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use crate::errors::{
self, MultipleWhereClauses, UnexpectedDefaultValueForLifetimeInGenericParameters,
UnexpectedSelfInGenericParameters, WhereClauseBeforeTupleStructBody,
WhereClauseBeforeTupleStructBodySugg,
};
use super::{ForceCollect, Parser, TrailingToken};
use ast::token::Delimiter;
use rustc_ast::token;
use rustc_ast::{
self as ast, AttrVec, GenericBounds, GenericParam, GenericParamKind, TyKind, WhereClause,
};
use rustc_errors::{Applicability, PResult};
use rustc_span::symbol::{kw, Ident};
use rustc_span::Span;
use thin_vec::ThinVec;
enum PredicateOrStructBody {
Predicate(ast::WherePredicate),
StructBody(ThinVec<ast::FieldDef>),
}
impl<'a> Parser<'a> {
/// Parses bounds of a lifetime parameter `BOUND + BOUND + BOUND`, possibly with trailing `+`.
///
/// ```text
/// BOUND = LT_BOUND (e.g., `'a`)
/// ```
fn parse_lt_param_bounds(&mut self) -> GenericBounds {
let mut lifetimes = Vec::new();
while self.check_lifetime() {
lifetimes.push(ast::GenericBound::Outlives(self.expect_lifetime()));
if !self.eat_plus() {
break;
}
}
lifetimes
}
/// Matches `typaram = IDENT (`?` unbound)? optbounds ( EQ ty )?`.
fn parse_ty_param(&mut self, preceding_attrs: AttrVec) -> PResult<'a, GenericParam> {
let ident = self.parse_ident()?;
// We might have a typo'd `Const` that was parsed as a type parameter.
if self.may_recover()
&& ident.name.as_str().to_ascii_lowercase() == kw::Const.as_str()
&& self.check_ident()
// `Const` followed by IDENT
{
return self.recover_const_param_with_mistyped_const(preceding_attrs, ident);
}
// Parse optional colon and param bounds.
let mut colon_span = None;
let bounds = if self.eat(&token::Colon) {
colon_span = Some(self.prev_token.span);
// recover from `impl Trait` in type param bound
if self.token.is_keyword(kw::Impl) {
let impl_span = self.token.span;
let snapshot = self.create_snapshot_for_diagnostic();
match self.parse_ty() {
Ok(p) => {
if let TyKind::ImplTrait(_, bounds) = &p.kind {
let span = impl_span.to(self.token.span.shrink_to_lo());
let mut err = self.struct_span_err(
span,
"expected trait bound, found `impl Trait` type",
);
err.span_label(span, "not a trait");
if let [bound, ..] = &bounds[..] {
err.span_suggestion_verbose(
impl_span.until(bound.span()),
"use the trait bounds directly",
String::new(),
Applicability::MachineApplicable,
);
}
err.emit();
return Err(err);
}
}
Err(err) => {
err.cancel();
}
}
self.restore_snapshot(snapshot);
}
self.parse_generic_bounds()?
} else {
Vec::new()
};
let default = if self.eat(&token::Eq) { Some(self.parse_ty()?) } else { None };
Ok(GenericParam {
ident,
id: ast::DUMMY_NODE_ID,
attrs: preceding_attrs,
bounds,
kind: GenericParamKind::Type { default },
is_placeholder: false,
colon_span,
})
}
pub(crate) fn parse_const_param(
&mut self,
preceding_attrs: AttrVec,
) -> PResult<'a, GenericParam> {
let const_span = self.token.span;
self.expect_keyword(kw::Const)?;
let ident = self.parse_ident()?;
self.expect(&token::Colon)?;
let ty = self.parse_ty()?;
// Parse optional const generics default value.
let default = if self.eat(&token::Eq) { Some(self.parse_const_arg()?) } else { None };
Ok(GenericParam {
ident,
id: ast::DUMMY_NODE_ID,
attrs: preceding_attrs,
bounds: Vec::new(),
kind: GenericParamKind::Const { ty, kw_span: const_span, default },
is_placeholder: false,
colon_span: None,
})
}
pub(crate) fn recover_const_param_with_mistyped_const(
&mut self,
preceding_attrs: AttrVec,
mistyped_const_ident: Ident,
) -> PResult<'a, GenericParam> {
let ident = self.parse_ident()?;
self.expect(&token::Colon)?;
let ty = self.parse_ty()?;
// Parse optional const generics default value.
