compiler/rustc_typeck/src/astconv/errors.rs

   1 use crate::astconv::AstConv;
   2 use rustc_data_structures::fx::FxHashMap;
   3 use rustc_errors::{pluralize, struct_span_err, Applicability};
   4 use rustc_hir as hir;
   5 use rustc_hir::def_id::DefId;
   6 use rustc_middle::ty;
   7 use rustc_session::parse::feature_err;
   8 use rustc_span::lev_distance::find_best_match_for_name;
   9 use rustc_span::symbol::{sym, Ident};
  10 use rustc_span::{Span, DUMMY_SP};
  11
  12 use std::collections::BTreeSet;
  13
  14 impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
  15     /// On missing type parameters, emit an E0393 error and provide a structured suggestion using
  16     /// the type parameter's name as a placeholder.
  17     pub(crate) fn complain_about_missing_type_params(
  18         &self,
  19         missing_type_params: Vec<String>,
  20         def_id: DefId,
  21         span: Span,
  22         empty_generic_args: bool,
  23     ) {
  24         if missing_type_params.is_empty() {
  25             return;
  26         }
  27         let display =
  28             missing_type_params.iter().map(|n| format!("`{}`", n)).collect::<Vec<_>>().join(", ");
  29         let mut err = struct_span_err!(
  30             self.tcx().sess,
  31             span,
  32             E0393,
  33             "the type parameter{} {} must be explicitly specified",
  34             pluralize!(missing_type_params.len()),
  35             display,
  36         );
  37         err.span_label(
  38             self.tcx().def_span(def_id),
  39             &format!(
  40                 "type parameter{} {} must be specified for this",
  41                 pluralize!(missing_type_params.len()),
  42                 display,
  43             ),
  44         );
  45         let mut suggested = false;
  46         if let (Ok(snippet), true) = (
  47             self.tcx().sess.source_map().span_to_snippet(span),
  48             // Don't suggest setting the type params if there are some already: the order is
  49             // tricky to get right and the user will already know what the syntax is.
  50             empty_generic_args,
  51         ) {
  52             if snippet.ends_with('>') {
  53                 // The user wrote `Trait<'a, T>` or similar. To provide an accurate suggestion
  54                 // we would have to preserve the right order. For now, as clearly the user is
  55                 // aware of the syntax, we do nothing.
  56             } else {
  57                 // The user wrote `Iterator`, so we don't have a type we can suggest, but at
  58                 // least we can clue them to the correct syntax `Iterator<Type>`.
  59                 err.span_suggestion(
  60                     span,
  61                     &format!(
  62                         "set the type parameter{plural} to the desired type{plural}",
  63                         plural = pluralize!(missing_type_params.len()),
  64                     ),
  65                     format!("{}<{}>", snippet, missing_type_params.join(", ")),
  66                     Applicability::HasPlaceholders,
  67                 );
  68                 suggested = true;
  69             }
  70         }
  71         if !suggested {
  72             err.span_label(
  73                 span,
  74                 format!(
  75                     "missing reference{} to {}",
  76                     pluralize!(missing_type_params.len()),
  77                     display,
  78                 ),
  79             );
  80         }
  81         err.note(
  82             "because of the default `Self` reference, type parameters must be \
  83                   specified on object types",
  84         );
  85         err.emit();
  86     }
  87
  88     /// When the code is using the `Fn` traits directly, instead of the `Fn(A) -> B` syntax, emit
  89     /// an error and attempt to build a reasonable structured suggestion.
  90     pub(crate) fn complain_about_internal_fn_trait(
  91         &self,
  92         span: Span,
  93         trait_def_id: DefId,
  94         trait_segment: &'a hir::PathSegment<'a>,
  95     ) {
  96         let trait_def = self.tcx().trait_def(trait_def_id);
  97
  98         if !self.tcx().features().unboxed_closures
  99             && trait_segment.generic_args().parenthesized != trait_def.paren_sugar
 100         {
 101             let sess = &self.tcx().sess.parse_sess;
 102             // For now, require that parenthetical notation be used only with `Fn()` etc.
