compiler/rustc_typeck/src/astconv/errors.rs

   1 use crate::astconv::AstConv;
   2 use crate::errors::{ManualImplementation, MissingTypeParams};
   3 use rustc_data_structures::fx::FxHashMap;
   4 use rustc_errors::{pluralize, struct_span_err, Applicability, ErrorGuaranteed};
   5 use rustc_hir as hir;
   6 use rustc_hir::def_id::DefId;
   7 use rustc_middle::ty;
   8 use rustc_session::parse::feature_err;
   9 use rustc_span::lev_distance::find_best_match_for_name;
  10 use rustc_span::symbol::{sym, Ident};
  11 use rustc_span::{Span, DUMMY_SP};
  12
  13 use std::collections::BTreeSet;
  14
  15 impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
  16     /// On missing type parameters, emit an E0393 error and provide a structured suggestion using
  17     /// the type parameter's name as a placeholder.
  18     pub(crate) fn complain_about_missing_type_params(
  19         &self,
  20         missing_type_params: Vec<String>,
  21         def_id: DefId,
  22         span: Span,
  23         empty_generic_args: bool,
  24     ) {
  25         if missing_type_params.is_empty() {
  26             return;
  27         }
  28
  29         self.tcx().sess.emit_err(MissingTypeParams {
  30             span,
  31             def_span: self.tcx().def_span(def_id),
  32             missing_type_params,
  33             empty_generic_args,
  34         });
  35     }
  36
  37     /// When the code is using the `Fn` traits directly, instead of the `Fn(A) -> B` syntax, emit
  38     /// an error and attempt to build a reasonable structured suggestion.
  39     pub(crate) fn complain_about_internal_fn_trait(
  40         &self,
  41         span: Span,
  42         trait_def_id: DefId,
  43         trait_segment: &'_ hir::PathSegment<'_>,
  44         is_impl: bool,
  45     ) {
  46         if self.tcx().features().unboxed_closures {
  47             return;
  48         }
  49
  50         let trait_def = self.tcx().trait_def(trait_def_id);
  51         if !trait_def.paren_sugar {
  52             if trait_segment.args().parenthesized {
  53                 // For now, require that parenthetical notation be used only with `Fn()` etc.
  54                 let mut err = feature_err(
  55                     &self.tcx().sess.parse_sess,
  56                     sym::unboxed_closures,
  57                     span,
  58                     "parenthetical notation is only stable when used with `Fn`-family traits",
  59                 );
  60                 err.emit();
  61             }
  62
  63             return;
  64         }
  65
  66         let sess = self.tcx().sess;
  67
  68         if !trait_segment.args().parenthesized {
  69             // For now, require that parenthetical notation be used only with `Fn()` etc.
  70             let mut err = feature_err(
  71                 &sess.parse_sess,
  72                 sym::unboxed_closures,
  73                 span,
  74                 "the precise format of `Fn`-family traits' type parameters is subject to change",
  75             );
  76             // Do not suggest the other syntax if we are in trait impl:
  77             // the desugaring would contain an associated type constraint.
  78             if !is_impl {
  79                 let args = trait_segment
  80                     .args
  81                     .as_ref()
  82                     .and_then(|args| args.args.get(0))
  83                     .and_then(|arg| match arg {
  84                         hir::GenericArg::Type(ty) => match ty.kind {
  85                             hir::TyKind::Tup(t) => t
  86                                 .iter()
  87                                 .map(|e| sess.source_map().span_to_snippet(e.span))
  88                                 .collect::<Result<Vec<_>, _>>()
  89                                 .map(|a| a.join(", ")),
  90                             _ => sess.source_map().span_to_snippet(ty.span),
  91                         }
  92                         .map(|s| format!("({})", s))
  93                         .ok(),
  94                         _ => None,
  95                     })
  96                     .unwrap_or_else(|| "()".to_string());
  97                 let ret = trait_segment
  98                     .args()
  99                     .bindings
 100                     .iter()
 101                     .find_map(|b| match (b.ident.name == sym::Output, &b.kind) {
 102                         (true, hir::TypeBindingKind::Equality { term }) => {
 103                             let span = match term {
 104                                 hir::Term::Ty(ty) => ty.span,
 105                                 hir::Term::Const(c) => self.tcx().hir().span(c.hir_id),
 106                             };
 107                             sess.source_map().span_to_snippet(span).ok()
 108                         }
 109                         _ => None,
 110                     })
 111                     .unwrap_or_else(|| "()".to_string());
 112                 err.span_suggestion(
 113                     span,
 114                     "use parenthetical notation instead",
 115                     format!("{}{} -> {}", trait_segment.ident, args, ret),
 116                     Applicability::MaybeIncorrect,
 117                 );
 118             }
 119             err.emit();
 120         }
 121
 122         if is_impl {
 123             let trait_name = self.tcx().def_path_str(trait_def_id);
 124             self.tcx().sess.emit_err(ManualImplementation { span, trait_name });
 125         }
 126     }
 127
 128     pub(crate) fn complain_about_assoc_type_not_found<I>(
 129         &self,
 130         all_candidates: impl Fn() -> I,
 131         ty_param_name: &str,
 132         assoc_name: Ident,
 133         span: Span,
 134     ) -> ErrorGuaranteed
 135     where
 136         I: Iterator<Item = ty::PolyTraitRef<'tcx>>,
 137     {
 138         // The fallback span is needed because `assoc_name` might be an `Fn()`'s `Output` without a
 139         // valid span, so we point at the whole path segment instead.
