src/librustc_ast_lowering/path.rs

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