src/librustc/ty/error.rs

   1 use crate::ty::{self, BoundRegion, Region, Ty, TyCtxt};
   2 use rustc_errors::{pluralize, Applicability, DiagnosticBuilder};
   3 use rustc_hir as hir;
   4 use rustc_hir::def_id::DefId;
   5 use rustc_span::Span;
   6 use rustc_target::spec::abi;
   7 use syntax::ast;
   8
   9 use std::borrow::Cow;
  10 use std::fmt;
  11
  12 #[derive(Clone, Copy, Debug, PartialEq, Eq, TypeFoldable)]
  13 pub struct ExpectedFound<T> {
  14     pub expected: T,
  15     pub found: T,
  16 }
  17
  18 // Data structures used in type unification
  19 #[derive(Clone, Debug, TypeFoldable)]
  20 pub enum TypeError<'tcx> {
  21     Mismatch,
  22     UnsafetyMismatch(ExpectedFound<hir::Unsafety>),
  23     AbiMismatch(ExpectedFound<abi::Abi>),
  24     Mutability,
  25     TupleSize(ExpectedFound<usize>),
  26     FixedArraySize(ExpectedFound<u64>),
  27     ArgCount,
  28
  29     RegionsDoesNotOutlive(Region<'tcx>, Region<'tcx>),
  30     RegionsInsufficientlyPolymorphic(BoundRegion, Region<'tcx>),
  31     RegionsOverlyPolymorphic(BoundRegion, Region<'tcx>),
  32     RegionsPlaceholderMismatch,
  33
  34     Sorts(ExpectedFound<Ty<'tcx>>),
  35     IntMismatch(ExpectedFound<ty::IntVarValue>),
  36     FloatMismatch(ExpectedFound<ast::FloatTy>),
  37     Traits(ExpectedFound<DefId>),
  38     VariadicMismatch(ExpectedFound<bool>),
  39
  40     /// Instantiating a type variable with the given type would have
  41     /// created a cycle (because it appears somewhere within that
  42     /// type).
  43     CyclicTy(Ty<'tcx>),
  44     ProjectionMismatched(ExpectedFound<DefId>),
  45     ProjectionBoundsLength(ExpectedFound<usize>),
  46     ExistentialMismatch(ExpectedFound<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>>),
  47     ObjectUnsafeCoercion(DefId),
  48     ConstMismatch(ExpectedFound<&'tcx ty::Const<'tcx>>),
  49
  50     IntrinsicCast,
  51 }
  52
  53 pub enum UnconstrainedNumeric {
  54     UnconstrainedFloat,
  55     UnconstrainedInt,
  56     Neither,
  57 }
  58
  59 /// Explains the source of a type err in a short, human readable way. This is meant to be placed
  60 /// in parentheses after some larger message. You should also invoke `note_and_explain_type_err()`
  61 /// afterwards to present additional details, particularly when it comes to lifetime-related
  62 /// errors.
  63 impl<'tcx> fmt::Display for TypeError<'tcx> {
  64     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
  65         use self::TypeError::*;
  66         fn report_maybe_different(
  67             f: &mut fmt::Formatter<'_>,
  68             expected: &str,
  69             found: &str,
  70         ) -> fmt::Result {
  71             // A naive approach to making sure that we're not reporting silly errors such as:
  72             // (expected closure, found closure).
