compiler/rustc_ast_lowering/src/path.rs

   1 use crate::ImplTraitPosition;
   2
   3 use super::errors::{GenericTypeWithParentheses, UseAngleBrackets};
   4 use super::ResolverAstLoweringExt;
   5 use super::{GenericArgsCtor, LifetimeRes, ParenthesizedGenericArgs};
   6 use super::{ImplTraitContext, LoweringContext, ParamMode};
   7
   8 use rustc_ast::{self as ast, *};
   9 use rustc_hir as hir;
  10 use rustc_hir::def::{DefKind, PartialRes, Res};
  11 use rustc_hir::GenericArg;
  12 use rustc_span::symbol::{kw, 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     #[instrument(level = "trace", skip(self))]
  20     pub(crate) fn lower_qpath(
  21         &mut self,
  22         id: NodeId,
  23         qself: &Option<QSelf>,
  24         p: &Path,
  25         param_mode: ParamMode,
  26         itctx: ImplTraitContext,
  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));
  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                     let parenthesized_generic_args = match partial_res.base_res() {
  51                         // `a::b::Trait(Args)`
  52                         Res::Def(DefKind::Trait, _) if i + 1 == proj_start => {
  53                             ParenthesizedGenericArgs::Ok
  54                         }
  55                         // `a::b::Trait(Args)::TraitItem`
  56                         Res::Def(DefKind::AssocFn, _)
  57                         | Res::Def(DefKind::AssocConst, _)
  58                         | Res::Def(DefKind::AssocTy, _)
  59                             if i + 2 == proj_start =>
  60                         {
  61                             ParenthesizedGenericArgs::Ok
  62                         }
  63                         // Avoid duplicated errors.
  64                         Res::Err => ParenthesizedGenericArgs::Ok,
  65                         // An error
  66                         _ => ParenthesizedGenericArgs::Err,
  67                     };
  68
  69                     self.lower_path_segment(
  70                         p.span,
  71                         segment,
  72                         param_mode,
  73                         parenthesized_generic_args,
  74                         itctx,
  75                     )
  76                 },
  77             )),
  78             span: self.lower_span(
  79                 p.segments[..proj_start]
  80                     .last()
  81                     .map_or(path_span_lo, |segment| path_span_lo.to(segment.span())),
  82             ),
  83         });
  84
  85         // Simple case, either no projections, or only fully-qualified.
  86         // E.g., `std::mem::size_of` or `<I as Iterator>::Item`.
  87         if partial_res.unresolved_segments() == 0 {
  88             return hir::QPath::Resolved(qself, path);
  89         }
  90
  91         // Create the innermost type that we're projecting from.
  92         let mut ty = if path.segments.is_empty() {
  93             // If the base path is empty that means there exists a
  94             // syntactical `Self`, e.g., `&i32` in `<&i32>::clone`.
  95             qself.expect("missing QSelf for <T>::...")
  96         } else {
  97             // Otherwise, the base path is an implicit `Self` type path,
  98             // e.g., `Vec` in `Vec::new` or `<I as Iterator>::Item` in
  99             // `<I as Iterator>::Item::default`.
 100             let new_id = self.next_id();
 101             self.arena.alloc(self.ty_path(new_id, path.span, hir::QPath::Resolved(qself, path)))
 102         };
 103
 104         // Anything after the base path are associated "extensions",
 105         // out of which all but the last one are associated types,
 106         // e.g., for `std::vec::Vec::<T>::IntoIter::Item::clone`:
 107         // * base path is `std::vec::Vec<T>`
 108         // * "extensions" are `IntoIter`, `Item` and `clone`
 109         // * type nodes are:
 110         //   1. `std::vec::Vec<T>` (created above)
 111         //   2. `<std::vec::Vec<T>>::IntoIter`
 112         //   3. `<<std::vec::Vec<T>>::IntoIter>::Item`
 113         // * final path is `<<<std::vec::Vec<T>>::IntoIter>::Item>::clone`
 114         for (i, segment) in p.segments.iter().enumerate().skip(proj_start) {
 115             let hir_segment = self.arena.alloc(self.lower_path_segment(
 116                 p.span,
 117                 segment,
 118                 param_mode,
 119                 ParenthesizedGenericArgs::Err,
 120                 itctx,
 121             ));
 122             let qpath = hir::QPath::TypeRelative(ty, hir_segment);
 123
 124             // It's finished, return the extension of the right node type.
