stars. The rules for moving the · without
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//! consuming any input are called epsilon transitions. It only advances or calls
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//! out to the real Rust parser when no `cur_items` threads remain.
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//!
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//! Example:
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//!
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//! ```text, ignore
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//! Start parsing a a a a b against [· a $( a )* a b].
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//!
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//! Remaining input: a a a a b
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//! next: [· a $( a )* a b]
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//!
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//! - - - Advance over an a. - - -
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//!
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//! Remaining input: a a a b
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//! cur: [a · $( a )* a b]
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//! Descend/Skip (first item).
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//! next: [a $( · a )* a b] [a $( a )* · a b].
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//!
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//! - - - Advance over an a. - - -
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//!
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//! Remaining input: a a b
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//! cur: [a $( a · )* a b] [a $( a )* a · b]
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//! Follow epsilon transition: Finish/Repeat (first item)
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//! next: [a $( a )* · a b] [a $( · a )* a b] [a $( a )* a · b]
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//!
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//! - - - Advance over an a. - - - (this looks exactly like the last step)
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//!
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//! Remaining input: a b
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//! cur: [a $( a · )* a b] [a $( a )* a · b]
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//! Follow epsilon transition: Finish/Repeat (first item)
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//! next: [a $( a )* · a b] [a $( · a )* a b] [a $( a )* a · b]
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//!
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//! - - - Advance over an a. - - - (this looks exactly like the last step)
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//!
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//! Remaining input: b
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//! cur: [a $( a · )* a b] [a $( a )* a · b]
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//! Follow epsilon transition: Finish/Repeat (first item)
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//! next: [a $( a )* · a b] [a $( · a )* a b] [a $( a )* a · b]
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//!
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//! - - - Advance over a b. - - -
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//!
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//! Remaining input: ''
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//! eof: [a $( a )* a b ·]
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//! ```
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pub use self::NamedMatch::*;
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pub use self::ParseResult::*;
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use self::TokenTreeOrTokenTreeSlice::*;
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use ast::Ident;
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use syntax_pos::{self, BytePos, Span};
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use errors::FatalError;
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use ext::tt::quoted::{self, TokenTree};
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use parse::{Directory, ParseSess};
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use parse::parser::{Parser, PathStyle};
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use parse::token::{self, DocComment, Nonterminal, Token};
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use print::pprust;
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use OneVector;
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use symbol::keywords;
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use tokenstream::TokenStream;
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use std::mem;
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use std::ops::{Deref, DerefMut};
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use std::rc::Rc;
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use std::collections::HashMap;
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use std::collections::hash_map::Entry::{Occupied, Vacant};
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// To avoid costly uniqueness checks, we require that `MatchSeq` always has a nonempty body.
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/// Either a sequence of token trees or a single one. This is used as the representation of the
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/// sequence of tokens that make up a matcher.
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#[derive(Clone)]
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enum TokenTreeOrTokenTreeSlice<'a> {
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Tt(TokenTree),
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TtSeq(&'a [TokenTree]),
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}
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impl<'a> TokenTreeOrTokenTreeSlice<'a> {
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/// Returns the number of constituent top-level token trees of `self` (top-level in that it
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/// will not recursively descend into subtrees).
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fn len(&self) -> usize {
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match *self {
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TtSeq(ref v) => v.len(),
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Tt(ref tt) => tt.len(),
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}
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}
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/// The the `index`-th token tree of `self`.
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fn get_tt(&self, index: usize) -> TokenTree {
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match *self {
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TtSeq(ref v) => v[index].clone(),
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Tt(ref tt) => tt.get_tt(index),
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}
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}
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}
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/// An unzipping of `TokenTree`s... see the `stack` field of `MatcherPos`.
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///
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/// This is used by `inner_parse_loop` to keep track of delimited submatchers that we have
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/// descended into.
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#[derive(Clone)]
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struct MatcherTtFrame<'a> {
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/// The "parent" matcher that we are descending into.
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elts: TokenTreeOrTokenTreeSlice<'a>,
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/// The position of the "dot" in `elts` at the time we descended.
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idx: usize,
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}
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/// Represents a single "position" (aka "matcher position", aka "item"), as described in the module
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/// documentation.
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#[derive(Clone)]
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struct MatcherPos<'a> {
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/// The token or sequence of tokens that make up the matcher
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top_elts: TokenTreeOrTokenTreeSlice<'a>,
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/// The position of the "dot" in this matcher
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idx: usize,
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/// The beginning position in the source that the beginning of this matcher corresponds to. In
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/// other words, the token in the source at `sp_lo` is matched against the first token of the
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/// matcher.
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sp_lo: BytePos,
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/// For each named metavar in the matcher, we keep track of token trees matched against the
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/// metavar by the black box parser. In particular, there may be more than one match per
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/// metavar if we are in a repetition (each repetition matches each of the variables).
