rustc_hir_typeck/
cast.rs

1//! Code for type-checking cast expressions.
2//!
3//! A cast `e as U` is valid if one of the following holds:
4//! * `e` has type `T` and `T` coerces to `U`; *coercion-cast*
5//! * `e` has type `*T`, `U` is `*U_0`, and either `U_0: Sized` or
6//!    pointer_kind(`T`) = pointer_kind(`U_0`); *ptr-ptr-cast*
7//! * `e` has type `*T` and `U` is a numeric type, while `T: Sized`; *ptr-addr-cast*
8//! * `e` is an integer and `U` is `*U_0`, while `U_0: Sized`; *addr-ptr-cast*
9//! * `e` has type `T` and `T` and `U` are any numeric types; *numeric-cast*
10//! * `e` is a C-like enum and `U` is an integer type; *enum-cast*
11//! * `e` has type `bool` or `char` and `U` is an integer; *prim-int-cast*
12//! * `e` has type `u8` and `U` is `char`; *u8-char-cast*
13//! * `e` has type `&[T; n]` and `U` is `*const T`; *array-ptr-cast*
14//! * `e` is a function pointer type and `U` has type `*T`,
15//!   while `T: Sized`; *fptr-ptr-cast*
16//! * `e` is a function pointer type and `U` is an integer; *fptr-addr-cast*
17//!
18//! where `&.T` and `*T` are references of either mutability,
19//! and where pointer_kind(`T`) is the kind of the unsize info
20//! in `T` - the vtable for a trait definition (e.g., `fmt::Display` or
21//! `Iterator`, not `Iterator<Item=u8>`) or a length (or `()` if `T: Sized`).
22//!
23//! Note that lengths are not adjusted when casting raw slices -
24//! `T: *const [u16] as *const [u8]` creates a slice that only includes
25//! half of the original memory.
26//!
27//! Casting is not transitive, that is, even if `e as U1 as U2` is a valid
28//! expression, `e as U2` is not necessarily so (in fact it will only be valid if
29//! `U1` coerces to `U2`).
30
31use rustc_ast::util::parser::ExprPrecedence;
32use rustc_data_structures::fx::FxHashSet;
33use rustc_errors::codes::*;
34use rustc_errors::{Applicability, Diag, ErrorGuaranteed};
35use rustc_hir::def_id::DefId;
36use rustc_hir::{self as hir, ExprKind};
37use rustc_infer::infer::DefineOpaqueTypes;
38use rustc_macros::{TypeFoldable, TypeVisitable};
39use rustc_middle::mir::Mutability;
40use rustc_middle::ty::adjustment::AllowTwoPhase;
41use rustc_middle::ty::cast::{CastKind, CastTy};
42use rustc_middle::ty::error::TypeError;
43use rustc_middle::ty::{self, Ty, TyCtxt, TypeAndMut, TypeVisitableExt, VariantDef, elaborate};
44use rustc_middle::{bug, span_bug};
45use rustc_session::lint;
46use rustc_span::{DUMMY_SP, Span, sym};
47use rustc_trait_selection::infer::InferCtxtExt;
48use tracing::{debug, instrument};
49
50use super::FnCtxt;
51use crate::{errors, type_error_struct};
52
53/// Reifies a cast check to be checked once we have full type information for
54/// a function context.
55#[derive(Debug)]
56pub(crate) struct CastCheck<'tcx> {
57    /// The expression whose value is being casted
58    expr: &'tcx hir::Expr<'tcx>,
59    /// The source type for the cast expression
60    expr_ty: Ty<'tcx>,
61    expr_span: Span,
62    /// The target type. That is, the type we are casting to.
63    cast_ty: Ty<'tcx>,
64    cast_span: Span,
65    span: Span,
66}
67
68/// The kind of pointer and associated metadata (thin, length or vtable) - we
69/// only allow casts between wide pointers if their metadata have the same
70/// kind.
71#[derive(Debug, Copy, Clone, PartialEq, Eq, TypeVisitable, TypeFoldable)]
72enum PointerKind<'tcx> {
73    /// No metadata attached, ie pointer to sized type or foreign type
74    Thin,
75    /// A trait object
76    VTable(&'tcx ty::List<ty::Binder<'tcx, ty::ExistentialPredicate<'tcx>>>),
77    /// Slice
78    Length,
79    /// The unsize info of this projection or opaque type
80    OfAlias(ty::AliasTy<'tcx>),
81    /// The unsize info of this parameter
82    OfParam(ty::ParamTy),
83}
84
85impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
86    /// Returns the kind of unsize information of t, or None
87    /// if t is unknown.
