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(f: &mut fmt::Formatter<'_>,
  69                                   expected: &str, found: &str) -> fmt::Result {
  70             // A naive approach to making sure that we're not reporting silly errors such as:
  71             // (expected closure, found closure).
  72             if expected == found {
  73                 write!(f, "expected {}, found a different {}", expected, found)
  74             } else {
  75                 write!(f, "expected {}, found {}", expected, found)
  76             }
  77         }
  78
  79         let br_string = |br: ty::BoundRegion| {
  80             match br {
  81                 ty::BrNamed(_, name) => format!(" {}", name),
  82                 _ => String::new(),
  83             }
  84         };
  85
  86         match *self {
  87             CyclicTy(_) => write!(f, "cyclic type of infinite size"),
  88             Mismatch => write!(f, "types differ"),
  89             UnsafetyMismatch(values) => {
  90                 write!(f, "expected {} fn, found {} fn",
  91                        values.expected,
  92                        values.found)
  93             }
  94             AbiMismatch(values) => {
  95                 write!(f, "expected {} fn, found {} fn",
  96                        values.expected,
  97                        values.found)
  98             }
  99             Mutability => write!(f, "types differ in mutability"),
 100             TupleSize(values) => {
 101                 write!(f, "expected a tuple with {} element{}, \
 102                            found one with {} element{}",
 103                        values.expected,
 104                        pluralize!(values.expected),
 105                        values.found,
 106                        pluralize!(values.found))
 107             }
 108             FixedArraySize(values) => {
 109                 write!(f, "expected an array with a fixed size of {} element{}, \
 110                            found one with {} element{}",
 111                        values.expected,
 112                        pluralize!(values.expected),
 113                        values.found,
 114                        pluralize!(values.found))
 115             }
 116             ArgCount => {
 117                 write!(f, "incorrect number of function parameters")
 118             }
 119             RegionsDoesNotOutlive(..) => {
 120                 write!(f, "lifetime mismatch")
 121             }
 122             RegionsInsufficientlyPolymorphic(br, _) => {
 123                 write!(f,
 124                        "expected bound lifetime parameter{}, found concrete lifetime",
 125                        br_string(br))
 126             }
 127             RegionsOverlyPolymorphic(br, _) => {
 128                 write!(f,
 129                        "expected concrete lifetime, found bound lifetime parameter{}",
 130                        br_string(br))
 131             }
 132             RegionsPlaceholderMismatch => {
 133                 write!(f, "one type is more general than the other")
 134             }
 135             Sorts(values) => ty::tls::with(|tcx| {
 136                 report_maybe_different(f, &values.expected.sort_string(tcx),
 137                                        &values.found.sort_string(tcx))
 138             }),
 139             Traits(values) => ty::tls::with(|tcx| {
 140                 report_maybe_different(f,
 141                                        &format!("trait `{}`",
 142                                                 tcx.def_path_str(values.expected)),
 143                                        &format!("trait `{}`",
 144                                                 tcx.def_path_str(values.found)))
 145             }),
 146             IntMismatch(ref values) => {
 147                 write!(f, "expected `{:?}`, found `{:?}`",
 148                        values.expected,
 149                        values.found)
 150             }
 151             FloatMismatch(ref values) => {
 152                 write!(f, "expected `{:?}`, found `{:?}`",
 153                        values.expected,
 154                        values.found)
 155             }
 156             VariadicMismatch(ref values) => {
 157                 write!(f, "expected {} fn, found {} function",
 158                        if values.expected { "variadic" } else { "non-variadic" },
 159                        if values.found { "variadic" } else { "non-variadic" })
 160             }
 161             ProjectionMismatched(ref values) => ty::tls::with(|tcx| {
 162                 write!(f, "expected {}, found {}",
 163                        tcx.def_path_str(values.expected),
 164                        tcx.def_path_str(values.found))
 165             }),
 166             ProjectionBoundsLength(ref values) => {
 167                 write!(f, "expected {} associated type binding{}, found {}",
 168                        values.expected,
 169                        pluralize!(values.expected),
 170                        values.found)
 171             },
 172             ExistentialMismatch(ref values) => {
 173                 report_maybe_different(f, &format!("trait `{}`", values.expected),