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/// Moreover, matchers and repetitions can be nested; the `matches` field is shared (hence the
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/// `Rc`) among all "nested" matchers. `match_lo`, `match_cur`, and `match_hi` keep track of
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/// the current position of the `self` matcher position in the shared `matches` list.
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///
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/// Also, note that while we are descending into a sequence, matchers are given their own
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/// `matches` vector. Only once we reach the end of a full repetition of the sequence do we add
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/// all bound matches from the submatcher into the shared top-level `matches` vector. If `sep`
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/// and `up` are `Some`, then `matches` is _not_ the shared top-level list. Instead, if one
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/// wants the shared `matches`, one should use `up.matches`.
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matches: Vec<Rc<Vec<NamedMatch>>>,
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/// The position in `matches` corresponding to the first metavar in this matcher's sequence of
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/// token trees. In other words, the first metavar in the first token of `top_elts` corresponds
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/// to `matches[match_lo]`.
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match_lo: usize,
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/// The position in `matches` corresponding to the metavar we are currently trying to match
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/// against the source token stream. `match_lo <= match_cur <= match_hi`.
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match_cur: usize,
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/// Similar to `match_lo` except `match_hi` is the position in `matches` of the _last_ metavar
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/// in this matcher.
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match_hi: usize,
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// Specifically used if we are matching a repetition. If we aren't both should be `None`.
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/// The KleeneOp of this sequence if we are in a repetition.
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seq_op: Option<quoted::KleeneOp>,
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/// The separator if we are in a repetition
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sep: Option<Token>,
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/// The "parent" matcher position if we are in a repetition. That is, the matcher position just
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/// before we enter the sequence.
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up: Option<MatcherPosHandle<'a>>,
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// Specifically used to "unzip" token trees. By "unzip", we mean to unwrap the delimiters from
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// a delimited token tree (e.g. something wrapped in `(` `)`) or to get the contents of a doc
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// comment...
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/// When matching against matchers with nested delimited submatchers (e.g. `pat ( pat ( .. )
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/// pat ) pat`), we need to keep track of the matchers we are descending into. This stack does
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/// that where the bottom of the stack is the outermost matcher.
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// Also, throughout the comments, this "descent" is often referred to as "unzipping"...
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stack: Vec<MatcherTtFrame<'a>>,
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}
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impl<'a> MatcherPos<'a> {
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/// Add `m` as a named match for the `idx`-th metavar.
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fn push_match(&mut self, idx: usize, m: NamedMatch) {
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let matches = Rc::make_mut(&mut self.matches[idx]);
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matches.push(m);
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}
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}
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// Lots of MatcherPos instances are created at runtime. Allocating them on the
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// heap is slow. Furthermore, using SmallVec<MatcherPos> to allocate them all
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// on the stack is also slow, because MatcherPos is quite a large type and
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// instances get moved around a lot between vectors, which requires lots of
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// slow memcpy calls.
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//
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// Therefore, the initial MatcherPos is always allocated on the stack,
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// subsequent ones (of which there aren't that many) are allocated on the heap,
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// and this type is used to encapsulate both cases.
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enum MatcherPosHandle<'a> {
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Ref(&'a mut MatcherPos<'a>),
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Box(Box<MatcherPos<'a>>),
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}
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impl<'a> Clone for MatcherPosHandle<'a> {
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// This always produces a new Box.
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fn clone(&self) -> Self {
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MatcherPosHandle::Box(match *self {
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MatcherPosHandle::Ref(ref r) => Box::new((**r).clone()),
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MatcherPosHandle::Box(ref b) => b.clone(),
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})
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}
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}
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impl<'a> Deref for MatcherPosHandle<'a> {
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type Target = MatcherPos<'a>;
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fn deref(&self) -> &Self::Target {
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match *self {
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MatcherPosHandle::Ref(ref r) => r,
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MatcherPosHandle::Box(ref b) => b,
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}
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}
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}
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impl<'a> DerefMut for MatcherPosHandle<'a> {
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fn deref_mut(&mut self) -> &mut MatcherPos<'a> {
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match *self {
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MatcherPosHandle::Ref(ref mut r) => r,
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MatcherPosHandle::Box(ref mut b) => b,
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}
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}
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}
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/// Represents the possible results of an attempted parse.
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pub enum ParseResult<T> {
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/// Parsed successfully.
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Success(T),
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/// Arm failed to match. If the second parameter is `token::Eof`, it indicates an unexpected
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/// end of macro invocation. Otherwise, it indicates that no rules expected the given token.
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Failure(syntax_pos::Span, Token),
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/// Fatal error (malformed macro?). Abort compilation.
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Error(syntax_pos::Span, String),
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}
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/// A `ParseResult` where the `Success` variant contains a mapping of `Ident`s to `NamedMatch`es.
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/// This represents the mapping of metavars to the token trees they bind to.