 103             let (msg, sugg) = if trait_def.paren_sugar {
 104                 (
 105                     "the precise format of `Fn`-family traits' type parameters is subject to \
 106                      change",
 107                     Some(format!(
 108                         "{}{} -> {}",
 109                         trait_segment.ident,
 110                         trait_segment
 111                             .args
 112                             .as_ref()
 113                             .and_then(|args| args.args.get(0))
 114                             .and_then(|arg| match arg {
 115                                 hir::GenericArg::Type(ty) => match ty.kind {
 116                                     hir::TyKind::Tup(t) => t
 117                                         .iter()
 118                                         .map(|e| sess.source_map().span_to_snippet(e.span))
 119                                         .collect::<Result<Vec<_>, _>>()
 120                                         .map(|a| a.join(", ")),
 121                                     _ => sess.source_map().span_to_snippet(ty.span),
 122                                 }
 123                                 .map(|s| format!("({})", s))
 124                                 .ok(),
 125                                 _ => None,
 126                             })
 127                             .unwrap_or_else(|| "()".to_string()),
 128                         trait_segment
 129                             .generic_args()
 130                             .bindings
 131                             .iter()
 132                             .find_map(|b| match (b.ident.name == sym::Output, &b.kind) {
 133                                 (true, hir::TypeBindingKind::Equality { ty }) => {
 134                                     sess.source_map().span_to_snippet(ty.span).ok()
 135                                 }
 136                                 _ => None,
 137                             })
 138                             .unwrap_or_else(|| "()".to_string()),
 139                     )),
 140                 )
 141             } else {
 142                 ("parenthetical notation is only stable when used with `Fn`-family traits", None)
 143             };
 144             let mut err = feature_err(sess, sym::unboxed_closures, span, msg);
 145             if let Some(sugg) = sugg {
 146                 let msg = "use parenthetical notation instead";
 147                 err.span_suggestion(span, msg, sugg, Applicability::MaybeIncorrect);
 148             }
 149             err.emit();
 150         }
 151     }
 152
 153     pub(crate) fn complain_about_assoc_type_not_found<I>(
 154         &self,
 155         all_candidates: impl Fn() -> I,
 156         ty_param_name: &str,
 157         assoc_name: Ident,
 158         span: Span,
 159     ) where
 160         I: Iterator<Item = ty::PolyTraitRef<'tcx>>,
 161     {
 162         // The fallback span is needed because `assoc_name` might be an `Fn()`'s `Output` without a
 163         // valid span, so we point at the whole path segment instead.
 164         let span = if assoc_name.span != DUMMY_SP { assoc_name.span } else { span };
 165         let mut err = struct_span_err!(
 166             self.tcx().sess,
 167             span,
 168             E0220,
 169             "associated type `{}` not found for `{}`",
 170             assoc_name,
 171             ty_param_name
 172         );
 173
 174         let all_candidate_names: Vec<_> = all_candidates()
 175             .map(|r| self.tcx().associated_items(r.def_id()).in_definition_order())
 176             .flatten()
 177             .filter_map(
 178                 |item| if item.kind == ty::AssocKind::Type { Some(item.ident.name) } else { None },
 179             )
 180             .collect();
 181
 182         if let (Some(suggested_name), true) = (
 183             find_best_match_for_name(&all_candidate_names, assoc_name.name, None),
 184             assoc_name.span != DUMMY_SP,
 185         ) {
 186             err.span_suggestion(
 187                 assoc_name.span,
 188                 "there is an associated type with a similar name",
 189                 suggested_name.to_string(),
 190                 Applicability::MaybeIncorrect,
 191             );
 192         } else {
 193             err.span_label(span, format!("associated type `{}` not found", assoc_name));
 194         }
 195
 196         err.emit();
 197     }
 198
 199     /// When there are any missing associated types, emit an E0191 error and attempt to supply a
 200     /// reasonable suggestion on how to write it. For the case of multiple associated types in the
 201     /// same trait bound have the same name (as they come from different super-traits), we instead
 202     /// emit a generic note suggesting using a `where` clause to constraint instead.