88    fn pointer_kind(
89        &self,
90        t: Ty<'tcx>,
91        span: Span,
92    ) -> Result<Option<PointerKind<'tcx>>, ErrorGuaranteed> {
93        debug!("pointer_kind({:?}, {:?})", t, span);
94
95        let t = self.resolve_vars_if_possible(t);
96        t.error_reported()?;
97
98        if self.type_is_sized_modulo_regions(self.param_env, t) {
99            return Ok(Some(PointerKind::Thin));
100        }
101
102        let t = self.try_structurally_resolve_type(span, t);
103
104        Ok(match *t.kind() {
105            ty::Slice(_) | ty::Str => Some(PointerKind::Length),
106            ty::Dynamic(tty, _, ty::Dyn) => Some(PointerKind::VTable(tty)),
107            ty::Adt(def, args) if def.is_struct() => match def.non_enum_variant().tail_opt() {
108                None => Some(PointerKind::Thin),
109                Some(f) => {
110                    let field_ty = self.field_ty(span, f, args);
111                    self.pointer_kind(field_ty, span)?
112                }
113            },
114            ty::Tuple(fields) => match fields.last() {
115                None => Some(PointerKind::Thin),
116                Some(&f) => self.pointer_kind(f, span)?,
117            },
118
119            ty::UnsafeBinder(_) => todo!("FIXME(unsafe_binder)"),
120
121            // Pointers to foreign types are thin, despite being unsized
122            ty::Foreign(..) => Some(PointerKind::Thin),
123            // We should really try to normalize here.
124            ty::Alias(_, pi) => Some(PointerKind::OfAlias(pi)),
125            ty::Param(p) => Some(PointerKind::OfParam(p)),
126            // Insufficient type information.
127            ty::Placeholder(..) | ty::Bound(..) | ty::Infer(_) => None,
128
129            ty::Bool
130            | ty::Char
131            | ty::Int(..)
132            | ty::Uint(..)
133            | ty::Float(_)
134            | ty::Array(..)
135            | ty::CoroutineWitness(..)
136            | ty::RawPtr(_, _)
137            | ty::Ref(..)
138            | ty::Pat(..)
139            | ty::FnDef(..)
140            | ty::FnPtr(..)
141            | ty::Closure(..)
142            | ty::CoroutineClosure(..)
143            | ty::Coroutine(..)
144            | ty::Adt(..)
145            | ty::Never
146            | ty::Error(_) => {
147                let guar = self
148                    .dcx()
149                    .span_delayed_bug(span, format!("`{t:?}` should be sized but is not?"));
150                return Err(guar);
151            }
152        })
153    }
154}
155
156#[derive(Debug)]
157enum CastError<'tcx> {
158    ErrorGuaranteed(ErrorGuaranteed),
159
160    CastToBool,
161    CastToChar,
162    DifferingKinds {
163        src_kind: PointerKind<'tcx>,
164        dst_kind: PointerKind<'tcx>,
165    },
166    /// Cast of thin to wide raw ptr (e.g., `*const () as *const [u8]`).
167    SizedUnsizedCast,
168    IllegalCast,
169    NeedDeref,
170    NeedViaPtr,
171    NeedViaThinPtr,
172    NeedViaInt,
173    NonScalar,
174    UnknownExprPtrKind,
175    UnknownCastPtrKind,
176    /// Cast of int to (possibly) wide raw pointer.
177    ///
178    /// Argument is the specific name of the metadata in plain words, such as "a vtable"
179    /// or "a length". If this argument is None, then the metadata is unknown, for example,
180    /// when we're typechecking a type parameter with a ?Sized bound.
181    IntToWideCast(Option<&'static str>),
182    ForeignNonExhaustiveAdt,
183    PtrPtrAddingAutoTrait(Vec<DefId>),
184}
185
186impl From<ErrorGuaranteed> for CastError<'_> {
187    fn from(err: ErrorGuaranteed) -> Self {
188        CastError::ErrorGuaranteed(err)
189    }
190}
191
192fn make_invalid_casting_error<'a, 'tcx>(
193    span: Span,
194    expr_ty: Ty<'tcx>,
195    cast_ty: Ty<'tcx>,
196    fcx: &FnCtxt<'a, 'tcx>,
197) -> Diag<'a> {
198    type_error_struct!(
199        fcx.dcx(),
200        span,
201        expr_ty,
202        E0606,
203        "casting `{}` as `{}` is invalid",
204        fcx.ty_to_string(expr_ty),
205        fcx.ty_to_string(cast_ty)
206    )
207}
208
209/// If a cast from `from_ty` to `to_ty` is valid, returns a `Some` containing the kind
210/// of the cast.