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pub type NamedParseResult = ParseResult<HashMap<Ident, Rc<NamedMatch>>>;
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/// Count how many metavars are named in the given matcher `ms`.
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pub fn count_names(ms: &[TokenTree]) -> usize {
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ms.iter().fold(0, |count, elt| {
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count + match *elt {
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TokenTree::Sequence(_, ref seq) => seq.num_captures,
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TokenTree::Delimited(_, ref delim) => count_names(&delim.tts),
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TokenTree::MetaVar(..) => 0,
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TokenTree::MetaVarDecl(..) => 1,
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TokenTree::Token(..) => 0,
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}
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})
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}
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/// Initialize `len` empty shared `Vec`s to be used to store matches of metavars.
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fn create_matches(len: usize) -> Vec<Rc<Vec<NamedMatch>>> {
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(0..len).into_iter().map(|_| Rc::new(Vec::new())).collect()
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}
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/// Generate the top-level matcher position in which the "dot" is before the first token of the
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/// matcher `ms` and we are going to start matching at position `lo` in the source.
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fn initial_matcher_pos(ms: &[TokenTree], lo: BytePos) -> MatcherPos {
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let match_idx_hi = count_names(ms);
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let matches = create_matches(match_idx_hi);
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MatcherPos {
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// Start with the top level matcher given to us
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top_elts: TtSeq(ms), // "elts" is an abbr. for "elements"
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// The "dot" is before the first token of the matcher
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idx: 0,
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// We start matching with byte `lo` in the source code
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sp_lo: lo,
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// Initialize `matches` to a bunch of empty `Vec`s -- one for each metavar in `top_elts`.
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// `match_lo` for `top_elts` is 0 and `match_hi` is `matches.len()`. `match_cur` is 0 since
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// we haven't actually matched anything yet.
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matches,
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match_lo: 0,
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match_cur: 0,
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match_hi: match_idx_hi,
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// Haven't descended into any delimiters, so empty stack
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stack: vec![],
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// Haven't descended into any sequences, so both of these are `None`.
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seq_op: None,
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sep: None,
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up: None,
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}
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}
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/// `NamedMatch` is a pattern-match result for a single `token::MATCH_NONTERMINAL`:
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/// so it is associated with a single ident in a parse, and all
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/// `MatchedNonterminal`s in the `NamedMatch` have the same nonterminal type
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/// (expr, item, etc). Each leaf in a single `NamedMatch` corresponds to a
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/// single `token::MATCH_NONTERMINAL` in the `TokenTree` that produced it.
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///
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/// The in-memory structure of a particular `NamedMatch` represents the match
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/// that occurred when a particular subset of a matcher was applied to a
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/// particular token tree.
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///
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/// The width of each `MatchedSeq` in the `NamedMatch`, and the identity of
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/// the `MatchedNonterminal`s, will depend on the token tree it was applied
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/// to: each `MatchedSeq` corresponds to a single `TTSeq` in the originating
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/// token tree. The depth of the `NamedMatch` structure will therefore depend
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/// only on the nesting depth of `ast::TTSeq`s in the originating
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/// token tree it was derived from.
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#[derive(Debug, Clone)]
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pub enum NamedMatch {
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MatchedSeq(Rc<Vec<NamedMatch>>, syntax_pos::Span),
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MatchedNonterminal(Rc<Nonterminal>),
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}
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/// Takes a sequence of token trees `ms` representing a matcher which successfully matched input
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/// and an iterator of items that matched input and produces a `NamedParseResult`.
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fn nameize<I: Iterator<Item = NamedMatch>>(
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sess: &ParseSess,
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ms: &[TokenTree],
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mut res: I,
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) -> NamedParseResult {
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// Recursively descend into each type of matcher (e.g. sequences, delimited, metavars) and make
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// sure that each metavar has _exactly one_ binding. If a metavar does not have exactly one
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// binding, then there is an error. If it does, then we insert the binding into the
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// `NamedParseResult`.
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fn n_rec<I: Iterator<Item = NamedMatch>>(
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sess: &ParseSess,
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m: &TokenTree,
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res: &mut I,
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ret_val: &mut HashMap<Ident, Rc<NamedMatch>>,
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) -> Result<(), (syntax_pos::Span, String)> {
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match *m {
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TokenTree::Sequence(_, ref seq) => for next_m in &seq.tts {
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n_rec(sess, next_m, res.by_ref(), ret_val)?
