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rust/compiler/rustc_parse/src/parser/ty.rs

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use super::{Parser, PathStyle, TokenType};
use crate::{maybe_recover_from_interpolated_ty_qpath, maybe_whole};
use rustc_ast::ptr::P;
use rustc_ast::token::{self, Delimiter, Token, TokenKind};
use rustc_ast::{
self as ast, BareFnTy, FnRetTy, GenericBound, GenericBounds, GenericParam, Generics, Lifetime,
MacCall, MutTy, Mutability, PolyTraitRef, TraitBoundModifier, TraitObjectSyntax, Ty, TyKind,
};
use rustc_errors::{pluralize, struct_span_err, Applicability, PResult};
use rustc_span::source_map::Span;
use rustc_span::symbol::{kw, sym};
/// Any `?` or `~const` modifiers that appear at the start of a bound.
struct BoundModifiers {
/// `?Trait`.
maybe: Option<Span>,
/// `~const Trait`.
maybe_const: Option<Span>,
}
impl BoundModifiers {
fn to_trait_bound_modifier(&self) -> TraitBoundModifier {
match (self.maybe, self.maybe_const) {
(None, None) => TraitBoundModifier::None,
(Some(_), None) => TraitBoundModifier::Maybe,
(None, Some(_)) => TraitBoundModifier::MaybeConst,
(Some(_), Some(_)) => TraitBoundModifier::MaybeConstMaybe,
}
}
}
#[derive(Copy, Clone, PartialEq)]
pub(super) enum AllowPlus {
Yes,
No,
}
#[derive(PartialEq)]
pub(super) enum RecoverQPath {
Yes,
No,
}
pub(super) enum RecoverQuestionMark {
Yes,
No,
}
/// Signals whether parsing a type should recover `->`.
///
/// More specifically, when parsing a function like:
/// ```compile_fail
/// fn foo() => u8 { 0 }
/// fn bar(): u8 { 0 }
/// ```
/// The compiler will try to recover interpreting `foo() => u8` as `foo() -> u8` when calling
/// `parse_ty` with anything except `RecoverReturnSign::No`, and it will try to recover `bar(): u8`
/// as `bar() -> u8` when passing `RecoverReturnSign::Yes` to `parse_ty`
#[derive(Copy, Clone, PartialEq)]
pub(super) enum RecoverReturnSign {
Yes,
OnlyFatArrow,
No,
}
impl RecoverReturnSign {
/// [RecoverReturnSign::Yes] allows for recovering `fn foo() => u8` and `fn foo(): u8`,
/// [RecoverReturnSign::OnlyFatArrow] allows for recovering only `fn foo() => u8` (recovering
/// colons can cause problems when parsing where clauses), and
/// [RecoverReturnSign::No] doesn't allow for any recovery of the return type arrow
fn can_recover(self, token: &TokenKind) -> bool {
match self {
Self::Yes => matches!(token, token::FatArrow | token::Colon),
Self::OnlyFatArrow => matches!(token, token::FatArrow),
Self::No => false,
}
}
}
// Is `...` (`CVarArgs`) legal at this level of type parsing?
#[derive(PartialEq)]
enum AllowCVariadic {
Yes,
No,
}
/// Returns `true` if `IDENT t` can start a type -- `IDENT::a::b`, `IDENT<u8, u8>`,
/// `IDENT<<u8 as Trait>::AssocTy>`.
///
/// Types can also be of the form `IDENT(u8, u8) -> u8`, however this assumes
/// that `IDENT` is not the ident of a fn trait.
fn can_continue_type_after_non_fn_ident(t: &Token) -> bool {
t == &token::ModSep || t == &token::Lt || t == &token::BinOp(token::Shl)
}
impl<'a> Parser<'a> {
/// Parses a type.
pub fn parse_ty(&mut self) -> PResult<'a, P<Ty>> {
self.parse_ty_common(
AllowPlus::Yes,
AllowCVariadic::No,
RecoverQPath::Yes,
RecoverReturnSign::Yes,
None,
RecoverQuestionMark::Yes,
)
}
pub(super) fn parse_ty_with_generics_recovery(
&mut self,
ty_params: &Generics,
) -> PResult<'a, P<Ty>> {
self.parse_ty_common(
AllowPlus::Yes,
AllowCVariadic::No,
RecoverQPath::Yes,
RecoverReturnSign::Yes,
Some(ty_params),
RecoverQuestionMark::Yes,
)
}
/// Parse a type suitable for a function or function pointer parameter.