  73             if expected == found {
  74                 write!(f, "expected {}, found a different {}", expected, found)
  75             } else {
  76                 write!(f, "expected {}, found {}", expected, found)
  77             }
  78         }
  79
  80         let br_string = |br: ty::BoundRegion| match br {
  81             ty::BrNamed(_, name) => format!(" {}", name),
  82             _ => String::new(),
  83         };
  84
  85         match *self {
  86             CyclicTy(_) => write!(f, "cyclic type of infinite size"),
  87             Mismatch => write!(f, "types differ"),
  88             UnsafetyMismatch(values) => {
  89                 write!(f, "expected {} fn, found {} fn", values.expected, values.found)
  90             }
  91             AbiMismatch(values) => {
  92                 write!(f, "expected {} fn, found {} fn", values.expected, values.found)
  93             }
  94             Mutability => write!(f, "types differ in mutability"),
  95             TupleSize(values) => write!(
  96                 f,
  97                 "expected a tuple with {} element{}, \
  98                            found one with {} element{}",
  99                 values.expected,
 100                 pluralize!(values.expected),
 101                 values.found,
 102                 pluralize!(values.found)
 103             ),
 104             FixedArraySize(values) => write!(
 105                 f,
 106                 "expected an array with a fixed size of {} element{}, \
 107                            found one with {} element{}",
 108                 values.expected,
 109                 pluralize!(values.expected),
 110                 values.found,
 111                 pluralize!(values.found)
 112             ),
 113             ArgCount => write!(f, "incorrect number of function parameters"),
 114             RegionsDoesNotOutlive(..) => write!(f, "lifetime mismatch"),
 115             RegionsInsufficientlyPolymorphic(br, _) => write!(
 116                 f,
 117                 "expected bound lifetime parameter{}, found concrete lifetime",
 118                 br_string(br)
 119             ),
 120             RegionsOverlyPolymorphic(br, _) => write!(
 121                 f,
 122                 "expected concrete lifetime, found bound lifetime parameter{}",
 123                 br_string(br)
 124             ),
 125             RegionsPlaceholderMismatch => write!(f, "one type is more general than the other"),
 126             Sorts(values) => ty::tls::with(|tcx| {
 127                 report_maybe_different(
 128                     f,
 129                     &values.expected.sort_string(tcx),
 130                     &values.found.sort_string(tcx),
 131                 )
 132             }),
 133             Traits(values) => ty::tls::with(|tcx| {
 134                 report_maybe_different(
 135                     f,
 136                     &format!("trait `{}`", tcx.def_path_str(values.expected)),
 137                     &format!("trait `{}`", tcx.def_path_str(values.found)),
 138                 )
 139             }),
 140             IntMismatch(ref values) => {
 141                 write!(f, "expected `{:?}`, found `{:?}`", values.expected, values.found)
 142             }
 143             FloatMismatch(ref values) => {
 144                 write!(f, "expected `{:?}`, found `{:?}`", values.expected, values.found)
 145             }
 146             VariadicMismatch(ref values) => write!(
 147                 f,
 148                 "expected {} fn, found {} function",
 149                 if values.expected { "variadic" } else { "non-variadic" },
 150                 if values.found { "variadic" } else { "non-variadic" }
 151             ),
 152             ProjectionMismatched(ref values) => ty::tls::with(|tcx| {
 153                 write!(
 154                     f,
 155                     "expected {}, found {}",
 156                     tcx.def_path_str(values.expected),
 157                     tcx.def_path_str(values.found)
 158                 )
 159             }),
 160             ProjectionBoundsLength(ref values) => write!(
 161                 f,
 162                 "expected {} associated type binding{}, found {}",
 163                 values.expected,
 164                 pluralize!(values.expected),
 165                 values.found
 166             ),
 167             ExistentialMismatch(ref values) => report_maybe_different(
 168                 f,
 169                 &format!("trait `{}`", values.expected),
 170                 &format!("trait `{}`", values.found),
 171             ),
 172             ConstMismatch(ref values) => {
 173                 write!(f, "expected `{}`, found `{}`", values.expected, values.found)
 174             }
 175             IntrinsicCast => write!(f, "cannot coerce intrinsics to function pointers"),
 176             ObjectUnsafeCoercion(_) => write!(f, "coercion to object-unsafe trait object"),
 177         }
 178     }
 179 }
 180
 181 impl<'tcx> TypeError<'tcx> {
 182     pub fn must_include_note(&self) -> bool {
 183         use self::TypeError::*;
 184         match self {
 185             CyclicTy(_) | UnsafetyMismatch(_) | Mismatch | AbiMismatch(_) | FixedArraySize(_)
 186             | Sorts(_) | IntMismatch(_) | FloatMismatch(_) | VariadicMismatch(_) => false,
 187
 188             Mutability
 189             | TupleSize(_)
 190             | ArgCount
 191             | RegionsDoesNotOutlive(..)
 192             | RegionsInsufficientlyPolymorphic(..)
 193             | RegionsOverlyPolymorphic(..)