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},
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TokenTree::Delimited(_, ref delim) => for next_m in &delim.tts {
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n_rec(sess, next_m, res.by_ref(), ret_val)?;
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},
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TokenTree::MetaVarDecl(span, _, id) if id.name == keywords::Invalid.name() => {
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if sess.missing_fragment_specifiers.borrow_mut().remove(&span) {
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return Err((span, "missing fragment specifier".to_string()));
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}
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}
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TokenTree::MetaVarDecl(sp, bind_name, _) => {
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match ret_val.entry(bind_name) {
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Vacant(spot) => {
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// FIXME(simulacrum): Don't construct Rc here
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spot.insert(Rc::new(res.next().unwrap()));
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}
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Occupied(..) => {
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return Err((sp, format!("duplicated bind name: {}", bind_name)))
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}
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}
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}
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TokenTree::MetaVar(..) | TokenTree::Token(..) => (),
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}
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Ok(())
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}
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let mut ret_val = HashMap::new();
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for m in ms {
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match n_rec(sess, m, res.by_ref(), &mut ret_val) {
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Ok(_) => {}
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Err((sp, msg)) => return Error(sp, msg),
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}
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}
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Success(ret_val)
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}
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/// Generate an appropriate parsing failure message. For EOF, this is "unexpected end...". For
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/// other tokens, this is "unexpected token...".
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pub fn parse_failure_msg(tok: Token) -> String {
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match tok {
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token::Eof => "unexpected end of macro invocation".to_string(),
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_ => format!(
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"no rules expected the token `{}`",
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pprust::token_to_string(&tok)
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),
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}
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}
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/// Perform a token equality check, ignoring syntax context (that is, an unhygienic comparison)
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fn token_name_eq(t1: &Token, t2: &Token) -> bool {
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if let (Some((id1, is_raw1)), Some((id2, is_raw2))) = (t1.ident(), t2.ident()) {
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id1.name == id2.name && is_raw1 == is_raw2
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} else if let (Some(id1), Some(id2)) = (t1.lifetime(), t2.lifetime()) {
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id1.name == id2.name
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} else {
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*t1 == *t2
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}
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}
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/// Process the matcher positions of `cur_items` until it is empty. In the process, this will
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/// produce more items in `next_items`, `eof_items`, and `bb_items`.
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///
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/// For more info about the how this happens, see the module-level doc comments and the inline
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/// comments of this function.
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///
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/// # Parameters
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///
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/// - `sess`: the parsing session into which errors are emitted.
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/// - `cur_items`: the set of current items to be processed. This should be empty by the end of a
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/// successful execution of this function.
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/// - `next_items`: the set of newly generated items. These are used to replenish `cur_items` in
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/// the function `parse`.
|
|
/// - `eof_items`: the set of items that would be valid if this was the EOF.
|
|
/// - `bb_items`: the set of items that are waiting for the black-box parser.
|
|
/// - `token`: the current token of the parser.
|
|
/// - `span`: the `Span` in the source code corresponding to the token trees we are trying to match
|
|
/// against the matcher positions in `cur_items`.
|
|
///
|
|
/// # Returns
|
|
///
|
|
/// A `ParseResult`. Note that matches are kept track of through the items generated.
|
|
fn inner_parse_loop<'a>(
|
|
sess: &ParseSess,
|
|
cur_items: &mut OneVector<MatcherPosHandle<'a>>,
|
|
next_items: &mut Vec<MatcherPosHandle<'a>>,
|
|
eof_items: &mut OneVector<MatcherPosHandle<'a>>,
|
|
bb_items: &mut OneVector<MatcherPosHandle<'a>>,
|
|
token: &Token,
|
|
span: syntax_pos::Span,
|
|
) -> ParseResult<()> {
|
|
// Pop items from `cur_items` until it is empty.
|
|
while let Some(mut item) = cur_items.pop() {
|
|
// When unzipped trees end, remove them. This corresponds to backtracking out of a
|
|
// delimited submatcher into which we already descended. In backtracking out again, we need
|
|
// to advance the "dot" past the delimiters in the outer matcher.
|
|
while item.idx >= item.top_elts.len() {
|
|
match item.stack.pop() {
|
|
Some(MatcherTtFrame { elts, idx }) => {
|
|
item.top_elts = elts;
|
|
item.idx = idx + 1;
|
|
}
|
|
None => break,
|
|
}
|
|
}
|
|
|
|
// Get the current position of the "dot" (`idx`) in `item` and the number of token trees in
|
|
// the matcher (`len`).
|
|
let idx = item.idx;
|
|
let len = item.top_elts.len();
|
|
|
|
// If `idx >= len`, then we are at or past the end of the matcher of `item`.
|
|
if idx >= len {
|
|
// We are repeating iff there is a parent. If the matcher is inside of a repetition,
|
|
// then we could be at the end of a sequence or at the beginning of the next
|
|
// repetition.
|
|
if item.up.is_some() {
|
|
// At this point, regardless of whether there is a separator, we should add all
|
|
// matches from the complete repetition of the sequence to the shared, top-level
|
|
// `matches` list (actually, `up.matches`, which could itself not be the top-level,
|
|
// but anyway...). Moreover, we add another item to `cur_items` in which the "dot"
|
|
// is at the end of the `up` matcher. This ensures that the "dot" in the `up`
|
|
// matcher is also advanced sufficiently.