 125             if i == p.segments.len() - 1 {
 126                 return qpath;
 127             }
 128
 129             // Wrap the associated extension in another type node.
 130             let new_id = self.next_id();
 131             ty = self.arena.alloc(self.ty_path(new_id, path_span_lo.to(segment.span()), qpath));
 132         }
 133
 134         // We should've returned in the for loop above.
 135
 136         self.diagnostic().span_bug(
 137             p.span,
 138             &format!(
 139                 "lower_qpath: no final extension segment in {}..{}",
 140                 proj_start,
 141                 p.segments.len()
 142             ),
 143         );
 144     }
 145
 146     pub(crate) fn lower_path_extra(
 147         &mut self,
 148         res: Res,
 149         p: &Path,
 150         param_mode: ParamMode,
 151     ) -> &'hir hir::Path<'hir> {
 152         self.arena.alloc(hir::Path {
 153             res,
 154             segments: self.arena.alloc_from_iter(p.segments.iter().map(|segment| {
 155                 self.lower_path_segment(
 156                     p.span,
 157                     segment,
 158                     param_mode,
 159                     ParenthesizedGenericArgs::Err,
 160                     ImplTraitContext::Disallowed(ImplTraitPosition::Path),
 161                 )
 162             })),
 163             span: self.lower_span(p.span),
 164         })
 165     }
 166
 167     pub(crate) fn lower_path(
 168         &mut self,
 169         id: NodeId,
 170         p: &Path,
 171         param_mode: ParamMode,
 172     ) -> &'hir hir::Path<'hir> {
 173         let res = self.expect_full_res(id);
 174         let res = self.lower_res(res);
 175         self.lower_path_extra(res, p, param_mode)
 176     }
 177
 178     pub(crate) fn lower_path_segment(
 179         &mut self,
 180         path_span: Span,
 181         segment: &PathSegment,
 182         param_mode: ParamMode,
 183         parenthesized_generic_args: ParenthesizedGenericArgs,
 184         itctx: ImplTraitContext,
 185     ) -> hir::PathSegment<'hir> {
 186         debug!("path_span: {:?}, lower_path_segment(segment: {:?})", path_span, segment,);
 187         let (mut generic_args, infer_args) = if let Some(ref generic_args) = segment.args {
 188             match **generic_args {
 189                 GenericArgs::AngleBracketed(ref data) => {
 190                     self.lower_angle_bracketed_parameter_data(data, param_mode, itctx)
 191                 }
 192                 GenericArgs::Parenthesized(ref data) => match parenthesized_generic_args {
 193                     ParenthesizedGenericArgs::Ok => self.lower_parenthesized_parameter_data(data),
 194                     ParenthesizedGenericArgs::Err => {
 195                         // Suggest replacing parentheses with angle brackets `Trait(params...)` to `Trait<params...>`
 196                         let sub = if !data.inputs.is_empty() {
 197                             // Start of the span to the 1st character of 1st argument
 198                             let open_param = data.inputs_span.shrink_to_lo().to(data
 199                                 .inputs
 200                                 .first()
 201                                 .unwrap()
 202                                 .span
 203                                 .shrink_to_lo());
 204                             // Last character position of last argument to the end of the span
 205                             let close_param = data
 206                                 .inputs
 207                                 .last()
 208                                 .unwrap()
 209                                 .span
 210                                 .shrink_to_hi()
 211                                 .to(data.inputs_span.shrink_to_hi());
 212