let default = if self.eat(&token::Eq) { Some(self.parse_const_arg()?) } else { None };
let mut err = self.struct_span_err(
mistyped_const_ident.span,
format!("`const` keyword was mistyped as `{}`", mistyped_const_ident.as_str()),
);
err.span_suggestion_verbose(
mistyped_const_ident.span,
"use the `const` keyword",
kw::Const.as_str(),
Applicability::MachineApplicable,
);
err.emit();
Ok(GenericParam {
ident,
id: ast::DUMMY_NODE_ID,
attrs: preceding_attrs,
bounds: Vec::new(),
kind: GenericParamKind::Const { ty, kw_span: mistyped_const_ident.span, default },
is_placeholder: false,
colon_span: None,
})
}
/// Parses a (possibly empty) list of lifetime and type parameters, possibly including
/// a trailing comma and erroneous trailing attributes.
pub(super) fn parse_generic_params(&mut self) -> PResult<'a, ThinVec<ast::GenericParam>> {
let mut params = ThinVec::new();
let mut done = false;
while !done {
let attrs = self.parse_outer_attributes()?;
let param =
self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
if this.eat_keyword_noexpect(kw::SelfUpper) {
// `Self` as a generic param is invalid. Here we emit the diagnostic and continue parsing
// as if `Self` never existed.
this.sess.emit_err(UnexpectedSelfInGenericParameters {
span: this.prev_token.span,
});
this.eat(&token::Comma);
}
let param = if this.check_lifetime() {
let lifetime = this.expect_lifetime();
// Parse lifetime parameter.
let (colon_span, bounds) = if this.eat(&token::Colon) {
(Some(this.prev_token.span), this.parse_lt_param_bounds())
} else {
(None, Vec::new())
};
if this.check_noexpect(&token::Eq)
&& this.look_ahead(1, |t| t.is_lifetime())
{
let lo = this.token.span;
// Parse `= 'lifetime`.
this.bump(); // `=`
this.bump(); // `'lifetime`
let span = lo.to(this.prev_token.span);
this.sess.emit_err(
UnexpectedDefaultValueForLifetimeInGenericParameters { span },
);
}
Some(ast::GenericParam {
ident: lifetime.ident,
id: lifetime.id,
attrs,
bounds,
kind: ast::GenericParamKind::Lifetime,
is_placeholder: false,
colon_span,
})
} else if this.check_keyword(kw::Const) {
// Parse const parameter.
Some(this.parse_const_param(attrs)?)
} else if this.check_ident() {
// Parse type parameter.
Some(this.parse_ty_param(attrs)?)
} else if this.token.can_begin_type() {
// Trying to write an associated type bound? (#26271)
let snapshot = this.create_snapshot_for_diagnostic();
match this.parse_ty_where_predicate() {
Ok(where_predicate) => {
this.sess.emit_err(errors::BadAssocTypeBounds {
span: where_predicate.span(),
});
// FIXME - try to continue parsing other generics?
return Ok((None, TrailingToken::None));
}
Err(err) => {
err.cancel();
// FIXME - maybe we should overwrite 'self' outside of `collect_tokens`?
this.restore_snapshot(snapshot);
return Ok((None, TrailingToken::None));
}
}
} else {
// Check for trailing attributes and stop parsing.
if !attrs.is_empty() {
if !params.is_empty() {
this.sess
.emit_err(errors::AttrAfterGeneric { span: attrs[0].span });
} else {
this.sess
.emit_err(errors::AttrWithoutGenerics { span: attrs[0].span });
}
}
return Ok((None, TrailingToken::None));
};
if !this.eat(&token::Comma) {
done = true;
}
// We just ate the comma, so no need to use `TrailingToken`
Ok((param, TrailingToken::None))
})?;
if let Some(param) = param {
params.push(param);
} else {
break;
}
}
Ok(params)
}
/// Parses a set of optional generic type parameter declarations. Where
/// clauses are not parsed here, and must be added later via
/// `parse_where_clause()`.
///
/// matches generics = ( ) | ( < > ) | ( < typaramseq ( , )? > ) | ( < lifetimes ( , )? > )
/// | ( < lifetimes , typaramseq ( , )? > )
/// where typaramseq = ( typaram ) | ( typaram , typaramseq )
pub(super) fn parse_generics(&mut self) -> PResult<'a, ast::Generics> {
let span_lo = self.token.span;
let (params, span) = if self.eat_lt() {
let params = self.parse_generic_params()?;
self.expect_gt()?;
(params, span_lo.to(self.prev_token.span))
} else {
(ThinVec::new(), self.prev_token.span.shrink_to_hi())
};
Ok(ast::Generics {
params,
where_clause: WhereClause {
has_where_token: false,
predicates: ThinVec::new(),
span: self.prev_token.span.shrink_to_hi(),
},
span,
})
}
/// Parses an optional where-clause.
