| use super::ty::{AllowPlus, RecoverQPath, RecoverReturnSign}; |
| use super::{Parser, TokenType}; |
| use crate::maybe_whole; |
| use rustc_ast::ptr::P; |
| use rustc_ast::token::{self, Token}; |
| use rustc_ast::{self as ast, AngleBracketedArg, AngleBracketedArgs, ParenthesizedArgs}; |
| use rustc_ast::{AnonConst, AssocTyConstraint, AssocTyConstraintKind, BlockCheckMode}; |
| use rustc_ast::{GenericArg, GenericArgs}; |
| use rustc_ast::{Path, PathSegment, QSelf}; |
| use rustc_errors::{pluralize, Applicability, PResult}; |
| use rustc_span::source_map::{BytePos, Span}; |
| use rustc_span::symbol::{kw, sym, Ident}; |
| |
| use std::mem; |
| use tracing::debug; |
| |
| /// Specifies how to parse a path. |
| #[derive(Copy, Clone, PartialEq)] |
| pub enum PathStyle { |
| /// In some contexts, notably in expressions, paths with generic arguments are ambiguous |
| /// with something else. For example, in expressions `segment < ....` can be interpreted |
| /// as a comparison and `segment ( ....` can be interpreted as a function call. |
| /// In all such contexts the non-path interpretation is preferred by default for practical |
| /// reasons, but the path interpretation can be forced by the disambiguator `::`, e.g. |
| /// `x<y>` - comparisons, `x::<y>` - unambiguously a path. |
| Expr, |
| /// In other contexts, notably in types, no ambiguity exists and paths can be written |
| /// without the disambiguator, e.g., `x<y>` - unambiguously a path. |
| /// Paths with disambiguators are still accepted, `x::<Y>` - unambiguously a path too. |
| Type, |
| /// A path with generic arguments disallowed, e.g., `foo::bar::Baz`, used in imports, |
| /// visibilities or attributes. |
| /// Technically, this variant is unnecessary and e.g., `Expr` can be used instead |
| /// (paths in "mod" contexts have to be checked later for absence of generic arguments |
| /// anyway, due to macros), but it is used to avoid weird suggestions about expected |
| /// tokens when something goes wrong. |
| Mod, |
| } |
| |
| impl<'a> Parser<'a> { |
| /// Parses a qualified path. |
| /// Assumes that the leading `<` has been parsed already. |
| /// |
| /// `qualified_path = <type [as trait_ref]>::path` |
| /// |
| /// # Examples |
| /// `<T>::default` |
| /// `<T as U>::a` |
| /// `<T as U>::F::a<S>` (without disambiguator) |
| /// `<T as U>::F::a::<S>` (with disambiguator) |
| pub(super) fn parse_qpath(&mut self, style: PathStyle) -> PResult<'a, (QSelf, Path)> { |
| let lo = self.prev_token.span; |
| let ty = self.parse_ty()?; |
| |
| // `path` will contain the prefix of the path up to the `>`, |
| // if any (e.g., `U` in the `<T as U>::*` examples |
| // above). `path_span` has the span of that path, or an empty |
| // span in the case of something like `<T>::Bar`. |
| let (mut path, path_span); |
| if self.eat_keyword(kw::As) { |
| let path_lo = self.token.span; |
| path = self.parse_path(PathStyle::Type)?; |
| path_span = path_lo.to(self.prev_token.span); |
| } else { |
| path_span = self.token.span.to(self.token.span); |
| path = ast::Path { segments: Vec::new(), span: path_span, tokens: None }; |
| } |
| |
| // See doc comment for `unmatched_angle_bracket_count`. |
| self.expect(&token::Gt)?; |
| if self.unmatched_angle_bracket_count > 0 { |
| self.unmatched_angle_bracket_count -= 1; |
| debug!("parse_qpath: (decrement) count={:?}", self.unmatched_angle_bracket_count); |
| } |
| |
| if !self.recover_colon_before_qpath_proj() { |
| self.expect(&token::ModSep)?; |
| } |
| |
| let qself = QSelf { ty, path_span, position: path.segments.len() }; |
| self.parse_path_segments(&mut path.segments, style)?; |
| |
| Ok(( |
| qself, |