|
|
//
|
|
// NOTE: removing the condition `idx == len` allows trailing separators.
|
|
if idx == len {
|
|
// Get the `up` matcher
|
|
let mut new_pos = item.up.clone().unwrap();
|
|
|
|
// Add matches from this repetition to the `matches` of `up`
|
|
for idx in item.match_lo..item.match_hi {
|
|
let sub = item.matches[idx].clone();
|
|
let span = span.with_lo(item.sp_lo);
|
|
new_pos.push_match(idx, MatchedSeq(sub, span));
|
|
}
|
|
|
|
// Move the "dot" past the repetition in `up`
|
|
new_pos.match_cur = item.match_hi;
|
|
new_pos.idx += 1;
|
|
cur_items.push(new_pos);
|
|
}
|
|
|
|
// Check if we need a separator.
|
|
if idx == len && item.sep.is_some() {
|
|
// We have a separator, and it is the current token. We can advance past the
|
|
// separator token.
|
|
if item.sep
|
|
.as_ref()
|
|
.map(|sep| token_name_eq(token, sep))
|
|
.unwrap_or(false)
|
|
{
|
|
item.idx += 1;
|
|
next_items.push(item);
|
|
}
|
|
}
|
|
// We don't need a separator. Move the "dot" back to the beginning of the matcher
|
|
// and try to match again UNLESS we are only allowed to have _one_ repetition.
|
|
else if item.seq_op != Some(quoted::KleeneOp::ZeroOrOne) {
|
|
item.match_cur = item.match_lo;
|
|
item.idx = 0;
|
|
cur_items.push(item);
|
|
}
|
|
}
|
|
// If we are not in a repetition, then being at the end of a matcher means that we have
|
|
// reached the potential end of the input.
|
|
else {
|
|
eof_items.push(item);
|
|
}
|
|
}
|
|
// We are in the middle of a matcher.
|
|
else {
|
|
// Look at what token in the matcher we are trying to match the current token (`token`)
|
|
// against. Depending on that, we may generate new items.
|
|
match item.top_elts.get_tt(idx) {
|
|
// Need to descend into a sequence
|
|
TokenTree::Sequence(sp, seq) => {
|
|
// Examine the case where there are 0 matches of this sequence
|
|
if seq.op == quoted::KleeneOp::ZeroOrMore
|
|
|| seq.op == quoted::KleeneOp::ZeroOrOne
|
|
{
|
|
let mut new_item = item.clone();
|
|
new_item.match_cur += seq.num_captures;
|
|
new_item.idx += 1;
|
|
for idx in item.match_cur..item.match_cur + seq.num_captures {
|
|
new_item.push_match(idx, MatchedSeq(Rc::new(vec![]), sp));
|
|
}
|
|
cur_items.push(new_item);
|
|
}
|
|
|
|
let matches = create_matches(item.matches.len());
|
|
cur_items.push(MatcherPosHandle::Box(Box::new(MatcherPos {
|
|
stack: vec![],
|
|
sep: seq.separator.clone(),
|
|
seq_op: Some(seq.op),
|
|
idx: 0,
|
|
matches,
|
|
match_lo: item.match_cur,
|
|
match_cur: item.match_cur,
|
|
match_hi: item.match_cur + seq.num_captures,
|
|
up: Some(item),
|
|
sp_lo: sp.lo(),
|
|
top_elts: Tt(TokenTree::Sequence(sp, seq)),
|
|
})));
|
|
}
|
|
|
|
// We need to match a metavar (but the identifier is invalid)... this is an error
|
|
TokenTree::MetaVarDecl(span, _, id) if id.name == keywords::Invalid.name() => {
|
|
if sess.missing_fragment_specifiers.borrow_mut().remove(&span) {
|
|
return Error(span, "missing fragment specifier".to_string());
|
|
}
|
|
}
|
|
|
|
// We need to match a metavar with a valid ident... call out to the black-box
|
|
// parser by adding an item to `bb_items`.
|
|
TokenTree::MetaVarDecl(_, _, id) => {
|
|
// Built-in nonterminals never start with these tokens,
|
|
// so we can eliminate them from consideration.
|
|
if may_begin_with(&*id.as_str(), token) {
|
|
bb_items.push(item);
|
|
}
|
|
}
|
|
|
|
// We need to descend into a delimited submatcher or a doc comment. To do this, we
|
|
// push the current matcher onto a stack and push a new item containing the
|
|
// submatcher onto `cur_items`.
|
|
//
|
|
// At the beginning of the loop, if we reach the end of the delimited submatcher,
|
|
// we pop the stack to backtrack out of the descent.
