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 impl<T> ExpectedFound<T> {
  19     pub fn new(a_is_expected: bool, a: T, b: T) -> Self {
  20         if a_is_expected {
  21             ExpectedFound { expected: a, found: b }
  22         } else {
  23             ExpectedFound { expected: b, found: a }
  24         }
  25     }
  26 }
  27
  28 // Data structures used in type unification
  29 #[derive(Clone, Debug, TypeFoldable)]
  30 pub enum TypeError<'tcx> {
  31     Mismatch,
  32     UnsafetyMismatch(ExpectedFound<hir::Unsafety>),
  33     AbiMismatch(ExpectedFound<abi::Abi>),
  34     Mutability,
  35     TupleSize(ExpectedFound<usize>),
  36     FixedArraySize(ExpectedFound<u64>),
  37     ArgCount,
  38
  39     RegionsDoesNotOutlive(Region<'tcx>, Region<'tcx>),
  40     RegionsInsufficientlyPolymorphic(BoundRegion, Region<'tcx>),
  41     RegionsOverlyPolymorphic(BoundRegion, Region<'tcx>),
  42     RegionsPlaceholderMismatch,
  43
  44     Sorts(ExpectedFound<Ty<'tcx>>),
  45     IntMismatch(ExpectedFound<ty::IntVarValue>),
  46     FloatMismatch(ExpectedFound<ast::FloatTy>),
  47     Traits(ExpectedFound<DefId>),
  48     VariadicMismatch(ExpectedFound<bool>),
  49
  50     /// Instantiating a type variable with the given type would have
  51     /// created a cycle (because it appears somewhere within that
  52     /// type).
  53     CyclicTy(Ty<'tcx>),
  54     ProjectionMismatched(ExpectedFound<DefId>),
  55     ProjectionBoundsLength(ExpectedFound<usize>),
  56     ExistentialMismatch(ExpectedFound<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>>),
  57     ObjectUnsafeCoercion(DefId),
  58     ConstMismatch(ExpectedFound<&'tcx ty::Const<'tcx>>),
  59
  60     IntrinsicCast,
  61 }
  62
  63 pub enum UnconstrainedNumeric {
  64     UnconstrainedFloat,
  65     UnconstrainedInt,
  66     Neither,
  67 }
  68
  69 /// Explains the source of a type err in a short, human readable way. This is meant to be placed
  70 /// in parentheses after some larger message. You should also invoke `note_and_explain_type_err()`
  71 /// afterwards to present additional details, particularly when it comes to lifetime-related
  72 /// errors.
  73 impl<'tcx> fmt::Display for TypeError<'tcx> {
  74     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
  75         use self::TypeError::*;
  76         fn report_maybe_different(
  77             f: &mut fmt::Formatter<'_>,
  78             expected: &str,
  79             found: &str,
  80         ) -> fmt::Result {
  81             // A naive approach to making sure that we're not reporting silly errors such as:
  82             // (expected closure, found closure).