/// The difference from `parse_ty` is that this version allows `...`
/// (`CVarArgs`) at the top level of the type.
pub(super) fn parse_ty_for_param(&mut self) -> PResult<'a, P<Ty>> {
self.parse_ty_common(
AllowPlus::Yes,
AllowCVariadic::Yes,
RecoverQPath::Yes,
RecoverReturnSign::Yes,
None,
RecoverQuestionMark::Yes,
)
}
/// Parses a type in restricted contexts where `+` is not permitted.
///
/// Example 1: `&'a TYPE`
/// `+` is prohibited to maintain operator priority (P(+) < P(&)).
/// Example 2: `value1 as TYPE + value2`
/// `+` is prohibited to avoid interactions with expression grammar.
pub(super) fn parse_ty_no_plus(&mut self) -> PResult<'a, P<Ty>> {
self.parse_ty_common(
AllowPlus::No,
AllowCVariadic::No,
RecoverQPath::Yes,
RecoverReturnSign::Yes,
None,
RecoverQuestionMark::Yes,
)
}
/// Parses a type following an `as` cast. Similar to `parse_ty_no_plus`, but signaling origin
/// for better diagnostics involving `?`.
pub(super) fn parse_as_cast_ty(&mut self) -> PResult<'a, P<Ty>> {
self.parse_ty_common(
AllowPlus::No,
AllowCVariadic::No,
RecoverQPath::Yes,
RecoverReturnSign::Yes,
None,
RecoverQuestionMark::No,
)
}
pub(super) fn parse_no_question_mark_recover(&mut self) -> PResult<'a, P<Ty>> {
self.parse_ty_common(
AllowPlus::Yes,
AllowCVariadic::No,
RecoverQPath::Yes,
RecoverReturnSign::Yes,
None,
RecoverQuestionMark::No,
)
}
/// Parse a type without recovering `:` as `->` to avoid breaking code such as `where fn() : for<'a>`
pub(super) fn parse_ty_for_where_clause(&mut self) -> PResult<'a, P<Ty>> {
self.parse_ty_common(
AllowPlus::Yes,
AllowCVariadic::Yes,
RecoverQPath::Yes,
RecoverReturnSign::OnlyFatArrow,
None,
RecoverQuestionMark::Yes,
)
}
/// Parses an optional return type `[ -> TY ]` in a function declaration.
pub(super) fn parse_ret_ty(
&mut self,
allow_plus: AllowPlus,
recover_qpath: RecoverQPath,
recover_return_sign: RecoverReturnSign,
) -> PResult<'a, FnRetTy> {
Ok(if self.eat(&token::RArrow) {
// FIXME(Centril): Can we unconditionally `allow_plus`?
let ty = self.parse_ty_common(
allow_plus,
AllowCVariadic::No,
recover_qpath,
recover_return_sign,
None,
RecoverQuestionMark::Yes,
)?;
FnRetTy::Ty(ty)
} else if recover_return_sign.can_recover(&self.token.kind) {
// Don't `eat` to prevent `=>` from being added as an expected token which isn't
// actually expected and could only confuse users
self.bump();
self.struct_span_err(self.prev_token.span, "return types are denoted using `->`")
.span_suggestion_short(
self.prev_token.span,
"use `->` instead",
"->",
Applicability::MachineApplicable,
)
.emit();
let ty = self.parse_ty_common(
allow_plus,
AllowCVariadic::No,
recover_qpath,
recover_return_sign,
None,
RecoverQuestionMark::Yes,
)?;
FnRetTy::Ty(ty)
} else {
FnRetTy::Default(self.token.span.shrink_to_lo())
})
}
fn parse_ty_common(
&mut self,
allow_plus: AllowPlus,
allow_c_variadic: AllowCVariadic,
recover_qpath: RecoverQPath,
recover_return_sign: RecoverReturnSign,
ty_generics: Option<&Generics>,
recover_question_mark: RecoverQuestionMark,
) -> PResult<'a, P<Ty>> {
let allow_qpath_recovery = recover_qpath == RecoverQPath::Yes;
maybe_recover_from_interpolated_ty_qpath!(self, allow_qpath_recovery);
maybe_whole!(self, NtTy, |x| x);
let lo = self.token.span;
let mut impl_dyn_multi = false;
let kind = if self.check(&token::OpenDelim(Delimiter::Parenthesis)) {
self.parse_ty_tuple_or_parens(lo, allow_plus)?