211///
212/// This is a helper used from clippy.
213pub fn check_cast<'tcx>(
214    tcx: TyCtxt<'tcx>,
215    param_env: ty::ParamEnv<'tcx>,
216    e: &'tcx hir::Expr<'tcx>,
217    from_ty: Ty<'tcx>,
218    to_ty: Ty<'tcx>,
219) -> Option<CastKind> {
220    let hir_id = e.hir_id;
221    let local_def_id = hir_id.owner.def_id;
222
223    let root_ctxt = crate::TypeckRootCtxt::new(tcx, local_def_id);
224    let fn_ctxt = FnCtxt::new(&root_ctxt, param_env, local_def_id);
225
226    if let Ok(check) = CastCheck::new(
227        &fn_ctxt, e, from_ty, to_ty,
228        // We won't show any errors to the user, so the span is irrelevant here.
229        DUMMY_SP, DUMMY_SP,
230    ) {
231        check.do_check(&fn_ctxt).ok()
232    } else {
233        None
234    }
235}
236
237impl<'a, 'tcx> CastCheck<'tcx> {
238    pub(crate) fn new(
239        fcx: &FnCtxt<'a, 'tcx>,
240        expr: &'tcx hir::Expr<'tcx>,
241        expr_ty: Ty<'tcx>,
242        cast_ty: Ty<'tcx>,
243        cast_span: Span,
244        span: Span,
245    ) -> Result<CastCheck<'tcx>, ErrorGuaranteed> {
246        let expr_span = expr.span.find_ancestor_inside(span).unwrap_or(expr.span);
247        let check = CastCheck { expr, expr_ty, expr_span, cast_ty, cast_span, span };
248
249        // For better error messages, check for some obviously unsized
250        // cases now. We do a more thorough check at the end, once
251        // inference is more completely known.
252        match cast_ty.kind() {
253            ty::Dynamic(_, _, ty::Dyn) | ty::Slice(..) => {
254                Err(check.report_cast_to_unsized_type(fcx))
255            }
256            _ => Ok(check),
257        }
258    }
259
260    fn report_cast_error(&self, fcx: &FnCtxt<'a, 'tcx>, e: CastError<'tcx>) {
261        match e {
262            CastError::ErrorGuaranteed(_) => {
263                // an error has already been reported
264            }
265            CastError::NeedDeref => {
266                let mut err =
267                    make_invalid_casting_error(self.span, self.expr_ty, self.cast_ty, fcx);
268
269                if matches!(self.expr.kind, ExprKind::AddrOf(..)) {
270                    // get just the borrow part of the expression
271                    let span = self.expr_span.with_hi(self.expr.peel_borrows().span.lo());
272                    err.span_suggestion_verbose(
273                        span,
274                        "remove the unneeded borrow",
275                        "",
276                        Applicability::MachineApplicable,
277                    );
278                } else {
279                    err.span_suggestion_verbose(
280                        self.expr_span.shrink_to_lo(),
281                        "dereference the expression",
282                        "*",
283                        Applicability::MachineApplicable,
284                    );
285                }
286
287                err.emit();
288            }
289            CastError::NeedViaThinPtr | CastError::NeedViaPtr => {
290                let mut err =
291                    make_invalid_casting_error(self.span, self.expr_ty, self.cast_ty, fcx);
292                if self.cast_ty.is_integral() {
293                    err.help(format!("cast through {} first", match e {
294                        CastError::NeedViaPtr => "a raw pointer",
295                        CastError::NeedViaThinPtr => "a thin pointer",
296                        e => unreachable!("control flow means we should never encounter a {e:?}"),
297                    }));
298                }
299
300                self.try_suggest_collection_to_bool(fcx, &mut err);
301
302                err.emit();
303            }
304            CastError::NeedViaInt => {
305                make_invalid_casting_error(self.span, self.expr_ty, self.cast_ty, fcx)
306                    .with_help("cast through an integer first")
307                    .emit();
308            }
309            CastError::IllegalCast => {
310                make_invalid_casting_error(self.span, self.expr_ty, self.cast_ty, fcx).emit();
311            }
312            CastError::DifferingKinds { src_kind, dst_kind } => {
313                let mut err =
314                    make_invalid_casting_error(self.span, self.expr_ty, self.cast_ty, fcx);
315
316                match (src_kind, dst_kind) {
317                    (PointerKind::VTable(_), PointerKind::VTable(_)) => {
318                        err.note("the trait objects may have different vtables");
