rustc_parse/parser/
nonterminal.rs

1use rustc_ast::ptr::P;
2use rustc_ast::token::NtExprKind::*;
3use rustc_ast::token::NtPatKind::*;
4use rustc_ast::token::{self, InvisibleOrigin, MetaVarKind, NonterminalKind, Token};
5use rustc_errors::PResult;
6use rustc_span::{Ident, kw};
7
8use crate::errors::UnexpectedNonterminal;
9use crate::parser::pat::{CommaRecoveryMode, RecoverColon, RecoverComma};
10use crate::parser::{FollowedByType, ForceCollect, ParseNtResult, Parser, PathStyle};
11
12impl<'a> Parser<'a> {
13    /// Checks whether a non-terminal may begin with a particular token.
14    ///
15    /// Returning `false` is a *stability guarantee* that such a matcher will *never* begin with
16    /// that token. Be conservative (return true) if not sure. Inlined because it has a single call
17    /// site.
18    #[inline]
19    pub fn nonterminal_may_begin_with(kind: NonterminalKind, token: &Token) -> bool {
20        /// Checks whether the non-terminal may contain a single (non-keyword) identifier.
21        fn may_be_ident(kind: MetaVarKind) -> bool {
22            match kind {
23                MetaVarKind::Stmt
24                | MetaVarKind::Pat(_)
25                | MetaVarKind::Expr { .. }
26                | MetaVarKind::Ty { .. }
27                | MetaVarKind::Literal // `true`, `false`
28                | MetaVarKind::Meta { .. }
29                | MetaVarKind::Path => true,
30
31                MetaVarKind::Item
32                | MetaVarKind::Block
33                | MetaVarKind::Vis => false,
34
35                MetaVarKind::Ident
36                | MetaVarKind::Lifetime
37                | MetaVarKind::TT => unreachable!(),
38            }
39        }
40
41        match kind {
42            // `expr_2021` and earlier
43            NonterminalKind::Expr(Expr2021 { .. }) => {
44                token.can_begin_expr()
45                // This exception is here for backwards compatibility.
46                && !token.is_keyword(kw::Let)
47                // This exception is here for backwards compatibility.
48                && !token.is_keyword(kw::Const)
49            }
50            // Current edition expressions
51            NonterminalKind::Expr(Expr) => {
52                // In Edition 2024, `_` is considered an expression, so we
53                // need to allow it here because `token.can_begin_expr()` does
54                // not consider `_` to be an expression.
55                //
56                // Because `can_begin_expr` is used elsewhere, we need to reduce
57                // the scope of where the `_` is considered an expression to
58                // just macro parsing code.
59                (token.can_begin_expr() || token.is_keyword(kw::Underscore))
60                // This exception is here for backwards compatibility.
61                && !token.is_keyword(kw::Let)
62            }
63            NonterminalKind::Ty => token.can_begin_type(),
64            NonterminalKind::Ident => get_macro_ident(token).is_some(),
65            NonterminalKind::Literal => token.can_begin_literal_maybe_minus(),
66            NonterminalKind::Vis => match token.kind {
67                // The follow-set of :vis + "priv" keyword + interpolated/metavar-expansion.
68                token::Comma
69                | token::Ident(..)
70                | token::NtIdent(..)
71                | token::NtLifetime(..)
72                | token::OpenInvisible(InvisibleOrigin::MetaVar(_)) => true,
73                _ => token.can_begin_type(),
74            },
75            NonterminalKind::Block => match &token.kind {
76                token::OpenBrace => true,
77                token::NtLifetime(..) => true,
78                token::OpenInvisible(InvisibleOrigin::MetaVar(k)) => match k {
79                    MetaVarKind::Block
80                    | MetaVarKind::Stmt
81                    | MetaVarKind::Expr { .. }
82                    | MetaVarKind::Literal => true,
83                    MetaVarKind::Item
84                    | MetaVarKind::Pat(_)
85                    | MetaVarKind::Ty { .. }
86                    | MetaVarKind::Meta { .. }
87                    | MetaVarKind::Path
88                    | MetaVarKind::Vis => false,
89                    MetaVarKind::Lifetime | MetaVarKind::Ident | MetaVarKind::TT => {
90                        unreachable!()
91                    }
92                },
93                _ => false,
94            },
95            NonterminalKind::Path | NonterminalKind::Meta => match &token.kind {
96                token::PathSep | token::Ident(..) | token::NtIdent(..) => true,
97                token::OpenInvisible(InvisibleOrigin::MetaVar(kind)) => may_be_ident(*kind),
98                _ => false,
99            },
100            NonterminalKind::Pat(pat_kind) => token.can_begin_pattern(pat_kind),
101            NonterminalKind::Lifetime => match &token.kind {
102                token::Lifetime(..) | token::NtLifetime(..) => true,
103                _ => false,
104            },
105            NonterminalKind::TT | NonterminalKind::Item | NonterminalKind::Stmt => {
106                token.kind.close_delim().is_none()
107            }
108        }
109    }
110
111    /// Parse a non-terminal (e.g. MBE `:pat` or `:ident`). Inlined because there is only one call
112    /// site.
