compiler/rustc_parse/src/parser/nonterminal.rs

   1 use rustc_ast::ptr::P;
   2 use rustc_ast::token::{self, Nonterminal, NonterminalKind, Token};
   3 use rustc_ast::AstLike;
   4 use rustc_ast_pretty::pprust;
   5 use rustc_errors::PResult;
   6 use rustc_span::symbol::{kw, Ident};
   7
   8 use crate::parser::pat::{RecoverColon, RecoverComma};
   9 use crate::parser::{FollowedByType, ForceCollect, Parser, PathStyle};
  10
  11 impl<'a> Parser<'a> {
  12     /// Checks whether a non-terminal may begin with a particular token.
  13     ///
  14     /// Returning `false` is a *stability guarantee* that such a matcher will *never* begin with that
  15     /// token. Be conservative (return true) if not sure.
  16     pub fn nonterminal_may_begin_with(kind: NonterminalKind, token: &Token) -> bool {
  17         /// Checks whether the non-terminal may contain a single (non-keyword) identifier.
  18         fn may_be_ident(nt: &token::Nonterminal) -> bool {
  19             match *nt {
  20                 token::NtItem(_) | token::NtBlock(_) | token::NtVis(_) | token::NtLifetime(_) => {
  21                     false
  22                 }
  23                 _ => true,
  24             }
  25         }
  26
  27         match kind {
  28             NonterminalKind::Expr => {
  29                 token.can_begin_expr()
  30                 // This exception is here for backwards compatibility.
  31                 && !token.is_keyword(kw::Let)
  32                 // This exception is here for backwards compatibility.
  33                 && !token.is_keyword(kw::Const)
  34             }
  35             NonterminalKind::Ty => token.can_begin_type(),
  36             NonterminalKind::Ident => get_macro_ident(token).is_some(),
  37             NonterminalKind::Literal => token.can_begin_literal_maybe_minus(),
  38             NonterminalKind::Vis => match token.kind {
  39                 // The follow-set of :vis + "priv" keyword + interpolated
  40                 token::Comma | token::Ident(..) | token::Interpolated(..) => true,
  41                 _ => token.can_begin_type(),
  42             },
  43             NonterminalKind::Block => match token.kind {
  44                 token::OpenDelim(token::Brace) => true,
  45                 token::Interpolated(ref nt) => !matches!(
  46                     **nt,
  47                     token::NtItem(_)
  48                         | token::NtPat(_)
  49                         | token::NtTy(_)
  50                         | token::NtIdent(..)
  51                         | token::NtMeta(_)
  52                         | token::NtPath(_)
  53                         | token::NtVis(_)
  54                 ),
  55                 _ => false,
  56             },
  57             NonterminalKind::Path | NonterminalKind::Meta => match token.kind {
  58                 token::ModSep | token::Ident(..) => true,
  59                 token::Interpolated(ref nt) => match **nt {
  60                     token::NtPath(_) | token::NtMeta(_) => true,
  61                     _ => may_be_ident(&nt),
  62                 },
  63                 _ => false,
  64             },
  65             NonterminalKind::PatParam { .. } | NonterminalKind::PatWithOr { .. } => {
  66                 match token.kind {
  67                 token::Ident(..) |                  // box, ref, mut, and other identifiers (can stricten)
  68                 token::OpenDelim(token::Paren) |    // tuple pattern
  69                 token::OpenDelim(token::Bracket) |  // slice pattern
  70                 token::BinOp(token::And) |          // reference
  71                 token::BinOp(token::Minus) |        // negative literal
  72                 token::AndAnd |                     // double reference
  73                 token::Literal(..) |                // literal
  74                 token::DotDot |                     // range pattern (future compat)
  75                 token::DotDotDot |                  // range pattern (future compat)
  76                 token::ModSep |                     // path
  77                 token::Lt |                         // path (UFCS constant)
  78                 token::BinOp(token::Shl) => true,   // path (double UFCS)
  79                 // leading vert `|` or-pattern
  80                 token::BinOp(token::Or) =>  matches!(kind, NonterminalKind::PatWithOr {..}),
  81                 token::Interpolated(ref nt) => may_be_ident(nt),
  82                 _ => false,
  83             }
  84             }
  85             NonterminalKind::Lifetime => match token.kind {
  86                 token::Lifetime(_) => true,
  87                 token::Interpolated(ref nt) => {
  88                     matches!(**nt, token::NtLifetime(_) | token::NtTT(_))
  89                 }
  90                 _ => false,
  91             },
  92             NonterminalKind::TT | NonterminalKind::Item | NonterminalKind::Stmt => {
  93                 !matches!(token.kind, token::CloseDelim(_))
  94             }
  95         }
  96     }
  97
  98     /// Parse a non-terminal (e.g. MBE `:pat` or `:ident`).