  83             if expected == found {
  84                 write!(f, "expected {}, found a different {}", expected, found)
  85             } else {
  86                 write!(f, "expected {}, found {}", expected, found)
  87             }
  88         }
  89
  90         let br_string = |br: ty::BoundRegion| match br {
  91             ty::BrNamed(_, name) => format!(" {}", name),
  92             _ => String::new(),
  93         };
  94
  95         match *self {
  96             CyclicTy(_) => write!(f, "cyclic type of infinite size"),
  97             Mismatch => write!(f, "types differ"),
  98             UnsafetyMismatch(values) => {
  99                 write!(f, "expected {} fn, found {} fn", values.expected, values.found)
 100             }
 101             AbiMismatch(values) => {
 102                 write!(f, "expected {} fn, found {} fn", values.expected, values.found)
 103             }
 104             Mutability => write!(f, "types differ in mutability"),
 105             TupleSize(values) => write!(
 106                 f,
 107                 "expected a tuple with {} element{}, \
 108                            found one with {} element{}",
 109                 values.expected,
 110                 pluralize!(values.expected),
 111                 values.found,
 112                 pluralize!(values.found)
 113             ),
 114             FixedArraySize(values) => write!(
 115                 f,
 116                 "expected an array with a fixed size of {} element{}, \
 117                            found one with {} element{}",
 118                 values.expected,
 119                 pluralize!(values.expected),
 120                 values.found,
 121                 pluralize!(values.found)
 122             ),
 123             ArgCount => write!(f, "incorrect number of function parameters"),
 124             RegionsDoesNotOutlive(..) => write!(f, "lifetime mismatch"),
 125             RegionsInsufficientlyPolymorphic(br, _) => write!(
 126                 f,
 127                 "expected bound lifetime parameter{}, found concrete lifetime",
 128                 br_string(br)
 129             ),
 130             RegionsOverlyPolymorphic(br, _) => write!(
 131                 f,
 132                 "expected concrete lifetime, found bound lifetime parameter{}",
 133                 br_string(br)
 134             ),
 135             RegionsPlaceholderMismatch => write!(f, "one type is more general than the other"),
 136             Sorts(values) => ty::tls::with(|tcx| {
 137                 report_maybe_different(
 138                     f,
 139                     &values.expected.sort_string(tcx),
 140                     &values.found.sort_string(tcx),
 141                 )
 142             }),
 143             Traits(values) => ty::tls::with(|tcx| {
 144                 report_maybe_different(
 145                     f,
 146                     &format!("trait `{}`", tcx.def_path_str(values.expected)),
 147                     &format!("trait `{}`", tcx.def_path_str(values.found)),
 148                 )
 149             }),
 150             IntMismatch(ref values) => {
 151                 write!(f, "expected `{:?}`, found `{:?}`", values.expected, values.found)
 152             }
 153             FloatMismatch(ref values) => {
 154                 write!(f, "expected `{:?}`, found `{:?}`", values.expected, values.found)
 155             }
 156             VariadicMismatch(ref values) => write!(
 157                 f,
 158                 "expected {} fn, found {} function",
 159                 if values.expected { "variadic" } else { "non-variadic" },
 160                 if values.found { "variadic" } else { "non-variadic" }
 161             ),
 162             ProjectionMismatched(ref values) => ty::tls::with(|tcx| {
 163                 write!(
 164                     f,
 165                     "expected {}, found {}",
 166                     tcx.def_path_str(values.expected),
 167                     tcx.def_path_str(values.found)
 168                 )
 169             }),
 170             ProjectionBoundsLength(ref values) => write!(
 171                 f,
 172                 "expected {} associated type binding{}, found {}",
 173                 values.expected,
 174                 pluralize!(values.expected),
 175                 values.found
 176             ),
 177             ExistentialMismatch(ref values) => report_maybe_different(
 178                 f,
 179                 &format!("trait `{}`", values.expected),
 180                 &format!("trait `{}`", values.found),
 181             ),
 182             ConstMismatch(ref values) => {
 183                 write!(f, "expected `{}`, found `{}`", values.expected, values.found)
 184             }
 185             IntrinsicCast => write!(f, "cannot coerce intrinsics to function pointers"),
 186             ObjectUnsafeCoercion(_) => write!(f, "coercion to object-unsafe trait object"),
 187         }
 188     }
 189 }
 190
 191 impl<'tcx> TypeError<'tcx> {
 192     pub fn must_include_note(&self) -> bool {
 193         use self::TypeError::*;
 194         match self {
 195             CyclicTy(_) | UnsafetyMismatch(_) | Mismatch | AbiMismatch(_) | FixedArraySize(_)
 196             | Sorts(_) | IntMismatch(_) | FloatMismatch(_) | VariadicMismatch(_) => false,
 197
 198             Mutability
 199             | TupleSize(_)
 200             | ArgCount
 201             | RegionsDoesNotOutlive(..)
 202             | RegionsInsufficientlyPolymorphic(..)
 203             | RegionsOverlyPolymorphic(..)