 213                             Some(UseAngleBrackets { open_param, close_param })
 214                         } else {
 215                             None
 216                         };
 217                         self.tcx.sess.emit_err(GenericTypeWithParentheses { span: data.span, sub });
 218                         (
 219                             self.lower_angle_bracketed_parameter_data(
 220                                 &data.as_angle_bracketed_args(),
 221                                 param_mode,
 222                                 itctx,
 223                             )
 224                             .0,
 225                             false,
 226                         )
 227                     }
 228                 },
 229             }
 230         } else {
 231             (
 232                 GenericArgsCtor {
 233                     args: Default::default(),
 234                     bindings: &[],
 235                     parenthesized: false,
 236                     span: path_span.shrink_to_hi(),
 237                 },
 238                 param_mode == ParamMode::Optional,
 239             )
 240         };
 241
 242         let has_lifetimes =
 243             generic_args.args.iter().any(|arg| matches!(arg, GenericArg::Lifetime(_)));
 244         if !generic_args.parenthesized && !has_lifetimes {
 245             self.maybe_insert_elided_lifetimes_in_path(
 246                 path_span,
 247                 segment.id,
 248                 segment.ident.span,
 249                 &mut generic_args,
 250             );
 251         }
 252
 253         let res = self.expect_full_res(segment.id);
 254         let id = self.lower_node_id(segment.id);
 255         debug!(
 256             "lower_path_segment: ident={:?} original-id={:?} new-id={:?}",
 257             segment.ident, segment.id, id,
 258         );
 259
 260         hir::PathSegment {
 261             ident: self.lower_ident(segment.ident),
 262             hir_id: Some(id),
 263             res: Some(self.lower_res(res)),
 264             infer_args,
 265             args: if generic_args.is_empty() && generic_args.span.is_empty() {
 266                 None
 267             } else {
 268                 Some(generic_args.into_generic_args(self))
 269             },
 270         }
 271     }
 272
 273     fn maybe_insert_elided_lifetimes_in_path(
 274         &mut self,
 275         path_span: Span,
 276         segment_id: NodeId,
 277         segment_ident_span: Span,
 278         generic_args: &mut GenericArgsCtor<'hir>,
 279     ) {
 280         let (start, end) = match self.resolver.get_lifetime_res(segment_id) {
 281             Some(LifetimeRes::ElidedAnchor { start, end }) => (start, end),
 282             None => return,
 283             Some(_) => panic!(),
 284         };
 285         let expected_lifetimes = end.as_usize() - start.as_usize();
 286         debug!(expected_lifetimes);
 287
 288         // Note: these spans are used for diagnostics when they can't be inferred.
 289         // See rustc_resolve::late::lifetimes::LifetimeContext::add_missing_lifetime_specifiers_label
 290         let elided_lifetime_span = if generic_args.span.is_empty() {
 291             // If there are no brackets, use the identifier span.
 292             // HACK: we use find_ancestor_inside to properly suggest elided spans in paths
 293             // originating from macros, since the segment's span might be from a macro arg.
 294             segment_ident_span.find_ancestor_inside(path_span).unwrap_or(path_span)
 295         } else if generic_args.is_empty() {
 296             // If there are brackets, but not generic arguments, then use the opening bracket
 297             generic_args.span.with_hi(generic_args.span.lo() + BytePos(1))
 298         } else {
 299             // Else use an empty span right after the opening bracket.
