src/librustc_ast_lowering/path.rs

   1 use super::{AnonymousLifetimeMode, ImplTraitContext, LoweringContext, ParamMode};
   2 use super::{GenericArgsCtor, ParenthesizedGenericArgs};
   3
   4 use rustc_ast::ast::{self, *};
   5 use rustc_errors::{struct_span_err, Applicability};
   6 use rustc_hir as hir;
   7 use rustc_hir::def::{DefKind, PartialRes, Res};
   8 use rustc_hir::def_id::DefId;
   9 use rustc_hir::GenericArg;
  10 use rustc_session::lint::builtin::ELIDED_LIFETIMES_IN_PATHS;
  11 use rustc_session::lint::BuiltinLintDiagnostics;
  12 use rustc_span::symbol::Ident;
  13 use rustc_span::Span;
  14
  15 use log::debug;
  16 use smallvec::smallvec;
  17
  18 impl<'a, 'hir> LoweringContext<'a, 'hir> {
  19     crate fn lower_qpath(
  20         &mut self,
  21         id: NodeId,
  22         qself: &Option<QSelf>,
  23         p: &Path,
  24         param_mode: ParamMode,
  25         mut itctx: ImplTraitContext<'_, 'hir>,
  26     ) -> hir::QPath<'hir> {
  27         let qself_position = qself.as_ref().map(|q| q.position);
  28         let qself = qself.as_ref().map(|q| self.lower_ty(&q.ty, itctx.reborrow()));
  29
  30         let partial_res =
  31             self.resolver.get_partial_res(id).unwrap_or_else(|| PartialRes::new(Res::Err));
  32
  33         let proj_start = p.segments.len() - partial_res.unresolved_segments();
  34         let path = self.arena.alloc(hir::Path {
  35             res: self.lower_res(partial_res.base_res()),
  36             segments: self.arena.alloc_from_iter(p.segments[..proj_start].iter().enumerate().map(
  37                 |(i, segment)| {
  38                     let param_mode = match (qself_position, param_mode) {
  39                         (Some(j), ParamMode::Optional) if i < j => {
  40                             // This segment is part of the trait path in a
  41                             // qualified path - one of `a`, `b` or `Trait`
  42                             // in `<X as a::b::Trait>::T::U::method`.
  43                             ParamMode::Explicit
  44                         }
  45                         _ => param_mode,
  46                     };
  47
  48                     // Figure out if this is a type/trait segment,
  49                     // which may need lifetime elision performed.
  50                     let parent_def_id = |this: &mut Self, def_id: DefId| DefId {
  51                         krate: def_id.krate,
  52                         index: this.resolver.def_key(def_id).parent.expect("missing parent"),
  53                     };
  54                     let type_def_id = match partial_res.base_res() {
  55                         Res::Def(DefKind::AssocTy, def_id) if i + 2 == proj_start => {
  56                             Some(parent_def_id(self, def_id))
  57                         }
  58                         Res::Def(DefKind::Variant, def_id) if i + 1 == proj_start => {
  59                             Some(parent_def_id(self, def_id))
  60                         }
  61                         Res::Def(DefKind::Struct, def_id)
  62                         | Res::Def(DefKind::Union, def_id)
  63                         | Res::Def(DefKind::Enum, def_id)
  64                         | Res::Def(DefKind::TyAlias, def_id)
  65                         | Res::Def(DefKind::Trait, def_id)
  66                             if i + 1 == proj_start =>
  67                         {
  68                             Some(def_id)
  69                         }
  70                         _ => None,
  71                     };
  72                     let parenthesized_generic_args = match partial_res.base_res() {
  73                         // `a::b::Trait(Args)`
  74                         Res::Def(DefKind::Trait, _) if i + 1 == proj_start => {
  75                             ParenthesizedGenericArgs::Ok
  76                         }
  77                         // `a::b::Trait(Args)::TraitItem`
  78                         Res::Def(DefKind::AssocFn, _)
  79                         | Res::Def(DefKind::AssocConst, _)
  80                         | Res::Def(DefKind::AssocTy, _)
  81                             if i + 2 == proj_start =>
  82                         {
  83                             ParenthesizedGenericArgs::Ok
  84                         }
  85                         // Avoid duplicated errors.