} else if self.eat(&token::Not) {
// Never type `!`
TyKind::Never
} else if self.eat(&token::BinOp(token::Star)) {
self.parse_ty_ptr()?
} else if self.eat(&token::OpenDelim(Delimiter::Bracket)) {
self.parse_array_or_slice_ty()?
} else if self.check(&token::BinOp(token::And)) || self.check(&token::AndAnd) {
// Reference
self.expect_and()?;
self.parse_borrowed_pointee()?
} else if self.eat_keyword_noexpect(kw::Typeof) {
self.parse_typeof_ty()?
} else if self.eat_keyword(kw::Underscore) {
// A type to be inferred `_`
TyKind::Infer
} else if self.check_fn_front_matter(false) {
// Function pointer type
self.parse_ty_bare_fn(lo, Vec::new(), recover_return_sign)?
} else if self.check_keyword(kw::For) {
// Function pointer type or bound list (trait object type) starting with a poly-trait.
// `for<'lt> [unsafe] [extern "ABI"] fn (&'lt S) -> T`
// `for<'lt> Trait1<'lt> + Trait2 + 'a`
let lifetime_defs = self.parse_late_bound_lifetime_defs()?;
if self.check_fn_front_matter(false) {
self.parse_ty_bare_fn(lo, lifetime_defs, recover_return_sign)?
} else {
let path = self.parse_path(PathStyle::Type)?;
let parse_plus = allow_plus == AllowPlus::Yes && self.check_plus();
self.parse_remaining_bounds_path(lifetime_defs, path, lo, parse_plus)?
}
} else if self.eat_keyword(kw::Impl) {
self.parse_impl_ty(&mut impl_dyn_multi)?
} else if self.is_explicit_dyn_type() {
self.parse_dyn_ty(&mut impl_dyn_multi)?
} else if self.eat_lt() {
// Qualified path
let (qself, path) = self.parse_qpath(PathStyle::Type)?;
TyKind::Path(Some(qself), path)
} else if self.check_path() {
self.parse_path_start_ty(lo, allow_plus, ty_generics)?
} else if self.can_begin_bound() {
self.parse_bare_trait_object(lo, allow_plus)?
} else if self.eat(&token::DotDotDot) {
if allow_c_variadic == AllowCVariadic::Yes {
TyKind::CVarArgs
} else {
// FIXME(Centril): Should we just allow `...` syntactically
// anywhere in a type and use semantic restrictions instead?
self.error_illegal_c_varadic_ty(lo);
TyKind::Err
}
} else {
let msg = format!("expected type, found {}", super::token_descr(&self.token));
let mut err = self.struct_span_err(self.token.span, &msg);
err.span_label(self.token.span, "expected type");
self.maybe_annotate_with_ascription(&mut err, true);
return Err(err);
};
let span = lo.to(self.prev_token.span);
let mut ty = self.mk_ty(span, kind);
// Try to recover from use of `+` with incorrect priority.
if matches!(allow_plus, AllowPlus::Yes) {
self.maybe_recover_from_bad_type_plus(&ty)?;
} else {
self.maybe_report_ambiguous_plus(impl_dyn_multi, &ty);
}
if let RecoverQuestionMark::Yes = recover_question_mark {
ty = self.maybe_recover_from_question_mark(ty);
}
if allow_qpath_recovery { self.maybe_recover_from_bad_qpath(ty) } else { Ok(ty) }
}
/// Parses either:
/// - `(TYPE)`, a parenthesized type.
/// - `(TYPE,)`, a tuple with a single field of type TYPE.
fn parse_ty_tuple_or_parens(&mut self, lo: Span, allow_plus: AllowPlus) -> PResult<'a, TyKind> {
let mut trailing_plus = false;
let (ts, trailing) = self.parse_paren_comma_seq(|p| {
let ty = p.parse_ty()?;
trailing_plus = p.prev_token.kind == TokenKind::BinOp(token::Plus);
Ok(ty)
})?;
if ts.len() == 1 && !trailing {
let ty = ts.into_iter().next().unwrap().into_inner();
let maybe_bounds = allow_plus == AllowPlus::Yes && self.token.is_like_plus();
match ty.kind {
// `(TY_BOUND_NOPAREN) + BOUND + ...`.
