compiler/rustc_ast_lowering/src/path.rs

   1 use super::{AnonymousLifetimeMode, ImplTraitContext, LoweringContext, ParamMode};
   2 use super::{GenericArgsCtor, ParenthesizedGenericArgs};
   3
   4 use rustc_ast::{self as ast, *};
   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::{BytePos, Span, DUMMY_SP};
  14
  15 use smallvec::smallvec;
  16 use tracing::debug;
  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         debug!("lower_qpath(id: {:?}, qself: {:?}, p: {:?})", id, qself, p);
  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 path_span_lo = p.span.shrink_to_lo();
  35         let proj_start = p.segments.len() - partial_res.unresolved_segments();
  36         let path = self.arena.alloc(hir::Path {
  37             res: self.lower_res(partial_res.base_res()),
  38             segments: self.arena.alloc_from_iter(p.segments[..proj_start].iter().enumerate().map(
  39                 |(i, segment)| {
  40                     let param_mode = match (qself_position, param_mode) {
  41                         (Some(j), ParamMode::Optional) if i < j => {
  42                             // This segment is part of the trait path in a
  43                             // qualified path - one of `a`, `b` or `Trait`
  44                             // in `<X as a::b::Trait>::T::U::method`.
  45                             ParamMode::Explicit
  46                         }
  47                         _ => param_mode,
  48                     };
  49
  50                     // Figure out if this is a type/trait segment,
  51                     // which may need lifetime elision performed.
  52                     let parent_def_id = |this: &mut Self, def_id: DefId| DefId {
  53                         krate: def_id.krate,
  54                         index: this.resolver.def_key(def_id).parent.expect("missing parent"),
  55                     };
  56                     let type_def_id = match partial_res.base_res() {
  57                         Res::Def(DefKind::AssocTy, def_id) if i + 2 == proj_start => {
  58                             Some(parent_def_id(self, def_id))
  59                         }
  60                         Res::Def(DefKind::Variant, def_id) if i + 1 == proj_start => {
  61                             Some(parent_def_id(self, def_id))
  62                         }
  63                         Res::Def(DefKind::Struct, def_id)
  64                         | Res::Def(DefKind::Union, def_id)
  65                         | Res::Def(DefKind::Enum, def_id)
  66                         | Res::Def(DefKind::TyAlias, def_id)
  67                         | Res::Def(DefKind::Trait, def_id)
  68                             if i + 1 == proj_start =>
  69                         {
  70                             Some(def_id)
  71                         }
  72                         _ => None,
  73                     };
  74                     let parenthesized_generic_args = match partial_res.base_res() {
  75                         // `a::b::Trait(Args)`
  76                         Res::Def(DefKind::Trait, _) if i + 1 == proj_start => {
  77                             ParenthesizedGenericArgs::Ok
  78                         }
  79                         // `a::b::Trait(Args)::TraitItem`
  80                         Res::Def(DefKind::AssocFn, _)
  81                         | Res::Def(DefKind::AssocConst, _)
  82                         | Res::Def(DefKind::AssocTy, _)
  83                             if i + 2 == proj_start =>
  84                         {
  85                             ParenthesizedGenericArgs::Ok
  86                         }
  87                         // Avoid duplicated errors.
  88                         Res::Err => ParenthesizedGenericArgs::Ok,
  89                         // An error
  90                         _ => ParenthesizedGenericArgs::Err,
  91                     };
  92
  93                     let num_lifetimes = type_def_id.map_or(0, |def_id| {
  94                         if let Some(&n) = self.type_def_lifetime_params.get(&def_id) {
  95                             return n;
  96                         }
  97                         assert!(!def_id.is_local());
  98                         let n = self.resolver.item_generics_num_lifetimes(def_id, self.sess);
  99                         self.type_def_lifetime_params.insert(def_id, n);
 100                         n
 101                     });
 102                     self.lower_path_segment(
 103                         p.span,
 104                         segment,
 105                         param_mode,
 106                         num_lifetimes,
 107                         parenthesized_generic_args,
 108                         itctx.reborrow(),
 109                         None,
 110                     )
 111                 },
 112             )),
 113             span: p.segments[..proj_start]
 114                 .last()
 115                 .map_or(path_span_lo, |segment| path_span_lo.to(segment.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, path.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 hir_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, hir_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, path_span_lo.to(segment.span()), qpath));
 167         }
 168
 169         // We should've returned in the for loop above.