 194             | RegionsPlaceholderMismatch
 195             | Traits(_)
 196             | ProjectionMismatched(_)
 197             | ProjectionBoundsLength(_)
 198             | ExistentialMismatch(_)
 199             | ConstMismatch(_)
 200             | IntrinsicCast
 201             | ObjectUnsafeCoercion(_) => true,
 202         }
 203     }
 204 }
 205
 206 impl<'tcx> ty::TyS<'tcx> {
 207     pub fn sort_string(&self, tcx: TyCtxt<'_>) -> Cow<'static, str> {
 208         match self.kind {
 209             ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::Str | ty::Never => {
 210                 format!("`{}`", self).into()
 211             }
 212             ty::Tuple(ref tys) if tys.is_empty() => format!("`{}`", self).into(),
 213
 214             ty::Adt(def, _) => format!("{} `{}`", def.descr(), tcx.def_path_str(def.did)).into(),
 215             ty::Foreign(def_id) => format!("extern type `{}`", tcx.def_path_str(def_id)).into(),
 216             ty::Array(t, n) => {
 217                 let n = tcx.lift(&n).unwrap();
 218                 match n.try_eval_usize(tcx, ty::ParamEnv::empty()) {
 219                     _ if t.is_simple_ty() => format!("array `{}`", self).into(),
 220                     Some(n) => format!("array of {} element{} ", n, pluralize!(n)).into(),
 221                     None => "array".into(),
 222                 }
 223             }
 224             ty::Slice(ty) if ty.is_simple_ty() => format!("slice `{}`", self).into(),
 225             ty::Slice(_) => "slice".into(),
 226             ty::RawPtr(_) => "*-ptr".into(),
 227             ty::Ref(_, ty, mutbl) => {
 228                 let tymut = ty::TypeAndMut { ty, mutbl };
 229                 let tymut_string = tymut.to_string();
 230                 if tymut_string != "_"
 231                     && (ty.is_simple_text() || tymut_string.len() < "mutable reference".len())
 232                 {
 233                     format!("`&{}`", tymut_string).into()
 234                 } else {
 235                     // Unknown type name, it's long or has type arguments
 236                     match mutbl {
 237                         hir::Mutability::Mut => "mutable reference",
 238                         _ => "reference",
 239                     }
 240                     .into()
 241                 }
 242             }
 243             ty::FnDef(..) => "fn item".into(),
 244             ty::FnPtr(_) => "fn pointer".into(),
 245             ty::Dynamic(ref inner, ..) => {
 246                 if let Some(principal) = inner.principal() {
 247                     format!("trait object `dyn {}`", tcx.def_path_str(principal.def_id())).into()
 248                 } else {
 249                     "trait object".into()
 250                 }
 251             }
 252             ty::Closure(..) => "closure".into(),
 253             ty::Generator(..) => "generator".into(),
 254             ty::GeneratorWitness(..) => "generator witness".into(),
 255             ty::Tuple(..) => "tuple".into(),
 256             ty::Infer(ty::TyVar(_)) => "inferred type".into(),
 257             ty::Infer(ty::IntVar(_)) => "integer".into(),
 258             ty::Infer(ty::FloatVar(_)) => "floating-point number".into(),
 259             ty::Placeholder(..) => "placeholder type".into(),
 260             ty::Bound(..) => "bound type".into(),
 261             ty::Infer(ty::FreshTy(_)) => "fresh type".into(),
 262             ty::Infer(ty::FreshIntTy(_)) => "fresh integral type".into(),
 263             ty::Infer(ty::FreshFloatTy(_)) => "fresh floating-point type".into(),
 264             ty::Projection(_) => "associated type".into(),
 265             ty::UnnormalizedProjection(_) => "non-normalized associated type".into(),
 266             ty::Param(p) => format!("type parameter `{}`", p).into(),
 267             ty::Opaque(..) => "opaque type".into(),
 268             ty::Error => "type error".into(),
 269         }
 270     }
 271
 272     pub fn prefix_string(&self) -> Cow<'static, str> {
 273         match self.kind {
 274             ty::Infer(_)
 275             | ty::Error
 276             | ty::Bool
 277             | ty::Char
 278             | ty::Int(_)
 279             | ty::Uint(_)
 280             | ty::Float(_)
 281             | ty::Str
 282             | ty::Never => "type".into(),
 283             ty::Tuple(ref tys) if tys.is_empty() => "unit type".into(),
 284             ty::Adt(def, _) => def.descr().into(),
 285             ty::Foreign(_) => "extern type".into(),
 286             ty::Array(..) => "array".into(),
 287             ty::Slice(_) => "slice".into(),
 288             ty::RawPtr(_) => "raw pointer".into(),
 289             ty::Ref(.., mutbl) => match mutbl {
 290                 hir::Mutability::Mut => "mutable reference",