 204             | RegionsPlaceholderMismatch
 205             | Traits(_)
 206             | ProjectionMismatched(_)
 207             | ProjectionBoundsLength(_)
 208             | ExistentialMismatch(_)
 209             | ConstMismatch(_)
 210             | IntrinsicCast
 211             | ObjectUnsafeCoercion(_) => true,
 212         }
 213     }
 214 }
 215
 216 impl<'tcx> ty::TyS<'tcx> {
 217     pub fn sort_string(&self, tcx: TyCtxt<'_>) -> Cow<'static, str> {
 218         match self.kind {
 219             ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::Str | ty::Never => {
 220                 format!("`{}`", self).into()
 221             }
 222             ty::Tuple(ref tys) if tys.is_empty() => format!("`{}`", self).into(),
 223
 224             ty::Adt(def, _) => format!("{} `{}`", def.descr(), tcx.def_path_str(def.did)).into(),
 225             ty::Foreign(def_id) => format!("extern type `{}`", tcx.def_path_str(def_id)).into(),
 226             ty::Array(t, n) => {
 227                 let n = tcx.lift(&n).unwrap();
 228                 match n.try_eval_usize(tcx, ty::ParamEnv::empty()) {
 229                     _ if t.is_simple_ty() => format!("array `{}`", self).into(),
 230                     Some(n) => format!("array of {} element{} ", n, pluralize!(n)).into(),
 231                     None => "array".into(),
 232                 }
 233             }
 234             ty::Slice(ty) if ty.is_simple_ty() => format!("slice `{}`", self).into(),
 235             ty::Slice(_) => "slice".into(),
 236             ty::RawPtr(_) => "*-ptr".into(),
 237             ty::Ref(_, ty, mutbl) => {
 238                 let tymut = ty::TypeAndMut { ty, mutbl };
 239                 let tymut_string = tymut.to_string();
 240                 if tymut_string != "_"
 241                     && (ty.is_simple_text() || tymut_string.len() < "mutable reference".len())
 242                 {
 243                     format!("`&{}`", tymut_string).into()
 244                 } else {
 245                     // Unknown type name, it's long or has type arguments
 246                     match mutbl {
 247                         hir::Mutability::Mut => "mutable reference",
 248                         _ => "reference",
 249                     }
 250                     .into()
 251                 }
 252             }
 253             ty::FnDef(..) => "fn item".into(),
 254             ty::FnPtr(_) => "fn pointer".into(),
 255             ty::Dynamic(ref inner, ..) => {
 256                 if let Some(principal) = inner.principal() {
 257                     format!("trait object `dyn {}`", tcx.def_path_str(principal.def_id())).into()
 258                 } else {
 259                     "trait object".into()
 260                 }
 261             }
 262             ty::Closure(..) => "closure".into(),
 263             ty::Generator(..) => "generator".into(),
 264             ty::GeneratorWitness(..) => "generator witness".into(),
 265             ty::Tuple(..) => "tuple".into(),
 266             ty::Infer(ty::TyVar(_)) => "inferred type".into(),
 267             ty::Infer(ty::IntVar(_)) => "integer".into(),
 268             ty::Infer(ty::FloatVar(_)) => "floating-point number".into(),
 269             ty::Placeholder(..) => "placeholder type".into(),
 270             ty::Bound(..) => "bound type".into(),
 271             ty::Infer(ty::FreshTy(_)) => "fresh type".into(),
 272             ty::Infer(ty::FreshIntTy(_)) => "fresh integral type".into(),
 273             ty::Infer(ty::FreshFloatTy(_)) => "fresh floating-point type".into(),
 274             ty::Projection(_) => "associated type".into(),
 275             ty::UnnormalizedProjection(_) => "non-normalized associated type".into(),
 276             ty::Param(p) => format!("type parameter `{}`", p).into(),
 277             ty::Opaque(..) => "opaque type".into(),
 278             ty::Error => "type error".into(),
 279         }
 280     }
 281
 282     pub fn prefix_string(&self) -> Cow<'static, str> {
 283         match self.kind {
 284             ty::Infer(_)
 285             | ty::Error
 286             | ty::Bool
 287             | ty::Char
 288             | ty::Int(_)
 289             | ty::Uint(_)
 290             | ty::Float(_)
 291             | ty::Str
 292             | ty::Never => "type".into(),
 293             ty::Tuple(ref tys) if tys.is_empty() => "unit type".into(),
 294             ty::Adt(def, _) => def.descr().into(),
 295             ty::Foreign(_) => "extern type".into(),
 296             ty::Array(..) => "array".into(),
 297             ty::Slice(_) => "slice".into(),
 298             ty::RawPtr(_) => "raw pointer".into(),
 299             ty::Ref(.., mutbl) => match mutbl {
 300                 hir::Mutability::Mut => "mutable reference",