| Path { segments: path.segments, span: lo.to(self.prev_token.span), tokens: None }, |
| )) |
| } |
| |
| /// Recover from an invalid single colon, when the user likely meant a qualified path. |
| /// We avoid emitting this if not followed by an identifier, as our assumption that the user |
| /// intended this to be a qualified path may not be correct. |
| /// |
| /// ```ignore (diagnostics) |
| /// <Bar as Baz<T>>:Qux |
| /// ^ help: use double colon |
| /// ``` |
| fn recover_colon_before_qpath_proj(&mut self) -> bool { |
| if self.token.kind != token::Colon |
| || self.look_ahead(1, |t| !t.is_ident() || t.is_reserved_ident()) |
| { |
| return false; |
| } |
| |
| self.bump(); // colon |
| |
| self.diagnostic() |
| .struct_span_err( |
| self.prev_token.span, |
| "found single colon before projection in qualified path", |
| ) |
| .span_suggestion( |
| self.prev_token.span, |
| "use double colon", |
| "::".to_string(), |
| Applicability::MachineApplicable, |
| ) |
| .emit(); |
| |
| true |
| } |
| |
| /// Parses simple paths. |
| /// |
| /// `path = [::] segment+` |
| /// `segment = ident | ident[::]<args> | ident[::](args) [-> type]` |
| /// |
| /// # Examples |
| /// `a::b::C<D>` (without disambiguator) |
| /// `a::b::C::<D>` (with disambiguator) |
| /// `Fn(Args)` (without disambiguator) |
| /// `Fn::(Args)` (with disambiguator) |
| pub(super) fn parse_path(&mut self, style: PathStyle) -> PResult<'a, Path> { |
| maybe_whole!(self, NtPath, |path| { |
| if style == PathStyle::Mod && path.segments.iter().any(|segment| segment.args.is_some()) |
| { |
| self.struct_span_err(path.span, "unexpected generic arguments in path").emit(); |
| } |
| path |
| }); |
| |
| let lo = self.token.span; |
| let mut segments = Vec::new(); |
| let mod_sep_ctxt = self.token.span.ctxt(); |
| if self.eat(&token::ModSep) { |
| segments.push(PathSegment::path_root(lo.shrink_to_lo().with_ctxt(mod_sep_ctxt))); |
| } |
| self.parse_path_segments(&mut segments, style)?; |
| |
| Ok(Path { segments, span: lo.to(self.prev_token.span), tokens: None }) |
| } |
| |
| pub(super) fn parse_path_segments( |
| &mut self, |
| segments: &mut Vec<PathSegment>, |
| style: PathStyle, |
| ) -> PResult<'a, ()> { |
| loop { |
| let segment = self.parse_path_segment(style)?; |
| if style == PathStyle::Expr { |
| // In order to check for trailing angle brackets, we must have finished |
| // recursing (`parse_path_segment` can indirectly call this function), |
| // that is, the next token must be the highlighted part of the below example: |
| // |
| // `Foo::<Bar as Baz<T>>::Qux` |
| // ^ here |
| // |
| // As opposed to the below highlight (if we had only finished the first |
| // recursion): |
| // |
| // `Foo::<Bar as Baz<T>>::Qux` |
| // ^ here |
| // |
| // `PathStyle::Expr` is only provided at the root invocation and never in |
| // `parse_path_segment` to recurse and therefore can be checked to maintain |
| // this invariant. |
| self.check_trailing_angle_brackets(&segment, &[&token::ModSep]); |
| } |
| segments.push(segment); |
| |
| if self.is_import_coupler() || !self.eat(&token::ModSep) { |
| return Ok(()); |
| } |
| } |
| } |
| |
| pub(super) fn parse_path_segment(&mut self, style: PathStyle) -> PResult<'a, PathSegment> { |
| let ident = self.parse_path_segment_ident()?; |
| |
| let is_args_start = |token: &Token| { |
| matches!( |
| token.kind, |
| token::Lt |
| | token::BinOp(token::Shl) |
| | token::OpenDelim(token::Paren) |
| | token::LArrow |
| ) |
| }; |
| let check_args_start = |this: &mut Self| { |
| this.expected_tokens.extend_from_slice(&[ |
| TokenType::Token(token::Lt), |
| TokenType::Token(token::OpenDelim(token::Paren)), |