 203     pub(crate) fn complain_about_missing_associated_types(
 204         &self,
 205         associated_types: FxHashMap<Span, BTreeSet<DefId>>,
 206         potential_assoc_types: Vec<Span>,
 207         trait_bounds: &[hir::PolyTraitRef<'_>],
 208     ) {
 209         if associated_types.values().all(|v| v.is_empty()) {
 210             return;
 211         }
 212         let tcx = self.tcx();
 213         // FIXME: Marked `mut` so that we can replace the spans further below with a more
 214         // appropriate one, but this should be handled earlier in the span assignment.
 215         let mut associated_types: FxHashMap<Span, Vec<_>> = associated_types
 216             .into_iter()
 217             .map(|(span, def_ids)| {
 218                 (span, def_ids.into_iter().map(|did| tcx.associated_item(did)).collect())
 219             })
 220             .collect();
 221         let mut names = vec![];
 222
 223         // Account for things like `dyn Foo + 'a`, like in tests `issue-22434.rs` and
 224         // `issue-22560.rs`.
 225         let mut trait_bound_spans: Vec<Span> = vec![];
 226         for (span, items) in &associated_types {
 227             if !items.is_empty() {
 228                 trait_bound_spans.push(*span);
 229             }
 230             for assoc_item in items {
 231                 let trait_def_id = assoc_item.container.id();
 232                 names.push(format!(
 233                     "`{}` (from trait `{}`)",
 234                     assoc_item.ident,
 235                     tcx.def_path_str(trait_def_id),
 236                 ));
 237             }
 238         }
 239         if let ([], [bound]) = (&potential_assoc_types[..], &trait_bounds) {
 240             match &bound.trait_ref.path.segments[..] {
 241                 // FIXME: `trait_ref.path.span` can point to a full path with multiple
 242                 // segments, even though `trait_ref.path.segments` is of length `1`. Work
 243                 // around that bug here, even though it should be fixed elsewhere.
 244                 // This would otherwise cause an invalid suggestion. For an example, look at
 245                 // `src/test/ui/issues/issue-28344.rs` where instead of the following:
 246                 //
 247                 //   error[E0191]: the value of the associated type `Output`
 248                 //                 (from trait `std::ops::BitXor`) must be specified
 249                 //   --> $DIR/issue-28344.rs:4:17
 250                 //    |
 251                 // LL |     let x: u8 = BitXor::bitor(0 as u8, 0 as u8);
 252                 //    |                 ^^^^^^ help: specify the associated type:
 253                 //    |                              `BitXor<Output = Type>`
 254                 //
 255                 // we would output:
 256                 //
 257                 //   error[E0191]: the value of the associated type `Output`
 258                 //                 (from trait `std::ops::BitXor`) must be specified
 259                 //   --> $DIR/issue-28344.rs:4:17
 260                 //    |
 261                 // LL |     let x: u8 = BitXor::bitor(0 as u8, 0 as u8);
 262                 //    |                 ^^^^^^^^^^^^^ help: specify the associated type:
 263                 //    |                                     `BitXor::bitor<Output = Type>`
 264                 [segment] if segment.args.is_none() => {
 265                     trait_bound_spans = vec![segment.ident.span];
 266                     associated_types = associated_types
 267                         .into_iter()
 268                         .map(|(_, items)| (segment.ident.span, items))
 269                         .collect();
 270                 }
 271                 _ => {}
 272             }
 273         }
 274         names.sort();
 275         trait_bound_spans.sort();
 276         let mut err = struct_span_err!(
 277             tcx.sess,
 278             trait_bound_spans,
 279             E0191,
 280             "the value of the associated type{} {} must be specified",
 281             pluralize!(names.len()),
 282             names.join(", "),
 283         );
 284         let mut suggestions = vec![];
 285         let mut types_count = 0;
 286         let mut where_constraints = vec![];
 287         for (span, assoc_items) in &associated_types {
 288             let mut names: FxHashMap<_, usize> = FxHashMap::default();
 289             for item in assoc_items {
 290                 types_count += 1;
 291                 *names.entry(item.ident.name).or_insert(0) += 1;
 292             }
 293             let mut dupes = false;
 294             for item in assoc_items {
 295                 let prefix = if names[&item.ident.name] > 1 {
 296                     let trait_def_id = item.container.id();
 297                     dupes = true;
 298                     format!("{}::", tcx.def_path_str(trait_def_id))
 299                 } else {
 300                     String::new()
 301                 };
 302                 if let Some(sp) = tcx.hir().span_if_local(item.def_id) {
 303                     err.span_label(sp, format!("`{}{}` defined here", prefix, item.ident));
 304                 }
 305             }
 306             if potential_assoc_types.len() == assoc_items.len() {
 307                 // Only suggest when the amount of missing associated types equals the number of
 308                 // extra type arguments present, as that gives us a relatively high confidence
 309                 // that the user forgot to give the associtated type's name. The canonical
 310                 // example would be trying to use `Iterator<isize>` instead of
 311                 // `Iterator<Item = isize>`.
