rust/src/libsyntax/ext/tt/macro_rules.rs

// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

use ast::{self, TokenTree, TtDelimited, TtSequence, TtToken};
use codemap::{Span, DUMMY_SP};
use ext::base::{ExtCtxt, MacResult, SyntaxExtension};
use ext::base::{NormalTT, TTMacroExpander};
use ext::tt::macro_parser::{Success, Error, Failure};
use ext::tt::macro_parser::{NamedMatch, MatchedSeq, MatchedNonterminal};
use ext::tt::macro_parser::{parse, parse_or_else};
use parse::lexer::new_tt_reader;
use parse::parser::Parser;
use parse::token::{self, special_idents, gensym_ident, NtTT, Token};
use parse::token::Token::*;
use print;
use ptr::P;

use util::small_vector::SmallVector;

use std::cell::RefCell;
use std::rc::Rc;

struct ParserAnyMacro<'a> {
    parser: RefCell<Parser<'a>>,
}

impl<'a> ParserAnyMacro<'a> {
    /// Make sure we don't have any tokens left to parse, so we don't
    /// silently drop anything. `allow_semi` is so that "optional"
    /// semicolons at the end of normal expressions aren't complained
    /// about e.g. the semicolon in `macro_rules! kapow { () => {
    /// panic!(); } }` doesn't get picked up by .parse_expr(), but it's
    /// allowed to be there.
    fn ensure_complete_parse(&self, allow_semi: bool) {
        let mut parser = self.parser.borrow_mut();
        if allow_semi && parser.token == token::Semi {
            panictry!(parser.bump())
        }
        if parser.token != token::Eof {
            let token_str = parser.this_token_to_string();
            let msg = format!("macro expansion ignores token `{}` and any \
                               following",
                              token_str);
            let span = parser.span;
            parser.span_err(span, &msg[..]);
        }
    }
}

impl<'a> MacResult for ParserAnyMacro<'a> {
    fn make_expr(self: Box<ParserAnyMacro<'a>>) -> Option<P<ast::Expr>> {
        let ret = self.parser.borrow_mut().parse_expr();
        self.ensure_complete_parse(true);
        Some(ret)
    }
    fn make_pat(self: Box<ParserAnyMacro<'a>>) -> Option<P<ast::Pat>> {
        let ret = self.parser.borrow_mut().parse_pat();
        self.ensure_complete_parse(false);
        Some(ret)
    }
    fn make_items(self: Box<ParserAnyMacro<'a>>) -> Option<SmallVector<P<ast::Item>>> {
        let mut ret = SmallVector::zero();
        while let Some(item) = self.parser.borrow_mut().parse_item() {
            ret.push(item);
        }
        self.ensure_complete_parse(false);
        Some(ret)
    }

    fn make_impl_items(self: Box<ParserAnyMacro<'a>>)
                       -> Option<SmallVector<P<ast::ImplItem>>> {
        let mut ret = SmallVector::zero();
        loop {
            let mut parser = self.parser.borrow_mut();
            match parser.token {
                token::Eof => break,
                _ => ret.push(panictry!(parser.parse_impl_item()))
            }
        }
        self.ensure_complete_parse(false);
        Some(ret)
    }

    fn make_stmt(self: Box<ParserAnyMacro<'a>>) -> Option<P<ast::Stmt>> {
        let ret = self.parser.borrow_mut().parse_stmt();
        self.ensure_complete_parse(true);
        ret
    }
}

struct MacroRulesMacroExpander {
    name: ast::Ident,
    imported_from: Option<ast::Ident>,
    lhses: Vec<Rc<NamedMatch>>,
    rhses: Vec<Rc<NamedMatch>>,
}

impl TTMacroExpander for MacroRulesMacroExpander {
    fn expand<'cx>(&self,
                   cx: &'cx mut ExtCtxt,
                   sp: Span,
                   arg: &[ast::TokenTree])
                   -> Box<MacResult+'cx> {
        generic_extension(cx,
                          sp,
                          self.name,
                          self.imported_from,
                          arg,
                          &self.lhses,
                          &self.rhses)
    }
}