 291                 _ => "reference",
 292             }
 293             .into(),
 294             ty::FnDef(..) => "fn item".into(),
 295             ty::FnPtr(_) => "fn pointer".into(),
 296             ty::Dynamic(..) => "trait object".into(),
 297             ty::Closure(..) => "closure".into(),
 298             ty::Generator(..) => "generator".into(),
 299             ty::GeneratorWitness(..) => "generator witness".into(),
 300             ty::Tuple(..) => "tuple".into(),
 301             ty::Placeholder(..) => "higher-ranked type".into(),
 302             ty::Bound(..) => "bound type variable".into(),
 303             ty::Projection(_) => "associated type".into(),
 304             ty::UnnormalizedProjection(_) => "associated type".into(),
 305             ty::Param(_) => "type parameter".into(),
 306             ty::Opaque(..) => "opaque type".into(),
 307         }
 308     }
 309 }
 310
 311 impl<'tcx> TyCtxt<'tcx> {
 312     pub fn note_and_explain_type_err(
 313         self,
 314         db: &mut DiagnosticBuilder<'_>,
 315         err: &TypeError<'tcx>,
 316         sp: Span,
 317         body_owner_def_id: DefId,
 318     ) {
 319         use self::TypeError::*;
 320
 321         match err {
 322             Sorts(values) => {
 323                 let expected_str = values.expected.sort_string(self);
 324                 let found_str = values.found.sort_string(self);
 325                 if expected_str == found_str && expected_str == "closure" {
 326                     db.note("no two closures, even if identical, have the same type");
 327                     db.help("consider boxing your closure and/or using it as a trait object");
 328                 }
 329                 if expected_str == found_str && expected_str == "opaque type" {
 330                     // Issue #63167
 331                     db.note("distinct uses of `impl Trait` result in different opaque types");
 332                     let e_str = values.expected.to_string();
 333                     let f_str = values.found.to_string();
 334                     if &e_str == &f_str && &e_str == "impl std::future::Future" {
 335                         // FIXME: use non-string based check.
 336                         db.help(
 337                             "if both `Future`s have the same `Output` type, consider \
 338                                  `.await`ing on both of them",
 339                         );
 340                     }
 341                 }
 342                 match (&values.expected.kind, &values.found.kind) {
 343                     (ty::Float(_), ty::Infer(ty::IntVar(_))) => {
 344                         if let Ok(
 345                             // Issue #53280
 346                             snippet,
 347                         ) = self.sess.source_map().span_to_snippet(sp)
 348                         {
 349                             if snippet.chars().all(|c| c.is_digit(10) || c == '-' || c == '_') {
 350                                 db.span_suggestion(
 351                                     sp,
 352                                     "use a float literal",
 353                                     format!("{}.0", snippet),
 354                                     Applicability::MachineApplicable,
 355                                 );
 356                             }
 357                         }
 358                     }
 359                     (ty::Param(expected), ty::Param(found)) => {
 360                         let generics = self.generics_of(body_owner_def_id);
 361                         let e_span = self.def_span(generics.type_param(expected, self).def_id);
 362                         if !sp.contains(e_span) {
 363                             db.span_label(e_span, "expected type parameter");
 364                         }
 365                         let f_span = self.def_span(generics.type_param(found, self).def_id);
 366                         if !sp.contains(f_span) {
 367                             db.span_label(f_span, "found type parameter");
 368                         }
 369                         db.note(
 370                             "a type parameter was expected, but a different one was found; \
 371                                  you might be missing a type parameter or trait bound",
 372                         );
 373                         db.note(
 374                             "for more information, visit \
 375                                  https://doc.rust-lang.org/book/ch10-02-traits.html\
 376                                  #traits-as-parameters",
 377                         );
 378                     }
 379                     (ty::Projection(_), ty::Projection(_)) => {