TyKind::Path(None, path) if maybe_bounds => {
self.parse_remaining_bounds_path(Vec::new(), path, lo, true)
}
TyKind::TraitObject(bounds, TraitObjectSyntax::None)
if maybe_bounds && bounds.len() == 1 && !trailing_plus =>
{
self.parse_remaining_bounds(bounds, true)
}
// `(TYPE)`
_ => Ok(TyKind::Paren(P(ty))),
}
} else {
Ok(TyKind::Tup(ts))
}
}
fn parse_bare_trait_object(&mut self, lo: Span, allow_plus: AllowPlus) -> PResult<'a, TyKind> {
let lt_no_plus = self.check_lifetime() && !self.look_ahead(1, |t| t.is_like_plus());
let bounds = self.parse_generic_bounds_common(allow_plus, None)?;
if lt_no_plus {
self.struct_span_err(lo, "lifetime in trait object type must be followed by `+`")
.emit();
}
Ok(TyKind::TraitObject(bounds, TraitObjectSyntax::None))
}
fn parse_remaining_bounds_path(
&mut self,
generic_params: Vec<GenericParam>,
path: ast::Path,
lo: Span,
parse_plus: bool,
) -> PResult<'a, TyKind> {
let poly_trait_ref = PolyTraitRef::new(generic_params, path, lo.to(self.prev_token.span));
let bounds = vec![GenericBound::Trait(poly_trait_ref, TraitBoundModifier::None)];
self.parse_remaining_bounds(bounds, parse_plus)
}
/// Parse the remainder of a bare trait object type given an already parsed list.
fn parse_remaining_bounds(
&mut self,
mut bounds: GenericBounds,
plus: bool,
) -> PResult<'a, TyKind> {
if plus {
self.eat_plus(); // `+`, or `+=` gets split and `+` is discarded
bounds.append(&mut self.parse_generic_bounds(Some(self.prev_token.span))?);
}
Ok(TyKind::TraitObject(bounds, TraitObjectSyntax::None))
}
/// Parses a raw pointer type: `*[const | mut] $type`.
fn parse_ty_ptr(&mut self) -> PResult<'a, TyKind> {
let mutbl = self.parse_const_or_mut().unwrap_or_else(|| {
let span = self.prev_token.span;
self.struct_span_err(span, "expected `mut` or `const` keyword in raw pointer type")
.span_suggestions(
span.shrink_to_hi(),
"add `mut` or `const` here",
["mut ".to_string(), "const ".to_string()].into_iter(),
Applicability::HasPlaceholders,
)
.emit();
Mutability::Not
});
let ty = self.parse_ty_no_plus()?;
Ok(TyKind::Ptr(MutTy { ty, mutbl }))
}
/// Parses an array (`[TYPE; EXPR]`) or slice (`[TYPE]`) type.
/// The opening `[` bracket is already eaten.
fn parse_array_or_slice_ty(&mut self) -> PResult<'a, TyKind> {
let elt_ty = match self.parse_ty() {
Ok(ty) => ty,
Err(mut err)
if self.look_ahead(1, |t| t.kind == token::CloseDelim(Delimiter::Bracket))
| self.look_ahead(1, |t| t.kind == token::Semi) =>
{
// Recover from `[LIT; EXPR]` and `[LIT]`
self.bump();
err.emit();
self.mk_ty(self.prev_token.span, TyKind::Err)
}
Err(err) => return Err(err),
};
let ty = if self.eat(&token::Semi) {
let mut length = self.parse_anon_const_expr()?;
if let Err(e) = self.expect(&token::CloseDelim(Delimiter::Bracket)) {
// Try to recover from `X<Y, ...>` when `X::<Y, ...>` works
self.check_mistyped_turbofish_with_multiple_type_params(e, &mut length.value)?;
self.expect(&token::CloseDelim(Delimiter::Bracket))?;
}
TyKind::Array(elt_ty, length)
} else {
self.expect(&token::CloseDelim(Delimiter::Bracket))?;
TyKind::Slice(elt_ty)
};
Ok(ty)
}
fn parse_borrowed_pointee(&mut self) -> PResult<'a, TyKind> {
let and_span = self.prev_token.span;
let mut opt_lifetime =
if self.check_lifetime() { Some(self.expect_lifetime()) } else { None };
let mut 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());
}
} else if self.token.is_keyword(kw::Dyn)
&& mutbl == Mutability::Not
&& self.look_ahead(1, |t| t.is_keyword(kw::Mut))
{
// We have `&dyn mut ...`, which is invalid and should be `&mut dyn ...`.
