src/librustc/ty/error.rs

   1 use crate::hir;
   2 use crate::hir::def_id::DefId;
   3 use crate::ty::{self, BoundRegion, Region, Ty, TyCtxt};
   4
   5 use errors::{Applicability, DiagnosticBuilder};
   6 use rustc_span::Span;
   7 use rustc_target::spec::abi;
   8 use syntax::ast;
   9 use syntax::errors::pluralize;
  10
  11 use std::borrow::Cow;
  12 use std::fmt;
  13
  14 #[derive(Clone, Copy, Debug, PartialEq, Eq, TypeFoldable)]
  15 pub struct ExpectedFound<T> {
  16     pub expected: T,
  17     pub found: T,
  18 }
  19
  20 // Data structures used in type unification
  21 #[derive(Clone, Debug, TypeFoldable)]
  22 pub enum TypeError<'tcx> {
  23     Mismatch,
  24     UnsafetyMismatch(ExpectedFound<hir::Unsafety>),
  25     AbiMismatch(ExpectedFound<abi::Abi>),
  26     Mutability,
  27     TupleSize(ExpectedFound<usize>),
  28     FixedArraySize(ExpectedFound<u64>),
  29     ArgCount,
  30
  31     RegionsDoesNotOutlive(Region<'tcx>, Region<'tcx>),
  32     RegionsInsufficientlyPolymorphic(BoundRegion, Region<'tcx>),
  33     RegionsOverlyPolymorphic(BoundRegion, Region<'tcx>),
  34     RegionsPlaceholderMismatch,
  35
  36     Sorts(ExpectedFound<Ty<'tcx>>),
  37     IntMismatch(ExpectedFound<ty::IntVarValue>),
  38     FloatMismatch(ExpectedFound<ast::FloatTy>),
  39     Traits(ExpectedFound<DefId>),
  40     VariadicMismatch(ExpectedFound<bool>),
  41
  42     /// Instantiating a type variable with the given type would have
  43     /// created a cycle (because it appears somewhere within that
  44     /// type).
  45     CyclicTy(Ty<'tcx>),
  46     ProjectionMismatched(ExpectedFound<DefId>),
  47     ProjectionBoundsLength(ExpectedFound<usize>),
  48     ExistentialMismatch(ExpectedFound<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>>),
  49     ObjectUnsafeCoercion(DefId),
  50     ConstMismatch(ExpectedFound<&'tcx ty::Const<'tcx>>),
  51
  52     IntrinsicCast,
  53 }
  54
  55 pub enum UnconstrainedNumeric {
  56     UnconstrainedFloat,
  57     UnconstrainedInt,
  58     Neither,
  59 }
  60
  61 /// Explains the source of a type err in a short, human readable way. This is meant to be placed
  62 /// in parentheses after some larger message. You should also invoke `note_and_explain_type_err()`
  63 /// afterwards to present additional details, particularly when it comes to lifetime-related
  64 /// errors.
  65 impl<'tcx> fmt::Display for TypeError<'tcx> {
  66     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
  67         use self::TypeError::*;
  68         fn report_maybe_different(
  69             f: &mut fmt::Formatter<'_>,
  70             expected: &str,
  71             found: &str,
  72         ) -> fmt::Result {
  73             // A naive approach to making sure that we're not reporting silly errors such as:
  74             // (expected closure, found closure).