319                    }
320                    (
321                        PointerKind::OfParam(_) | PointerKind::OfAlias(_),
322                        PointerKind::OfParam(_)
323                        | PointerKind::OfAlias(_)
324                        | PointerKind::VTable(_)
325                        | PointerKind::Length,
326                    )
327                    | (
328                        PointerKind::VTable(_) | PointerKind::Length,
329                        PointerKind::OfParam(_) | PointerKind::OfAlias(_),
330                    ) => {
331                        err.note("the pointers may have different metadata");
332                    }
333                    (PointerKind::VTable(_), PointerKind::Length)
334                    | (PointerKind::Length, PointerKind::VTable(_)) => {
335                        err.note("the pointers have different metadata");
336                    }
337                    (
338                        PointerKind::Thin,
339                        PointerKind::Thin
340                        | PointerKind::VTable(_)
341                        | PointerKind::Length
342                        | PointerKind::OfParam(_)
343                        | PointerKind::OfAlias(_),
344                    )
345                    | (
346                        PointerKind::VTable(_)
347                        | PointerKind::Length
348                        | PointerKind::OfParam(_)
349                        | PointerKind::OfAlias(_),
350                        PointerKind::Thin,
351                    )
352                    | (PointerKind::Length, PointerKind::Length) => {
353                        span_bug!(self.span, "unexpected cast error: {e:?}")
354                    }
355                }
356
357                err.emit();
358            }
359            CastError::CastToBool => {
360                let expr_ty = fcx.resolve_vars_if_possible(self.expr_ty);
361                let help = if self.expr_ty.is_numeric() {
362                    errors::CannotCastToBoolHelp::Numeric(
363                        self.expr_span.shrink_to_hi().with_hi(self.span.hi()),
364                    )
365                } else {
366                    errors::CannotCastToBoolHelp::Unsupported(self.span)
367                };
368                fcx.dcx().emit_err(errors::CannotCastToBool { span: self.span, expr_ty, help });
369            }
370            CastError::CastToChar => {
371                let mut err = type_error_struct!(
372                    fcx.dcx(),
373                    self.span,
374                    self.expr_ty,
375                    E0604,
376                    "only `u8` can be cast as `char`, not `{}`",
377                    self.expr_ty
378                );
379                err.span_label(self.span, "invalid cast");
380                if self.expr_ty.is_numeric() {
381                    if self.expr_ty == fcx.tcx.types.u32 {
382                        err.multipart_suggestion(
383                            "consider using `char::from_u32` instead",
384                            vec![
385                                (self.expr_span.shrink_to_lo(), "char::from_u32(".to_string()),
386                                (self.expr_span.shrink_to_hi().to(self.cast_span), ")".to_string()),
387                            ],
388                            Applicability::MachineApplicable,
389                        );
390                    } else if self.expr_ty == fcx.tcx.types.i8 {
391                        err.span_help(self.span, "consider casting from `u8` instead");
392                    } else {
393                        err.span_help(
394                            self.span,
395                            "consider using `char::from_u32` instead (via a `u32`)",
396                        );
397                    };
398                }
399                err.emit();
400            }
401            CastError::NonScalar => {
402                let mut err = type_error_struct!(
403                    fcx.dcx(),
404                    self.span,
405                    self.expr_ty,
406                    E0605,
407                    "non-primitive cast: `{}` as `{}`",
408                    self.expr_ty,
409                    fcx.ty_to_string(self.cast_ty)
410                );
411
412                if let Ok(snippet) = fcx.tcx.sess.source_map().span_to_snippet(self.expr_span)
413                    && matches!(self.expr.kind, ExprKind::AddrOf(..))
