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