| ]); |
| is_args_start(&this.token) |
| }; |
| |
| Ok( |
| if style == PathStyle::Type && check_args_start(self) |
| || style != PathStyle::Mod |
| && self.check(&token::ModSep) |
| && self.look_ahead(1, |t| is_args_start(t)) |
| { |
| // We use `style == PathStyle::Expr` to check if this is in a recursion or not. If |
| // it isn't, then we reset the unmatched angle bracket count as we're about to start |
| // parsing a new path. |
| if style == PathStyle::Expr { |
| self.unmatched_angle_bracket_count = 0; |
| self.max_angle_bracket_count = 0; |
| } |
| |
| // Generic arguments are found - `<`, `(`, `::<` or `::(`. |
| self.eat(&token::ModSep); |
| let lo = self.token.span; |
| let args = if self.eat_lt() { |
| // `<'a, T, A = U>` |
| let args = |
| self.parse_angle_args_with_leading_angle_bracket_recovery(style, lo)?; |
| self.expect_gt()?; |
| let span = lo.to(self.prev_token.span); |
| AngleBracketedArgs { args, span }.into() |
| } else { |
| // `(T, U) -> R` |
| let (inputs, _) = self.parse_paren_comma_seq(|p| p.parse_ty())?; |
| let inputs_span = lo.to(self.prev_token.span); |
| let span = ident.span.to(self.prev_token.span); |
| let output = |
| self.parse_ret_ty(AllowPlus::No, RecoverQPath::No, RecoverReturnSign::No)?; |
| ParenthesizedArgs { span, inputs, inputs_span, output }.into() |
| }; |
| |
| PathSegment { ident, args, id: ast::DUMMY_NODE_ID } |
| } else { |
| // Generic arguments are not found. |
| PathSegment::from_ident(ident) |
| }, |
| ) |
| } |
| |
| pub(super) fn parse_path_segment_ident(&mut self) -> PResult<'a, Ident> { |
| match self.token.ident() { |
| Some((ident, false)) if ident.is_path_segment_keyword() => { |
| self.bump(); |
| Ok(ident) |
| } |
| _ => self.parse_ident(), |
| } |
| } |
| |
| /// Parses generic args (within a path segment) with recovery for extra leading angle brackets. |
| /// For the purposes of understanding the parsing logic of generic arguments, this function |
| /// can be thought of being the same as just calling `self.parse_angle_args()` if the source |
| /// had the correct amount of leading angle brackets. |
| /// |
| /// ```ignore (diagnostics) |
| /// bar::<<<<T as Foo>::Output>(); |
| /// ^^ help: remove extra angle brackets |
| /// ``` |
| fn parse_angle_args_with_leading_angle_bracket_recovery( |
| &mut self, |
| style: PathStyle, |
| lo: Span, |
| ) -> PResult<'a, Vec<AngleBracketedArg>> { |
| // We need to detect whether there are extra leading left angle brackets and produce an |
| // appropriate error and suggestion. This cannot be implemented by looking ahead at |
| // upcoming tokens for a matching `>` character - if there are unmatched `<` tokens |
| // then there won't be matching `>` tokens to find. |
| // |
| // To explain how this detection works, consider the following example: |
| // |
| // ```ignore (diagnostics) |
| // bar::<<<<T as Foo>::Output>(); |
| // ^^ help: remove extra angle brackets |
| // ``` |
| // |
| // Parsing of the left angle brackets starts in this function. We start by parsing the |
| // `<` token (incrementing the counter of unmatched angle brackets on `Parser` via |
| // `eat_lt`): |
| // |
| // *Upcoming tokens:* `<<<<T as Foo>::Output>;` |
| // *Unmatched count:* 1 |
| // *`parse_path_segment` calls deep:* 0 |
| // |
| // This has the effect of recursing as this function is called if a `<` character |
| // is found within the expected generic arguments: |
| // |
| // *Upcoming tokens:* `<<<T as Foo>::Output>;` |
| // *Unmatched count:* 2 |
| // *`parse_path_segment` calls deep:* 1 |
| // |
| // Eventually we will have recursed until having consumed all of the `<` tokens and |