  75             if expected == found {
  76                 write!(f, "expected {}, found a different {}", expected, found)
  77             } else {
  78                 write!(f, "expected {}, found {}", expected, found)
  79             }
  80         }
  81
  82         let br_string = |br: ty::BoundRegion| match br {
  83             ty::BrNamed(_, name) => format!(" {}", name),
  84             _ => String::new(),
  85         };
  86
  87         match *self {
  88             CyclicTy(_) => write!(f, "cyclic type of infinite size"),
  89             Mismatch => write!(f, "types differ"),
  90             UnsafetyMismatch(values) => {
  91                 write!(f, "expected {} fn, found {} fn", values.expected, values.found)
  92             }
  93             AbiMismatch(values) => {
  94                 write!(f, "expected {} fn, found {} fn", values.expected, values.found)
  95             }
  96             Mutability => write!(f, "types differ in mutability"),
  97             TupleSize(values) => write!(
  98                 f,
  99                 "expected a tuple with {} element{}, \
 100                            found one with {} element{}",
 101                 values.expected,
 102                 pluralize!(values.expected),
 103                 values.found,
 104                 pluralize!(values.found)
 105             ),
 106             FixedArraySize(values) => write!(
 107                 f,
 108                 "expected an array with a fixed size of {} element{}, \
 109                            found one with {} element{}",
 110                 values.expected,
 111                 pluralize!(values.expected),
 112                 values.found,
 113                 pluralize!(values.found)
 114             ),
 115             ArgCount => write!(f, "incorrect number of function parameters"),
 116             RegionsDoesNotOutlive(..) => write!(f, "lifetime mismatch"),
 117             RegionsInsufficientlyPolymorphic(br, _) => write!(
 118                 f,
 119                 "expected bound lifetime parameter{}, found concrete lifetime",
 120                 br_string(br)
 121             ),
 122             RegionsOverlyPolymorphic(br, _) => write!(
 123                 f,
 124                 "expected concrete lifetime, found bound lifetime parameter{}",
 125                 br_string(br)
 126             ),
 127             RegionsPlaceholderMismatch => write!(f, "one type is more general than the other"),
 128             Sorts(values) => ty::tls::with(|tcx| {
 129                 report_maybe_different(
 130                     f,
 131                     &values.expected.sort_string(tcx),
 132                     &values.found.sort_string(tcx),
 133                 )
 134             }),
 135             Traits(values) => ty::tls::with(|tcx| {
 136                 report_maybe_different(
 137                     f,
 138                     &format!("trait `{}`", tcx.def_path_str(values.expected)),
 139                     &format!("trait `{}`", tcx.def_path_str(values.found)),
 140                 )
 141             }),
 142             IntMismatch(ref values) => {
 143                 write!(f, "expected `{:?}`, found `{:?}`", values.expected, values.found)
 144             }
 145             FloatMismatch(ref values) => {
 146                 write!(f, "expected `{:?}`, found `{:?}`", values.expected, values.found)
 147             }
 148             VariadicMismatch(ref values) => write!(
 149                 f,
 150                 "expected {} fn, found {} function",
 151                 if values.expected { "variadic" } else { "non-variadic" },
 152                 if values.found { "variadic" } else { "non-variadic" }
 153             ),
 154             ProjectionMismatched(ref values) => ty::tls::with(|tcx| {
 155                 write!(
 156                     f,
 157                     "expected {}, found {}",
 158                     tcx.def_path_str(values.expected),
 159                     tcx.def_path_str(values.found)
 160                 )
 161             }),
 162             ProjectionBoundsLength(ref values) => write!(
 163                 f,
 164                 "expected {} associated type binding{}, found {}",
 165                 values.expected,
 166                 pluralize!(values.expected),
 167                 values.found
 168             ),
 169             ExistentialMismatch(ref values) => report_maybe_different(
 170                 f,
 171                 &format!("trait `{}`", values.expected),
 172                 &format!("trait `{}`", values.found),
 173             ),
 174             ConstMismatch(ref values) => {
 175                 write!(f, "expected `{}`, found `{}`", values.expected, values.found)
 176             }
 177             IntrinsicCast => write!(f, "cannot coerce intrinsics to function pointers"),
 178             ObjectUnsafeCoercion(_) => write!(f, "coercion to object-unsafe trait object"),
 179         }
 180     }
 181 }
 182
 183 impl<'tcx> TypeError<'tcx> {
 184     pub fn must_include_note(&self) -> bool {
 185         use self::TypeError::*;
 186         match self {
 187             CyclicTy(_) | UnsafetyMismatch(_) | Mismatch | AbiMismatch(_) | FixedArraySize(_)
 188             | Sorts(_) | IntMismatch(_) | FloatMismatch(_) | VariadicMismatch(_) => false,
 189
 190             Mutability
 191             | TupleSize(_)
 192             | ArgCount
 193             | RegionsDoesNotOutlive(..)
 194             | RegionsInsufficientlyPolymorphic(..)
 195             | RegionsOverlyPolymorphic(..)
