src/librustc_ast_lowering/path.rs

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