src/librustc_expand/mbe.rs

   1 //! This module implements declarative macros: old `macro_rules` and the newer
   2 //! `macro`. Declarative macros are also known as "macro by example", and that's
   3 //! why we call this module `mbe`. For external documentation, prefer the
   4 //! official terminology: "declarative macros".
   5
   6 crate mod macro_check;
   7 crate mod macro_parser;
   8 crate mod macro_rules;
   9 crate mod quoted;
  10 crate mod transcribe;
  11
  12 use syntax::ast;
  13 use syntax::token::{self, Token, TokenKind};
  14 use syntax::tokenstream::DelimSpan;
  15
  16 use rustc_span::Span;
  17
  18 use rustc_data_structures::sync::Lrc;
  19
  20 /// Contains the sub-token-trees of a "delimited" token tree, such as the contents of `(`. Note
  21 /// that the delimiter itself might be `NoDelim`.
  22 #[derive(Clone, PartialEq, RustcEncodable, RustcDecodable, Debug)]
  23 struct Delimited {
  24     delim: token::DelimToken,
  25     tts: Vec<TokenTree>,
  26 }
  27
  28 impl Delimited {
  29     /// Returns a `self::TokenTree` with a `Span` corresponding to the opening delimiter.
  30     fn open_tt(&self, span: DelimSpan) -> TokenTree {
  31         TokenTree::token(token::OpenDelim(self.delim), span.open)
  32     }
  33
  34     /// Returns a `self::TokenTree` with a `Span` corresponding to the closing delimiter.
  35     fn close_tt(&self, span: DelimSpan) -> TokenTree {
  36         TokenTree::token(token::CloseDelim(self.delim), span.close)
  37     }
  38 }
  39
  40 #[derive(Clone, PartialEq, RustcEncodable, RustcDecodable, Debug)]
  41 struct SequenceRepetition {
  42     /// The sequence of token trees
  43     tts: Vec<TokenTree>,
  44     /// The optional separator
  45     separator: Option<Token>,
  46     /// Whether the sequence can be repeated zero (*), or one or more times (+)
  47     kleene: KleeneToken,
  48     /// The number of `Match`s that appear in the sequence (and subsequences)
  49     num_captures: usize,
  50 }
  51
  52 #[derive(Clone, PartialEq, RustcEncodable, RustcDecodable, Debug, Copy)]
  53 struct KleeneToken {
  54     span: Span,
  55     op: KleeneOp,
  56 }
  57
  58 impl KleeneToken {
  59     fn new(op: KleeneOp, span: Span) -> KleeneToken {
  60         KleeneToken { span, op }
  61     }
  62 }
  63
  64 /// A Kleene-style [repetition operator](http://en.wikipedia.org/wiki/Kleene_star)
  65 /// for token sequences.
  66 #[derive(Clone, PartialEq, RustcEncodable, RustcDecodable, Debug, Copy)]
  67 enum KleeneOp {
  68     /// Kleene star (`*`) for zero or more repetitions
  69     ZeroOrMore,
  70     /// Kleene plus (`+`) for one or more repetitions
  71     OneOrMore,
  72     /// Kleene optional (`?`) for zero or one reptitions
  73     ZeroOrOne,
  74 }
  75
  76 /// Similar to `tokenstream::TokenTree`, except that `$i`, `$i:ident`, and `$(...)`
  77 /// are "first-class" token trees. Useful for parsing macros.
  78 #[derive(Debug, Clone, PartialEq, RustcEncodable, RustcDecodable)]
  79 enum TokenTree {
  80     Token(Token),
  81     Delimited(DelimSpan, Lrc<Delimited>),
  82     /// A kleene-style repetition sequence
  83     Sequence(DelimSpan, Lrc<SequenceRepetition>),
  84     /// e.g., `$var`
  85     MetaVar(Span, ast::Ident),
  86     /// e.g., `$var:expr`. This is only used in the left hand side of MBE macros.
  87     MetaVarDecl(
  88         Span,
  89         ast::Ident, /* name to bind */
  90         ast::Ident, /* kind of nonterminal */
  91     ),
  92 }
  93
  94 impl TokenTree {
  95     /// Return the number of tokens in the tree.
  96     fn len(&self) -> usize {
  97         match *self {
  98             TokenTree::Delimited(_, ref delimed) => match delimed.delim {
  99                 token::NoDelim => delimed.tts.len(),
 100                 _ => delimed.tts.len() + 2,
 101             },
 102             TokenTree::Sequence(_, ref seq) => seq.tts.len(),
 103             _ => 0,
 104         }
 105     }
 106
 107     /// Returns `true` if the given token tree is delimited.
 108     fn is_delimited(&self) -> bool {
 109         match *self {
 110             TokenTree::Delimited(..) => true,
 111             _ => false,
 112         }
 113     }
 114
 115     /// Returns `true` if the given token tree is a token of the given kind.
 116     fn is_token(&self, expected_kind: &TokenKind) -> bool {
 117         match self {
 118             TokenTree::Token(Token { kind: actual_kind, .. }) => actual_kind == expected_kind,
 119             _ => false,
 120         }
 121     }
 122
 123     /// Gets the `index`-th sub-token-tree. This only makes sense for delimited trees and sequences.
 124     fn get_tt(&self, index: usize) -> TokenTree {
 125         match (self, index) {
 126             (&TokenTree::Delimited(_, ref delimed), _) if delimed.delim == token::NoDelim => {
 127                 delimed.tts[index].clone()
 128             }
 129             (&TokenTree::Delimited(span, ref delimed), _) => {
 130                 if index == 0 {
 131                     return delimed.open_tt(span);
 132                 }
 133                 if index == delimed.tts.len() + 1 {
 134                     return delimed.close_tt(span);
 135                 }
 136                 delimed.tts[index - 1].clone()
 137             }
 138             (&TokenTree::Sequence(_, ref seq), _) => seq.tts[index].clone(),
 139             _ => panic!("Cannot expand a token tree"),
 140         }
 141     }
 142
 143     /// Retrieves the `TokenTree`'s span.
 144     fn span(&self) -> Span {
 145         match *self {
 146             TokenTree::Token(Token { span, .. })
 147             | TokenTree::MetaVar(span, _)
 148             | TokenTree::MetaVarDecl(span, _, _) => span,
 149             TokenTree::Delimited(span, _) | TokenTree::Sequence(span, _) => span.entire(),
 150         }
 151     }
 152
 153     fn token(kind: TokenKind, span: Span) -> TokenTree {
 154         TokenTree::Token(Token::new(kind, span))
 155     }
 156 }