src/librustc/ty/error.rs

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