| // this will be reflected in the count: |
| // |
| // *Upcoming tokens:* `T as Foo>::Output>;` |
| // *Unmatched count:* 4 |
| // `parse_path_segment` calls deep:* 3 |
| // |
| // The parser will continue until reaching the first `>` - this will decrement the |
| // unmatched angle bracket count and return to the parent invocation of this function |
| // having succeeded in parsing: |
| // |
| // *Upcoming tokens:* `::Output>;` |
| // *Unmatched count:* 3 |
| // *`parse_path_segment` calls deep:* 2 |
| // |
| // This will continue until the next `>` character which will also return successfully |
| // to the parent invocation of this function and decrement the count: |
| // |
| // *Upcoming tokens:* `;` |
| // *Unmatched count:* 2 |
| // *`parse_path_segment` calls deep:* 1 |
| // |
| // At this point, this function will expect to find another matching `>` character but |
| // won't be able to and will return an error. This will continue all the way up the |
| // call stack until the first invocation: |
| // |
| // *Upcoming tokens:* `;` |
| // *Unmatched count:* 2 |
| // *`parse_path_segment` calls deep:* 0 |
| // |
| // In doing this, we have managed to work out how many unmatched leading left angle |
| // brackets there are, but we cannot recover as the unmatched angle brackets have |
| // already been consumed. To remedy this, we keep a snapshot of the parser state |
| // before we do the above. We can then inspect whether we ended up with a parsing error |
| // and unmatched left angle brackets and if so, restore the parser state before we |
| // consumed any `<` characters to emit an error and consume the erroneous tokens to |
| // recover by attempting to parse again. |
| // |
| // In practice, the recursion of this function is indirect and there will be other |
| // locations that consume some `<` characters - as long as we update the count when |
| // this happens, it isn't an issue. |
| |
| let is_first_invocation = style == PathStyle::Expr; |
| // Take a snapshot before attempting to parse - we can restore this later. |
| let snapshot = if is_first_invocation { Some(self.clone()) } else { None }; |
| |
| debug!("parse_generic_args_with_leading_angle_bracket_recovery: (snapshotting)"); |
| match self.parse_angle_args() { |
| Ok(args) => Ok(args), |
| Err(ref mut e) if is_first_invocation && self.unmatched_angle_bracket_count > 0 => { |
| // Cancel error from being unable to find `>`. We know the error |
| // must have been this due to a non-zero unmatched angle bracket |
| // count. |
| e.cancel(); |
| |
| // Swap `self` with our backup of the parser state before attempting to parse |
| // generic arguments. |
| let snapshot = mem::replace(self, snapshot.unwrap()); |
| |
| debug!( |
| "parse_generic_args_with_leading_angle_bracket_recovery: (snapshot failure) \ |
| snapshot.count={:?}", |
| snapshot.unmatched_angle_bracket_count, |
| ); |
| |
| // Eat the unmatched angle brackets. |
| for _ in 0..snapshot.unmatched_angle_bracket_count { |
| self.eat_lt(); |
| } |
| |
| // Make a span over ${unmatched angle bracket count} characters. |
| let span = lo.with_hi(lo.lo() + BytePos(snapshot.unmatched_angle_bracket_count)); |
| self.struct_span_err( |
| span, |
| &format!( |
| "unmatched angle bracket{}", |
| pluralize!(snapshot.unmatched_angle_bracket_count) |
| ), |
| ) |
| .span_suggestion( |
| span, |
| &format!( |
| "remove extra angle bracket{}", |
| pluralize!(snapshot.unmatched_angle_bracket_count) |
| ), |
| String::new(), |
| Applicability::MachineApplicable, |
| ) |
| .emit(); |
| |
| // Try again without unmatched angle bracket characters. |
| self.parse_angle_args() |
| } |