let span = and_span.to(self.look_ahead(1, |t| t.span));
let mut err = self.struct_span_err(span, "`mut` must precede `dyn`");
err.span_suggestion(
span,
"place `mut` before `dyn`",
"&mut dyn",
Applicability::MachineApplicable,
);
err.emit();
// Recovery
mutbl = Mutability::Mut;
let (dyn_tok, dyn_tok_sp) = (self.token.clone(), self.token_spacing);
self.bump();
self.bump_with((dyn_tok, dyn_tok_sp));
}
let ty = self.parse_ty_no_plus()?;
Ok(TyKind::Rptr(opt_lifetime, MutTy { ty, mutbl }))
}
// Parses the `typeof(EXPR)`.
// To avoid ambiguity, the type is surrounded by parentheses.
fn parse_typeof_ty(&mut self) -> PResult<'a, TyKind> {
self.expect(&token::OpenDelim(Delimiter::Parenthesis))?;
let expr = self.parse_anon_const_expr()?;
self.expect(&token::CloseDelim(Delimiter::Parenthesis))?;
Ok(TyKind::Typeof(expr))
}
/// Parses a function pointer type (`TyKind::BareFn`).
/// ```ignore (illustrative)
/// [unsafe] [extern "ABI"] fn (S) -> T
/// // ^~~~~^ ^~~~^ ^~^ ^
/// // | | | |
/// // | | | Return type
/// // Function Style ABI Parameter types
/// ```
/// We actually parse `FnHeader FnDecl`, but we error on `const` and `async` qualifiers.
fn parse_ty_bare_fn(
&mut self,
lo: Span,
params: Vec<GenericParam>,
recover_return_sign: RecoverReturnSign,
) -> PResult<'a, TyKind> {
let inherited_vis = rustc_ast::Visibility {
span: rustc_span::DUMMY_SP,
kind: rustc_ast::VisibilityKind::Inherited,
tokens: None,
};
let span_start = self.token.span;
let ast::FnHeader { ext, unsafety, constness, asyncness } =
self.parse_fn_front_matter(&inherited_vis)?;
let decl = self.parse_fn_decl(|_| false, AllowPlus::No, recover_return_sign)?;
let whole_span = lo.to(self.prev_token.span);
if let ast::Const::Yes(span) = constness {
// If we ever start to allow `const fn()`, then update
// feature gating for `#![feature(const_extern_fn)]` to
// cover it.
self.error_fn_ptr_bad_qualifier(whole_span, span, "const");
}
if let ast::Async::Yes { span, .. } = asyncness {
self.error_fn_ptr_bad_qualifier(whole_span, span, "async");
}
let decl_span = span_start.to(self.token.span);
Ok(TyKind::BareFn(P(BareFnTy { ext, unsafety, generic_params: params, decl, decl_span })))
}
/// Emit an error for the given bad function pointer qualifier.
fn error_fn_ptr_bad_qualifier(&self, span: Span, qual_span: Span, qual: &str) {
self.struct_span_err(span, &format!("an `fn` pointer type cannot be `{}`", qual))
.span_label(qual_span, format!("`{}` because of this", qual))
.span_suggestion_short(
qual_span,
&format!("remove the `{}` qualifier", qual),
"",
Applicability::MaybeIncorrect,
)
.emit();
}
/// Parses an `impl B0 + ... + Bn` type.
fn parse_impl_ty(&mut self, impl_dyn_multi: &mut bool) -> PResult<'a, TyKind> {
// Always parse bounds greedily for better error recovery.
let bounds = self.parse_generic_bounds(None)?;
*impl_dyn_multi = bounds.len() > 1 || self.prev_token.kind == TokenKind::BinOp(token::Plus);
Ok(TyKind::ImplTrait(ast::DUMMY_NODE_ID, bounds))
}
/// Is a `dyn B0 + ... + Bn` type allowed here?
fn is_explicit_dyn_type(&mut self) -> bool {
self.check_keyword(kw::Dyn)
&& (!self.token.uninterpolated_span().rust_2015()
|| self.look_ahead(1, |t| {
(t.can_begin_bound() || t.kind == TokenKind::BinOp(token::Star))
&& !can_continue_type_after_non_fn_ident(t)
}))
}
/// Parses a `dyn B0 + ... + Bn` type.