 196             | RegionsPlaceholderMismatch
 197             | Traits(_)
 198             | ProjectionMismatched(_)
 199             | ProjectionBoundsLength(_)
 200             | ExistentialMismatch(_)
 201             | ConstMismatch(_)
 202             | IntrinsicCast
 203             | ObjectUnsafeCoercion(_) => true,
 204         }
 205     }
 206 }
 207
 208 impl<'tcx> ty::TyS<'tcx> {
 209     pub fn sort_string(&self, tcx: TyCtxt<'_>) -> Cow<'static, str> {
 210         match self.kind {
 211             ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::Str | ty::Never => {
 212                 format!("`{}`", self).into()
 213             }
 214             ty::Tuple(ref tys) if tys.is_empty() => format!("`{}`", self).into(),
 215
 216             ty::Adt(def, _) => format!("{} `{}`", def.descr(), tcx.def_path_str(def.did)).into(),
 217             ty::Foreign(def_id) => format!("extern type `{}`", tcx.def_path_str(def_id)).into(),
 218             ty::Array(t, n) => {
 219                 let n = tcx.lift(&n).unwrap();
 220                 match n.try_eval_usize(tcx, ty::ParamEnv::empty()) {
 221                     _ if t.is_simple_ty() => format!("array `{}`", self).into(),
 222                     Some(n) => format!("array of {} element{} ", n, pluralize!(n)).into(),
 223                     None => "array".into(),
 224                 }
 225             }
 226             ty::Slice(ty) if ty.is_simple_ty() => format!("slice `{}`", self).into(),
 227             ty::Slice(_) => "slice".into(),
 228             ty::RawPtr(_) => "*-ptr".into(),
 229             ty::Ref(_, ty, mutbl) => {
 230                 let tymut = ty::TypeAndMut { ty, mutbl };
 231                 let tymut_string = tymut.to_string();
 232                 if tymut_string != "_"
 233                     && (ty.is_simple_text() || tymut_string.len() < "mutable reference".len())
 234                 {
 235                     format!("`&{}`", tymut_string).into()
 236                 } else {
 237                     // Unknown type name, it's long or has type arguments
 238                     match mutbl {
 239                         hir::Mutability::Mut => "mutable reference",
 240                         _ => "reference",
 241                     }
 242                     .into()
 243                 }
 244             }
 245             ty::FnDef(..) => "fn item".into(),
 246             ty::FnPtr(_) => "fn pointer".into(),
 247             ty::Dynamic(ref inner, ..) => {
 248                 if let Some(principal) = inner.principal() {
 249                     format!("trait `{}`", tcx.def_path_str(principal.def_id())).into()
 250                 } else {
 251                     "trait".into()
 252                 }
 253             }
 254             ty::Closure(..) => "closure".into(),
 255             ty::Generator(..) => "generator".into(),
 256             ty::GeneratorWitness(..) => "generator witness".into(),
 257             ty::Tuple(..) => "tuple".into(),
 258             ty::Infer(ty::TyVar(_)) => "inferred type".into(),
 259             ty::Infer(ty::IntVar(_)) => "integer".into(),
 260             ty::Infer(ty::FloatVar(_)) => "floating-point number".into(),
 261             ty::Placeholder(..) => "placeholder type".into(),
 262             ty::Bound(..) => "bound type".into(),
 263             ty::Infer(ty::FreshTy(_)) => "fresh type".into(),
 264             ty::Infer(ty::FreshIntTy(_)) => "fresh integral type".into(),
 265             ty::Infer(ty::FreshFloatTy(_)) => "fresh floating-point type".into(),
 266             ty::Projection(_) => "associated type".into(),
 267             ty::UnnormalizedProjection(_) => "non-normalized associated type".into(),
 268             ty::Param(p) => format!("type parameter `{}`", p).into(),
 269             ty::Opaque(..) => "opaque type".into(),
 270             ty::Error => "type error".into(),
 271         }
 272     }
 273
 274     pub fn prefix_string(&self) -> Cow<'static, str> {
 275         match self.kind {
 276             ty::Infer(_)
 277             | ty::Error
 278             | ty::Bool
 279             | ty::Char
 280             | ty::Int(_)
 281             | ty::Uint(_)
 282             | ty::Float(_)
 283             | ty::Str
 284             | ty::Never => "type".into(),
 285             ty::Tuple(ref tys) if tys.is_empty() => "unit type".into(),
 286             ty::Adt(def, _) => def.descr().into(),
 287             ty::Foreign(_) => "extern type".into(),
 288             ty::Array(..) => "array".into(),
 289             ty::Slice(_) => "slice".into(),
 290             ty::RawPtr(_) => "raw pointer".into(),
 291             ty::Ref(.., mutbl) => match mutbl {
 292                 hir::Mutability::Mut => "mutable reference",
