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use rustc_ast::ptr::P;
use rustc_ast::token::{self, Nonterminal, NonterminalKind, Token};
use rustc_ast::AstLike;
use rustc_ast_pretty::pprust;
use rustc_errors::PResult;
use rustc_span::symbol::{kw, Ident};
use crate::parser::pat::RecoverComma;
use crate::parser::{FollowedByType, ForceCollect, 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)
// 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(token::Brace) => true,
token::Interpolated(ref 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(ref 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(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)
// leading vert `|` or-pattern
token::BinOp(token::Or) => matches!(kind, NonterminalKind::PatWithOr {..}),
token::Interpolated(ref nt) => may_be_ident(nt),
_ => false,
}
}
NonterminalKind::Lifetime => match token.kind {
token::Lifetime(_) => true,
token::Interpolated(ref nt) => {
matches!(**nt, token::NtLifetime(_) | token::NtTT(_))
}
_ => false,
},
NonterminalKind::TT | NonterminalKind::Item | NonterminalKind::Stmt => {
!matches!(token.kind, token::CloseDelim(_))
}
}
}
/// Parse a non-terminal (e.g. MBE `:pat` or `:ident`).
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.
let mut nt = match kind {
NonterminalKind::Item => match self.parse_item(ForceCollect::Yes)? {
Some(item) => token::NtItem(item),
None => {
return Err(self.struct_span_err(self.token.span, "expected an item keyword"));
}
},
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(s),
None => {
return Err(self.struct_span_err(self.token.span, "expected a statement"));
}
},
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)
}
_ => 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_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.collect_tokens_no_attrs(|this| this.parse_path(PathStyle::Type))?,
),
NonterminalKind::Meta => token::NtMeta(P(self.parse_attr_item(true)?)),
NonterminalKind::TT => token::NtTT(self.parse_token_tree()),
NonterminalKind::Vis => token::NtVis(
self.collect_tokens_no_attrs(|this| this.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));
}
}
};
// 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(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)
}