use super::ty::{AllowPlus, RecoverQPath, RecoverReturnSign}; use super::{Parser, Restrictions, TokenType}; use crate::maybe_whole; use rustc_ast::ptr::P; use rustc_ast::token::{self, Delimiter, Token, TokenKind}; use rustc_ast::{ self as ast, AngleBracketedArg, AngleBracketedArgs, AnonConst, AssocConstraint, AssocConstraintKind, BlockCheckMode, GenericArg, GenericArgs, Generics, ParenthesizedArgs, 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; /// 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` - comparisons, `x::` - unambiguously a path. Expr, /// In other contexts, notably in types, no ambiguity exists and paths can be written /// without the disambiguator, e.g., `x` - unambiguously a path. /// Paths with disambiguators are still accepted, `x::` - 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 = ::path` /// /// # Examples /// `::default` /// `::a` /// `::F::a` (without disambiguator) /// `::F::a::` (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 `::*` examples // above). `path_span` has the span of that path, or an empty // span in the case of something like `::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, None)?; 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) /// >:Qux /// ^ help: use double colon /// ``` fn recover_colon_before_qpath_proj(&mut self) -> bool { if !self.check_noexpect(&TokenKind::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", "::", Applicability::MachineApplicable, ) .emit(); true } pub(super) fn parse_path(&mut self, style: PathStyle) -> PResult<'a, Path> { self.parse_path_inner(style, None) } /// Parses simple paths. /// /// `path = [::] segment+` /// `segment = ident | ident[::] | ident[::](args) [-> type]` /// /// # Examples /// `a::b::C` (without disambiguator) /// `a::b::C::` (with disambiguator) /// `Fn(Args)` (without disambiguator) /// `Fn::(Args)` (with disambiguator) pub(super) fn parse_path_inner( &mut self, style: PathStyle, ty_generics: Option<&Generics>, ) -> PResult<'a, Path> { let reject_generics_if_mod_style = |parser: &Parser<'_>, path: &Path| { // Ensure generic arguments don't end up in attribute paths, such as: // // macro_rules! m { // ($p:path) => { #[$p] struct S; } // } // // m!(inline); //~ ERROR: unexpected generic arguments in path // if style == PathStyle::Mod && path.segments.iter().any(|segment| segment.args.is_some()) { parser .struct_span_err( path.segments .iter() .filter_map(|segment| segment.args.as_ref()) .map(|arg| arg.span()) .collect::>(), "unexpected generic arguments in path", ) .emit(); } }; maybe_whole!(self, NtPath, |path| { reject_generics_if_mod_style(self, &path); path.into_inner() }); if let token::Interpolated(nt) = &self.token.kind { if let token::NtTy(ty) = &**nt { if let ast::TyKind::Path(None, path) = &ty.kind { let path = path.clone(); self.bump(); reject_generics_if_mod_style(self, &path); return Ok(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, ty_generics)?; Ok(Path { segments, span: lo.to(self.prev_token.span), tokens: None }) } pub(super) fn parse_path_segments( &mut self, segments: &mut Vec, style: PathStyle, ty_generics: Option<&Generics>, ) -> PResult<'a, ()> { loop { let segment = self.parse_path_segment(style, ty_generics)?; 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::>::Qux` // ^ here // // As opposed to the below highlight (if we had only finished the first // recursion): // // `Foo::>::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, ty_generics: Option<&Generics>, ) -> 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(Delimiter::Parenthesis) | token::LArrow ) }; let check_args_start = |this: &mut Self| { this.expected_tokens.extend_from_slice(&[ TokenType::Token(token::Lt), TokenType::Token(token::OpenDelim(Delimiter::Parenthesis)), ]); 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, ty_generics, )?; self.expect_gt().map_err(|mut err| { // Attempt to find places where a missing `>` might belong. if let Some(arg) = args .iter() .rev() .skip_while(|arg| matches!