 293                 _ => "reference",
 294             }
 295             .into(),
 296             ty::FnDef(..) => "fn item".into(),
 297             ty::FnPtr(_) => "fn pointer".into(),
 298             ty::Dynamic(..) => "trait object".into(),
 299             ty::Closure(..) => "closure".into(),
 300             ty::Generator(..) => "generator".into(),
 301             ty::GeneratorWitness(..) => "generator witness".into(),
 302             ty::Tuple(..) => "tuple".into(),
 303             ty::Placeholder(..) => "higher-ranked type".into(),
 304             ty::Bound(..) => "bound type variable".into(),
 305             ty::Projection(_) => "associated type".into(),
 306             ty::UnnormalizedProjection(_) => "associated type".into(),
 307             ty::Param(_) => "type parameter".into(),
 308             ty::Opaque(..) => "opaque type".into(),
 309         }
 310     }
 311 }
 312
 313 impl<'tcx> TyCtxt<'tcx> {
 314     pub fn note_and_explain_type_err(
 315         self,
 316         db: &mut DiagnosticBuilder<'_>,
 317         err: &TypeError<'tcx>,
 318         sp: Span,
 319         body_owner_def_id: DefId,
 320     ) {
 321         use self::TypeError::*;
 322
 323         match err {
 324             Sorts(values) => {
 325                 let expected_str = values.expected.sort_string(self);
 326                 let found_str = values.found.sort_string(self);
 327                 if expected_str == found_str && expected_str == "closure" {
 328                     db.note("no two closures, even if identical, have the same type");
 329                     db.help("consider boxing your closure and/or using it as a trait object");
 330                 }
 331                 if expected_str == found_str && expected_str == "opaque type" {
 332                     // Issue #63167
 333                     db.note("distinct uses of `impl Trait` result in different opaque types");
 334                     let e_str = values.expected.to_string();
 335                     let f_str = values.found.to_string();
 336                     if &e_str == &f_str && &e_str == "impl std::future::Future" {
 337                         // FIXME: use non-string based check.
 338                         db.help(
 339                             "if both `Future`s have the same `Output` type, consider \
 340                                  `.await`ing on both of them",
 341                         );
 342                     }
 343                 }
 344                 match (&values.expected.kind, &values.found.kind) {
 345                     (ty::Float(_), ty::Infer(ty::IntVar(_))) => {
 346                         if let Ok(
 347                             // Issue #53280
 348                             snippet,
 349                         ) = self.sess.source_map().span_to_snippet(sp)
 350                         {
 351                             if snippet.chars().all(|c| c.is_digit(10) || c == '-' || c == '_') {
 352                                 db.span_suggestion(
 353                                     sp,
 354                                     "use a float literal",
 355                                     format!("{}.0", snippet),
 356                                     Applicability::MachineApplicable,
 357                                 );
 358                             }
 359                         }
 360                     }
 361                     (ty::Param(expected), ty::Param(found)) => {
 362                         let generics = self.generics_of(body_owner_def_id);
 363                         let e_span = self.def_span(generics.type_param(expected, self).def_id);
 364                         if !sp.contains(e_span) {
 365                             db.span_label(e_span, "expected type parameter");
 366                         }
 367                         let f_span = self.def_span(generics.type_param(found, self).def_id);
 368                         if !sp.contains(f_span) {
 369                             db.span_label(f_span, "found type parameter");
 370                         }
 371                         db.note(
 372                             "a type parameter was expected, but a different one was found; \
 373                                  you might be missing a type parameter or trait bound",
 374                         );
 375                         db.note(
 376                             "for more information, visit \
 377                                  https://doc.rust-lang.org/book/ch10-02-traits.html\
 378                                  #traits-as-parameters",
 379                         );
 380                     }
 381                     (ty::Projection(_), ty::Projection(_)) => {