///
/// Note that this does *not* parse bare trait objects.
fn parse_dyn_ty(&mut self, impl_dyn_multi: &mut bool) -> PResult<'a, TyKind> {
self.bump(); // `dyn`
// parse dyn* types
let syntax = if self.eat(&TokenKind::BinOp(token::Star)) {
TraitObjectSyntax::DynStar
} else {
TraitObjectSyntax::Dyn
};
// Always parse bounds greedily for better error recovery.
let bounds = self.parse_generic_bounds(None)?;
*impl_dyn_multi = bounds.len() > 1 || self.prev_token.kind == TokenKind::BinOp(token::Plus);
Ok(TyKind::TraitObject(bounds, syntax))
}
/// Parses a type starting with a path.
///
/// This can be:
/// 1. a type macro, `mac!(...)`,
/// 2. a bare trait object, `B0 + ... + Bn`,
/// 3. or a path, `path::to::MyType`.
fn parse_path_start_ty(
&mut self,
lo: Span,
allow_plus: AllowPlus,
ty_generics: Option<&Generics>,
) -> PResult<'a, TyKind> {
// Simple path
let path = self.parse_path_inner(PathStyle::Type, ty_generics)?;
if self.eat(&token::Not) {
// Macro invocation in type position
Ok(TyKind::MacCall(P(MacCall {
path,
args: self.parse_mac_args()?,
prior_type_ascription: self.last_type_ascription,
})))
} else if allow_plus == AllowPlus::Yes && self.check_plus() {
// `Trait1 + Trait2 + 'a`
self.parse_remaining_bounds_path(Vec::new(), path, lo, true)
} else {
// Just a type path.
Ok(TyKind::Path(None, path))
}
}
fn error_illegal_c_varadic_ty(&self, lo: Span) {
struct_span_err!(
self.sess.span_diagnostic,
lo.to(self.prev_token.span),
E0743,
"C-variadic type `...` may not be nested inside another type",
)
.emit();
}
pub(super) fn parse_generic_bounds(
&mut self,
colon_span: Option<Span>,
) -> PResult<'a, GenericBounds> {
self.parse_generic_bounds_common(AllowPlus::Yes, colon_span)
}
/// Parses bounds of a type parameter `BOUND + BOUND + ...`, possibly with trailing `+`.
///
/// See `parse_generic_bound` for the `BOUND` grammar.
fn parse_generic_bounds_common(
&mut self,
allow_plus: AllowPlus,
colon_span: Option<Span>,
) -> PResult<'a, GenericBounds> {
let mut bounds = Vec::new();
let mut negative_bounds = Vec::new();
while self.can_begin_bound()
// Continue even if we find a keyword.
// This is necessary for error recover on, for example, `impl fn()`.
//
// The only keyword that can go after generic bounds is `where`, so stop if it's it.
|| (self.token.is_reserved_ident() && !self.token.is_keyword(kw::Where))
{
if self.token.is_keyword(kw::Dyn) {
// Account for `&dyn Trait + dyn Other`.
self.struct_span_err(self.token.span, "invalid `dyn` keyword")
.help("`dyn` is only needed at the start of a trait `+`-separated list")
.span_suggestion(
self.token.span,
"remove this keyword",
"",
Applicability::MachineApplicable,
)
.emit();
self.bump();
}
match self.parse_generic_bound()? {
Ok(bound) => bounds.push(bound),
Err(neg_sp) => negative_bounds.push(neg_sp),
}
if allow_plus == AllowPlus::No || !self.eat_plus() {
break;
}
}
if !negative_bounds.is_empty() {
self.error_negative_bounds(colon_span, &bounds, negative_bounds);
}
Ok(bounds)
}
/// Can the current token begin a bound?
