src/libsyntax/ext/tt/macro_rules.rs

   1 // Copyright 2012 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use ast::{Ident, TtDelimited, TtSequence, TtToken};
  12 use ast;
  13 use codemap::{Span, DUMMY_SP};
  14 use ext::base::{ExtCtxt, MacResult, SyntaxExtension};
  15 use ext::base::{NormalTT, TTMacroExpander};
  16 use ext::tt::macro_parser::{Success, Error, Failure};
  17 use ext::tt::macro_parser::{NamedMatch, MatchedSeq, MatchedNonterminal};
  18 use ext::tt::macro_parser::{parse, parse_or_else};
  19 use parse::lexer::new_tt_reader;
  20 use parse::parser::Parser;
  21 use parse::attr::ParserAttr;
  22 use parse::token::{special_idents, gensym_ident};
  23 use parse::token::{MatchNt, NtTT};
  24 use parse::token;
  25 use print;
  26 use ptr::P;
  27
  28 use util::small_vector::SmallVector;
  29
  30 use std::cell::RefCell;
  31 use std::rc::Rc;
  32
  33 struct ParserAnyMacro<'a> {
  34     parser: RefCell<Parser<'a>>,
  35 }
  36
  37 impl<'a> ParserAnyMacro<'a> {
  38     /// Make sure we don't have any tokens left to parse, so we don't
  39     /// silently drop anything. `allow_semi` is so that "optional"
  40     /// semicolons at the end of normal expressions aren't complained
  41     /// about e.g. the semicolon in `macro_rules! kapow { () => {
  42     /// panic!(); } }` doesn't get picked up by .parse_expr(), but it's
  43     /// allowed to be there.
  44     fn ensure_complete_parse(&self, allow_semi: bool) {
  45         let mut parser = self.parser.borrow_mut();
  46         if allow_semi && parser.token == token::Semi {
  47             parser.bump()
  48         }
  49         if parser.token != token::Eof {
  50             let token_str = parser.this_token_to_string();
  51             let msg = format!("macro expansion ignores token `{}` and any \
  52                                following",
  53                               token_str);
  54             let span = parser.span;
  55             parser.span_err(span, msg[]);
  56         }
  57     }
  58 }
  59
  60 impl<'a> MacResult for ParserAnyMacro<'a> {
  61     fn make_expr(self: Box<ParserAnyMacro<'a>>) -> Option<P<ast::Expr>> {
  62         let ret = self.parser.borrow_mut().parse_expr();
  63         self.ensure_complete_parse(true);
  64         Some(ret)
  65     }
  66     fn make_pat(self: Box<ParserAnyMacro<'a>>) -> Option<P<ast::Pat>> {
  67         let ret = self.parser.borrow_mut().parse_pat();
  68         self.ensure_complete_parse(false);
  69         Some(ret)
  70     }
  71     fn make_items(self: Box<ParserAnyMacro<'a>>) -> Option<SmallVector<P<ast::Item>>> {
  72         let mut ret = SmallVector::zero();
  73         loop {
  74             let mut parser = self.parser.borrow_mut();
  75             // so... do outer attributes attached to the macro invocation
  76             // just disappear? This question applies to make_methods, as
  77             // well.