  86                         Res::Err => ParenthesizedGenericArgs::Ok,
  87                         // An error
  88                         _ => ParenthesizedGenericArgs::Err,
  89                     };
  90
  91                     let num_lifetimes = type_def_id.map_or(0, |def_id| {
  92                         if let Some(&n) = self.type_def_lifetime_params.get(&def_id) {
  93                             return n;
  94                         }
  95                         assert!(!def_id.is_local());
  96                         let n = self.resolver.item_generics_num_lifetimes(def_id, self.sess);
  97                         self.type_def_lifetime_params.insert(def_id, n);
  98                         n
  99                     });
 100                     self.lower_path_segment(
 101                         p.span,
 102                         segment,
 103                         param_mode,
 104                         num_lifetimes,
 105                         parenthesized_generic_args,
 106                         itctx.reborrow(),
 107                         None,
 108                     )
 109                 },
 110             )),
 111             span: p.span,
 112         });
 113
 114         // Simple case, either no projections, or only fully-qualified.
 115         // E.g., `std::mem::size_of` or `<I as Iterator>::Item`.
 116         if partial_res.unresolved_segments() == 0 {
 117             return hir::QPath::Resolved(qself, path);
 118         }
 119
 120         // Create the innermost type that we're projecting from.
 121         let mut ty = if path.segments.is_empty() {
 122             // If the base path is empty that means there exists a
 123             // syntactical `Self`, e.g., `&i32` in `<&i32>::clone`.
 124             qself.expect("missing QSelf for <T>::...")
 125         } else {
 126             // Otherwise, the base path is an implicit `Self` type path,
 127             // e.g., `Vec` in `Vec::new` or `<I as Iterator>::Item` in
 128             // `<I as Iterator>::Item::default`.
 129             let new_id = self.next_id();
 130             self.arena.alloc(self.ty_path(new_id, p.span, hir::QPath::Resolved(qself, path)))
 131         };
 132
 133         // Anything after the base path are associated "extensions",
 134         // out of which all but the last one are associated types,
 135         // e.g., for `std::vec::Vec::<T>::IntoIter::Item::clone`:
 136         // * base path is `std::vec::Vec<T>`
 137         // * "extensions" are `IntoIter`, `Item` and `clone`
 138         // * type nodes are:
 139         //   1. `std::vec::Vec<T>` (created above)
 140         //   2. `<std::vec::Vec<T>>::IntoIter`
 141         //   3. `<<std::vec::Vec<T>>::IntoIter>::Item`
 142         // * final path is `<<<std::vec::Vec<T>>::IntoIter>::Item>::clone`
 143         for (i, segment) in p.segments.iter().enumerate().skip(proj_start) {
 144             let segment = self.arena.alloc(self.lower_path_segment(
 145                 p.span,
 146                 segment,
 147                 param_mode,
 148                 0,
 149                 ParenthesizedGenericArgs::Err,
 150                 itctx.reborrow(),
 151                 None,
 152             ));
 153             let qpath = hir::QPath::TypeRelative(ty, segment);
 154
 155             // It's finished, return the extension of the right node type.
 156             if i == p.segments.len() - 1 {
 157                 return qpath;
 158             }
 159
 160             // Wrap the associated extension in another type node.
 161             let new_id = self.next_id();
 162             ty = self.arena.alloc(self.ty_path(new_id, p.span, qpath));
 163         }
 164
 165         // We should've returned in the for loop above.