414                {
415                    err.note(format!(
416                        "casting reference expression `{}` because `&` binds tighter than `as`",
417                        snippet
418                    ));
419                }
420
421                let mut sugg = None;
422                let mut sugg_mutref = false;
423                if let ty::Ref(reg, cast_ty, mutbl) = *self.cast_ty.kind() {
424                    if let ty::RawPtr(expr_ty, _) = *self.expr_ty.kind()
425                        && fcx.may_coerce(
426                            Ty::new_ref(fcx.tcx, fcx.tcx.lifetimes.re_erased, expr_ty, mutbl),
427                            self.cast_ty,
428                        )
429                    {
430                        sugg = Some((format!("&{}*", mutbl.prefix_str()), cast_ty == expr_ty));
431                    } else if let ty::Ref(expr_reg, expr_ty, expr_mutbl) = *self.expr_ty.kind()
432                        && expr_mutbl == Mutability::Not
433                        && mutbl == Mutability::Mut
434                        && fcx.may_coerce(Ty::new_mut_ref(fcx.tcx, expr_reg, expr_ty), self.cast_ty)
435                    {
436                        sugg_mutref = true;
437                    }
438
439                    if !sugg_mutref
440                        && sugg == None
441                        && fcx.may_coerce(
442                            Ty::new_ref(fcx.tcx, reg, self.expr_ty, mutbl),
443                            self.cast_ty,
444                        )
445                    {
446                        sugg = Some((format!("&{}", mutbl.prefix_str()), false));
447                    }
448                } else if let ty::RawPtr(_, mutbl) = *self.cast_ty.kind()
449                    && fcx.may_coerce(
450                        Ty::new_ref(fcx.tcx, fcx.tcx.lifetimes.re_erased, self.expr_ty, mutbl),
451                        self.cast_ty,
452                    )
453                {
454                    sugg = Some((format!("&{}", mutbl.prefix_str()), false));
455                }
456                if sugg_mutref {
457                    err.span_label(self.span, "invalid cast");
458                    err.span_note(self.expr_span, "this reference is immutable");
459                    err.span_note(self.cast_span, "trying to cast to a mutable reference type");
460                } else if let Some((sugg, remove_cast)) = sugg {
461                    err.span_label(self.span, "invalid cast");
462
463                    let has_parens = fcx
464                        .tcx
465                        .sess
466                        .source_map()
467                        .span_to_snippet(self.expr_span)
468                        .is_ok_and(|snip| snip.starts_with('('));
469
470                    // Very crude check to see whether the expression must be wrapped
471                    // in parentheses for the suggestion to work (issue #89497).
472                    // Can/should be extended in the future.
473                    let needs_parens =
474                        !has_parens && matches!(self.expr.kind, hir::ExprKind::Cast(..));
475
476                    let mut suggestion = vec![(self.expr_span.shrink_to_lo(), sugg)];
477                    if needs_parens {
478                        suggestion[0].1 += "(";
479                        suggestion.push((self.expr_span.shrink_to_hi(), ")".to_string()));
480                    }
481                    if remove_cast {
482                        suggestion.push((
483                            self.expr_span.shrink_to_hi().to(self.cast_span),
484                            String::new(),
485                        ));
486                    }
487
488                    err.multipart_suggestion_verbose(
489                        "consider borrowing the value",
490                        suggestion,
491                        Applicability::MachineApplicable,
492                    );
493                } else if !matches!(
494                    self.cast_ty.kind(),
495                    ty::FnDef(..) | ty::FnPtr(..) | ty::Closure(..)
496                ) {
497                    // Check `impl From<self.expr_ty> for self.cast_ty {}` for accurate suggestion:
498                    if let Some(from_trait) = fcx.tcx.get_diagnostic_item(sym::From) {
499                        let ty = fcx.resolve_vars_if_possible(self.cast_ty);
500                        let expr_ty = fcx.resolve_vars_if_possible(self.expr_ty);
501                        if fcx
502                            .infcx
503                            .type_implements_trait(from_trait, [ty, expr_ty], fcx.param_env)
504                            .must_apply_modulo_regions()
505                        {
506                            let to_ty = if let ty::Adt(def, args) = self.cast_ty.kind() {
507                                fcx.tcx.value_path_str_with_args(def.did(), args)
508                            } else {
509                                self.cast_ty.to_string()
510                            };
511                            err.multipart_suggestion(
512                                "consider using the `From` trait instead",
513                                vec![
514                                    (self.expr_span.shrink_to_lo(), format!("{to_ty}::from(")),
515                                    (
516                                        self.expr_span.shrink_to_hi().to(self.cast_span),
517                                        ")".to_string(),
518                                    ),
519                                ],