| Err(e) => Err(e), |
| } |
| } |
| |
| /// Parses (possibly empty) list of generic arguments / associated item constraints, |
| /// possibly including trailing comma. |
| pub(super) fn parse_angle_args(&mut self) -> PResult<'a, Vec<AngleBracketedArg>> { |
| let mut args = Vec::new(); |
| while let Some(arg) = self.parse_angle_arg()? { |
| args.push(arg); |
| if !self.eat(&token::Comma) { |
| if !self.token.kind.should_end_const_arg() { |
| if self.handle_ambiguous_unbraced_const_arg(&mut args)? { |
| // We've managed to (partially) recover, so continue trying to parse |
| // arguments. |
| continue; |
| } |
| } |
| break; |
| } |
| } |
| Ok(args) |
| } |
| |
| /// Parses a single argument in the angle arguments `<...>` of a path segment. |
| fn parse_angle_arg(&mut self) -> PResult<'a, Option<AngleBracketedArg>> { |
| let lo = self.token.span; |
| let arg = self.parse_generic_arg()?; |
| match arg { |
| Some(arg) => { |
| if self.check(&token::Colon) | self.check(&token::Eq) { |
| let (ident, gen_args) = self.get_ident_from_generic_arg(arg, lo)?; |
| let kind = if self.eat(&token::Colon) { |
| // Parse associated type constraint bound. |
| |
| let bounds = self.parse_generic_bounds(Some(self.prev_token.span))?; |
| AssocTyConstraintKind::Bound { bounds } |
| } else if self.eat(&token::Eq) { |
| // Parse associated type equality constraint |
| |
| let ty = self.parse_assoc_equality_term(ident, self.prev_token.span)?; |
| AssocTyConstraintKind::Equality { ty } |
| } else { |
| unreachable!(); |
| }; |
| |
| let span = lo.to(self.prev_token.span); |
| |
| // Gate associated type bounds, e.g., `Iterator<Item: Ord>`. |
| if let AssocTyConstraintKind::Bound { .. } = kind { |
| self.sess.gated_spans.gate(sym::associated_type_bounds, span); |
| } |
| let constraint = |
| AssocTyConstraint { id: ast::DUMMY_NODE_ID, ident, gen_args, kind, span }; |
| Ok(Some(AngleBracketedArg::Constraint(constraint))) |
| } else { |
| Ok(Some(AngleBracketedArg::Arg(arg))) |
| } |
| } |
| _ => Ok(None), |
| } |
| } |
| |
| /// Parse the term to the right of an associated item equality constraint. |
| /// That is, parse `<term>` in `Item = <term>`. |
| /// Right now, this only admits types in `<term>`. |
| fn parse_assoc_equality_term(&mut self, ident: Ident, eq: Span) -> PResult<'a, P<ast::Ty>> { |
| let arg = self.parse_generic_arg()?; |
| let span = ident.span.to(self.prev_token.span); |
| match arg { |
| Some(GenericArg::Type(ty)) => return Ok(ty), |
| Some(GenericArg::Const(expr)) => { |
| self.struct_span_err(span, "cannot constrain an associated constant to a value") |
| .span_label(ident.span, "this associated constant...") |
| .span_label(expr.value.span, "...cannot be constrained to this value") |
| .emit(); |
| } |
| Some(GenericArg::Lifetime(lt)) => { |
| self.struct_span_err(span, "associated lifetimes are not supported") |
| .span_label(lt.ident.span, "the lifetime is given here") |
| .help("if you meant to specify a trait object, write `dyn Trait + 'lifetime`") |
| .emit(); |
| } |
| None => { |
| let after_eq = eq.shrink_to_hi(); |
| let before_next = self.token.span.shrink_to_lo(); |
| self.struct_span_err(after_eq.to(before_next), "missing type to the right of `=`") |
| .span_suggestion( |
| self.sess.source_map().next_point(eq).to(before_next), |
| "to constrain the associated type, add a type after `=`", |
| " TheType".to_string(), |
| Applicability::HasPlaceholders, |
| ) |
| .span_suggestion( |
| eq.to(before_next), |
| &format!("remove the `=` if `{}` is a type", ident), |
| String::new(), |
| Applicability::MaybeIncorrect, |
| ) |
| .emit(); |
| } |
| } |
| Ok(self.mk_ty(span, ast::TyKind::Err)) |
| } |
| |