 174                                        &format!("trait `{}`", values.found))
 175             }
 176             ConstMismatch(ref values) => {
 177                 write!(f, "expected `{}`, found `{}`", values.expected, values.found)
 178             }
 179             IntrinsicCast => {
 180                 write!(f, "cannot coerce intrinsics to function pointers")
 181             }
 182             ObjectUnsafeCoercion(_) => write!(f, "coercion to object-unsafe trait object"),
 183         }
 184     }
 185 }
 186
 187 impl<'tcx> ty::TyS<'tcx> {
 188     pub fn sort_string(&self, tcx: TyCtxt<'_>) -> Cow<'static, str> {
 189         match self.kind {
 190             ty::Bool | ty::Char | ty::Int(_) |
 191             ty::Uint(_) | ty::Float(_) | ty::Str | ty::Never => self.to_string().into(),
 192             ty::Tuple(ref tys) if tys.is_empty() => self.to_string().into(),
 193
 194             ty::Adt(def, _) => format!("{} `{}`", def.descr(), tcx.def_path_str(def.did)).into(),
 195             ty::Foreign(def_id) => format!("extern type `{}`", tcx.def_path_str(def_id)).into(),
 196             ty::Array(_, n) => {
 197                 let n = tcx.lift(&n).unwrap();
 198                 match n.try_eval_usize(tcx, ty::ParamEnv::empty()) {
 199                     Some(n) => {
 200                         format!("array of {} element{}", n, pluralize!(n)).into()
 201                     }
 202                     None => "array".into(),
 203                 }
 204             }
 205             ty::Slice(_) => "slice".into(),
 206             ty::RawPtr(_) => "*-ptr".into(),
 207             ty::Ref(region, ty, mutbl) => {
 208                 let tymut = ty::TypeAndMut { ty, mutbl };
 209                 let tymut_string = tymut.to_string();
 210                 if tymut_string == "_" ||         //unknown type name,
 211                    tymut_string.len() > 10 ||     //name longer than saying "reference",
 212                    region.to_string() != "'_"     //... or a complex type
 213                 {
 214                     format!("{}reference", match mutbl {
 215                         hir::Mutability::Mutable => "mutable ",
 216                         _ => ""
 217                     }).into()
 218                 } else {
 219                     format!("&{}", tymut_string).into()
 220                 }
 221             }
 222             ty::FnDef(..) => "fn item".into(),
 223             ty::FnPtr(_) => "fn pointer".into(),
 224             ty::Dynamic(ref inner, ..) => {
 225                 if let Some(principal) = inner.principal() {
 226                     format!("trait {}", tcx.def_path_str(principal.def_id())).into()
 227                 } else {
 228                     "trait".into()
 229                 }
 230             }
 231             ty::Closure(..) => "closure".into(),
 232             ty::Generator(..) => "generator".into(),
 233             ty::GeneratorWitness(..) => "generator witness".into(),
 234             ty::Tuple(..) => "tuple".into(),
 235             ty::Infer(ty::TyVar(_)) => "inferred type".into(),
 236             ty::Infer(ty::IntVar(_)) => "integer".into(),
 237             ty::Infer(ty::FloatVar(_)) => "floating-point number".into(),
 238             ty::Placeholder(..) => "placeholder type".into(),
 239             ty::Bound(..) => "bound type".into(),
 240             ty::Infer(ty::FreshTy(_)) => "fresh type".into(),
 241             ty::Infer(ty::FreshIntTy(_)) => "fresh integral type".into(),
 242             ty::Infer(ty::FreshFloatTy(_)) => "fresh floating-point type".into(),
 243             ty::Projection(_) => "associated type".into(),
 244             ty::UnnormalizedProjection(_) => "non-normalized associated type".into(),
 245             ty::Param(p) => format!("type parameter `{}`", p).into(),
 246             ty::Opaque(..) => "opaque type".into(),
 247             ty::Error => "type error".into(),
 248         }
 249     }
 250 }
 251
 252 impl<'tcx> TyCtxt<'tcx> {
 253     pub fn note_and_explain_type_err(
 254         self,
 255         db: &mut DiagnosticBuilder<'_>,
 256         err: &TypeError<'tcx>,
 257         sp: Span,
 258         body_owner_def_id: DefId,
 259     ) {
 260         use self::TypeError::*;
 261
 262         match err {
 263             Sorts(values) => {
 264                 let expected_str = values.expected.sort_string(self);
 265                 let found_str = values.found.sort_string(self);
 266                 if expected_str == found_str && expected_str == "closure" {
 267                     db.note("no two closures, even if identical, have the same type");
 268                     db.help("consider boxing your closure and/or using it as a trait object");
 269                 }
 270                 if expected_str == found_str && expected_str == "opaque type" { // Issue #63167
 271                     db.note("distinct uses of `impl Trait` result in different opaque types");
 272                     let e_str = values.expected.to_string();
 273                     let f_str = values.found.to_string();
 274                     if &e_str == &f_str && &e_str == "impl std::future::Future" {
 275                         // FIXME: use non-string based check.