 170
 171         self.sess.diagnostic().span_bug(
 172             p.span,
 173             &format!(
 174                 "lower_qpath: no final extension segment in {}..{}",
 175                 proj_start,
 176                 p.segments.len()
 177             ),
 178         );
 179     }
 180
 181     crate fn lower_path_extra(
 182         &mut self,
 183         res: Res,
 184         p: &Path,
 185         param_mode: ParamMode,
 186         explicit_owner: Option<NodeId>,
 187     ) -> &'hir hir::Path<'hir> {
 188         self.arena.alloc(hir::Path {
 189             res,
 190             segments: self.arena.alloc_from_iter(p.segments.iter().map(|segment| {
 191                 self.lower_path_segment(
 192                     p.span,
 193                     segment,
 194                     param_mode,
 195                     0,
 196                     ParenthesizedGenericArgs::Err,
 197                     ImplTraitContext::disallowed(),
 198                     explicit_owner,
 199                 )
 200             })),
 201             span: p.span,
 202         })
 203     }
 204
 205     crate fn lower_path(
 206         &mut self,
 207         id: NodeId,
 208         p: &Path,
 209         param_mode: ParamMode,
 210     ) -> &'hir hir::Path<'hir> {
 211         let res = self.expect_full_res(id);
 212         let res = self.lower_res(res);
 213         self.lower_path_extra(res, p, param_mode, None)
 214     }
 215
 216     crate fn lower_path_segment(
 217         &mut self,
 218         path_span: Span,
 219         segment: &PathSegment,
 220         param_mode: ParamMode,
 221         expected_lifetimes: usize,
 222         parenthesized_generic_args: ParenthesizedGenericArgs,
 223         itctx: ImplTraitContext<'_, 'hir>,
 224         explicit_owner: Option<NodeId>,
 225     ) -> hir::PathSegment<'hir> {
 226         debug!(
 227             "path_span: {:?}, lower_path_segment(segment: {:?}, expected_lifetimes: {:?})",
 228             path_span, segment, expected_lifetimes
 229         );
 230         let (mut generic_args, infer_args) = if let Some(ref generic_args) = segment.args {
 231             let msg = "parenthesized type parameters may only be used with a `Fn` trait";
 232             match **generic_args {
 233                 GenericArgs::AngleBracketed(ref data) => {
 234                     self.lower_angle_bracketed_parameter_data(data, param_mode, itctx)
 235                 }
 236                 GenericArgs::Parenthesized(ref data) => match parenthesized_generic_args {
 237                     ParenthesizedGenericArgs::Ok => self.lower_parenthesized_parameter_data(data),
 238                     ParenthesizedGenericArgs::Err => {
 239                         let mut err = struct_span_err!(self.sess, data.span, E0214, "{}", msg);
 240                         err.span_label(data.span, "only `Fn` traits may use parentheses");
 241                         if let Ok(snippet) = self.sess.source_map().span_to_snippet(data.span) {
 242                             // Do not suggest going from `Trait()` to `Trait<>`
 243                             if !data.inputs.is_empty() {
 244                                 if let Some(split) = snippet.find('(') {
 245                                     let trait_name = &snippet[0..split];
 246                                     let args = &snippet[split + 1..snippet.len() - 1];
 247                                     err.span_suggestion(
 248                                         data.span,
 249                                         "use angle brackets instead",
 250                                         format!("{}<{}>", trait_name, args),
 251                                         Applicability::MaybeIncorrect,
 252                                     );
 253                                 }
 254                             }
 255                         };
 256                         err.emit();
 257                         (
 258                             self.lower_angle_bracketed_parameter_data(
 259                                 &data.as_angle_bracketed_args(),
 260                                 param_mode,
 261                                 itctx,
 262                             )
 263                             .0,
 264                             false,
 265                         )
 266                     }
 267                 },
 268             }
 269         } else {
 270             (
 271                 GenericArgsCtor {
 272                     args: Default::default(),
 273                     bindings: &[],
 274                     parenthesized: false,
 275                     span: path_span.shrink_to_hi(),
 276                 },
 277                 param_mode == ParamMode::Optional,
 278             )
 279         };
 280
 281         let has_lifetimes =
 282             generic_args.args.iter().any(|arg| matches!(arg, GenericArg::Lifetime(_)));
 283         if !generic_args.parenthesized && !has_lifetimes {
 284             // Note: these spans are used for diagnostics when they can't be inferred.