 166
 167         self.sess.diagnostic().span_bug(
 168             p.span,
 169             &format!(
 170                 "lower_qpath: no final extension segment in {}..{}",
 171                 proj_start,
 172                 p.segments.len()
 173             ),
 174         );
 175     }
 176
 177     crate fn lower_path_extra(
 178         &mut self,
 179         res: Res,
 180         p: &Path,
 181         param_mode: ParamMode,
 182         explicit_owner: Option<NodeId>,
 183     ) -> &'hir hir::Path<'hir> {
 184         self.arena.alloc(hir::Path {
 185             res,
 186             segments: self.arena.alloc_from_iter(p.segments.iter().map(|segment| {
 187                 self.lower_path_segment(
 188                     p.span,
 189                     segment,
 190                     param_mode,
 191                     0,
 192                     ParenthesizedGenericArgs::Err,
 193                     ImplTraitContext::disallowed(),
 194                     explicit_owner,
 195                 )
 196             })),
 197             span: p.span,
 198         })
 199     }
 200
 201     crate fn lower_path(
 202         &mut self,
 203         id: NodeId,
 204         p: &Path,
 205         param_mode: ParamMode,
 206     ) -> &'hir hir::Path<'hir> {
 207         let res = self.expect_full_res(id);
 208         let res = self.lower_res(res);
 209         self.lower_path_extra(res, p, param_mode, None)
 210     }
 211
 212     crate fn lower_path_segment(
 213         &mut self,
 214         path_span: Span,
 215         segment: &PathSegment,
 216         param_mode: ParamMode,
 217         expected_lifetimes: usize,
 218         parenthesized_generic_args: ParenthesizedGenericArgs,
 219         itctx: ImplTraitContext<'_, 'hir>,
 220         explicit_owner: Option<NodeId>,
 221     ) -> hir::PathSegment<'hir> {
 222         let (mut generic_args, infer_args) = if let Some(ref generic_args) = segment.args {
 223             let msg = "parenthesized type parameters may only be used with a `Fn` trait";
 224             match **generic_args {
 225                 GenericArgs::AngleBracketed(ref data) => {
 226                     self.lower_angle_bracketed_parameter_data(data, param_mode, itctx)
 227                 }
 228                 GenericArgs::Parenthesized(ref data) => match parenthesized_generic_args {
 229                     ParenthesizedGenericArgs::Ok => self.lower_parenthesized_parameter_data(data),
 230                     ParenthesizedGenericArgs::Err => {
 231                         let mut err = struct_span_err!(self.sess, data.span, E0214, "{}", msg);
 232                         err.span_label(data.span, "only `Fn` traits may use parentheses");
 233                         if let Ok(snippet) = self.sess.source_map().span_to_snippet(data.span) {
 234                             // Do not suggest going from `Trait()` to `Trait<>`
 235                             if !data.inputs.is_empty() {
 236                                 if let Some(split) = snippet.find('(') {
 237                                     let trait_name = &snippet[0..split];
 238                                     let args = &snippet[split + 1..snippet.len() - 1];
 239                                     err.span_suggestion(
 240                                         data.span,
 241                                         "use angle brackets instead",
 242                                         format!("{}<{}>", trait_name, args),
 243                                         Applicability::MaybeIncorrect,
 244                                     );
 245                                 }
 246                             }
 247                         };
 248                         err.emit();
 249                         (
 250                             self.lower_angle_bracketed_parameter_data(
 251                                 &data.as_angle_bracketed_args(),
 252                                 param_mode,
 253                                 itctx,
 254                             )
 255                             .0,
 256                             false,
 257                         )
 258                     }
 259                 },
 260             }
 261         } else {
 262             self.lower_angle_bracketed_parameter_data(&Default::default(), param_mode, itctx)
 263         };
 264
 265         let has_lifetimes = generic_args.args.iter().any(|arg| match arg {
 266             GenericArg::Lifetime(_) => true,
 267             _ => false,
 268         });
 269         let first_generic_span = generic_args
 270             .args
 271             .iter()
 272             .map(|a| a.span())
 273             .chain(generic_args.bindings.iter().map(|b| b.span))
 274             .next();
 275         if !generic_args.parenthesized && !has_lifetimes {
 276             generic_args.args = self
 277                 .elided_path_lifetimes(
 278                     first_generic_span.map(|s| s.shrink_to_lo()).unwrap_or(segment.ident.span),
 279                     expected_lifetimes,
 280                 )
 281                 .map(GenericArg::Lifetime)
 282                 .chain(generic_args.args.into_iter())
 283                 .collect();
 284             if expected_lifetimes > 0 && param_mode == ParamMode::Explicit {
 285                 let anon_lt_suggestion = vec!["'_"; expected_lifetimes].join(", ");
 286                 let no_non_lt_args = generic_args.args.len() == expected_lifetimes;
 287                 let no_bindings = generic_args.bindings.is_empty();
 288                 let (incl_angl_brckt, insertion_sp, suggestion) = if no_non_lt_args && no_bindings {
 289                     // If there are no (non-implicit) generic args or associated type
 290                     // bindings, our suggestion includes the angle brackets.