(arg, AngleBracketedArg::Constraint(_))) .next() { err.span_suggestion_verbose( arg.span().shrink_to_hi(), "you might have meant to end the type parameters here", ">", Applicability::MaybeIncorrect, ); } err })?; 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 output = self.parse_ret_ty(AllowPlus::No, RecoverQPath::No, RecoverReturnSign::No)?; let span = ident.span.to(self.prev_token.span); 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::<<<::Output>(); /// ^^ help: remove extra angle brackets /// ``` fn parse_angle_args_with_leading_angle_bracket_recovery( &mut self, style: PathStyle, lo: Span, ty_generics: Option<&Generics>, ) -> PResult<'a, Vec> { // 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::<<<::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:* `<<<::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:* `<<::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(ty_generics) { Ok(args) => Ok(args), Err(e) if is_first_invocation && self.unmatched_angle_bracket_count > 0 => { // Swap `self` with our backup of the parser state before attempting to parse // generic arguments. let snapshot = mem::replace(self, snapshot.unwrap()); // Eat the unmatched angle brackets. let all_angle_brackets = (0..snapshot.unmatched_angle_bracket_count) .fold(true, |a, _| a && self.eat_lt()); if !all_angle_brackets { // If there are other tokens in between the extraneous `<`s, we cannot simply // suggest to remove them. This check also prevents us from accidentally ending // up in the middle of a multibyte character (issue #84104). let _ = mem::replace(self, snapshot); Err(e) } else { // 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(); debug!( "parse_generic_args_with_leading_angle_bracket_recovery: (snapshot failure) \ snapshot.count={:?}", snapshot.unmatched_angle_bracket_count, ); // Make a span over ${unmatched angle bracket count} characters. // This is safe because `all_angle_brackets` ensures that there are only `<`s, // i.e. no multibyte characters, in this range. 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) ), "", Applicability::MachineApplicable, ) .emit(); // Try again without unmatched angle bracket characters. self.parse_angle_args(ty_generics) } } 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, ty_generics: Option<&Generics>, ) -> PResult<'a, Vec> { let mut args = Vec::new(); while let Some(arg) = self.parse_angle_arg(ty_generics)? { args.push(arg); if !self.eat(&token::Comma) { if self.check_noexpect(&TokenKind::Semi) && self.look_ahead(1, |t| t.is_ident() || t.is_lifetime()) { // Add `>` to the list of expected tokens. self.check(&token::Gt); // Handle `,` to `;` substitution let mut err = self.unexpected::<()>().unwrap_err(); self.bump(); err.span_suggestion_verbose( self.prev_token.span.until(self.token.span), "use a comma to separate type parameters", ", ", Applicability::MachineApplicable, ); err.emit(); continue; } 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, ty_generics: Option<&Generics>, ) -> PResult<'a, Option> { let lo = self.token.span; let arg = self.parse_generic_arg(ty_generics)?; match arg { Some(arg) => { // we are using noexpect here because we first want to find out if either `=` or `:` // is present and then use that info to push the other token onto the tokens list let separated = self.check_noexpect(&token::Colon) || self.check_noexpect(&token::Eq); if separated && (self.check(&token::Colon) | self.check(&token::Eq)) { let arg_span = arg.span(); let (binder, ident, gen_args) = match self.get_ident_from_generic_arg(&arg) { Ok(ident_gen_args) => ident_gen_args, Err(()) => return Ok(Some(AngleBracketedArg::Arg(arg))), }; if binder { // FIXME(compiler-errors): this could be improved by suggesting lifting // this up to the trait, at least before this becomes real syntax. // e.g. `Trait Assoc = Ty>` -> `for<'a> Trait` return Err(self.struct_span_err( arg_span, "`for<...>` is not allowed on associated type bounds", )); } let kind = if self.eat(&token::Colon) { // Parse associated type constraint bound. let bounds = self.parse_generic_bounds(Some(self.prev_token.span))?; AssocConstraintKind::Bound { bounds } } else if self.eat(&token::Eq) { self.parse_assoc_equality_term(ident, self.prev_token.span)? } else { unreachable!