/// Given `lhses` and `rhses`, this is the new macro we create
fn generic_extension<'cx>(cx: &'cx ExtCtxt,
                          sp: Span,
                          name: ast::Ident,
                          imported_from: Option<ast::Ident>,
                          arg: &[ast::TokenTree],
                          lhses: &[Rc<NamedMatch>],
                          rhses: &[Rc<NamedMatch>])
                          -> Box<MacResult+'cx> {
    if cx.trace_macros() {
        println!("{}! {{ {} }}",
                 token::get_ident(name),
                 print::pprust::tts_to_string(arg));
    }

    // Which arm's failure should we report? (the one furthest along)
    let mut best_fail_spot = DUMMY_SP;
    let mut best_fail_msg = "internal error: ran no matchers".to_string();

    for (i, lhs) in lhses.iter().enumerate() { // try each arm's matchers
        match **lhs {
          MatchedNonterminal(NtTT(ref lhs_tt)) => {
            let lhs_tt = match **lhs_tt {
                TtDelimited(_, ref delim) => &delim.tts[..],
                _ => panic!(cx.span_fatal(sp, "malformed macro lhs"))
            };

            match TokenTree::parse(cx, lhs_tt, arg) {
              Success(named_matches) => {
                let rhs = match *rhses[i] {
                    // okay, what's your transcriber?
                    MatchedNonterminal(NtTT(ref tt)) => {
                        match **tt {
                            // ignore delimiters
                            TtDelimited(_, ref delimed) => delimed.tts.clone(),
                            _ => panic!(cx.span_fatal(sp, "macro rhs must be delimited")),
                        }
                    },
                    _ => cx.span_bug(sp, "bad thing in rhs")
                };
                // rhs has holes ( `$id` and `$(...)` that need filled)
                let trncbr = new_tt_reader(&cx.parse_sess().span_diagnostic,
                                           Some(named_matches),
                                           imported_from,
                                           rhs);
                let mut p = Parser::new(cx.parse_sess(), cx.cfg(), Box::new(trncbr));
                panictry!(p.check_unknown_macro_variable());
                // Let the context choose how to interpret the result.
                // Weird, but useful for X-macros.
                return box ParserAnyMacro {
                    parser: RefCell::new(p),
                }
              }
              Failure(sp, ref msg) => if sp.lo >= best_fail_spot.lo {
                best_fail_spot = sp;
                best_fail_msg = (*msg).clone();
              },
              Error(sp, ref msg) => panic!(cx.span_fatal(sp, &msg[..]))
            }
          }
          _ => cx.bug("non-matcher found in parsed lhses")
        }
    }
    panic!(cx.span_fatal(best_fail_spot, &best_fail_msg[..]));
}

// Note that macro-by-example's input is also matched against a token tree:
//                   $( $lhs:tt => $rhs:tt );+
//
// Holy self-referential!

/// Converts a `macro_rules!` invocation into a syntax extension.
pub fn compile<'cx>(cx: &'cx mut ExtCtxt,
                    def: &ast::MacroDef) -> SyntaxExtension {

    let lhs_nm =  gensym_ident("lhs");
    let rhs_nm =  gensym_ident("rhs");

    // The pattern that macro_rules matches.
    // The grammar for macro_rules! is:
    // $( $lhs:tt => $rhs:tt );+
    // ...quasiquoting this would be nice.
    // These spans won't matter, anyways
    let match_lhs_tok = MatchNt(lhs_nm, special_idents::tt, token::Plain, token::Plain);
    let match_rhs_tok = MatchNt(rhs_nm, special_idents::tt, token::Plain, token::Plain);
    let argument_gram = vec!(
        TtSequence(DUMMY_SP,
                   Rc::new(ast::SequenceRepetition {
                       tts: vec![
                           TtToken(DUMMY_SP, match_lhs_tok),
                           TtToken(DUMMY_SP, token::FatArrow),
                           TtToken(DUMMY_SP, match_rhs_tok)],
                       separator: Some(token::Semi),
                       op: ast::OneOrMore,
                       num_captures: 2
                   })),
        //to phase into semicolon-termination instead of
        //semicolon-separation
        TtSequence(DUMMY_SP,
                   Rc::new(ast::SequenceRepetition {
                       tts: vec![TtToken(DUMMY_SP, token::Semi)],
                       separator: None,
                       op: ast::ZeroOrMore,
                       num_captures: 0
                   })));