fn can_begin_bound(&mut self) -> bool {
// This needs to be synchronized with `TokenKind::can_begin_bound`.
self.check_path()
|| self.check_lifetime()
|| self.check(&token::Not) // Used for error reporting only.
|| self.check(&token::Question)
|| self.check(&token::Tilde)
|| self.check_keyword(kw::For)
|| self.check(&token::OpenDelim(Delimiter::Parenthesis))
}
fn error_negative_bounds(
&self,
colon_span: Option<Span>,
bounds: &[GenericBound],
negative_bounds: Vec<Span>,
) {
let negative_bounds_len = negative_bounds.len();
let last_span = *negative_bounds.last().expect("no negative bounds, but still error?");
let mut err = self.struct_span_err(negative_bounds, "negative bounds are not supported");
err.span_label(last_span, "negative bounds are not supported");
if let Some(bound_list) = colon_span {
let bound_list = bound_list.to(self.prev_token.span);
let mut new_bound_list = String::new();
if !bounds.is_empty() {
let mut snippets = bounds.iter().map(|bound| self.span_to_snippet(bound.span()));
while let Some(Ok(snippet)) = snippets.next() {
new_bound_list.push_str(" + ");
new_bound_list.push_str(&snippet);
}
new_bound_list = new_bound_list.replacen(" +", ":", 1);
}
err.tool_only_span_suggestion(
bound_list,
&format!("remove the bound{}", pluralize!(negative_bounds_len)),
new_bound_list,
Applicability::MachineApplicable,
);
}
err.emit();
}
/// Parses a bound according to the grammar:
/// ```ebnf
/// BOUND = TY_BOUND | LT_BOUND
/// ```
fn parse_generic_bound(&mut self) -> PResult<'a, Result<GenericBound, Span>> {
let anchor_lo = self.prev_token.span;
let lo = self.token.span;
let has_parens = self.eat(&token::OpenDelim(Delimiter::Parenthesis));
let inner_lo = self.token.span;
let is_negative = self.eat(&token::Not);
let modifiers = self.parse_ty_bound_modifiers()?;
let bound = if self.token.is_lifetime() {
self.error_lt_bound_with_modifiers(modifiers);
self.parse_generic_lt_bound(lo, inner_lo, has_parens)?
} else {
self.parse_generic_ty_bound(lo, has_parens, modifiers)?
};
Ok(if is_negative { Err(anchor_lo.to(self.prev_token.span)) } else { Ok(bound) })
}
/// Parses a lifetime ("outlives") bound, e.g. `'a`, according to:
/// ```ebnf
/// LT_BOUND = LIFETIME
/// ```
fn parse_generic_lt_bound(
&mut self,
lo: Span,
inner_lo: Span,
has_parens: bool,
) -> PResult<'a, GenericBound> {
let bound = GenericBound::Outlives(self.expect_lifetime());
if has_parens {
// FIXME(Centril): Consider not erroring here and accepting `('lt)` instead,
// possibly introducing `GenericBound::Paren(P<GenericBound>)`?
self.recover_paren_lifetime(lo, inner_lo)?;
}
Ok(bound)
}
/// Emits an error if any trait bound modifiers were present.
fn error_lt_bound_with_modifiers(&self, modifiers: BoundModifiers) {
if let Some(span) = modifiers.maybe_const {
self.struct_span_err(
span,
"`~const` may only modify trait bounds, not lifetime bounds",
)
.emit();
}
if let Some(span) = modifiers.maybe {
self.struct_span_err(span, "`?` may only modify trait bounds, not lifetime bounds")
.emit();
}
}
/// Recover on `('lifetime)` with `(` already eaten.
fn recover_paren_lifetime(&mut self, lo: Span, inner_lo: Span) -> PResult<'a, ()> {
let inner_span = inner_lo.to(self.prev_token.span);
self.expect(&token::CloseDelim(Delimiter::Parenthesis))?;
let mut err = self.struct_span_err(
lo.to(self.prev_token.span),
"parenthesized lifetime bounds are not supported",
);
if let Ok(snippet) = self.span_to_snippet(inner_span) {
err.span_suggestion_short(
lo.to(self.prev_token.span),
"remove the parentheses",
snippet,
Applicability::MachineApplicable,
);
}
err.emit();
Ok(())
}
/// Parses the modifiers that may precede a trait in a bound, e.g. `?Trait` or `~const Trait`.