 291                     (true, path_span.shrink_to_hi(), format!("<{}>", anon_lt_suggestion))
 292                 } else {
 293                     // Otherwise (sorry, this is kind of gross) we need to infer the
 294                     // place to splice in the `'_, ` from the generics that do exist.
 295                     let first_generic_span = first_generic_span
 296                         .expect("already checked that non-lifetime args or bindings exist");
 297                     (false, first_generic_span.shrink_to_lo(), format!("{}, ", anon_lt_suggestion))
 298                 };
 299                 match self.anonymous_lifetime_mode {
 300                     // In create-parameter mode we error here because we don't want to support
 301                     // deprecated impl elision in new features like impl elision and `async fn`,
 302                     // both of which work using the `CreateParameter` mode:
 303                     //
 304                     //     impl Foo for std::cell::Ref<u32> // note lack of '_
 305                     //     async fn foo(_: std::cell::Ref<u32>) { ... }
 306                     AnonymousLifetimeMode::CreateParameter => {
 307                         let mut err = struct_span_err!(
 308                             self.sess,
 309                             path_span,
 310                             E0726,
 311                             "implicit elided lifetime not allowed here"
 312                         );
 313                         rustc_session::lint::add_elided_lifetime_in_path_suggestion(
 314                             &self.sess,
 315                             &mut err,
 316                             expected_lifetimes,
 317                             path_span,
 318                             incl_angl_brckt,
 319                             insertion_sp,
 320                             suggestion,
 321                         );
 322                         err.emit();
 323                     }
 324                     AnonymousLifetimeMode::PassThrough | AnonymousLifetimeMode::ReportError => {
 325                         self.resolver.lint_buffer().buffer_lint_with_diagnostic(
 326                             ELIDED_LIFETIMES_IN_PATHS,
 327                             CRATE_NODE_ID,
 328                             path_span,
 329                             "hidden lifetime parameters in types are deprecated",
 330                             BuiltinLintDiagnostics::ElidedLifetimesInPaths(
 331                                 expected_lifetimes,
 332                                 path_span,
 333                                 incl_angl_brckt,
 334                                 insertion_sp,
 335                                 suggestion,
 336                             ),
 337                         );
 338                     }
 339                 }
 340             }
 341         }
 342
 343         let res = self.expect_full_res(segment.id);
 344         let id = if let Some(owner) = explicit_owner {
 345             self.lower_node_id_with_owner(segment.id, owner)
 346         } else {
 347             self.lower_node_id(segment.id)
 348         };
 349         debug!(
 350             "lower_path_segment: ident={:?} original-id={:?} new-id={:?}",
 351             segment.ident, segment.id, id,
 352         );
 353
 354         hir::PathSegment {
 355             ident: segment.ident,
 356             hir_id: Some(id),
 357             res: Some(self.lower_res(res)),
 358             infer_args,