 300             generic_args.span.with_lo(generic_args.span.lo() + BytePos(1)).shrink_to_lo()
 301         };
 302
 303         generic_args.args.insert_many(
 304             0,
 305             (start.as_u32()..end.as_u32()).map(|i| {
 306                 let id = NodeId::from_u32(i);
 307                 let l = self.lower_lifetime(&Lifetime {
 308                     id,
 309                     ident: Ident::new(kw::UnderscoreLifetime, elided_lifetime_span),
 310                 });
 311                 GenericArg::Lifetime(l)
 312             }),
 313         );
 314     }
 315
 316     pub(crate) fn lower_angle_bracketed_parameter_data(
 317         &mut self,
 318         data: &AngleBracketedArgs,
 319         param_mode: ParamMode,
 320         itctx: ImplTraitContext,
 321     ) -> (GenericArgsCtor<'hir>, bool) {
 322         let has_non_lt_args = data.args.iter().any(|arg| match arg {
 323             AngleBracketedArg::Arg(ast::GenericArg::Lifetime(_))
 324             | AngleBracketedArg::Constraint(_) => false,
 325             AngleBracketedArg::Arg(ast::GenericArg::Type(_) | ast::GenericArg::Const(_)) => true,
 326         });
 327         let args = data
 328             .args
 329             .iter()
 330             .filter_map(|arg| match arg {
 331                 AngleBracketedArg::Arg(arg) => Some(self.lower_generic_arg(arg, itctx)),
 332                 AngleBracketedArg::Constraint(_) => None,
 333             })
 334             .collect();
 335         let bindings = self.arena.alloc_from_iter(data.args.iter().filter_map(|arg| match arg {
 336             AngleBracketedArg::Constraint(c) => Some(self.lower_assoc_ty_constraint(c, itctx)),
 337             AngleBracketedArg::Arg(_) => None,
 338         }));
 339         let ctor = GenericArgsCtor { args, bindings, parenthesized: false, span: data.span };
 340         (ctor, !has_non_lt_args && param_mode == ParamMode::Optional)
 341     }
 342
 343     fn lower_parenthesized_parameter_data(
 344         &mut self,
 345         data: &ParenthesizedArgs,
 346     ) -> (GenericArgsCtor<'hir>, bool) {
 347         // Switch to `PassThrough` mode for anonymous lifetimes; this
 348         // means that we permit things like `&Ref<T>`, where `Ref` has
 349         // a hidden lifetime parameter. This is needed for backwards
 350         // compatibility, even in contexts like an impl header where
 351         // we generally don't permit such things (see #51008).
 352         let ParenthesizedArgs { span, inputs, inputs_span, output } = data;
 353         let inputs = self.arena.alloc_from_iter(inputs.iter().map(|ty| {
 354             self.lower_ty_direct(ty, ImplTraitContext::Disallowed(ImplTraitPosition::FnTraitParam))
 355         }));
 356         let output_ty = match output {
 357             FnRetTy::Ty(ty) => {
 358                 self.lower_ty(&ty, ImplTraitContext::Disallowed(ImplTraitPosition::FnTraitReturn))
 359             }
 360             FnRetTy::Default(_) => self.arena.alloc(self.ty_tup(*span, &[])),
 361         };
 362         let args = smallvec![GenericArg::Type(self.ty_tup(*inputs_span, inputs))];
 363         let binding = self.output_ty_binding(output_ty.span, output_ty);
 364         (
 365             GenericArgsCtor {
 366                 args,
 367                 bindings: arena_vec![self; binding],
 368                 parenthesized: true,
 369                 span: data.inputs_span,
 370             },
 371             false,
 372         )
 373     }
 374
 375     /// An associated type binding `Output = $ty`.
 376     pub(crate) fn output_ty_binding(
 377         &mut self,
 378         span: Span,
 379         ty: &'hir hir::Ty<'hir>,
 380     ) -> hir::TypeBinding<'hir> {
 381         let ident = Ident::with_dummy_span(hir::FN_OUTPUT_NAME);
 382         let kind = hir::TypeBindingKind::Equality { term: ty.into() };
 383         let args = arena_vec![self;];
 384         let bindings = arena_vec![self;];
 385         let gen_args = self.arena.alloc(hir::GenericArgs {
 386             args,
 387             bindings,
 388             parenthesized: false,
 389             span_ext: DUMMY_SP,
 390         });
 391         hir::TypeBinding {
 392             hir_id: self.next_id(),
 393             gen_args,
 394             span: self.lower_span(span),
 395             ident,
 396             kind,
 397         }
 398     }
 399 }