 285             // See rustc_resolve::late::lifetimes::LifetimeContext::add_missing_lifetime_specifiers_label
 286             let elided_lifetime_span = if generic_args.span.is_empty() {
 287                 // If there are no brackets, use the identifier span.
 288                 segment.ident.span
 289             } else if generic_args.is_empty() {
 290                 // If there are brackets, but not generic arguments, then use the opening bracket
 291                 generic_args.span.with_hi(generic_args.span.lo() + BytePos(1))
 292             } else {
 293                 // Else use an empty span right after the opening bracket.
 294                 generic_args.span.with_lo(generic_args.span.lo() + BytePos(1)).shrink_to_lo()
 295             };
 296             generic_args.args = self
 297                 .elided_path_lifetimes(elided_lifetime_span, expected_lifetimes)
 298                 .map(GenericArg::Lifetime)
 299                 .chain(generic_args.args.into_iter())
 300                 .collect();
 301             if expected_lifetimes > 0 && param_mode == ParamMode::Explicit {
 302                 let anon_lt_suggestion = vec!["'_"; expected_lifetimes].join(", ");
 303                 let no_non_lt_args = generic_args.args.len() == expected_lifetimes;
 304                 let no_bindings = generic_args.bindings.is_empty();
 305                 let (incl_angl_brckt, insertion_sp, suggestion) = if no_non_lt_args && no_bindings {
 306                     // If there are no generic args, our suggestion can include the angle brackets.
 307                     (true, path_span.shrink_to_hi(), format!("<{}>", anon_lt_suggestion))
 308                 } else {
 309                     // Otherwise we'll insert a `'_, ` right after the opening bracket.
 310                     let span = generic_args
 311                         .span
 312                         .with_lo(generic_args.span.lo() + BytePos(1))
 313                         .shrink_to_lo();
 314                     (false, span, format!("{}, ", anon_lt_suggestion))
 315                 };
 316                 match self.anonymous_lifetime_mode {
 317                     // In create-parameter mode we error here because we don't want to support
 318                     // deprecated impl elision in new features like impl elision and `async fn`,
 319                     // both of which work using the `CreateParameter` mode:
 320                     //
 321                     //     impl Foo for std::cell::Ref<u32> // note lack of '_
 322                     //     async fn foo(_: std::cell::Ref<u32>) { ... }
 323                     AnonymousLifetimeMode::CreateParameter => {
 324                         let mut err = struct_span_err!(
 325                             self.sess,
 326                             path_span,
 327                             E0726,
 328                             "implicit elided lifetime not allowed here"
 329                         );
 330                         rustc_errors::add_elided_lifetime_in_path_suggestion(
 331                             &self.sess.source_map(),
 332                             &mut err,
 333                             expected_lifetimes,
 334                             path_span,
 335                             incl_angl_brckt,
 336                             insertion_sp,
 337                             suggestion,
 338                         );
 339                         err.note("assuming a `'static` lifetime...");
 340                         err.emit();
 341                     }
 342                     AnonymousLifetimeMode::PassThrough | AnonymousLifetimeMode::ReportError => {
 343                         self.resolver.lint_buffer().buffer_lint_with_diagnostic(
 344                             ELIDED_LIFETIMES_IN_PATHS,
 345                             CRATE_NODE_ID,
 346                             path_span,
 347                             "hidden lifetime parameters in types are deprecated",
 348                             BuiltinLintDiagnostics::ElidedLifetimesInPaths(
 349                                 expected_lifetimes,
 350                                 path_span,
 351                                 incl_angl_brckt,
 352                                 insertion_sp,
 353                                 suggestion,
 354                             ),
 355                         );
 356                     }
 357                 }
 358             }
 359         }
 360
 361         let res = self.expect_full_res(segment.id);
 362         let id = if let Some(owner) = explicit_owner {