| /// We do not permit arbitrary expressions as const arguments. They must be one of: |
| /// - An expression surrounded in `{}`. |
| /// - A literal. |
| /// - A numeric literal prefixed by `-`. |
| /// - A single-segment path. |
| pub(super) fn expr_is_valid_const_arg(&self, expr: &P<rustc_ast::Expr>) -> bool { |
| match &expr.kind { |
| ast::ExprKind::Block(_, _) | ast::ExprKind::Lit(_) => true, |
| ast::ExprKind::Unary(ast::UnOp::Neg, expr) => { |
| matches!(expr.kind, ast::ExprKind::Lit(_)) |
| } |
| // We can only resolve single-segment paths at the moment, because multi-segment paths |
| // require type-checking: see `visit_generic_arg` in `src/librustc_resolve/late.rs`. |
| ast::ExprKind::Path(None, path) |
| if path.segments.len() == 1 && path.segments[0].args.is_none() => |
| { |
| true |
| } |
| _ => false, |
| } |
| } |
| |
| /// Parse a const argument, e.g. `<3>`. It is assumed the angle brackets will be parsed by |
| /// the caller. |
| pub(super) fn parse_const_arg(&mut self) -> PResult<'a, AnonConst> { |
| // Parse const argument. |
| let value = if let token::OpenDelim(token::Brace) = self.token.kind { |
| self.parse_block_expr( |
| None, |
| self.token.span, |
| BlockCheckMode::Default, |
| ast::AttrVec::new(), |
| )? |
| } else { |
| self.handle_unambiguous_unbraced_const_arg()? |
| }; |
| Ok(AnonConst { id: ast::DUMMY_NODE_ID, value }) |
| } |
| |
| /// Parse a generic argument in a path segment. |
| /// This does not include constraints, e.g., `Item = u8`, which is handled in `parse_angle_arg`. |
| fn parse_generic_arg(&mut self) -> PResult<'a, Option<GenericArg>> { |
| let start = self.token.span; |
| let arg = if self.check_lifetime() && self.look_ahead(1, |t| !t.is_like_plus()) { |
| // Parse lifetime argument. |
| GenericArg::Lifetime(self.expect_lifetime()) |
| } else if self.check_const_arg() { |
| // Parse const argument. |
| GenericArg::Const(self.parse_const_arg()?) |
| } else if self.check_type() { |
| // Parse type argument. |
| match self.parse_ty() { |
| Ok(ty) => GenericArg::Type(ty), |
| Err(err) => { |
| // Try to recover from possible `const` arg without braces. |
| return self.recover_const_arg(start, err).map(Some); |
| } |
| } |
| } else { |
| return Ok(None); |
| }; |
| Ok(Some(arg)) |
| } |
| |
| fn get_ident_from_generic_arg( |
| &self, |
| gen_arg: GenericArg, |
| lo: Span, |
| ) -> PResult<'a, (Ident, Option<GenericArgs>)> { |
| let gen_arg_span = gen_arg.span(); |
| match gen_arg { |
| GenericArg::Type(t) => match t.into_inner().kind { |
| ast::TyKind::Path(qself, mut path) => { |
| if let Some(qself) = qself { |
| let mut err = self.struct_span_err( |
| gen_arg_span, |
| "qualified paths cannot be used in associated type constraints", |
| ); |
| err.span_label( |
| qself.path_span, |
| "not allowed in associated type constraints", |
| ); |
| return Err(err); |
| } |
| if path.segments.len() == 1 { |
| let path_seg = path.segments.remove(0); |
| let ident = path_seg.ident; |
| let gen_args = path_seg.args.map(|args| args.into_inner()); |
| return Ok((ident, gen_args)); |
| } |
| let err = self.struct_span_err( |
| path.span, |
| "paths with multiple segments cannot be used in associated type constraints", |
| ); |
| return Err(err); |
| } |
| _ => { |
| let span = lo.to(self.prev_token.span); |
| let err = self.struct_span_err( |
| span, |
| "only path types can be used in associated type constraints", |
| ); |
| return Err(err); |
| } |
| }, |
| _ => { |
| let span = lo.to(self.prev_token.span); |
| let err = self |
| .struct_span_err(span, "only types can be used in associated type constraints"); |
| return Err(err); |
| } |
| } |
| } |
| } |