(); }; let span = lo.to(self.prev_token.span); // Gate associated type bounds, e.g., `Iterator`. if let AssocConstraintKind::Bound { .. } = kind { self.sess.gated_spans.gate(sym::associated_type_bounds, span); } let constraint = AssocConstraint { id: ast::DUMMY_NODE_ID, ident, gen_args, kind, span }; Ok(Some(AngleBracketedArg::Constraint(constraint))) } else { // we only want to suggest `:` and `=` in contexts where the previous token // is an ident and the current token or the next token is an ident if self.prev_token.is_ident() && (self.token.is_ident() || self.look_ahead(1, |token| token.is_ident())) { self.check(&token::Colon); self.check(&token::Eq); } Ok(Some(AngleBracketedArg::Arg(arg))) } } _ => Ok(None), } } /// Parse the term to the right of an associated item equality constraint. /// That is, parse `` in `Item = `. /// Right now, this only admits types in ``. fn parse_assoc_equality_term( &mut self, ident: Ident, eq: Span, ) -> PResult<'a, AssocConstraintKind> { let arg = self.parse_generic_arg(None)?; let span = ident.span.to(self.prev_token.span); let term = match arg { Some(GenericArg::Type(ty)) => ty.into(), Some(GenericArg::Const(c)) => { self.sess.gated_spans.gate(sym::associated_const_equality, span); c.into() } 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(); self.mk_ty(span, ast::TyKind::Err).into() } None => { let after_eq = eq.shrink_to_hi(); let before_next = self.token.span.shrink_to_lo(); let mut err = self .struct_span_err(after_eq.to(before_next), "missing type to the right of `=`"); if matches!(self.token.kind, token::Comma | token::Gt) { err.span_suggestion( self.sess.source_map().next_point(eq).to(before_next), "to constrain the associated type, add a type after `=`", " TheType", Applicability::HasPlaceholders, ); err.span_suggestion( eq.to(before_next), &format!("remove the `=` if `{}` is a type", ident), "", Applicability::MaybeIncorrect, ) } else { err.span_label( self.token.span, &format!("expected type, found {}", super::token_descr(&self.token)), ) }; return Err(err); } }; Ok(AssocConstraintKind::Equality { term }) } /// 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) -> 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(Delimiter::Brace) = self.token.kind { self.parse_block_expr(None, self.token.span, BlockCheckMode::Default)? } 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`. pub(super) fn parse_generic_arg( &mut self, ty_generics: Option<&Generics>, ) -> PResult<'a, Option> { 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. let is_const_fn = self.look_ahead(1, |t| t.kind == token::OpenDelim(Delimiter::Parenthesis)); let mut snapshot = self.create_snapshot_for_diagnostic(); match self.parse_ty() { Ok(ty) => GenericArg::Type(ty), Err(err) => { if is_const_fn { match (*snapshot).parse_expr_res(Restrictions::CONST_EXPR, None) { Ok(expr) => { self.restore_snapshot(snapshot); return Ok(Some(self.dummy_const_arg_needs_braces(err, expr.span))); } Err(err) => { err.cancel(); } } } // Try to recover from possible `const` arg without braces. return self.recover_const_arg(start, err).map(Some); } } } else if self.token.is_keyword(kw::Const) { return self.recover_const_param_declaration(ty_generics); } else { // Fall back by trying to parse a const-expr expression. If we successfully do so, // then we should report an error that it needs to be wrapped in braces. let snapshot = self.create_snapshot_for_diagnostic(); match self.parse_expr_res(Restrictions::CONST_EXPR, None) { Ok(expr) => { return Ok(Some(self.dummy_const_arg_needs_braces( self.struct_span_err(expr.span, "invalid const generic expression"), expr.span, ))); } Err(err) => { self.restore_snapshot(snapshot); err.cancel(); return Ok(None); } } }; Ok(Some(arg)) } /// Given a arg inside of generics, we try to destructure it as if it were the LHS in /// `LHS = ...`, i.e. an associated type binding. /// This returns a bool indicating if there are any `for<'a, 'b>` binder args, the /// identifier, and any GAT arguments. fn get_ident_from_generic_arg( &self, gen_arg: &GenericArg, ) -> Result<(bool, Ident, Option), ()> { if let GenericArg::Type(ty) = gen_arg { if let ast::TyKind::Path(qself, path) = &ty.kind && qself.is_none() && let [seg] = path.segments.as_slice() { return Ok((false, seg.ident, seg.args.as_deref().cloned())); } else if let ast::TyKind::TraitObject(bounds, ast::TraitObjectSyntax::None) = &ty.kind && let [ast::GenericBound::Trait(trait_ref, ast::TraitBoundModifier::None)] = bounds.as_slice() && let [seg] = trait_ref.trait_ref.path.segments.as_slice() { return Ok((true, seg.ident, seg.args.as_deref().cloned())); } } Err(()) } }