 301                 _ => "reference",
 302             }
 303             .into(),
 304             ty::FnDef(..) => "fn item".into(),
 305             ty::FnPtr(_) => "fn pointer".into(),
 306             ty::Dynamic(..) => "trait object".into(),
 307             ty::Closure(..) => "closure".into(),
 308             ty::Generator(..) => "generator".into(),
 309             ty::GeneratorWitness(..) => "generator witness".into(),
 310             ty::Tuple(..) => "tuple".into(),
 311             ty::Placeholder(..) => "higher-ranked type".into(),
 312             ty::Bound(..) => "bound type variable".into(),
 313             ty::Projection(_) => "associated type".into(),
 314             ty::UnnormalizedProjection(_) => "associated type".into(),
 315             ty::Param(_) => "type parameter".into(),
 316             ty::Opaque(..) => "opaque type".into(),
 317         }
 318     }
 319 }
 320
 321 impl<'tcx> TyCtxt<'tcx> {
 322     pub fn note_and_explain_type_err(
 323         self,
 324         db: &mut DiagnosticBuilder<'_>,
 325         err: &TypeError<'tcx>,
 326         sp: Span,
 327         body_owner_def_id: DefId,
 328     ) {
 329         use self::TypeError::*;
 330
 331         match err {
 332             Sorts(values) => {
 333                 let expected_str = values.expected.sort_string(self);
 334                 let found_str = values.found.sort_string(self);
 335                 if expected_str == found_str && expected_str == "closure" {
 336                     db.note("no two closures, even if identical, have the same type");
 337                     db.help("consider boxing your closure and/or using it as a trait object");
 338                 }
 339                 if expected_str == found_str && expected_str == "opaque type" {
 340                     // Issue #63167
 341                     db.note("distinct uses of `impl Trait` result in different opaque types");
 342                     let e_str = values.expected.to_string();
 343                     let f_str = values.found.to_string();
 344                     if &e_str == &f_str && &e_str == "impl std::future::Future" {
 345                         // FIXME: use non-string based check.
 346                         db.help(
 347                             "if both `Future`s have the same `Output` type, consider \
 348                                  `.await`ing on both of them",
 349                         );
 350                     }
 351                 }
 352                 match (&values.expected.kind, &values.found.kind) {
 353                     (ty::Float(_), ty::Infer(ty::IntVar(_))) => {
 354                         if let Ok(
 355                             // Issue #53280
 356                             snippet,
 357                         ) = self.sess.source_map().span_to_snippet(sp)
 358                         {
 359                             if snippet.chars().all(|c| c.is_digit(10) || c == '-' || c == '_') {
 360                                 db.span_suggestion(
 361                                     sp,
 362                                     "use a float literal",
 363                                     format!("{}.0", snippet),
 364                                     Applicability::MachineApplicable,
 365                                 );
 366                             }
 367                         }
 368                     }
 369                     (ty::Param(expected), ty::Param(found)) => {
 370                         let generics = self.generics_of(body_owner_def_id);
 371                         let e_span = self.def_span(generics.type_param(expected, self).def_id);
 372                         if !sp.contains(e_span) {
 373                             db.span_label(e_span, "expected type parameter");
 374                         }
 375                         let f_span = self.def_span(generics.type_param(found, self).def_id);
 376                         if !sp.contains(f_span) {
 377                             db.span_label(f_span, "found type parameter");
 378                         }
 379                         db.note(
 380                             "a type parameter was expected, but a different one was found; \
 381                                  you might be missing a type parameter or trait bound",
 382                         );
 383                         db.note(
 384                             "for more information, visit \
 385                                  https://doc.rust-lang.org/book/ch10-02-traits.html\
 386                                  #traits-as-parameters",
 387                         );
 388                     }
 389                     (ty::Projection(_), ty::Projection(_)) => {