|
|
seq @ TokenTree::Delimited(..) | seq @ TokenTree::Token(_, DocComment(..)) => {
|
|
let lower_elts = mem::replace(&mut item.top_elts, Tt(seq));
|
|
let idx = item.idx;
|
|
item.stack.push(MatcherTtFrame {
|
|
elts: lower_elts,
|
|
idx,
|
|
});
|
|
item.idx = 0;
|
|
cur_items.push(item);
|
|
}
|
|
|
|
// We just matched a normal token. We can just advance the parser.
|
|
TokenTree::Token(_, ref t) if token_name_eq(t, token) => {
|
|
item.idx += 1;
|
|
next_items.push(item);
|
|
}
|
|
|
|
// There was another token that was not `token`... This means we can't add any
|
|
// rules. NOTE that this is not necessarily an error unless _all_ items in
|
|
// `cur_items` end up doing this. There may still be some other matchers that do
|
|
// end up working out.
|
|
TokenTree::Token(..) | TokenTree::MetaVar(..) => {}
|
|
}
|
|
}
|
|
}
|
|
|
|
// Yay a successful parse (so far)!
|
|
Success(())
|
|
}
|
|
|
|
/// Use the given sequence of token trees (`ms`) as a matcher. Match the given token stream `tts`
|
|
/// against it and return the match.
|
|
///
|
|
/// # Parameters
|
|
///
|
|
/// - `sess`: The session into which errors are emitted
|
|
/// - `tts`: The tokenstream we are matching against the pattern `ms`
|
|
/// - `ms`: A sequence of token trees representing a pattern against which we are matching
|
|
/// - `directory`: Information about the file locations (needed for the black-box parser)
|
|
/// - `recurse_into_modules`: Whether or not to recurse into modules (needed for the black-box
|
|
/// parser)
|
|
pub fn parse(
|
|
sess: &ParseSess,
|
|
tts: TokenStream,
|
|
ms: &[TokenTree],
|
|
directory: Option<Directory>,
|
|
recurse_into_modules: bool,
|
|
) -> NamedParseResult {
|
|
// Create a parser that can be used for the "black box" parts.
|
|
let mut parser = Parser::new(sess, tts, directory, recurse_into_modules, true);
|
|
|
|
// A queue of possible matcher positions. We initialize it with the matcher position in which
|
|
// the "dot" is before the first token of the first token tree in `ms`. `inner_parse_loop` then
|
|
// processes all of these possible matcher positions and produces posible next positions into
|
|
// `next_items`. After some post-processing, the contents of `next_items` replenish `cur_items`
|
|
// and we start over again.
|
|
//
|
|
// This MatcherPos instance is allocated on the stack. All others -- and
|
|
// there are frequently *no* others! -- are allocated on the heap.
|
|
let mut initial = initial_matcher_pos(ms, parser.span.lo());
|
|
let mut cur_items = OneVector::one(MatcherPosHandle::Ref(&mut initial));
|
|
let mut next_items = Vec::new();
|
|
|
|
loop {
|
|
// Matcher positions black-box parsed by parser.rs (`parser`)
|
|
let mut bb_items = OneVector::new();
|
|
|
|
// Matcher positions that would be valid if the macro invocation was over now
|
|
let mut eof_items = OneVector::new();
|
|
assert!(next_items.is_empty());
|
|
|
|
// Process `cur_items` until either we have finished the input or we need to get some
|
|
// parsing from the black-box parser done. The result is that `next_items` will contain a
|
|
// bunch of possible next matcher positions in `next_items`.
|
|
match inner_parse_loop(
|
|
sess,
|
|
&mut cur_items,
|
|
&mut next_items,
|
|
&mut eof_items,
|
|
&mut bb_items,
|
|
&parser.token,
|
|
parser.span,
|
|
) {
|
|
Success(_) => {}
|
|
Failure(sp, tok) => return Failure(sp, tok),
|
|
Error(sp, msg) => return Error(sp, msg),
|
|
}
|
|
|
|
// inner parse loop handled all cur_items, so it's empty
|
|
assert!(cur_items.is_empty());
|
|
|
|
// We need to do some post processing after the `inner_parser_loop`.
|
|
//
|
|
// Error messages here could be improved with links to original rules.
|
|
|
|
// If we reached the EOF, check that there is EXACTLY ONE possible matcher. Otherwise,
|
|
// either the parse is ambiguous (which should never happen) or their is a syntax error.
|
|
if token_name_eq(&parser.token, &token::Eof) {
|
|
if eof_items.len() == 1 {
|
|
let matches = eof_items[0]
|
|
.matches
|
|
.iter_mut()
|
|
.map(|dv| Rc::make_mut(dv).pop().unwrap());
|
|
return nameize(sess, ms, matches);
|
|
} else if eof_items.len() > 1 {
|
|
return Error(
|
|
parser.span,
|
|
"ambiguity: multiple successful parses".to_string(),
|
|
);
|
|
} else {
|
|
return Failure(parser.span, token::Eof);
|
|
}
|
|
}
|
|
// Performance hack: eof_items may share matchers via Rc with other things that we want
|
|
// to modify. Dropping eof_items now may drop these refcounts to 1, preventing an
|
|
// unnecessary implicit clone later in Rc::make_mut.