 312                 for (potential, item) in potential_assoc_types.iter().zip(assoc_items.iter()) {
 313                     if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(*potential) {
 314                         suggestions.push((*potential, format!("{} = {}", item.ident, snippet)));
 315                     }
 316                 }
 317             } else if let (Ok(snippet), false) =
 318                 (tcx.sess.source_map().span_to_snippet(*span), dupes)
 319             {
 320                 let types: Vec<_> =
 321                     assoc_items.iter().map(|item| format!("{} = Type", item.ident)).collect();
 322                 let code = if snippet.ends_with('>') {
 323                     // The user wrote `Trait<'a>` or similar and we don't have a type we can
 324                     // suggest, but at least we can clue them to the correct syntax
 325                     // `Trait<'a, Item = Type>` while accounting for the `<'a>` in the
 326                     // suggestion.
 327                     format!("{}, {}>", &snippet[..snippet.len() - 1], types.join(", "))
 328                 } else {
 329                     // The user wrote `Iterator`, so we don't have a type we can suggest, but at
 330                     // least we can clue them to the correct syntax `Iterator<Item = Type>`.
 331                     format!("{}<{}>", snippet, types.join(", "))
 332                 };
 333                 suggestions.push((*span, code));
 334             } else if dupes {
 335                 where_constraints.push(*span);
 336             }
 337         }
 338         let where_msg = "consider introducing a new type parameter, adding `where` constraints \
 339                          using the fully-qualified path to the associated types";
 340         if !where_constraints.is_empty() && suggestions.is_empty() {
 341             // If there are duplicates associated type names and a single trait bound do not
 342             // use structured suggestion, it means that there are multiple super-traits with
 343             // the same associated type name.
 344             err.help(where_msg);
 345         }
 346         if suggestions.len() != 1 {
 347             // We don't need this label if there's an inline suggestion, show otherwise.
 348             for (span, assoc_items) in &associated_types {
 349                 let mut names: FxHashMap<_, usize> = FxHashMap::default();
 350                 for item in assoc_items {
 351                     types_count += 1;
 352                     *names.entry(item.ident.name).or_insert(0) += 1;
 353                 }
 354                 let mut label = vec![];
 355                 for item in assoc_items {
 356                     let postfix = if names[&item.ident.name] > 1 {
 357                         let trait_def_id = item.container.id();
 358                         format!(" (from trait `{}`)", tcx.def_path_str(trait_def_id))
 359                     } else {
 360                         String::new()
 361                     };
 362                     label.push(format!("`{}`{}", item.ident, postfix));
 363                 }
 364                 if !label.is_empty() {
 365                     err.span_label(
 366                         *span,
 367                         format!(
 368                             "associated type{} {} must be specified",
 369                             pluralize!(label.len()),
 370                             label.join(", "),
 371                         ),
 372                     );
 373                 }
 374             }
 375         }
 376         if !suggestions.is_empty() {
 377             err.multipart_suggestion(
 378                 &format!("specify the associated type{}", pluralize!(types_count)),
 379                 suggestions,
 380                 Applicability::HasPlaceholders,
 381             );
 382             if !where_constraints.is_empty() {
 383                 err.span_help(where_constraints, where_msg);
 384             }
 385         }
 386         err.emit();
 387     }
 388 }