  78             match parser.parse_item_with_outer_attributes() {
  79                 Some(item) => ret.push(item),
  80                 None => break
  81             }
  82         }
  83         self.ensure_complete_parse(false);
  84         Some(ret)
  85     }
  86
  87     fn make_methods(self: Box<ParserAnyMacro<'a>>) -> Option<SmallVector<P<ast::Method>>> {
  88         let mut ret = SmallVector::zero();
  89         loop {
  90             let mut parser = self.parser.borrow_mut();
  91             match parser.token {
  92                 token::Eof => break,
  93                 _ => {
  94                     let attrs = parser.parse_outer_attributes();
  95                     ret.push(parser.parse_method(attrs, ast::Inherited))
  96                 }
  97             }
  98         }
  99         self.ensure_complete_parse(false);
 100         Some(ret)
 101     }
 102
 103     fn make_stmt(self: Box<ParserAnyMacro<'a>>) -> Option<P<ast::Stmt>> {
 104         let attrs = self.parser.borrow_mut().parse_outer_attributes();
 105         let ret = self.parser.borrow_mut().parse_stmt(attrs);
 106         self.ensure_complete_parse(true);
 107         Some(ret)
 108     }
 109 }
 110
 111 struct MacroRulesMacroExpander {
 112     name: Ident,
 113     imported_from: Option<Ident>,
 114     lhses: Vec<Rc<NamedMatch>>,
 115     rhses: Vec<Rc<NamedMatch>>,
 116 }
 117
 118 impl TTMacroExpander for MacroRulesMacroExpander {
 119     fn expand<'cx>(&self,
 120                    cx: &'cx mut ExtCtxt,
 121                    sp: Span,
 122                    arg: &[ast::TokenTree])
 123                    -> Box<MacResult+'cx> {
 124         generic_extension(cx,
 125                           sp,
 126                           self.name,
 127                           self.imported_from,
 128                           arg,
 129                           self.lhses[],
 130                           self.rhses[])
 131     }
 132 }
 133
 134 /// Given `lhses` and `rhses`, this is the new macro we create
 135 fn generic_extension<'cx>(cx: &'cx ExtCtxt,
 136                           sp: Span,
 137                           name: Ident,
 138                           imported_from: Option<Ident>,
 139                           arg: &[ast::TokenTree],
 140                           lhses: &[Rc<NamedMatch>],
 141                           rhses: &[Rc<NamedMatch>])
 142                           -> Box<MacResult+'cx> {
 143     if cx.trace_macros() {
 144         println!("{}! {{ {} }}",
 145                  token::get_ident(name),
 146                  print::pprust::tts_to_string(arg));
 147     }
 148
 149     // Which arm's failure should we report? (the one furthest along)
 150     let mut best_fail_spot = DUMMY_SP;
 151     let mut best_fail_msg = "internal error: ran no matchers".to_string();
 152
 153     for (i, lhs) in lhses.iter().enumerate() { // try each arm's matchers
 154         match **lhs {
 155           MatchedNonterminal(NtTT(ref lhs_tt)) => {
 156             let lhs_tt = match **lhs_tt {
 157                 TtDelimited(_, ref delim) => delim.tts[],
 158                 _ => cx.span_fatal(sp, "malformed macro lhs")
 159             };
 160             // `None` is because we're not interpolating
 161             let mut arg_rdr = new_tt_reader(&cx.parse_sess().span_diagnostic,
 162                                             None,
 163                                             None,
 164                                             arg.iter()
 165                                                .map(|x| (*x).clone())
 166                                                .collect());
 167             arg_rdr.desugar_doc_comments = true;
 168             match parse(cx.parse_sess(), cx.cfg(), arg_rdr, lhs_tt) {
 169               Success(named_matches) => {
 170                 let rhs = match *rhses[i] {
 171                     // okay, what's your transcriber?
 172                     MatchedNonterminal(NtTT(ref tt)) => {
 173                         match **tt {
 174                             // ignore delimiters
 175                             TtDelimited(_, ref delimed) => delimed.tts.clone(),
 176                             _ => cx.span_fatal(sp, "macro rhs must be delimited"),
 177                         }
 178                     },
 179                     _ => cx.span_bug(sp, "bad thing in rhs")
 180                 };
 181                 // rhs has holes ( `$id` and `$(...)` that need filled)
 182                 let trncbr = new_tt_reader(&cx.parse_sess().span_diagnostic,
 183                                            Some(named_matches),
 184                                            imported_from,
 185                                            rhs);
 186                 let p = Parser::new(cx.parse_sess(), cx.cfg(), box trncbr);
 187                 // Let the context choose how to interpret the result.