 390                         db.note("an associated type was expected, but a different one was found");
 391                     }
 392                     (ty::Param(_), ty::Projection(_)) | (ty::Projection(_), ty::Param(_)) => {
 393                         db.note("you might be missing a type parameter or trait bound");
 394                     }
 395                     (ty::Param(p), _) | (_, ty::Param(p)) => {
 396                         let generics = self.generics_of(body_owner_def_id);
 397                         let p_span = self.def_span(generics.type_param(p, self).def_id);
 398                         if !sp.contains(p_span) {
 399                             db.span_label(p_span, "this type parameter");
 400                         }
 401                         db.help("type parameters must be constrained to match other types");
 402                         if self.sess.teach(&db.get_code().unwrap()) {
 403                             db.help(
 404                                 "given a type parameter `T` and a method `foo`:
 405 ```
 406 trait Trait<T> { fn foo(&self) -> T; }
 407 ```
 408 the only ways to implement method `foo` are:
 409 - constrain `T` with an explicit type:
 410 ```
 411 impl Trait<String> for X {
 412     fn foo(&self) -> String { String::new() }
 413 }
 414 ```
 415 - add a trait bound to `T` and call a method on that trait that returns `Self`:
 416 ```
 417 impl<T: std::default::Default> Trait<T> for X {
 418     fn foo(&self) -> T { <T as std::default::Default>::default() }
 419 }
 420 ```
 421 - change `foo` to return an argument of type `T`:
 422 ```
 423 impl<T> Trait<T> for X {
 424     fn foo(&self, x: T) -> T { x }
 425 }
 426 ```",
 427                             );
 428                         }
 429                         db.note(
 430                             "for more information, visit \
 431                                  https://doc.rust-lang.org/book/ch10-02-traits.html\
 432                                  #traits-as-parameters",
 433                         );
 434                     }
 435                     (ty::Projection(_), _) => {
 436                         db.note(&format!(
 437                             "consider constraining the associated type `{}` to `{}` or calling a \
 438                              method that returns `{}`",
 439                             values.expected, values.found, values.expected,
 440                         ));
 441                         if self.sess.teach(&db.get_code().unwrap()) {
 442                             db.help(
 443                                 "given an associated type `T` and a method `foo`:
 444 ```
 445 trait Trait {
 446     type T;
 447     fn foo(&self) -> Self::T;
 448 }
 449 ```
 450 the only way of implementing method `foo` is to constrain `T` with an explicit associated type:
 451 ```
 452 impl Trait for X {
 453     type T = String;
 454     fn foo(&self) -> Self::T { String::new() }
 455 }
 456 ```",
 457                             );
 458                         }
 459                         db.note(
 460                             "for more information, visit \
 461                                  https://doc.rust-lang.org/book/ch19-03-advanced-traits.html",
 462                         );
 463                     }
 464                     (_, ty::Projection(_)) => {
 465                         db.note(&format!(
 466                             "consider constraining the associated type `{}` to `{}`",
 467                             values.found, values.expected,
 468                         ));
 469                         db.note(
 470                             "for more information, visit \
 471                                  https://doc.rust-lang.org/book/ch19-03-advanced-traits.html",
 472                         );
 473                     }
 474                     _ => {}
 475                 }
 476                 debug!(
 477                     "note_and_explain_type_err expected={:?} ({:?}) found={:?} ({:?})",
 478                     values.expected, values.expected.kind, values.found, values.found.kind,
 479                 );
 480             }
 481             CyclicTy(ty) => {
 482                 // Watch out for various cases of cyclic types and try to explain.
 483                 if ty.is_closure() || ty.is_generator() {
 484                     db.note(
 485                         "closures cannot capture themselves or take themselves as argument;\n\
 486                              this error may be the result of a recent compiler bug-fix,\n\
 487                              see https://github.com/rust-lang/rust/issues/46062 for more details",
 488                     );
 489                 }
 490             }
 491             _ => {}
 492         }
 493     }
 494 }