1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170

use rustc_ast::ptr::P;
use rustc_ast::token::{self, Nonterminal, NonterminalKind, Token};
use rustc_ast_pretty::pprust;
use rustc_errors::PResult;
use rustc_span::symbol::{kw, Ident};

use crate::parser::{FollowedByType, Parser, PathStyle};

impl<'a> Parser<'a> {
    /// Checks whether a non-terminal may begin with a particular token.
    ///
    /// Returning `false` is a *stability guarantee* that such a matcher will *never* begin with that
    /// token. Be conservative (return true) if not sure.
    pub fn nonterminal_may_begin_with(kind: NonterminalKind, token: &Token) -> bool {
        /// Checks whether the non-terminal may contain a single (non-keyword) identifier.
        fn may_be_ident(nt: &token::Nonterminal) -> bool {
            match *nt {
                token::NtItem(_) | token::NtBlock(_) | token::NtVis(_) | token::NtLifetime(_) => {
                    false
                }
                _ => true,
            }
        }

        match kind {
            NonterminalKind::Expr => {
                token.can_begin_expr()
                // This exception is here for backwards compatibility.
                && !token.is_keyword(kw::Let)
            }
            NonterminalKind::Ty => token.can_begin_type(),
            NonterminalKind::Ident => get_macro_ident(token).is_some(),
            NonterminalKind::Literal => token.can_begin_literal_maybe_minus(),
            NonterminalKind::Vis => match token.kind {
                // The follow-set of :vis + "priv" keyword + interpolated
                token::Comma | token::Ident(..) | token::Interpolated(..) => true,
                _ => token.can_begin_type(),
            },
            NonterminalKind::Block => match token.kind {
                token::OpenDelim(token::Brace) => true,
                token::Interpolated(ref nt) => match **nt {
                    token::NtItem(_)
                    | token::NtPat(_)
                    | token::NtTy(_)
                    | token::NtIdent(..)
                    | token::NtMeta(_)
                    | token::NtPath(_)
                    | token::NtVis(_) => false, // none of these may start with '{'.
                    _ => true,
                },
                _ => false,
            },
            NonterminalKind::Path | NonterminalKind::Meta => match token.kind {
                token::ModSep | token::Ident(..) => true,
                token::Interpolated(ref nt) => match **nt {
                    token::NtPath(_) | token::NtMeta(_) => true,
                    _ => may_be_ident(&nt),
                },
                _ => false,
            },
            NonterminalKind::Pat => match token.kind {
                token::Ident(..) |                  // box, ref, mut, and other identifiers (can stricten)
                token::OpenDelim(token::Paren) |    // tuple pattern
                token::OpenDelim(token::Bracket) |  // slice pattern
                token::BinOp(token::And) |          // reference
                token::BinOp(token::Minus) |        // negative literal
                token::AndAnd |                     // double reference
                token::Literal(..) |                // literal
                token::DotDot |                     // range pattern (future compat)
                token::DotDotDot |                  // range pattern (future compat)
                token::ModSep |                     // path
                token::Lt |                         // path (UFCS constant)
                token::BinOp(token::Shl) => true,   // path (double UFCS)
                token::Interpolated(ref nt) => may_be_ident(nt),
                _ => false,
            },
            NonterminalKind::Lifetime => match token.kind {
                token::Lifetime(_) => true,
                token::Interpolated(ref nt) => match **nt {
                    token::NtLifetime(_) | token::NtTT(_) => true,
                    _ => false,
                },
                _ => false,
            },
            NonterminalKind::TT | NonterminalKind::Item | NonterminalKind::Stmt => match token.kind
            {
                token::CloseDelim(_) => false,
                _ => true,
            },
        }
    }

    pub fn parse_nonterminal(&mut self, kind: NonterminalKind) -> PResult<'a, Nonterminal> {
        // Any `Nonterminal` which stores its tokens (currently `NtItem` and `NtExpr`)
        // needs to have them force-captured here.
        // A `macro_rules!` invocation may pass a captured item/expr to a proc-macro,
        // which requires having captured tokens available. Since we cannot determine
        // in advance whether or not a proc-macro will be (transitively) invoked,
        // we always capture tokens for any `Nonterminal` which needs them.
        Ok(match kind {
            NonterminalKind::Item => match self.collect_tokens(|this| this.parse_item())? {
                (Some(mut item), tokens) => {
                    // If we captured tokens during parsing (due to outer attributes),
                    // use those.
                    if item.tokens.is_none() {
                        item.tokens = Some(tokens);
                    }
                    token::NtItem(item)
                }
                (None, _) => {
                    return Err(self.struct_span_err(self.token.span, "expected an item keyword"));
                }
            },
            NonterminalKind::Block => token::NtBlock(self.parse_block()?),
            NonterminalKind::Stmt => match self.parse_stmt()? {
                Some(s) => token::NtStmt(s),
                None => return Err(self.struct_span_err(self.token.span, "expected a statement")),
            },
            NonterminalKind::Pat => {
                let (mut pat, tokens) = self.collect_tokens(|this| this.parse_pat(None))?;
                // We have have eaten an NtPat, which could already have tokens
                if pat.tokens.is_none() {
                    pat.tokens = Some(tokens);
                }
                token::NtPat(pat)
            }
            NonterminalKind::Expr => {
                let (mut expr, tokens) = self.collect_tokens(|this| this.parse_expr())?;
                // If we captured tokens during parsing (due to outer attributes),
                // use those.
                if expr.tokens.is_none() {
                    expr.tokens = Some(tokens);
                }
                token::NtExpr(expr)
            }
            NonterminalKind::Literal => token::NtLiteral(self.parse_literal_maybe_minus()?),
            NonterminalKind::Ty => token::NtTy(self.parse_ty()?),
            // this could be handled like a token, since it is one
            NonterminalKind::Ident => {
                if let Some((ident, is_raw)) = get_macro_ident(&self.token) {
                    self.bump();
                    token::NtIdent(ident, is_raw)
                } else {
                    let token_str = pprust::token_to_string(&self.token);
                    let msg = &format!("expected ident, found {}", &token_str);
                    return Err(self.struct_span_err(self.token.span, msg));
                }
            }
            NonterminalKind::Path => token::NtPath(self.parse_path(PathStyle::Type)?),
            NonterminalKind::Meta => token::NtMeta(P(self.parse_attr_item()?)),
            NonterminalKind::TT => token::NtTT(self.parse_token_tree()),
            NonterminalKind::Vis => token::NtVis(self.parse_visibility(FollowedByType::Yes)?),
            NonterminalKind::Lifetime => {
                if self.check_lifetime() {
                    token::NtLifetime(self.expect_lifetime().ident)
                } else {
                    let token_str = pprust::token_to_string(&self.token);
                    let msg = &format!("expected a lifetime, found `{}`", &token_str);
                    return Err(self.struct_span_err(self.token.span, msg));
                }
            }
        })
    }
}

/// The token is an identifier, but not `_`.
/// We prohibit passing `_` to macros expecting `ident` for now.
fn get_macro_ident(token: &Token) -> Option<(Ident, bool)> {
    token.ident().filter(|(ident, _)| ident.name != kw::Underscore)
}