///
/// If no modifiers are present, this does not consume any tokens.
///
/// ```ebnf
/// TY_BOUND_MODIFIERS = ["~const"] ["?"]
/// ```
fn parse_ty_bound_modifiers(&mut self) -> PResult<'a, BoundModifiers> {
let maybe_const = if self.eat(&token::Tilde) {
let tilde = self.prev_token.span;
self.expect_keyword(kw::Const)?;
let span = tilde.to(self.prev_token.span);
self.sess.gated_spans.gate(sym::const_trait_impl, span);
Some(span)
} else if self.eat_keyword(kw::Const) {
let span = self.prev_token.span;
self.sess.gated_spans.gate(sym::const_trait_impl, span);
self.struct_span_err(span, "const bounds must start with `~`")
.span_suggestion(
span.shrink_to_lo(),
"add `~`",
"~",
Applicability::MachineApplicable,
)
.emit();
Some(span)
} else {
None
};
let maybe = if self.eat(&token::Question) { Some(self.prev_token.span) } else { None };
Ok(BoundModifiers { maybe, maybe_const })
}
/// Parses a type bound according to:
/// ```ebnf
/// TY_BOUND = TY_BOUND_NOPAREN | (TY_BOUND_NOPAREN)
/// TY_BOUND_NOPAREN = [TY_BOUND_MODIFIERS] [for<LT_PARAM_DEFS>] SIMPLE_PATH
/// ```
///
/// For example, this grammar accepts `~const ?for<'a: 'b> m::Trait<'a>`.
fn parse_generic_ty_bound(
&mut self,
lo: Span,
has_parens: bool,
modifiers: BoundModifiers,
) -> PResult<'a, GenericBound> {
let lifetime_defs = self.parse_late_bound_lifetime_defs()?;
let path = self.parse_path(PathStyle::Type)?;
if has_parens {
if self.token.is_like_plus() {
// Someone has written something like `&dyn (Trait + Other)`. The correct code
// would be `&(dyn Trait + Other)`, but we don't have access to the appropriate
// span to suggest that. When written as `&dyn Trait + Other`, an appropriate
// suggestion is given.
let bounds = vec![];
self.parse_remaining_bounds(bounds, true)?;
self.expect(&token::CloseDelim(Delimiter::Parenthesis))?;
let sp = vec![lo, self.prev_token.span];
let sugg: Vec<_> = sp.iter().map(|sp| (*sp, String::new())).collect();
self.struct_span_err(sp, "incorrect braces around trait bounds")
.multipart_suggestion(
"remove the parentheses",
sugg,
Applicability::MachineApplicable,
)
.emit();
} else {
self.expect(&token::CloseDelim(Delimiter::Parenthesis))?;
}
}
let modifier = modifiers.to_trait_bound_modifier();
let poly_trait = PolyTraitRef::new(lifetime_defs, path, lo.to(self.prev_token.span));
Ok(GenericBound::Trait(poly_trait, modifier))
}
/// Optionally parses `for<$generic_params>`.
pub(super) fn parse_late_bound_lifetime_defs(&mut self) -> PResult<'a, Vec<GenericParam>> {
if self.eat_keyword(kw::For) {
self.expect_lt()?;
let params = self.parse_generic_params()?;
self.expect_gt()?;
// We rely on AST validation to rule out invalid cases: There must not be type
// parameters, and the lifetime parameters must not have bounds.
Ok(params)
} else {
Ok(Vec::new())
}
}
pub(super) fn check_lifetime(&mut self) -> bool {
self.expected_tokens.push(TokenType::Lifetime);
self.token.is_lifetime()
}
/// Parses a single lifetime `'a` or panics.
pub(super) fn expect_lifetime(&mut self) -> Lifetime {
if let Some(ident) = self.token.lifetime() {
self.bump();
Lifetime { ident, id: ast::DUMMY_NODE_ID }
} else {
self.span_bug(self.token.span, "not a lifetime")
}
}
pub(super) fn mk_ty(&self, span: Span, kind: TyKind) -> P<Ty> {
P(Ty { kind, span, id: ast::DUMMY_NODE_ID, tokens: None })
}
}
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