 363             self.lower_node_id_with_owner(segment.id, owner)
 364         } else {
 365             self.lower_node_id(segment.id)
 366         };
 367         debug!(
 368             "lower_path_segment: ident={:?} original-id={:?} new-id={:?}",
 369             segment.ident, segment.id, id,
 370         );
 371
 372         hir::PathSegment {
 373             ident: segment.ident,
 374             hir_id: Some(id),
 375             res: Some(self.lower_res(res)),
 376             infer_args,
 377             args: if generic_args.is_empty() && generic_args.span.is_empty() {
 378                 None
 379             } else {
 380                 Some(self.arena.alloc(generic_args.into_generic_args(self.arena)))
 381             },
 382         }
 383     }
 384
 385     pub(crate) fn lower_angle_bracketed_parameter_data(
 386         &mut self,
 387         data: &AngleBracketedArgs,
 388         param_mode: ParamMode,
 389         mut itctx: ImplTraitContext<'_, 'hir>,
 390     ) -> (GenericArgsCtor<'hir>, bool) {
 391         let has_non_lt_args = data.args.iter().any(|arg| match arg {
 392             AngleBracketedArg::Arg(ast::GenericArg::Lifetime(_))
 393             | AngleBracketedArg::Constraint(_) => false,
 394             AngleBracketedArg::Arg(ast::GenericArg::Type(_) | ast::GenericArg::Const(_)) => true,
 395         });
 396         let args = data
 397             .args
 398             .iter()
 399             .filter_map(|arg| match arg {
 400                 AngleBracketedArg::Arg(arg) => Some(self.lower_generic_arg(arg, itctx.reborrow())),
 401                 AngleBracketedArg::Constraint(_) => None,
 402             })
 403             .collect();
 404         let bindings = self.arena.alloc_from_iter(data.args.iter().filter_map(|arg| match arg {
 405             AngleBracketedArg::Constraint(c) => {
 406                 Some(self.lower_assoc_ty_constraint(c, itctx.reborrow()))
 407             }
 408             AngleBracketedArg::Arg(_) => None,
 409         }));
 410         let ctor = GenericArgsCtor { args, bindings, parenthesized: false, span: data.span };
 411         (ctor, !has_non_lt_args && param_mode == ParamMode::Optional)
 412     }
 413
 414     fn lower_parenthesized_parameter_data(
 415         &mut self,
 416         data: &ParenthesizedArgs,
 417     ) -> (GenericArgsCtor<'hir>, bool) {
 418         // Switch to `PassThrough` mode for anonymous lifetimes; this
 419         // means that we permit things like `&Ref<T>`, where `Ref` has
 420         // a hidden lifetime parameter. This is needed for backwards
 421         // compatibility, even in contexts like an impl header where
 422         // we generally don't permit such things (see #51008).
 423         self.with_anonymous_lifetime_mode(AnonymousLifetimeMode::PassThrough, |this| {
 424             let ParenthesizedArgs { span, inputs, inputs_span, output } = data;
 425             let inputs = this.arena.alloc_from_iter(
 426                 inputs.iter().map(|ty| this.lower_ty_direct(ty, ImplTraitContext::disallowed())),
 427             );
 428             let output_ty = match output {
 429                 FnRetTy::Ty(ty) => this.lower_ty(&ty, ImplTraitContext::disallowed()),
 430                 FnRetTy::Default(_) => this.arena.alloc(this.ty_tup(*span, &[])),
 431             };
 432             let args = smallvec![GenericArg::Type(this.ty_tup(*inputs_span, inputs))];
 433             let binding = this.output_ty_binding(output_ty.span, output_ty);
 434             (
 435                 GenericArgsCtor {
 436                     args,
 437                     bindings: arena_vec![this; binding],
 438                     parenthesized: true,
 439                     span: data.inputs_span,
 440                 },
 441                 false,
 442             )
 443         })
 444     }
 445
 446     /// An associated type binding `Output = $ty`.
 447     crate fn output_ty_binding(
 448         &mut self,
 449         span: Span,
 450         ty: &'hir hir::Ty<'hir>,
 451     ) -> hir::TypeBinding<'hir> {
 452         let ident = Ident::with_dummy_span(hir::FN_OUTPUT_NAME);
 453         let kind = hir::TypeBindingKind::Equality { ty };
 454         let args = arena_vec![self;];
 455         let bindings = arena_vec![self;];
 456         let gen_args = self.arena.alloc(hir::GenericArgs {
 457             args,
 458             bindings,
 459             parenthesized: false,
 460             span_ext: DUMMY_SP,
 461         });
 462         hir::TypeBinding { hir_id: self.next_id(), gen_args, span, ident, kind }
 463     }
 464 }