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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 => {
let (mut block, tokens) = self.collect_tokens(|this| this.parse_block())?;
// We have have eaten an NtBlock, which could already have tokens
if block.tokens.is_none() {
block.tokens = Some(tokens);
}
token::NtBlock(block)
}
NonterminalKind::Stmt => {
let (stmt, tokens) = self.collect_tokens(|this| this.parse_stmt())?;
match stmt {
Some(mut s) => {
if s.tokens.is_none() {
s.tokens = Some(tokens);
}
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 => {
let (mut lit, tokens) =
self.collect_tokens(|this| this.parse_literal_maybe_minus())?;
// We have have eaten a nonterminal, which could already have tokens
if lit.tokens.is_none() {
lit.tokens = Some(tokens);
}
token::NtLiteral(lit)
}
NonterminalKind::Ty => {
let (mut ty, tokens) = self.collect_tokens(|this| this.parse_ty())?;
// We have an eaten an NtTy, which could already have tokens
if ty.tokens.is_none() {
ty.tokens = Some(tokens);
}
token::NtTy(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 => {
let (mut path, tokens) =
self.collect_tokens(|this| this.parse_path(PathStyle::Type))?;
// We have have eaten an NtPath, which could already have tokens
if path.tokens.is_none() {
path.tokens = Some(tokens);
}
token::NtPath(path)
}
NonterminalKind::Meta => {
let (mut attr, tokens) = self.collect_tokens(|this| this.parse_attr_item())?;
// We may have eaten a nonterminal, which could already have tokens
if attr.tokens.is_none() {
attr.tokens = Some(tokens);
}
token::NtMeta(P(attr))
}
NonterminalKind::TT => token::NtTT(self.parse_token_tree()),
NonterminalKind::Vis => {
let (mut vis, tokens) =
self.collect_tokens(|this| this.parse_visibility(FollowedByType::Yes))?;
// We may have etan an `NtVis`, which could already have tokens
if vis.tokens.is_none() {
vis.tokens = Some(tokens);
}
token::NtVis(vis)
}
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)
}