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