113    #[inline]
114    pub fn parse_nonterminal(&mut self, kind: NonterminalKind) -> PResult<'a, ParseNtResult> {
115        // A `macro_rules!` invocation may pass a captured item/expr to a proc-macro,
116        // which requires having captured tokens available. Since we cannot determine
117        // in advance whether or not a proc-macro will be (transitively) invoked,
118        // we always capture tokens for any nonterminal that needs them.
119        match kind {
120            // Note that TT is treated differently to all the others.
121            NonterminalKind::TT => Ok(ParseNtResult::Tt(self.parse_token_tree())),
122            NonterminalKind::Item => match self.parse_item(ForceCollect::Yes)? {
123                Some(item) => Ok(ParseNtResult::Item(item)),
124                None => Err(self.dcx().create_err(UnexpectedNonterminal::Item(self.token.span))),
125            },
126            NonterminalKind::Block => {
127                // While a block *expression* may have attributes (e.g. `#[my_attr] { ... }`),
128                // the ':block' matcher does not support them
129                Ok(ParseNtResult::Block(self.collect_tokens_no_attrs(|this| this.parse_block())?))
130            }
131            NonterminalKind::Stmt => match self.parse_stmt(ForceCollect::Yes)? {
132                Some(stmt) => Ok(ParseNtResult::Stmt(P(stmt))),
133                None => {
134                    Err(self.dcx().create_err(UnexpectedNonterminal::Statement(self.token.span)))
135                }
136            },
137            NonterminalKind::Pat(pat_kind) => Ok(ParseNtResult::Pat(
138                self.collect_tokens_no_attrs(|this| match pat_kind {
139                    PatParam { .. } => this.parse_pat_no_top_alt(None, None),
140                    PatWithOr => this.parse_pat_no_top_guard(
141                        None,
142                        RecoverComma::No,
143                        RecoverColon::No,
144                        CommaRecoveryMode::EitherTupleOrPipe,
145                    ),
146                })?,
147                pat_kind,
148            )),
149            NonterminalKind::Expr(expr_kind) => {
150                Ok(ParseNtResult::Expr(self.parse_expr_force_collect()?, expr_kind))
151            }
152            NonterminalKind::Literal => {
153                // The `:literal` matcher does not support attributes.
154                Ok(ParseNtResult::Literal(
155                    self.collect_tokens_no_attrs(|this| this.parse_literal_maybe_minus())?,
156                ))
157            }
158            NonterminalKind::Ty => Ok(ParseNtResult::Ty(
159                self.collect_tokens_no_attrs(|this| this.parse_ty_no_question_mark_recover())?,
160            )),
161            // This could be handled like a token, since it is one.
162            NonterminalKind::Ident => {
163                if let Some((ident, is_raw)) = get_macro_ident(&self.token) {
164                    self.bump();
165                    Ok(ParseNtResult::Ident(ident, is_raw))
166                } else {
167                    Err(self.dcx().create_err(UnexpectedNonterminal::Ident {
168                        span: self.token.span,
169                        token: self.token,
170                    }))
171                }
172            }
173            NonterminalKind::Path => Ok(ParseNtResult::Path(P(
174                self.collect_tokens_no_attrs(|this| this.parse_path(PathStyle::Type))?
175            ))),
176            NonterminalKind::Meta => {
177                Ok(ParseNtResult::Meta(P(self.parse_attr_item(ForceCollect::Yes)?)))
178            }
179            NonterminalKind::Vis => {
180                Ok(ParseNtResult::Vis(P(self
181                    .collect_tokens_no_attrs(|this| this.parse_visibility(FollowedByType::Yes))?)))
182            }
183            NonterminalKind::Lifetime => {
184                // We want to keep `'keyword` parsing, just like `keyword` is still
185                // an ident for nonterminal purposes.
186                if let Some((ident, is_raw)) = self.token.lifetime() {
187                    self.bump();
188                    Ok(ParseNtResult::Lifetime(ident, is_raw))
189                } else {
190                    Err(self.dcx().create_err(UnexpectedNonterminal::Lifetime {
191                        span: self.token.span,
192                        token: self.token,
193                    }))
194                }
195            }
196        }
197    }
198}
199
200/// The token is an identifier, but not `_`.
201/// We prohibit passing `_` to macros expecting `ident` for now.
202fn get_macro_ident(token: &Token) -> Option<(Ident, token::IdentIsRaw)> {
203    token.ident().filter(|(ident, _)| ident.name != kw::Underscore)
204}
rustc_parse/parser/nonterminal.rs

rustc_parse/parser/
nonterminal.rs