 140         let span = if assoc_name.span != DUMMY_SP { assoc_name.span } else { span };
 141         let mut err = struct_span_err!(
 142             self.tcx().sess,
 143             span,
 144             E0220,
 145             "associated type `{}` not found for `{}`",
 146             assoc_name,
 147             ty_param_name
 148         );
 149
 150         let all_candidate_names: Vec<_> = all_candidates()
 151             .flat_map(|r| self.tcx().associated_items(r.def_id()).in_definition_order())
 152             .filter_map(
 153                 |item| if item.kind == ty::AssocKind::Type { Some(item.name) } else { None },
 154             )
 155             .collect();
 156
 157         if let (Some(suggested_name), true) = (
 158             find_best_match_for_name(&all_candidate_names, assoc_name.name, None),
 159             assoc_name.span != DUMMY_SP,
 160         ) {
 161             err.span_suggestion(
 162                 assoc_name.span,
 163                 "there is an associated type with a similar name",
 164                 suggested_name.to_string(),
 165                 Applicability::MaybeIncorrect,
 166             );
 167         } else {
 168             err.span_label(span, format!("associated type `{}` not found", assoc_name));
 169         }
 170
 171         err.emit()
 172     }
 173
 174     /// When there are any missing associated types, emit an E0191 error and attempt to supply a
 175     /// reasonable suggestion on how to write it. For the case of multiple associated types in the
 176     /// same trait bound have the same name (as they come from different supertraits), we instead
 177     /// emit a generic note suggesting using a `where` clause to constraint instead.
 178     pub(crate) fn complain_about_missing_associated_types(
 179         &self,
 180         associated_types: FxHashMap<Span, BTreeSet<DefId>>,
 181         potential_assoc_types: Vec<Span>,
 182         trait_bounds: &[hir::PolyTraitRef<'_>],
 183     ) {
 184         if associated_types.values().all(|v| v.is_empty()) {
 185             return;
 186         }
 187         let tcx = self.tcx();
 188         // FIXME: Marked `mut` so that we can replace the spans further below with a more
 189         // appropriate one, but this should be handled earlier in the span assignment.
 190         let mut associated_types: FxHashMap<Span, Vec<_>> = associated_types
 191             .into_iter()
 192             .map(|(span, def_ids)| {
 193                 (span, def_ids.into_iter().map(|did| tcx.associated_item(did)).collect())
 194             })
 195             .collect();
 196         let mut names = vec![];
 197
 198         // Account for things like `dyn Foo + 'a`, like in tests `issue-22434.rs` and
 199         // `issue-22560.rs`.
 200         let mut trait_bound_spans: Vec<Span> = vec![];
 201         for (span, items) in &associated_types {
 202             if !items.is_empty() {
 203                 trait_bound_spans.push(*span);
 204             }
 205             for assoc_item in items {
 206                 let trait_def_id = assoc_item.container.id();
 207                 names.push(format!(
 208                     "`{}` (from trait `{}`)",
 209                     assoc_item.name,
 210                     tcx.def_path_str(trait_def_id),
 211                 ));
 212             }
 213         }
 214         if let ([], [bound]) = (&potential_assoc_types[..], &trait_bounds) {
 215             match bound.trait_ref.path.segments {
 216                 // FIXME: `trait_ref.path.span` can point to a full path with multiple
 217                 // segments, even though `trait_ref.path.segments` is of length `1`. Work
 218                 // around that bug here, even though it should be fixed elsewhere.