    // Parse the macro_rules! invocation (`none` is for no interpolations):
    let arg_reader = new_tt_reader(&cx.parse_sess().span_diagnostic,
                                   None,
                                   None,
                                   def.body.clone());
    let argument_map = parse_or_else(cx.parse_sess(),
                                     cx.cfg(),
                                     arg_reader,
                                     argument_gram);

    // Extract the arguments:
    let lhses = match **argument_map.get(&lhs_nm).unwrap() {
        MatchedSeq(ref s, _) => /* FIXME (#2543) */ (*s).clone(),
        _ => cx.span_bug(def.span, "wrong-structured lhs")
    };

    for lhs in &lhses {
        check_lhs_nt_follows(cx, &**lhs, def.span);
    }

    let rhses = match **argument_map.get(&rhs_nm).unwrap() {
        MatchedSeq(ref s, _) => /* FIXME (#2543) */ (*s).clone(),
        _ => cx.span_bug(def.span, "wrong-structured rhs")
    };

    let exp: Box<_> = box MacroRulesMacroExpander {
        name: def.ident,
        imported_from: def.imported_from,
        lhses: lhses,
        rhses: rhses,
    };

    NormalTT(exp, Some(def.span), def.allow_internal_unstable)
}

fn check_lhs_nt_follows(cx: &mut ExtCtxt, lhs: &NamedMatch, sp: Span) {
    // lhs is going to be like MatchedNonterminal(NtTT(TtDelimited(...))), where the entire lhs is
    // those tts. Or, it can be a "bare sequence", not wrapped in parens.
    match lhs {
        &MatchedNonterminal(NtTT(ref inner)) => match &**inner {
            &TtDelimited(_, ref tts) => {
                check_matcher(cx, tts.tts.iter(), &Eof);
            },
            tt @ &TtSequence(..) => {
                check_matcher(cx, Some(tt).into_iter(), &Eof);
            },
            _ => cx.span_bug(sp, "wrong-structured lhs for follow check (didn't find \
            a TtDelimited or TtSequence)")
        },
        _ => cx.span_bug(sp, "wrong-structured lhs for follow check (didn't find a \
           MatchedNonterminal)")
    };
    // we don't abort on errors on rejection, the driver will do that for us
    // after parsing/expansion. we can report every error in every macro this way.
}

// returns the last token that was checked, for TtSequence. this gets used later on.
fn check_matcher<'a, I>(cx: &mut ExtCtxt, matcher: I, follow: &Token)
-> Option<(Span, Token)> where I: Iterator<Item=&'a TokenTree> {
    use print::pprust::token_to_string;

    let mut last = None;

    // 2. For each token T in M:
    let mut tokens = matcher.peekable();
    while let Some(token) = tokens.next() {
        last = match *token {
            TtToken(sp, MatchNt(ref name, ref frag_spec, _, _)) => {
                // ii. If T is a simple NT, look ahead to the next token T' in
                // M.
                let next_token = match tokens.peek() {
                    // If T' closes a complex NT, replace T' with F
                    Some(&&TtToken(_, CloseDelim(_))) => follow.clone(),
                    Some(&&TtToken(_, ref tok)) => tok.clone(),
                    Some(&&TtSequence(sp, _)) => {
                        cx.span_err(sp,
                                    &format!("`${0}:{1}` is followed by a \
                                              sequence repetition, which is not \
                                              allowed for `{1}` fragments",
                                             name.as_str(), frag_spec.as_str())
                                        );
                        Eof
                    },
                    // die next iteration
                    Some(&&TtDelimited(_, ref delim)) => delim.close_token(),
                    // else, we're at the end of the macro or sequence
                    None => follow.clone()
                };