|
|
drop(eof_items);
|
|
|
|
// Another possibility is that we need to call out to parse some rust nonterminal
|
|
// (black-box) parser. However, if there is not EXACTLY ONE of these, something is wrong.
|
|
if (!bb_items.is_empty() && !next_items.is_empty()) || bb_items.len() > 1 {
|
|
let nts = bb_items
|
|
.iter()
|
|
.map(|item| match item.top_elts.get_tt(item.idx) {
|
|
TokenTree::MetaVarDecl(_, bind, name) => format!("{} ('{}')", name, bind),
|
|
_ => panic!(),
|
|
})
|
|
.collect::<Vec<String>>()
|
|
.join(" or ");
|
|
|
|
return Error(
|
|
parser.span,
|
|
format!(
|
|
"local ambiguity: multiple parsing options: {}",
|
|
match next_items.len() {
|
|
0 => format!("built-in NTs {}.", nts),
|
|
1 => format!("built-in NTs {} or 1 other option.", nts),
|
|
n => format!("built-in NTs {} or {} other options.", nts, n),
|
|
}
|
|
),
|
|
);
|
|
}
|
|
// If there are no posible next positions AND we aren't waiting for the black-box parser,
|
|
// then their is a syntax error.
|
|
else if bb_items.is_empty() && next_items.is_empty() {
|
|
return Failure(parser.span, parser.token);
|
|
}
|
|
// Dump all possible `next_items` into `cur_items` for the next iteration.
|
|
else if !next_items.is_empty() {
|
|
// Now process the next token
|
|
cur_items.extend(next_items.drain(..));
|
|
parser.bump();
|
|
}
|
|
// Finally, we have the case where we need to call the black-box parser to get some
|
|
// nonterminal.
|
|
else {
|
|
assert_eq!(bb_items.len(), 1);
|
|
|
|
let mut item = bb_items.pop().unwrap();
|
|
if let TokenTree::MetaVarDecl(span, _, ident) = item.top_elts.get_tt(item.idx) {
|
|
let match_cur = item.match_cur;
|
|
item.push_match(
|
|
match_cur,
|
|
MatchedNonterminal(Rc::new(parse_nt(&mut parser, span, &ident.as_str()))),
|
|
);
|
|
item.idx += 1;
|
|
item.match_cur += 1;
|
|
} else {
|
|
unreachable!()
|
|
}
|
|
cur_items.push(item);
|
|
}
|
|
|
|
assert!(!cur_items.is_empty());
|
|
}
|
|
}
|
|
|
|
/// The token is an identifier, but not `_`.
|
|
/// We prohibit passing `_` to macros expecting `ident` for now.
|
|
fn get_macro_ident(token: &Token) -> Option<(Ident, bool)> {
|
|
match *token {
|
|
token::Ident(ident, is_raw) if ident.name != keywords::Underscore.name() =>
|
|
Some((ident, is_raw)),
|
|
_ => None,
|
|
}
|
|
}
|
|
|
|
/// Checks whether a non-terminal may begin with a particular token.
|
|
///
|
|
/// Returning `false` is a *stability guarantee* that such a matcher will *never* begin with that
|
|
/// token. Be conservative (return true) if not sure.
|
|
fn may_begin_with(name: &str, token: &Token) -> bool {
|
|
/// Checks whether the non-terminal may contain a single (non-keyword) identifier.
|
|
fn may_be_ident(nt: &token::Nonterminal) -> bool {
|
|
match *nt {
|
|
token::NtItem(_) | token::NtBlock(_) | token::NtVis(_) => false,
|
|
_ => true,
|
|
}
|
|
}
|
|
|
|
match name {
|
|
"expr" => token.can_begin_expr(),
|
|
"ty" => token.can_begin_type(),
|
|
"ident" => get_macro_ident(token).is_some(),
|
|
"literal" => token.can_begin_literal_or_bool(),
|
|
"vis" => match *token {
|
|
// The follow-set of :vis + "priv" keyword + interpolated
|
|
Token::Comma | Token::Ident(..) | Token::Interpolated(_) => true,
|
|
_ => token.can_begin_type(),
|
|
},
|
|
"block" => match *token {
|
|
Token::OpenDelim(token::Brace) => true,
|
|
Token::Interpolated(ref nt) => match nt.0 {
|
|
token::NtItem(_)
|
|
| token::NtPat(_)
|
|
| token::NtTy(_)
|
|
| token::NtIdent(..)
|
|
| token::NtMeta(_)
|
|
| token::NtPath(_)
|
|
| token::NtVis(_) => false, // none of these may start with '{'.