 219                 // This would otherwise cause an invalid suggestion. For an example, look at
 220                 // `src/test/ui/issues/issue-28344.rs` where instead of the following:
 221                 //
 222                 //   error[E0191]: the value of the associated type `Output`
 223                 //                 (from trait `std::ops::BitXor`) must be specified
 224                 //   --> $DIR/issue-28344.rs:4:17
 225                 //    |
 226                 // LL |     let x: u8 = BitXor::bitor(0 as u8, 0 as u8);
 227                 //    |                 ^^^^^^ help: specify the associated type:
 228                 //    |                              `BitXor<Output = Type>`
 229                 //
 230                 // we would output:
 231                 //
 232                 //   error[E0191]: the value of the associated type `Output`
 233                 //                 (from trait `std::ops::BitXor`) must be specified
 234                 //   --> $DIR/issue-28344.rs:4:17
 235                 //    |
 236                 // LL |     let x: u8 = BitXor::bitor(0 as u8, 0 as u8);
 237                 //    |                 ^^^^^^^^^^^^^ help: specify the associated type:
 238                 //    |                                     `BitXor::bitor<Output = Type>`
 239                 [segment] if segment.args.is_none() => {
 240                     trait_bound_spans = vec![segment.ident.span];
 241                     associated_types = associated_types
 242                         .into_iter()
 243                         .map(|(_, items)| (segment.ident.span, items))
 244                         .collect();
 245                 }
 246                 _ => {}
 247             }
 248         }
 249         names.sort();
 250         trait_bound_spans.sort();
 251         let mut err = struct_span_err!(
 252             tcx.sess,
 253             trait_bound_spans,
 254             E0191,
 255             "the value of the associated type{} {} must be specified",
 256             pluralize!(names.len()),
 257             names.join(", "),
 258         );
 259         let mut suggestions = vec![];
 260         let mut types_count = 0;
 261         let mut where_constraints = vec![];
 262         let mut already_has_generics_args_suggestion = false;
 263         for (span, assoc_items) in &associated_types {
 264             let mut names: FxHashMap<_, usize> = FxHashMap::default();
 265             for item in assoc_items {
 266                 types_count += 1;
 267                 *names.entry(item.name).or_insert(0) += 1;
 268             }
 269             let mut dupes = false;
 270             for item in assoc_items {
 271                 let prefix = if names[&item.name] > 1 {
 272                     let trait_def_id = item.container.id();
 273                     dupes = true;
 274                     format!("{}::", tcx.def_path_str(trait_def_id))
 275                 } else {
 276                     String::new()
 277                 };
 278                 if let Some(sp) = tcx.hir().span_if_local(item.def_id) {
 279                     err.span_label(sp, format!("`{}{}` defined here", prefix, item.name));
 280                 }
 281             }
 282             if potential_assoc_types.len() == assoc_items.len() {
 283                 // When the amount of missing associated types equals the number of
 284                 // extra type arguments present.  A suggesting to replace the generic args with
 285                 // associated types is already emitted.
 286                 already_has_generics_args_suggestion = true;
 287             } else if let (Ok(snippet), false) =
 288                 (tcx.sess.source_map().span_to_snippet(*span), dupes)
 289             {
 290                 let types: Vec<_> =
 291                     assoc_items.iter().map(|item| format!("{} = Type", item.name)).collect();
 292                 let code = if snippet.ends_with('>') {
 293                     // The user wrote `Trait<'a>` or similar and we don't have a type we can
 294                     // suggest, but at least we can clue them to the correct syntax
 295                     // `Trait<'a, Item = Type>` while accounting for the `<'a>` in the
 296                     // suggestion.
 297                     format!("{}, {}>", &snippet[..snippet.len() - 1], types.join(", "))
 298                 } else {
 299                     // The user wrote `Iterator`, so we don't have a type we can suggest, but at
 300                     // least we can clue them to the correct syntax `Iterator<Item = Type>`.
 301                     format!("{}<{}>", snippet, types.join(", "))
 302                 };
 303                 suggestions.push((*span, code));
 304             } else if dupes {
 305                 where_constraints.push(*span);
 306             }
 307         }
 308         let where_msg = "consider introducing a new type parameter, adding `where` constraints \
 309                          using the fully-qualified path to the associated types";
 310         if !where_constraints.is_empty() && suggestions.is_empty() {
 311             // If there are duplicates associated type names and a single trait bound do not
 312             // use structured suggestion, it means that there are multiple supertraits with
 313             // the same associated type name.
 314             err.help(where_msg);
 315         }
 316         if suggestions.len() != 1 || already_has_generics_args_suggestion {
 317             // We don't need this label if there's an inline suggestion, show otherwise.
 318             for (span, assoc_items) in &associated_types {
 319                 let mut names: FxHashMap<_, usize> = FxHashMap::default();
 320                 for item in assoc_items {
 321                     types_count += 1;
 322                     *names.entry(item.name).or_insert(0) += 1;
 323                 }
 324                 let mut label = vec![];
 325                 for item in assoc_items {
 326                     let postfix = if names[&item.name] > 1 {
 327                         let trait_def_id = item.container.id();
 328                         format!(" (from trait `{}`)", tcx.def_path_str(trait_def_id))
 329                     } else {
 330                         String::new()
 331                     };
 332                     label.push(format!("`{}`{}", item.name, postfix));
 333                 }
 334                 if !label.is_empty() {
 335                     err.span_label(
 336                         *span,
 337                         format!(
 338                             "associated type{} {} must be specified",
 339                             pluralize!(label.len()),
 340                             label.join(", "),
 341                         ),
 342                     );
 343                 }
 344             }
 345         }
 346         if !suggestions.is_empty() {
 347             err.multipart_suggestion(
 348                 &format!("specify the associated type{}", pluralize!(types_count)),
 349                 suggestions,
 350                 Applicability::HasPlaceholders,
 351             );
 352             if !where_constraints.is_empty() {
 353                 err.span_help(where_constraints, where_msg);
 354             }
 355         }
 356         err.emit();
 357     }
 358 }