                let tok = if let TtToken(_, ref tok) = *token { tok } else { unreachable!() };
                // If T' is in the set FOLLOW(NT), continue. Else, reject.
                match (&next_token, is_in_follow(cx, &next_token, frag_spec.as_str())) {
                    (_, Err(msg)) => {
                        cx.span_err(sp, &msg);
                        continue
                    }
                    (&Eof, _) => return Some((sp, tok.clone())),
                    (_, Ok(true)) => continue,
                    (next, Ok(false)) => {
                        cx.span_err(sp, &format!("`${0}:{1}` is followed by `{2}`, which \
                                                  is not allowed for `{1}` fragments",
                                                 name.as_str(), frag_spec.as_str(),
                                                 token_to_string(next)));
                        continue
                    },
                }
            },
            TtSequence(sp, ref seq) => {
                // iii. Else, T is a complex NT.
                match seq.separator {
                    // If T has the form $(...)U+ or $(...)U* for some token U,
                    // run the algorithm on the contents with F set to U. If it
                    // accepts, continue, else, reject.
                    Some(ref u) => {
                        let last = check_matcher(cx, seq.tts.iter(), u);
                        match last {
                            // Since the delimiter isn't required after the last
                            // repetition, make sure that the *next* token is
                            // sane. This doesn't actually compute the FIRST of
                            // the rest of the matcher yet, it only considers
                            // single tokens and simple NTs. This is imprecise,
                            // but conservatively correct.
                            Some((span, tok)) => {
                                let fol = match tokens.peek() {
                                    Some(&&TtToken(_, ref tok)) => tok.clone(),
                                    Some(&&TtDelimited(_, ref delim)) => delim.close_token(),
                                    Some(_) => {
                                        cx.span_err(sp, "sequence repetition followed by \
                                                another sequence repetition, which is not allowed");
                                        Eof
                                    },
                                    None => Eof
                                };
                                check_matcher(cx, Some(&TtToken(span, tok.clone())).into_iter(),
                                              &fol)
                            },
                            None => last,
                        }
                    },
                    // If T has the form $(...)+ or $(...)*, run the algorithm
                    // on the contents with F set to the token following the
                    // sequence. If it accepts, continue, else, reject.
                    None => {
                        let fol = match tokens.peek() {
                            Some(&&TtToken(_, ref tok)) => tok.clone(),
                            Some(&&TtDelimited(_, ref delim)) => delim.close_token(),
                            Some(_) => {
                                cx.span_err(sp, "sequence repetition followed by another \
                                             sequence repetition, which is not allowed");
                                Eof
                            },
                            None => Eof
                        };
                        check_matcher(cx, seq.tts.iter(), &fol)
                    }
                }
            },
            TtToken(..) => {
                // i. If T is not an NT, continue.
                continue
            },
            TtDelimited(_, ref tts) => {
                // if we don't pass in that close delimiter, we'll incorrectly consider the matcher
                // `{ $foo:ty }` as having a follow that isn't `RBrace`
                check_matcher(cx, tts.tts.iter(), &tts.close_token())
            }
        }
    }
    last
}

fn is_in_follow(_: &ExtCtxt, tok: &Token, frag: &str) -> Result<bool, String> {
    if let &CloseDelim(_) = tok {
        Ok(true)
    } else {
        match frag {
            "item" => {
                // since items *must* be followed by either a `;` or a `}`, we can
                // accept anything after them
                Ok(true)
            },
            "block" => {
                // anything can follow block, the braces provide a easy boundary to
                // maintain
                Ok(true)
            },
            "stmt" | "expr"  => {
                match *tok {
                    FatArrow | Comma | Semi => Ok(true),
                    _ => Ok(false)
                }
            },
            "pat" => {
                match *tok {
                    FatArrow | Comma | Eq => Ok(true),
                    _ => Ok(false)
                }
            },
            "path" | "ty" => {
                match *tok {
                    Comma | FatArrow | Colon | Eq | Gt => Ok(true),
                    Ident(i, _) if i.as_str() == "as" => Ok(true),
                    _ => Ok(false)
                }
            },
            "ident" => {
                // being a single token, idents are harmless
                Ok(true)
            },
            "meta" | "tt" => {
                // being either a single token or a delimited sequence, tt is
                // harmless
                Ok(true)
            },
            _ => Err(format!("invalid fragment specifier `{}`", frag))
        }
    }
}