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 errors::{Applicability, DiagnosticBuilder};
   8 use syntax_pos::Span;
   9
  10 use crate::hir;
  11
  12 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
  13 pub struct ExpectedFound<T> {
  14     pub expected: T,
  15     pub found: T,
  16 }
  17
  18 // Data structures used in type unification
  19 #[derive(Clone, Debug)]
  20 pub enum TypeError<'tcx> {
  21     Mismatch,
  22     UnsafetyMismatch(ExpectedFound<hir::Unsafety>),
  23     AbiMismatch(ExpectedFound<abi::Abi>),
  24     Mutability,
  25     TupleSize(ExpectedFound<usize>),
  26     FixedArraySize(ExpectedFound<u64>),
  27     ArgCount,
  28
  29     RegionsDoesNotOutlive(Region<'tcx>, Region<'tcx>),
  30     RegionsInsufficientlyPolymorphic(BoundRegion, Region<'tcx>),
  31     RegionsOverlyPolymorphic(BoundRegion, Region<'tcx>),
  32     RegionsPlaceholderMismatch,
  33
  34     Sorts(ExpectedFound<Ty<'tcx>>),
  35     IntMismatch(ExpectedFound<ty::IntVarValue>),
  36     FloatMismatch(ExpectedFound<ast::FloatTy>),
  37     Traits(ExpectedFound<DefId>),
  38     VariadicMismatch(ExpectedFound<bool>),
  39
  40     /// Instantiating a type variable with the given type would have
  41     /// created a cycle (because it appears somewhere within that
  42     /// type).
  43     CyclicTy(Ty<'tcx>),
  44     ProjectionMismatched(ExpectedFound<DefId>),
  45     ProjectionBoundsLength(ExpectedFound<usize>),
  46     ExistentialMismatch(ExpectedFound<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>>),
  47
  48     ConstMismatch(ExpectedFound<&'tcx ty::Const<'tcx>>),
  49 }
  50
  51 #[derive(Clone, RustcEncodable, RustcDecodable, PartialEq, Eq, Hash, Debug, Copy)]
  52 pub enum UnconstrainedNumeric {
  53     UnconstrainedFloat,
  54     UnconstrainedInt,
  55     Neither,
  56 }
  57
  58 /// Explains the source of a type err in a short, human readable way. This is meant to be placed
  59 /// in parentheses after some larger message. You should also invoke `note_and_explain_type_err()`
  60 /// afterwards to present additional details, particularly when it comes to lifetime-related
  61 /// errors.
  62 impl<'tcx> fmt::Display for TypeError<'tcx> {
  63     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
  64         use self::TypeError::*;
  65         fn report_maybe_different(f: &mut fmt::Formatter<'_>,
  66                                   expected: &str, found: &str) -> fmt::Result {
  67             // A naive approach to making sure that we're not reporting silly errors such as:
  68             // (expected closure, found closure).
  69             if expected == found {
  70                 write!(f, "expected {}, found a different {}", expected, found)
  71             } else {
  72                 write!(f, "expected {}, found {}", expected, found)
  73             }
  74         }
  75
  76         let br_string = |br: ty::BoundRegion| {
  77             match br {
  78                 ty::BrNamed(_, name) => format!(" {}", name),
  79                 _ => String::new(),
  80             }
  81         };
  82
  83         macro_rules! pluralise {
  84             ($x:expr) => {
  85                 if $x != 1 { "s" } else { "" }
  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                        pluralise!(values.expected),
 108                        values.found,
 109                        pluralise!(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                        pluralise!(values.expected),
 116                        values.found,
 117                        pluralise!(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                        pluralise!(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         }
 183     }
 184 }
 185
 186 impl<'gcx, 'lcx, 'tcx> ty::TyS<'tcx> {
 187     pub fn sort_string(&self, tcx: TyCtxt<'gcx, 'lcx>) -> Cow<'static, str> {
 188         match self.sty {
 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) => match n.assert_usize(tcx) {
 196                 Some(n) => format!("array of {} elements", n).into(),
 197                 None => "array".into(),
 198             }
 199             ty::Slice(_) => "slice".into(),
 200             ty::RawPtr(_) => "*-ptr".into(),
 201             ty::Ref(region, ty, mutbl) => {
 202                 let tymut = ty::TypeAndMut { ty, mutbl };
 203                 let tymut_string = tymut.to_string();
 204                 if tymut_string == "_" ||         //unknown type name,