///
/// ```ignore (only-for-syntax-highlight)
/// where T : Trait<U, V> + 'b, 'a : 'b
/// ```
pub(super) fn parse_where_clause(&mut self) -> PResult<'a, WhereClause> {
self.parse_where_clause_common(None).map(|(clause, _)| clause)
}
pub(super) fn parse_struct_where_clause(
&mut self,
struct_name: Ident,
body_insertion_point: Span,
) -> PResult<'a, (WhereClause, Option<ThinVec<ast::FieldDef>>)> {
self.parse_where_clause_common(Some((struct_name, body_insertion_point)))
}
fn parse_where_clause_common(
&mut self,
struct_: Option<(Ident, Span)>,
) -> PResult<'a, (WhereClause, Option<ThinVec<ast::FieldDef>>)> {
let mut where_clause = WhereClause {
has_where_token: false,
predicates: ThinVec::new(),
span: self.prev_token.span.shrink_to_hi(),
};
let mut tuple_struct_body = None;
if !self.eat_keyword(kw::Where) {
return Ok((where_clause, None));
}
where_clause.has_where_token = true;
let where_lo = self.prev_token.span;
// We are considering adding generics to the `where` keyword as an alternative higher-rank
// parameter syntax (as in `where<'a>` or `where<T>`. To avoid that being a breaking
// change we parse those generics now, but report an error.
if self.choose_generics_over_qpath(0) {
let generics = self.parse_generics()?;
self.sess.emit_err(errors::WhereOnGenerics { span: generics.span });
}
loop {
let where_sp = where_lo.to(self.prev_token.span);
let pred_lo = self.token.span;
if self.check_lifetime() && self.look_ahead(1, |t| !t.is_like_plus()) {
let lifetime = self.expect_lifetime();
// Bounds starting with a colon are mandatory, but possibly empty.
self.expect(&token::Colon)?;
let bounds = self.parse_lt_param_bounds();
where_clause.predicates.push(ast::WherePredicate::RegionPredicate(
ast::WhereRegionPredicate {
span: pred_lo.to(self.prev_token.span),
lifetime,
bounds,
},
));
} else if self.check_type() {
match self.parse_ty_where_predicate_or_recover_tuple_struct_body(
struct_, pred_lo, where_sp,
)? {
PredicateOrStructBody::Predicate(pred) => where_clause.predicates.push(pred),
PredicateOrStructBody::StructBody(body) => {
tuple_struct_body = Some(body);
break;
}
}
} else {
break;
}
let prev_token = self.prev_token.span;
let ate_comma = self.eat(&token::Comma);
if self.eat_keyword_noexpect(kw::Where) {
self.sess.emit_err(MultipleWhereClauses {
span: self.token.span,
previous: pred_lo,
between: prev_token.shrink_to_hi().to(self.prev_token.span),
});
} else if !ate_comma {
break;
}
}
where_clause.span = where_lo.to(self.prev_token.span);
Ok((where_clause, tuple_struct_body))
}
fn parse_ty_where_predicate_or_recover_tuple_struct_body(
&mut self,
struct_: Option<(Ident, Span)>,
pred_lo: Span,
where_sp: Span,
) -> PResult<'a, PredicateOrStructBody> {
let mut snapshot = None;
if let Some(struct_) = struct_
&& self.may_recover()
&& self.token.kind == token::OpenDelim(Delimiter::Parenthesis)
{
snapshot = Some((struct_, self.create_snapshot_for_diagnostic()));
};
match self.parse_ty_where_predicate() {
Ok(pred) => Ok(PredicateOrStructBody::Predicate(pred)),
Err(type_err) => {
let Some(((struct_name, body_insertion_point), mut snapshot)) = snapshot else {
return Err(type_err);
};
// Check if we might have encountered an out of place tuple struct body.
match snapshot.parse_tuple_struct_body() {
// Since we don't know the exact reason why we failed to parse the
// predicate (we might have stumbled upon something bogus like `(T): ?`),
// employ a simple heuristic to weed out some pathological cases:
// Look for a semicolon (strong indicator) or anything that might mark
// the end of the item (weak indicator) following the body.