 276                         db.help("if both `Future`s have the same `Output` type, consider \
 277                                  `.await`ing on both of them");
 278                     }
 279                 }
 280                 match (&values.expected.kind, &values.found.kind) {
 281                     (ty::Float(_), ty::Infer(ty::IntVar(_))) => if let Ok( // Issue #53280
 282                         snippet,
 283                     ) = self.sess.source_map().span_to_snippet(sp) {
 284                         if snippet.chars().all(|c| c.is_digit(10) || c == '-' || c == '_') {
 285                             db.span_suggestion(
 286                                 sp,
 287                                 "use a float literal",
 288                                 format!("{}.0", snippet),
 289                                 Applicability::MachineApplicable
 290                             );
 291                         }
 292                     },
 293                     (ty::Param(expected), ty::Param(found)) => {
 294                         let generics = self.generics_of(body_owner_def_id);
 295                         let e_span = self.def_span(generics.type_param(expected, self).def_id);
 296                         if !sp.contains(e_span) {
 297                             db.span_label(e_span, "expected type parameter");
 298                         }
 299                         let f_span = self.def_span(generics.type_param(found, self).def_id);
 300                         if !sp.contains(f_span) {
 301                             db.span_label(f_span, "found type parameter");
 302                         }
 303                         db.note("a type parameter was expected, but a different one was found; \
 304                                  you might be missing a type parameter or trait bound");
 305                         db.note("for more information, visit \
 306                                  https://doc.rust-lang.org/book/ch10-02-traits.html\
 307                                  #traits-as-parameters");
 308                     }
 309                     (ty::Projection(_), ty::Projection(_)) => {
 310                         db.note("an associated type was expected, but a different one was found");
 311                     }
 312                     (ty::Param(_), ty::Projection(_)) | (ty::Projection(_), ty::Param(_)) => {
 313                         db.note("you might be missing a type parameter or trait bound");
 314                     }
 315                     (ty::Param(p), _) | (_, ty::Param(p)) => {
 316                         let generics = self.generics_of(body_owner_def_id);
 317                         let p_span = self.def_span(generics.type_param(p, self).def_id);
 318                         if !sp.contains(p_span) {
 319                             db.span_label(p_span, "this type parameter");
 320                         }
 321                         db.help("type parameters must be constrained to match other types");
 322                         if self.sess.teach(&db.get_code().unwrap()) {
 323                             db.help("given a type parameter `T` and a method `foo`:
 324 ```
 325 trait Trait<T> { fn foo(&self) -> T; }
 326 ```
 327 the only ways to implement method `foo` are:
 328 - constrain `T` with an explicit type:
 329 ```
 330 impl Trait<String> for X {
 331     fn foo(&self) -> String { String::new() }
 332 }
 333 ```
 334 - add a trait bound to `T` and call a method on that trait that returns `Self`:
 335 ```
 336 impl<T: std::default::Default> Trait<T> for X {
 337     fn foo(&self) -> T { <T as std::default::Default>::default() }
 338 }
 339 ```
 340 - change `foo` to return an argument of type `T`:
 341 ```
 342 impl<T> Trait<T> for X {
 343     fn foo(&self, x: T) -> T { x }
 344 }
 345 ```");
 346                         }
 347                         db.note("for more information, visit \
 348                                  https://doc.rust-lang.org/book/ch10-02-traits.html\
 349                                  #traits-as-parameters");
 350                     }
 351                     (ty::Projection(_), _) => {
 352                         db.note(&format!(
 353                             "consider constraining the associated type `{}` to `{}` or calling a \
 354                              method that returns `{}`",
 355                             values.expected,
 356                             values.found,
 357                             values.expected,
 358                         ));
 359                         if self.sess.teach(&db.get_code().unwrap()) {
 360                             db.help("given an associated type `T` and a method `foo`:
 361 ```
 362 trait Trait {
 363     type T;
 364     fn foo(&self) -> Self::T;
 365 }
 366 ```
 367 the only way of implementing method `foo` is to constrain `T` with an explicit associated type:
 368 ```
 369 impl Trait for X {
 370     type T = String;
 371     fn foo(&self) -> Self::T { String::new() }
 372 }
 373 ```");
 374                         }
 375                         db.note("for more information, visit \
 376                                  https://doc.rust-lang.org/book/ch19-03-advanced-traits.html");
 377                     }
 378                     (_, ty::Projection(_)) => {
 379                         db.note(&format!(
 380                             "consider constraining the associated type `{}` to `{}`",
 381                             values.found,
 382                             values.expected,
 383                         ));
 384                         db.note("for more information, visit \
 385                                  https://doc.rust-lang.org/book/ch19-03-advanced-traits.html");
 386                     }
 387                     _ => {}
 388                 }
 389                 debug!(
 390                     "note_and_explain_type_err expected={:?} ({:?}) found={:?} ({:?})",
 391                     values.expected,
 392                     values.expected.kind,
 393                     values.found,
 394                     values.found.kind,
 395                 );
 396             },
 397             CyclicTy(ty) => {
 398                 // Watch out for various cases of cyclic types and try to explain.
 399                 if ty.is_closure() || ty.is_generator() {
 400                     db.note("closures cannot capture themselves or take themselves as argument;\n\
 401                              this error may be the result of a recent compiler bug-fix,\n\
 402                              see https://github.com/rust-lang/rust/issues/46062 for more details");
 403                 }
 404             }
 405             _ => {}
 406         }
 407     }
 408 }