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improve diagnostics for lifetime after &mut

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SNCPlay42 2020-06-21 21:37:17 +01:00 • committed by Mark Rousskov
parent 90b1f5ae59
commit 4de9a53d98
3 changed files with 101 additions and 1 deletions
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28
compiler/rustc_parse/src/parser/ty.rs
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@ -276,8 +276,34 @@ impl<'a> Parser<'a> {
}
fn parse_borrowed_pointee(&mut self) -> PResult<'a, TyKind> {
let opt_lifetime = if self.check_lifetime() { Some(self.expect_lifetime()) } else { None };
let and_span = self.prev_token.span;
let mut opt_lifetime =
if self.check_lifetime() { Some(self.expect_lifetime()) } else { None };
let mutbl = self.parse_mutability();
if self.token.is_lifetime() && mutbl == Mutability::Mut && opt_lifetime.is_none() {
// A lifetime is invalid here: it would be part of a bare trait bound, which requires
// it to be followed by a plus, but we disallow plus in the pointee type.
// So we can handle this case as an error here, and suggest `'a mut`.
// If there *is* a plus next though, handling the error later provides better suggestions
// (like adding parentheses)
if !self.look_ahead(1, |t| t.is_like_plus()) {
let lifetime_span = self.token.span;
let span = and_span.to(lifetime_span);
let mut err = self.struct_span_err(span, "lifetime must precede `mut`");
if let Ok(lifetime_src) = self.span_to_snippet(lifetime_span) {
err.span_suggestion(
span,
"place the lifetime before `mut`",
format!("&{} mut", lifetime_src),
Applicability::MaybeIncorrect,
);
}
err.emit();
opt_lifetime = Some(self.expect_lifetime());
}
}
let ty = self.parse_ty_no_plus()?;
Ok(TyKind::Rptr(opt_lifetime, MutTy { ty, mutbl }))
}