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
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
use rustc_ast::ptr::P;
use rustc_ast::token::{self, Delimiter, NonterminalKind, Token};
use rustc_ast::HasTokens;
use rustc_ast_pretty::pprust;
use rustc_errors::IntoDiagnostic;
use rustc_errors::PResult;
use rustc_span::symbol::{kw, Ident};

use crate::errors::UnexpectedNonterminal;
use crate::parser::pat::{CommaRecoveryMode, RecoverColon, RecoverComma};
use crate::parser::{FollowedByType, ForceCollect, NtOrTt, 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. Inlined because it has a single call
    /// site.
    #[inline]
    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)
                // This exception is here for backwards compatibility.
                && !token.is_keyword(kw::Const)
            }
            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(Delimiter::Brace) => true,
                token::Interpolated(nt) => !matches!(
                    **nt,
                    token::NtItem(_)
                        | token::NtPat(_)
                        | token::NtTy(_)
                        | token::NtIdent(..)
                        | token::NtMeta(_)
                        | token::NtPath(_)
                        | token::NtVis(_)
                ),
                _ => false,
            },
            NonterminalKind::Path | NonterminalKind::Meta => match &token.kind {
                token::ModSep | token::Ident(..) => true,
                token::Interpolated(nt) => match **nt {
                    token::NtPath(_) | token::NtMeta(_) => true,
                    _ => may_be_ident(&nt),
                },
                _ => false,
            },
            NonterminalKind::PatParam { .. } | NonterminalKind::PatWithOr { .. } => {
                match &token.kind {
                token::Ident(..) |                          // box, ref, mut, and other identifiers (can stricten)
                token::OpenDelim(Delimiter::Parenthesis) |  // tuple pattern
                token::OpenDelim(Delimiter::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)
                // leading vert `|` or-pattern
                token::BinOp(token::Or) =>  matches!(kind, NonterminalKind::PatWithOr {..}),
                token::Interpolated(nt) => may_be_ident(nt),
                _ => false,
            }
            }
            NonterminalKind::Lifetime => match &token.kind {
                token::Lifetime(_) => true,
                token::Interpolated(nt) => {
                    matches!(**nt, token::NtLifetime(_))
                }
                _ => false,
            },
            NonterminalKind::TT | NonterminalKind::Item | NonterminalKind::Stmt => {
                !matches!(token.kind, token::CloseDelim(_))
            }
        }
    }

    /// Parse a non-terminal (e.g. MBE `:pat` or `:ident`). Inlined because there is only one call
    /// site.
    #[inline]
    pub fn parse_nonterminal(&mut self, kind: NonterminalKind) -> PResult<'a, NtOrTt> {
        // 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.
        let mut nt = match kind {
            // Note that TT is treated differently to all the others.
            NonterminalKind::TT => return Ok(NtOrTt::Tt(self.parse_token_tree())),
            NonterminalKind::Item => match self.parse_item(ForceCollect::Yes)? {
                Some(item) => token::NtItem(item),
                None => {
                    return Err(UnexpectedNonterminal::Item(self.token.span)
                               .into_diagnostic(&self.sess.span_diagnostic));
                }
            },
            NonterminalKind::Block => {
                // While a block *expression* may have attributes (e.g. `#[my_attr] { ... }`),
                // the ':block' matcher does not support them
                token::NtBlock(self.collect_tokens_no_attrs(|this| this.parse_block())?)
            }
            NonterminalKind::Stmt => match self.parse_stmt(ForceCollect::Yes)? {
                Some(s) => token::NtStmt(P(s)),
                None => {
                    return Err(UnexpectedNonterminal::Statement(self.token.span)
                               .into_diagnostic(&self.sess.span_diagnostic));
                }
            },
            NonterminalKind::PatParam { .. } | NonterminalKind::PatWithOr { .. } => {
                token::NtPat(self.collect_tokens_no_attrs(|this| match kind {
                    NonterminalKind::PatParam { .. } => this.parse_pat_no_top_alt(None),
                    NonterminalKind::PatWithOr { .. } => this.parse_pat_allow_top_alt(
                        None,
                        RecoverComma::No,
                        RecoverColon::No,
                        CommaRecoveryMode::EitherTupleOrPipe,
                    ),
                    _ => unreachable!(),
                })?)
            }

            NonterminalKind::Expr => token::NtExpr(self.parse_expr_force_collect()?),
            NonterminalKind::Literal => {
                // The `:literal` matcher does not support attributes
                token::NtLiteral(
                    self.collect_tokens_no_attrs(|this| this.parse_literal_maybe_minus())?,
                )
            }

            NonterminalKind::Ty => token::NtTy(
                self.collect_tokens_no_attrs(|this| this.parse_no_question_mark_recover())?,
            ),

            // 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)
            }
            NonterminalKind::Ident => {
                return Err(UnexpectedNonterminal::Ident {
                    span: self.token.span,
                    token: self.token.clone(),
                }.into_diagnostic(&self.sess.span_diagnostic));
            }
            NonterminalKind::Path => token::NtPath(
                P(self.collect_tokens_no_attrs(|this| this.parse_path(PathStyle::Type))?),
            ),
            NonterminalKind::Meta => token::NtMeta(P(self.parse_attr_item(true)?)),
            NonterminalKind::Vis => token::NtVis(
                P(self.collect_tokens_no_attrs(|this| this.parse_visibility(FollowedByType::Yes))?),
            ),
            NonterminalKind::Lifetime => {
                if self.check_lifetime() {
                    token::NtLifetime(self.expect_lifetime().ident)
                } else {
                    return Err(UnexpectedNonterminal::Lifetime {
                        span: self.token.span,
                        token: self.token.clone(),
                    }.into_diagnostic(&self.sess.span_diagnostic));
                }
            }
        };

        // If tokens are supported at all, they should be collected.
        if matches!(nt.tokens_mut(), Some(None)) {
            panic!(
                "Missing tokens for nt {:?} at {:?}: {:?}",
                nt,
                nt.span(),
                pprust::nonterminal_to_string(&nt)
            );
        }

        Ok(NtOrTt::Nt(nt))
    }
}

/// 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)
}