 382                         db.note("an associated type was expected, but a different one was found");
 383                     }
 384                     (ty::Param(_), ty::Projection(_)) | (ty::Projection(_), ty::Param(_)) => {
 385                         db.note("you might be missing a type parameter or trait bound");
 386                     }
 387                     (ty::Param(p), _) | (_, ty::Param(p)) => {
 388                         let generics = self.generics_of(body_owner_def_id);
 389                         let p_span = self.def_span(generics.type_param(p, self).def_id);
 390                         if !sp.contains(p_span) {
 391                             db.span_label(p_span, "this type parameter");
 392                         }
 393                         db.help("type parameters must be constrained to match other types");
 394                         if self.sess.teach(&db.get_code().unwrap()) {
 395                             db.help(
 396                                 "given a type parameter `T` and a method `foo`:
 397 ```
 398 trait Trait<T> { fn foo(&self) -> T; }
 399 ```
 400 the only ways to implement method `foo` are:
 401 - constrain `T` with an explicit type:
 402 ```
 403 impl Trait<String> for X {
 404     fn foo(&self) -> String { String::new() }
 405 }
 406 ```
 407 - add a trait bound to `T` and call a method on that trait that returns `Self`:
 408 ```
 409 impl<T: std::default::Default> Trait<T> for X {
 410     fn foo(&self) -> T { <T as std::default::Default>::default() }
 411 }
 412 ```
 413 - change `foo` to return an argument of type `T`:
 414 ```
 415 impl<T> Trait<T> for X {
 416     fn foo(&self, x: T) -> T { x }
 417 }
 418 ```",
 419                             );
 420                         }
 421                         db.note(
 422                             "for more information, visit \
 423                                  https://doc.rust-lang.org/book/ch10-02-traits.html\
 424                                  #traits-as-parameters",
 425                         );
 426                     }
 427                     (ty::Projection(_), _) => {
 428                         db.note(&format!(
 429                             "consider constraining the associated type `{}` to `{}` or calling a \
 430                              method that returns `{}`",
 431                             values.expected, values.found, values.expected,
 432                         ));
 433                         if self.sess.teach(&db.get_code().unwrap()) {
 434                             db.help(
 435                                 "given an associated type `T` and a method `foo`:
 436 ```
 437 trait Trait {
 438     type T;
 439     fn foo(&self) -> Self::T;
 440 }
 441 ```
 442 the only way of implementing method `foo` is to constrain `T` with an explicit associated type:
 443 ```
 444 impl Trait for X {
 445     type T = String;
 446     fn foo(&self) -> Self::T { String::new() }
 447 }
 448 ```",
 449                             );
 450                         }
 451                         db.note(
 452                             "for more information, visit \
 453                                  https://doc.rust-lang.org/book/ch19-03-advanced-traits.html",
 454                         );
 455                     }
 456                     (_, ty::Projection(_)) => {
 457                         db.note(&format!(
 458                             "consider constraining the associated type `{}` to `{}`",
 459                             values.found, values.expected,
 460                         ));
 461                         db.note(
 462                             "for more information, visit \
 463                                  https://doc.rust-lang.org/book/ch19-03-advanced-traits.html",
 464                         );
 465                     }
 466                     _ => {}
 467                 }
 468                 debug!(
 469                     "note_and_explain_type_err expected={:?} ({:?}) found={:?} ({:?})",
 470                     values.expected, values.expected.kind, values.found, values.found.kind,
 471                 );
 472             }
 473             CyclicTy(ty) => {
 474                 // Watch out for various cases of cyclic types and try to explain.
 475                 if ty.is_closure() || ty.is_generator() {
 476                     db.note(
 477                         "closures cannot capture themselves or take themselves as argument;\n\
 478                              this error may be the result of a recent compiler bug-fix,\n\
 479                              see https://github.com/rust-lang/rust/issues/46062 for more details",
 480                     );
 481                 }
 482             }
 483             _ => {}
 484         }
 485     }
 486 }