 188                 // Weird, but useful for X-macros.
 189                 return box ParserAnyMacro {
 190                     parser: RefCell::new(p),
 191                 } as Box<MacResult+'cx>
 192               }
 193               Failure(sp, ref msg) => if sp.lo >= best_fail_spot.lo {
 194                 best_fail_spot = sp;
 195                 best_fail_msg = (*msg).clone();
 196               },
 197               Error(sp, ref msg) => cx.span_fatal(sp, msg[])
 198             }
 199           }
 200           _ => cx.bug("non-matcher found in parsed lhses")
 201         }
 202     }
 203     cx.span_fatal(best_fail_spot, best_fail_msg[]);
 204 }
 205
 206 // Note that macro-by-example's input is also matched against a token tree:
 207 //                   $( $lhs:tt => $rhs:tt );+
 208 //
 209 // Holy self-referential!
 210
 211 /// Converts a `macro_rules!` invocation into a syntax extension.
 212 pub fn compile<'cx>(cx: &'cx mut ExtCtxt,
 213                     def: &ast::MacroDef) -> SyntaxExtension {
 214
 215     let lhs_nm =  gensym_ident("lhs");
 216     let rhs_nm =  gensym_ident("rhs");
 217
 218     // The pattern that macro_rules matches.
 219     // The grammar for macro_rules! is:
 220     // $( $lhs:tt => $rhs:tt );+
 221     // ...quasiquoting this would be nice.
 222     // These spans won't matter, anyways
 223     let match_lhs_tok = MatchNt(lhs_nm, special_idents::tt, token::Plain, token::Plain);
 224     let match_rhs_tok = MatchNt(rhs_nm, special_idents::tt, token::Plain, token::Plain);
 225     let argument_gram = vec!(
 226         TtSequence(DUMMY_SP,
 227                    Rc::new(ast::SequenceRepetition {
 228                        tts: vec![
 229                            TtToken(DUMMY_SP, match_lhs_tok),
 230                            TtToken(DUMMY_SP, token::FatArrow),
 231                            TtToken(DUMMY_SP, match_rhs_tok)],
 232                        separator: Some(token::Semi),
 233                        op: ast::OneOrMore,
 234                        num_captures: 2
 235                    })),
 236         //to phase into semicolon-termination instead of
 237         //semicolon-separation
 238         TtSequence(DUMMY_SP,
 239                    Rc::new(ast::SequenceRepetition {
 240                        tts: vec![TtToken(DUMMY_SP, token::Semi)],
 241                        separator: None,
 242                        op: ast::ZeroOrMore,
 243                        num_captures: 0
 244                    })));
 245
 246
 247     // Parse the macro_rules! invocation (`none` is for no interpolations):
 248     let arg_reader = new_tt_reader(&cx.parse_sess().span_diagnostic,
 249                                    None,
 250                                    None,
 251                                    def.body.clone());
 252     let argument_map = parse_or_else(cx.parse_sess(),
 253                                      cx.cfg(),
 254                                      arg_reader,
 255                                      argument_gram);
 256
 257     // Extract the arguments:
 258     let lhses = match *argument_map[lhs_nm] {
 259         MatchedSeq(ref s, _) => /* FIXME (#2543) */ (*s).clone(),
 260         _ => cx.span_bug(def.span, "wrong-structured lhs")
 261     };
 262
 263     let rhses = match *argument_map[rhs_nm] {
 264         MatchedSeq(ref s, _) => /* FIXME (#2543) */ (*s).clone(),
 265         _ => cx.span_bug(def.span, "wrong-structured rhs")
 266     };
 267
 268     let exp = box MacroRulesMacroExpander {
 269         name: def.ident,
 270         imported_from: def.imported_from,
 271         lhses: lhses,
 272         rhses: rhses,
 273     };
 274
 275     NormalTT(exp, Some(def.span))
 276 }