Ok(body)
if matches!(snapshot.token.kind, token::Semi | token::Eof)
|| snapshot.token.can_begin_item() =>
{
type_err.cancel();
let body_sp = pred_lo.to(snapshot.prev_token.span);
let map = self.sess.source_map();
self.sess.emit_err(WhereClauseBeforeTupleStructBody {
span: where_sp,
name: struct_name.span,
body: body_sp,
sugg: map.span_to_snippet(body_sp).ok().map(|body| {
WhereClauseBeforeTupleStructBodySugg {
left: body_insertion_point.shrink_to_hi(),
snippet: body,
right: map.end_point(where_sp).to(body_sp),
}
}),
});
self.restore_snapshot(snapshot);
Ok(PredicateOrStructBody::StructBody(body))
}
Ok(_) => Err(type_err),
Err(body_err) => {
body_err.cancel();
Err(type_err)
}
}
}
}
}
fn parse_ty_where_predicate(&mut self) -> PResult<'a, ast::WherePredicate> {
let lo = self.token.span;
// Parse optional `for<'a, 'b>`.
// This `for` is parsed greedily and applies to the whole predicate,
// the bounded type can have its own `for` applying only to it.
// Examples:
// * `for<'a> Trait1<'a>: Trait2<'a /* ok */>`
// * `(for<'a> Trait1<'a>): Trait2<'a /* not ok */>`
// * `for<'a> for<'b> Trait1<'a, 'b>: Trait2<'a /* ok */, 'b /* not ok */>`
let lifetime_defs = self.parse_late_bound_lifetime_defs()?;
// Parse type with mandatory colon and (possibly empty) bounds,
// or with mandatory equality sign and the second type.
let ty = self.parse_ty_for_where_clause()?;
if self.eat(&token::Colon) {
let bounds = self.parse_generic_bounds()?;
Ok(ast::WherePredicate::BoundPredicate(ast::WhereBoundPredicate {
span: lo.to(self.prev_token.span),
bound_generic_params: lifetime_defs,
bounded_ty: ty,
bounds,
}))
// FIXME: Decide what should be used here, `=` or `==`.
// FIXME: We are just dropping the binders in lifetime_defs on the floor here.
} else if self.eat(&token::Eq) || self.eat(&token::EqEq) {
let rhs_ty = self.parse_ty()?;
Ok(ast::WherePredicate::EqPredicate(ast::WhereEqPredicate {
span: lo.to(self.prev_token.span),
lhs_ty: ty,
rhs_ty,
}))
} else {
self.maybe_recover_bounds_doubled_colon(&ty)?;
self.unexpected()
}
}
pub(super) fn choose_generics_over_qpath(&self, start: usize) -> bool {
// There's an ambiguity between generic parameters and qualified paths in impls.
// If we see `<` it may start both, so we have to inspect some following tokens.
// The following combinations can only start generics,
// but not qualified paths (with one exception):
// `<` `>` - empty generic parameters
// `<` `#` - generic parameters with attributes
// `<` (LIFETIME|IDENT) `>` - single generic parameter
// `<` (LIFETIME|IDENT) `,` - first generic parameter in a list
// `<` (LIFETIME|IDENT) `:` - generic parameter with bounds
// `<` (LIFETIME|IDENT) `=` - generic parameter with a default
// `<` const - generic const parameter
// `<` IDENT `?` - RECOVERY for `impl<T ?Bound` missing a `:`, meant to
// avoid the `T?` to `Option<T>` recovery for types.
// The only truly ambiguous case is
// `<` IDENT `>` `::` IDENT ...
// we disambiguate it in favor of generics (`impl<T> ::absolute::Path<T> { ... }`)
// because this is what almost always expected in practice, qualified paths in impls
// (`impl <Type>::AssocTy { ... }`) aren't even allowed by type checker at the moment.
self.look_ahead(start, |t| t == &token::Lt)
&& (self.look_ahead(start + 1, |t| t == &token::Pound || t == &token::Gt)
|| self.look_ahead(start + 1, |t| t.is_lifetime() || t.is_ident())
&& self.look_ahead(start + 2, |t| {
matches!(t.kind, token::Gt | token::Comma | token::Colon | token::Eq)
// Recovery-only branch -- this could be removed,
// since it only affects diagnostics currently.
|| matches!(t.kind, token::Question)
})
|| self.is_keyword_ahead(start + 1, &[kw::Const]))
}
}