 205                    tymut_string.len() > 10 ||     //name longer than saying "reference",
 206                    region.to_string() != "'_"     //... or a complex type
 207                 {
 208                     format!("{}reference", match mutbl {
 209                         hir::Mutability::MutMutable => "mutable ",
 210                         _ => ""
 211                     }).into()
 212                 } else {
 213                     format!("&{}", tymut_string).into()
 214                 }
 215             }
 216             ty::FnDef(..) => "fn item".into(),
 217             ty::FnPtr(_) => "fn pointer".into(),
 218             ty::Dynamic(ref inner, ..) => {
 219                 if let Some(principal) = inner.principal() {
 220                     format!("trait {}", tcx.def_path_str(principal.def_id())).into()
 221                 } else {
 222                     "trait".into()
 223                 }
 224             }
 225             ty::Closure(..) => "closure".into(),
 226             ty::Generator(..) => "generator".into(),
 227             ty::GeneratorWitness(..) => "generator witness".into(),
 228             ty::Tuple(..) => "tuple".into(),
 229             ty::Infer(ty::TyVar(_)) => "inferred type".into(),
 230             ty::Infer(ty::IntVar(_)) => "integer".into(),
 231             ty::Infer(ty::FloatVar(_)) => "floating-point number".into(),
 232             ty::Placeholder(..) => "placeholder type".into(),
 233             ty::Bound(..) => "bound type".into(),
 234             ty::Infer(ty::FreshTy(_)) => "fresh type".into(),
 235             ty::Infer(ty::FreshIntTy(_)) => "fresh integral type".into(),
 236             ty::Infer(ty::FreshFloatTy(_)) => "fresh floating-point type".into(),
 237             ty::Projection(_) => "associated type".into(),
 238             ty::UnnormalizedProjection(_) => "non-normalized associated type".into(),
 239             ty::Param(ref p) => {
 240                 if p.is_self() {
 241                     "Self".into()
 242                 } else {
 243                     "type parameter".into()
 244                 }
 245             }
 246             ty::Opaque(..) => "opaque type".into(),
 247             ty::Error => "type error".into(),
 248         }
 249     }
 250 }
 251
 252 impl<'gcx, 'tcx> TyCtxt<'gcx, 'tcx> {
 253     pub fn note_and_explain_type_err(self,
 254                                      db: &mut DiagnosticBuilder<'_>,
 255                                      err: &TypeError<'tcx>,
 256                                      sp: Span) {
 257         use self::TypeError::*;
 258
 259         match err.clone() {
 260             Sorts(values) => {
 261                 let expected_str = values.expected.sort_string(self);
 262                 let found_str = values.found.sort_string(self);
 263                 if expected_str == found_str && expected_str == "closure" {
 264                     db.note("no two closures, even if identical, have the same type");
 265                     db.help("consider boxing your closure and/or using it as a trait object");
 266                 }
 267                 if let (ty::Infer(ty::IntVar(_)), ty::Float(_)) =
 268                        (&values.found.sty, &values.expected.sty) // Issue #53280
 269                 {
 270                     if let Ok(snippet) = self.sess.source_map().span_to_snippet(sp) {
 271                         if snippet.chars().all(|c| c.is_digit(10) || c == '-' || c == '_') {
 272                             db.span_suggestion(
 273                                 sp,
 274                                 "use a float literal",
 275                                 format!("{}.0", snippet),
 276                                 Applicability::MachineApplicable
 277                             );
 278                         }
 279                     }
 280                 }
 281             },
 282             CyclicTy(ty) => {
 283                 // Watch out for various cases of cyclic types and try to explain.
 284                 if ty.is_closure() || ty.is_generator() {
 285                     db.note("closures cannot capture themselves or take themselves as argument;\n\
 286                              this error may be the result of a recent compiler bug-fix,\n\
 287                              see https://github.com/rust-lang/rust/issues/46062 for more details");
 288                 }
 289             }
 290             _ => {}
 291         }
 292     }
 293 }