 380                         db.note("an associated type was expected, but a different one was found");
 381                     }
 382                     (ty::Param(_), ty::Projection(_)) | (ty::Projection(_), ty::Param(_)) => {
 383                         db.note("you might be missing a type parameter or trait bound");
 384                     }
 385                     (ty::Param(p), _) | (_, ty::Param(p)) => {
 386                         let generics = self.generics_of(body_owner_def_id);
 387                         let p_span = self.def_span(generics.type_param(p, self).def_id);
 388                         if !sp.contains(p_span) {
 389                             db.span_label(p_span, "this type parameter");
 390                         }
 391                         db.help("type parameters must be constrained to match other types");
 392                         if self.sess.teach(&db.get_code().unwrap()) {
 393                             db.help(
 394                                 "given a type parameter `T` and a method `foo`:
 395 ```
 396 trait Trait<T> { fn foo(&self) -> T; }
 397 ```
 398 the only ways to implement method `foo` are:
 399 - constrain `T` with an explicit type:
 400 ```
 401 impl Trait<String> for X {
 402     fn foo(&self) -> String { String::new() }
 403 }
 404 ```
 405 - add a trait bound to `T` and call a method on that trait that returns `Self`:
 406 ```
 407 impl<T: std::default::Default> Trait<T> for X {
 408     fn foo(&self) -> T { <T as std::default::Default>::default() }
 409 }
 410 ```
 411 - change `foo` to return an argument of type `T`:
 412 ```
 413 impl<T> Trait<T> for X {
 414     fn foo(&self, x: T) -> T { x }
 415 }
 416 ```",
 417                             );
 418                         }
 419                         db.note(
 420                             "for more information, visit \
 421                                  https://doc.rust-lang.org/book/ch10-02-traits.html\
 422                                  #traits-as-parameters",
 423                         );
 424                     }
 425                     (ty::Projection(_), _) => {
 426                         db.note(&format!(
 427                             "consider constraining the associated type `{}` to `{}` or calling a \
 428                              method that returns `{}`",
 429                             values.expected, values.found, values.expected,
 430                         ));
 431                         if self.sess.teach(&db.get_code().unwrap()) {
 432                             db.help(
 433                                 "given an associated type `T` and a method `foo`:
 434 ```
 435 trait Trait {
 436     type T;
 437     fn foo(&self) -> Self::T;
 438 }
 439 ```
 440 the only way of implementing method `foo` is to constrain `T` with an explicit associated type:
 441 ```
 442 impl Trait for X {
 443     type T = String;
 444     fn foo(&self) -> Self::T { String::new() }
 445 }
 446 ```",
 447                             );
 448                         }
 449                         db.note(
 450                             "for more information, visit \
 451                                  https://doc.rust-lang.org/book/ch19-03-advanced-traits.html",
 452                         );
 453                     }
 454                     (_, ty::Projection(_)) => {
 455                         db.note(&format!(
 456                             "consider constraining the associated type `{}` to `{}`",
 457                             values.found, values.expected,
 458                         ));
 459                         db.note(
 460                             "for more information, visit \
 461                                  https://doc.rust-lang.org/book/ch19-03-advanced-traits.html",
 462                         );
 463                     }
 464                     _ => {}
 465                 }
 466                 debug!(
 467                     "note_and_explain_type_err expected={:?} ({:?}) found={:?} ({:?})",
 468                     values.expected, values.expected.kind, values.found, values.found.kind,
 469                 );
 470             }
 471             CyclicTy(ty) => {
 472                 // Watch out for various cases of cyclic types and try to explain.
 473                 if ty.is_closure() || ty.is_generator() {
 474                     db.note(
 475                         "closures cannot capture themselves or take themselves as argument;\n\
 476                              this error may be the result of a recent compiler bug-fix,\n\
 477                              see https://github.com/rust-lang/rust/issues/46062 for more details",
 478                     );
 479                 }
 480             }
 481             _ => {}
 482         }
 483     }
 484 }