|
|
_ => true,
|
|
},
|
|
_ => false,
|
|
},
|
|
"path" | "meta" => match *token {
|
|
Token::ModSep | Token::Ident(..) => true,
|
|
Token::Interpolated(ref nt) => match nt.0 {
|
|
token::NtPath(_) | token::NtMeta(_) => true,
|
|
_ => may_be_ident(&nt.0),
|
|
},
|
|
_ => false,
|
|
},
|
|
"pat" => match *token {
|
|
Token::Ident(..) | // box, ref, mut, and other identifiers (can stricten)
|
|
Token::OpenDelim(token::Paren) | // tuple pattern
|
|
Token::OpenDelim(token::Bracket) | // slice pattern
|
|
Token::BinOp(token::And) | // reference
|
|
Token::BinOp(token::Minus) | // negative literal
|
|
Token::AndAnd | // double reference
|
|
Token::Literal(..) | // literal
|
|
Token::DotDot | // range pattern (future compat)
|
|
Token::DotDotDot | // range pattern (future compat)
|
|
Token::ModSep | // path
|
|
Token::Lt | // path (UFCS constant)
|
|
Token::BinOp(token::Shl) => true, // path (double UFCS)
|
|
Token::Interpolated(ref nt) => may_be_ident(&nt.0),
|
|
_ => false,
|
|
},
|
|
"lifetime" => match *token {
|
|
Token::Lifetime(_) => true,
|
|
Token::Interpolated(ref nt) => match nt.0 {
|
|
token::NtLifetime(_) | token::NtTT(_) => true,
|
|
_ => false,
|
|
},
|
|
_ => false,
|
|
},
|
|
_ => match *token {
|
|
token::CloseDelim(_) => false,
|
|
_ => true,
|
|
},
|
|
}
|
|
}
|
|
|
|
/// A call to the "black-box" parser to parse some rust nonterminal.
|
|
///
|
|
/// # Parameters
|
|
///
|
|
/// - `p`: the "black-box" parser to use
|
|
/// - `sp`: the `Span` we want to parse
|
|
/// - `name`: the name of the metavar _matcher_ we want to match (e.g. `tt`, `ident`, `block`,
|
|
/// etc...)
|
|
///
|
|
/// # Returns
|
|
///
|
|
/// The parsed nonterminal.
|
|
fn parse_nt<'a>(p: &mut Parser<'a>, sp: Span, name: &str) -> Nonterminal {
|
|
if name == "tt" {
|
|
return token::NtTT(p.parse_token_tree());
|
|
}
|
|
// check at the beginning and the parser checks after each bump
|
|
p.process_potential_macro_variable();
|
|
match name {
|
|
"item" => match panictry!(p.parse_item()) {
|
|
Some(i) => token::NtItem(i),
|
|
None => {
|
|
p.fatal("expected an item keyword").emit();
|
|
FatalError.raise();
|
|
}
|
|
},
|
|
"block" => token::NtBlock(panictry!(p.parse_block())),
|
|
"stmt" => match panictry!(p.parse_stmt()) {
|
|
Some(s) => token::NtStmt(s),
|
|
None => {
|
|
p.fatal("expected a statement").emit();
|
|
FatalError.raise();
|
|
}
|
|
},
|
|
"pat" => token::NtPat(panictry!(p.parse_pat())),
|
|
"expr" => token::NtExpr(panictry!(p.parse_expr())),
|
|
"literal" => token::NtLiteral(panictry!(p.parse_literal_maybe_minus())),
|
|
"ty" => token::NtTy(panictry!(p.parse_ty())),
|
|
// this could be handled like a token, since it is one
|
|
"ident" => if let Some((ident, is_raw)) = get_macro_ident(&p.token) {
|
|
let span = p.span;
|
|
p.bump();
|
|
token::NtIdent(Ident::new(ident.name, span), is_raw)
|
|
} else {
|
|
let token_str = pprust::token_to_string(&p.token);
|
|
p.fatal(&format!("expected ident, found {}", &token_str)).emit();
|
|
FatalError.raise()
|
|
}
|
|
"path" => token::NtPath(panictry!(p.parse_path_common(PathStyle::Type, false))),
|
|
"meta" => token::NtMeta(panictry!(p.parse_meta_item())),
|
|
"vis" => token::NtVis(panictry!(p.parse_visibility(true))),
|
|
"lifetime" => if p.check_lifetime() {
|
|
token::NtLifetime(p.expect_lifetime().ident)
|
|
} else {
|
|
let token_str = pprust::token_to_string(&p.token);
|
|
p.fatal(&format!("expected a lifetime, found `{}`", &token_str)).emit();
|
|
FatalError.raise();
|
|
}
|
|
// this is not supposed to happen, since it has been checked
|
|
// when compiling the macro.
|
|
_ => p.span_bug(sp, "invalid fragment specifier"),
|
|
}
|
|
}
|