library/proc_macro/src/quote.rs

   1 //! # Quasiquoter
   2 //! This file contains the implementation internals of the quasiquoter provided by `quote!`.
   3
   4 //! This quasiquoter uses macros 2.0 hygiene to reliably access
   5 //! items from `proc_macro`, to build a `proc_macro::TokenStream`.
   6
   7 use crate::{Delimiter, Group, Ident, Literal, Punct, Spacing, Span, TokenStream, TokenTree};
   8
   9 macro_rules! quote_tt {
  10     (($($t:tt)*)) => { Group::new(Delimiter::Parenthesis, quote!($($t)*)) };
  11     ([$($t:tt)*]) => { Group::new(Delimiter::Bracket, quote!($($t)*)) };
  12     ({$($t:tt)*}) => { Group::new(Delimiter::Brace, quote!($($t)*)) };
  13     (,) => { Punct::new(',', Spacing::Alone) };
  14     (.) => { Punct::new('.', Spacing::Alone) };
  15     (;) => { Punct::new(';', Spacing::Alone) };
  16     (!) => { Punct::new('!', Spacing::Alone) };
  17     (<) => { Punct::new('<', Spacing::Alone) };
  18     (>) => { Punct::new('>', Spacing::Alone) };
  19     (&) => { Punct::new('&', Spacing::Alone) };
  20     (=) => { Punct::new('=', Spacing::Alone) };
  21     ($i:ident) => { Ident::new(stringify!($i), Span::def_site()) };
  22 }
  23
  24 macro_rules! quote_ts {
  25     ((@ $($t:tt)*)) => { $($t)* };
  26     (::) => {
  27         [
  28             TokenTree::from(Punct::new(':', Spacing::Joint)),
  29             TokenTree::from(Punct::new(':', Spacing::Alone)),
  30         ].iter()
  31             .cloned()
  32             .map(|mut x| {
  33                 x.set_span(Span::def_site());
  34                 x
  35             })
  36             .collect::<TokenStream>()
  37     };
  38     ($t:tt) => { TokenTree::from(quote_tt!($t)) };
  39 }
  40
  41 /// Simpler version of the real `quote!` macro, implemented solely
  42 /// through `macro_rules`, for bootstrapping the real implementation
  43 /// (see the `quote` function), which does not have access to the
  44 /// real `quote!` macro due to the `proc_macro` crate not being
  45 /// able to depend on itself.
  46 ///
  47 /// Note: supported tokens are a subset of the real `quote!`, but
  48 /// unquoting is different: instead of `$x`, this uses `(@ expr)`.
  49 macro_rules! quote {
  50     () => { TokenStream::new() };
  51     ($($t:tt)*) => {
  52         [
  53             $(TokenStream::from(quote_ts!($t)),)*
  54         ].iter().cloned().collect::<TokenStream>()
  55     };
  56 }
  57
  58 /// Quote a `TokenStream` into a `TokenStream`.
  59 /// This is the actual implementation of the `quote!()` proc macro.
  60 ///
  61 /// It is loaded by the compiler in `register_builtin_macros`.
  62 #[unstable(feature = "proc_macro_quote", issue = "54722")]
  63 pub fn quote(stream: TokenStream) -> TokenStream {
  64     if stream.is_empty() {
  65         return quote!(crate::TokenStream::new());
  66     }
  67     let proc_macro_crate = quote!(crate);
  68     let mut after_dollar = false;
  69     let tokens = stream
  70         .into_iter()
  71         .filter_map(|tree| {
  72             if after_dollar {
  73                 after_dollar = false;
  74                 match tree {
  75                     TokenTree::Ident(_) => {
  76                         return Some(quote!(Into::<crate::TokenStream>::into(
  77                         Clone::clone(&(@ tree))),));
  78                     }
  79                     TokenTree::Punct(ref tt) if tt.as_char() == '$' => {}
  80                     _ => panic!("`$` must be followed by an ident or `$` in `quote!`"),
  81                 }
  82             } else if let TokenTree::Punct(ref tt) = tree {
  83                 if tt.as_char() == '$' {
  84                     after_dollar = true;
  85                     return None;
  86                 }
  87             }
  88
  89             Some(quote!(crate::TokenStream::from((@ match tree {
  90                 TokenTree::Punct(tt) => quote!(crate::TokenTree::Punct(crate::Punct::new(
  91                     (@ TokenTree::from(Literal::character(tt.as_char()))),
  92                     (@ match tt.spacing() {
  93                         Spacing::Alone => quote!(crate::Spacing::Alone),
  94                         Spacing::Joint => quote!(crate::Spacing::Joint),
  95                     }),
  96                 ))),
  97                 TokenTree::Group(tt) => quote!(crate::TokenTree::Group(crate::Group::new(
  98                     (@ match tt.delimiter() {
  99                         Delimiter::Parenthesis => quote!(crate::Delimiter::Parenthesis),
 100                         Delimiter::Brace => quote!(crate::Delimiter::Brace),
 101                         Delimiter::Bracket => quote!(crate::Delimiter::Bracket),
 102                         Delimiter::None => quote!(crate::Delimiter::None),
 103                     }),
 104                     (@ quote(tt.stream())),
 105                 ))),
 106                 TokenTree::Ident(tt) => quote!(crate::TokenTree::Ident(crate::Ident::new(
 107                     (@ TokenTree::from(Literal::string(&tt.to_string()))),
 108                     (@ quote_span(proc_macro_crate.clone(), tt.span())),
 109                 ))),
 110                 TokenTree::Literal(tt) => quote!(crate::TokenTree::Literal({
 111                     let mut iter = (@ TokenTree::from(Literal::string(&tt.to_string())))
 112                         .parse::<crate::TokenStream>()
 113                         .unwrap()
 114                         .into_iter();
 115                     if let (Some(crate::TokenTree::Literal(mut lit)), None) =
 116                         (iter.next(), iter.next())
 117                     {
 118                         lit.set_span((@ quote_span(proc_macro_crate.clone(), tt.span())));
 119                         lit
 120                     } else {
 121                         unreachable!()
 122                     }
 123                 }))
 124             })),))
 125         })
 126         .collect::<TokenStream>();
 127
 128     if after_dollar {
 129         panic!("unexpected trailing `$` in `quote!`");
 130     }
 131
 132     quote!([(@ tokens)].iter().cloned().collect::<crate::TokenStream>())
 133 }
 134
 135 /// Quote a `Span` into a `TokenStream`.
 136 /// This is needed to implement a custom quoter.
 137 #[unstable(feature = "proc_macro_quote", issue = "54722")]
 138 pub fn quote_span(proc_macro_crate: TokenStream, span: Span) -> TokenStream {
 139     let id = span.save_span();
 140     quote!((@ proc_macro_crate ) ::Span::recover_proc_macro_span((@ TokenTree::from(Literal::usize_unsuffixed(id)))))
 141 }