--- /dev/null
+use super::Parser;
+
+use rustc_ast::token;
+use rustc_ast::{
+ self as ast, Attribute, GenericBounds, GenericParam, GenericParamKind, WhereClause,
+};
+use rustc_errors::PResult;
+use rustc_span::symbol::{kw, sym};
+
+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: Vec<Attribute>) -> PResult<'a, GenericParam> {
+ let ident = self.parse_ident()?;
+
+ // Parse optional colon and param bounds.
+ let bounds = if self.eat(&token::Colon) {
+ self.parse_generic_bounds(Some(self.prev_token.span))?
+ } 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.into(),
+ bounds,
+ kind: GenericParamKind::Type { default },
+ is_placeholder: false,
+ })
+ }
+
+ fn parse_const_param(&mut self, preceding_attrs: Vec<Attribute>) -> 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, taking care of feature gating the spans
+ // with the unstable syntax mechanism.
+ let default = if self.eat(&token::Eq) {
+ // The gated span goes from the `=` to the end of the const argument that follows (and
+ // which could be a block expression).
+ let start = self.prev_token.span;
+ let const_arg = self.parse_const_arg()?;
+ let span = start.to(const_arg.value.span);
+ self.sess.gated_spans.gate(sym::const_generics_defaults, span);
+ Some(const_arg)
+ } else {
+ None
+ };
+
+ Ok(GenericParam {
+ ident,
+ id: ast::DUMMY_NODE_ID,
+ attrs: preceding_attrs.into(),
+ bounds: Vec::new(),
+ kind: GenericParamKind::Const { ty, kw_span: const_span, default },
+ is_placeholder: false,
+ })
+ }
+
+ /// 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, Vec<ast::GenericParam>> {
+ let mut params = Vec::new();
+ loop {
+ let attrs = self.parse_outer_attributes()?;
+ if self.check_lifetime() {
+ let lifetime = self.expect_lifetime();
+ // Parse lifetime parameter.
+ let bounds =
+ if self.eat(&token::Colon) { self.parse_lt_param_bounds() } else { Vec::new() };
+ params.push(ast::GenericParam {
+ ident: lifetime.ident,
+ id: lifetime.id,
+ attrs: attrs.into(),
+ bounds,
+ kind: ast::GenericParamKind::Lifetime,
+ is_placeholder: false,
+ });
+ } else if self.check_keyword(kw::Const) {
+ // Parse const parameter.
+ params.push(self.parse_const_param(attrs)?);
+ } else if self.check_ident() {
+ // Parse type parameter.
+ params.push(self.parse_ty_param(attrs)?);
+ } else if self.token.can_begin_type() {
+ // Trying to write an associated type bound? (#26271)
+ let snapshot = self.clone();
+ match self.parse_ty_where_predicate() {
+ Ok(where_predicate) => {
+ self.struct_span_err(
+ where_predicate.span(),
+ "bounds on associated types do not belong here",
+ )
+ .span_label(where_predicate.span(), "belongs in `where` clause")
+ .emit();
+ }
+ Err(mut err) => {
+ err.cancel();
+ *self = snapshot;
+ break;
+ }
+ }
+ } else {
+ // Check for trailing attributes and stop parsing.
+ if !attrs.is_empty() {
+ if !params.is_empty() {
+ self.struct_span_err(
+ attrs[0].span,
+ "trailing attribute after generic parameter",
+ )
+ .span_label(attrs[0].span, "attributes must go before parameters")
+ .emit();
+ } else {
+ self.struct_span_err(attrs[0].span, "attribute without generic parameters")
+ .span_label(
+ attrs[0].span,
+ "attributes are only permitted when preceding parameters",
+ )
+ .emit();
+ }
+ }
+ break;
+ }
+
+ if !self.eat(&token::Comma) {
+ 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 {
+ (vec![], self.prev_token.span.shrink_to_hi())
+ };
+ Ok(ast::Generics {
+ params,
+ where_clause: WhereClause {
+ has_where_token: false,
+ predicates: Vec::new(),
+ span: self.prev_token.span.shrink_to_hi(),
+ },
+ span,
+ })
+ }
+
+ /// Parses an optional where-clause and places it in `generics`.
+ ///
+ /// ```ignore (only-for-syntax-highlight)
+ /// where T : Trait<U, V> + 'b, 'a : 'b
+ /// ```
+ pub(super) fn parse_where_clause(&mut self) -> PResult<'a, WhereClause> {
+ let mut where_clause = WhereClause {
+ has_where_token: false,
+ predicates: Vec::new(),
+ span: self.prev_token.span.shrink_to_hi(),
+ };
+
+ if !self.eat_keyword(kw::Where) {
+ return Ok(where_clause);
+ }
+ where_clause.has_where_token = true;
+ let 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.struct_span_err(
+ generics.span,
+ "generic parameters on `where` clauses are reserved for future use",
+ )
+ .span_label(generics.span, "currently unsupported")
+ .emit();
+ }
+
+ loop {
+ let 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: lo.to(self.prev_token.span),
+ lifetime,
+ bounds,
+ },
+ ));
+ } else if self.check_type() {
+ where_clause.predicates.push(self.parse_ty_where_predicate()?);
+ } else {
+ break;
+ }
+
+ if !self.eat(&token::Comma) {
+ break;
+ }
+ }
+
+ where_clause.span = lo.to(self.prev_token.span);
+ Ok(where_clause)
+ }
+
+ 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(Some(self.prev_token.span))?;
+ 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,
+ id: ast::DUMMY_NODE_ID,
+ }))
+ } else {
+ 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
+ // 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)
+ })
+ || self.is_keyword_ahead(start + 1, &[kw::Const]))
+ }
+}
projects / rustc.git / blobdiff