  99     pub fn parse_nonterminal(&mut self, kind: NonterminalKind) -> PResult<'a, Nonterminal> {
 100         // Any `Nonterminal` which stores its tokens (currently `NtItem` and `NtExpr`)
 101         // needs to have them force-captured here.
 102         // A `macro_rules!` invocation may pass a captured item/expr to a proc-macro,
 103         // which requires having captured tokens available. Since we cannot determine
 104         // in advance whether or not a proc-macro will be (transitively) invoked,
 105         // we always capture tokens for any `Nonterminal` which needs them.
 106         let mut nt = match kind {
 107             NonterminalKind::Item => match self.parse_item(ForceCollect::Yes)? {
 108                 Some(item) => token::NtItem(item),
 109                 None => {
 110                     return Err(self.struct_span_err(self.token.span, "expected an item keyword"));
 111                 }
 112             },
 113             NonterminalKind::Block => {
 114                 // While a block *expression* may have attributes (e.g. `#[my_attr] { ... }`),
 115                 // the ':block' matcher does not support them
 116                 token::NtBlock(self.collect_tokens_no_attrs(|this| this.parse_block())?)
 117             }
 118             NonterminalKind::Stmt => match self.parse_stmt(ForceCollect::Yes)? {
 119                 Some(s) => token::NtStmt(s),
 120                 None => {
 121                     return Err(self.struct_span_err(self.token.span, "expected a statement"));
 122                 }
 123             },
 124             NonterminalKind::PatParam { .. } | NonterminalKind::PatWithOr { .. } => {
 125                 token::NtPat(self.collect_tokens_no_attrs(|this| match kind {
 126                     NonterminalKind::PatParam { .. } => this.parse_pat_no_top_alt(None),
 127                     NonterminalKind::PatWithOr { .. } => {
 128                         this.parse_pat_allow_top_alt(None, RecoverComma::No, RecoverColon::No)
 129                     }
 130                     _ => unreachable!(),
 131                 })?)
 132             }
 133
 134             NonterminalKind::Expr => token::NtExpr(self.parse_expr_force_collect()?),
 135             NonterminalKind::Literal => {
 136                 // The `:literal` matcher does not support attributes
 137                 token::NtLiteral(
 138                     self.collect_tokens_no_attrs(|this| this.parse_literal_maybe_minus())?,
 139                 )
 140             }
 141
 142             NonterminalKind::Ty => {
 143                 token::NtTy(self.collect_tokens_no_attrs(|this| this.parse_ty())?)
 144             }
 145             // this could be handled like a token, since it is one
 146             NonterminalKind::Ident => {
 147                 if let Some((ident, is_raw)) = get_macro_ident(&self.token) {
 148                     self.bump();
 149                     token::NtIdent(ident, is_raw)
 150                 } else {
 151                     let token_str = pprust::token_to_string(&self.token);
 152                     let msg = &format!("expected ident, found {}", &token_str);
 153                     return Err(self.struct_span_err(self.token.span, msg));
 154                 }
 155             }
 156             NonterminalKind::Path => token::NtPath(
 157                 self.collect_tokens_no_attrs(|this| this.parse_path(PathStyle::Type))?,
 158             ),
 159             NonterminalKind::Meta => token::NtMeta(P(self.parse_attr_item(true)?)),
 160             NonterminalKind::TT => token::NtTT(self.parse_token_tree()),
 161             NonterminalKind::Vis => token::NtVis(
 162                 self.collect_tokens_no_attrs(|this| this.parse_visibility(FollowedByType::Yes))?,
 163             ),
 164             NonterminalKind::Lifetime => {
 165                 if self.check_lifetime() {
 166                     token::NtLifetime(self.expect_lifetime().ident)
 167                 } else {
 168                     let token_str = pprust::token_to_string(&self.token);
 169                     let msg = &format!("expected a lifetime, found `{}`", &token_str);
 170                     return Err(self.struct_span_err(self.token.span, msg));
 171                 }
 172             }
 173         };
 174
 175         // If tokens are supported at all, they should be collected.
 176         if matches!(nt.tokens_mut(), Some(None)) {
 177             panic!(
 178                 "Missing tokens for nt {:?} at {:?}: {:?}",
 179                 nt,
 180                 nt.span(),
 181                 pprust::nonterminal_to_string(&nt)
 182             );
 183         }
 184
 185         Ok(nt)
 186     }
 187 }
 188
 189 /// The token is an identifier, but not `_`.
 190 /// We prohibit passing `_` to macros expecting `ident` for now.
 191 fn get_macro_ident(token: &Token) -> Option<(Ident, bool)> {
 192     token.ident().filter(|(ident, _)| ident.name != kw::Underscore)
 193 }