 359             args: if generic_args.is_empty() {
 360                 None
 361             } else {
 362                 Some(self.arena.alloc(generic_args.into_generic_args(self.arena)))
 363             },
 364         }
 365     }
 366
 367     fn lower_angle_bracketed_parameter_data(
 368         &mut self,
 369         data: &AngleBracketedArgs,
 370         param_mode: ParamMode,
 371         mut itctx: ImplTraitContext<'_, 'hir>,
 372     ) -> (GenericArgsCtor<'hir>, bool) {
 373         let has_non_lt_args = data.args.iter().any(|arg| match arg {
 374             AngleBracketedArg::Arg(ast::GenericArg::Lifetime(_))
 375             | AngleBracketedArg::Constraint(_) => false,
 376             AngleBracketedArg::Arg(ast::GenericArg::Type(_) | ast::GenericArg::Const(_)) => true,
 377         });
 378         let args = data
 379             .args
 380             .iter()
 381             .filter_map(|arg| match arg {
 382                 AngleBracketedArg::Arg(arg) => Some(self.lower_generic_arg(arg, itctx.reborrow())),
 383                 AngleBracketedArg::Constraint(_) => None,
 384             })
 385             .collect();
 386         let bindings = self.arena.alloc_from_iter(data.args.iter().filter_map(|arg| match arg {
 387             AngleBracketedArg::Constraint(c) => {
 388                 Some(self.lower_assoc_ty_constraint(c, itctx.reborrow()))
 389             }
 390             AngleBracketedArg::Arg(_) => None,
 391         }));
 392         let ctor = GenericArgsCtor { args, bindings, parenthesized: false };
 393         (ctor, !has_non_lt_args && param_mode == ParamMode::Optional)
 394     }
 395
 396     fn lower_parenthesized_parameter_data(
 397         &mut self,
 398         data: &ParenthesizedArgs,
 399     ) -> (GenericArgsCtor<'hir>, bool) {
 400         // Switch to `PassThrough` mode for anonymous lifetimes; this
 401         // means that we permit things like `&Ref<T>`, where `Ref` has
 402         // a hidden lifetime parameter. This is needed for backwards
 403         // compatibility, even in contexts like an impl header where
 404         // we generally don't permit such things (see #51008).
 405         self.with_anonymous_lifetime_mode(AnonymousLifetimeMode::PassThrough, |this| {
 406             let &ParenthesizedArgs { ref inputs, ref output, span } = data;
 407             let inputs = this.arena.alloc_from_iter(
 408                 inputs.iter().map(|ty| this.lower_ty_direct(ty, ImplTraitContext::disallowed())),
 409             );
 410             let output_ty = match output {
 411                 FnRetTy::Ty(ty) => this.lower_ty(&ty, ImplTraitContext::disallowed()),
 412                 FnRetTy::Default(_) => this.arena.alloc(this.ty_tup(span, &[])),
 413             };
 414             let args = smallvec![GenericArg::Type(this.ty_tup(span, inputs))];
 415             let binding = this.output_ty_binding(output_ty.span, output_ty);
 416             (
 417                 GenericArgsCtor { args, bindings: arena_vec![this; binding], parenthesized: true },
 418                 false,
 419             )
 420         })
 421     }
 422
 423     /// An associated type binding `Output = $ty`.
 424     crate fn output_ty_binding(
 425         &mut self,
 426         span: Span,
 427         ty: &'hir hir::Ty<'hir>,
 428     ) -> hir::TypeBinding<'hir> {
 429         let ident = Ident::with_dummy_span(hir::FN_OUTPUT_NAME);
 430         let kind = hir::TypeBindingKind::Equality { ty };
 431         hir::TypeBinding { hir_id: self.next_id(), span, ident, kind }
 432     }
 433 }