520                                Applicability::MaybeIncorrect,
521                            );
522                        }
523                    }
524
525                    let (msg, note) = if let ty::Adt(adt, _) = self.expr_ty.kind()
526                        && adt.is_enum()
527                        && self.cast_ty.is_numeric()
528                    {
529                        (
530                            "an `as` expression can be used to convert enum types to numeric \
531                             types only if the enum type is unit-only or field-less",
532                            Some(
533                                "see https://doc.rust-lang.org/reference/items/enumerations.html#casting for more information",
534                            ),
535                        )
536                    } else {
537                        (
538                            "an `as` expression can only be used to convert between primitive \
539                             types or to coerce to a specific trait object",
540                            None,
541                        )
542                    };
543
544                    err.span_label(self.span, msg);
545
546                    if let Some(note) = note {
547                        err.note(note);
548                    }
549                } else {
550                    err.span_label(self.span, "invalid cast");
551                }
552
553                fcx.suggest_no_capture_closure(&mut err, self.cast_ty, self.expr_ty);
554                self.try_suggest_collection_to_bool(fcx, &mut err);
555
556                err.emit();
557            }
558            CastError::SizedUnsizedCast => {
559                let cast_ty = fcx.resolve_vars_if_possible(self.cast_ty);
560                let expr_ty = fcx.resolve_vars_if_possible(self.expr_ty);
561                fcx.dcx().emit_err(errors::CastThinPointerToWidePointer {
562                    span: self.span,
563                    expr_ty,
564                    cast_ty,
565                    teach: fcx.tcx.sess.teach(E0607),
566                });
567            }
568            CastError::IntToWideCast(known_metadata) => {
569                let expr_if_nightly = fcx.tcx.sess.is_nightly_build().then_some(self.expr_span);
570                let cast_ty = fcx.resolve_vars_if_possible(self.cast_ty);
571                let expr_ty = fcx.resolve_vars_if_possible(self.expr_ty);
572                let metadata = known_metadata.unwrap_or("type-specific metadata");
573                let known_wide = known_metadata.is_some();
574                let span = self.cast_span;
575                fcx.dcx().emit_err(errors::IntToWide {
576                    span,
577                    metadata,
578                    expr_ty,
579                    cast_ty,
580                    expr_if_nightly,
581                    known_wide,
582                });
583            }
584            CastError::UnknownCastPtrKind | CastError::UnknownExprPtrKind => {
585                let unknown_cast_to = match e {
586                    CastError::UnknownCastPtrKind => true,
587                    CastError::UnknownExprPtrKind => false,
588                    e => unreachable!("control flow means we should never encounter a {e:?}"),
589                };
590                let (span, sub) = if unknown_cast_to {
591                    (self.cast_span, errors::CastUnknownPointerSub::To(self.cast_span))
592                } else {
593                    (self.cast_span, errors::CastUnknownPointerSub::From(self.span))
594                };
595                fcx.dcx().emit_err(errors::CastUnknownPointer { span, to: unknown_cast_to, sub });
596            }
597            CastError::ForeignNonExhaustiveAdt => {
598                make_invalid_casting_error(
599                    self.span,
600                    self.expr_ty,
601                    self.cast_ty,
602                    fcx,
603                )
604                .with_note("cannot cast an enum with a non-exhaustive variant when it's defined in another crate")
605                .emit();
606            }
607            CastError::PtrPtrAddingAutoTrait(added) => {
608                fcx.dcx().emit_err(errors::PtrCastAddAutoToObject {
609                    span: self.span,
610                    traits_len: added.len(),
611                    traits: {
612                        let mut traits: Vec<_> = added
613                            .into_iter()
614                            .map(|trait_did| fcx.tcx.def_path_str(trait_did))
615                            .collect();
616
617                        traits.sort();
618                        traits.into()
619                    },
620                });
621            }
622        }
623    }
624
625    fn report_cast_to_unsized_type(&self, fcx: &FnCtxt<'a, 'tcx>) -> ErrorGuaranteed {
626        if let Err(err) = self.cast_ty.error_reported() {
627            return err;
628        }
629        if let Err(err) = self.expr_ty.error_reported() {
630            return err;
631        }
632
633        let tstr = fcx.ty_to_string(self.cast_ty);
634        let mut err = type_error_struct!(
635            fcx.dcx(),
636            self.span,
637            self.expr_ty,
638            E0620,
639            "cast to unsized type: `{}` as `{}`",
640            fcx.resolve_vars_if_possible(self.expr_ty),
641            tstr
642        );
643        match self.expr_ty.kind() {
644            ty::Ref(_, _, mt) => {
645                let mtstr = mt.prefix_str();
646                err.span_suggestion_verbose(
647                    self.cast_span.shrink_to_lo(),
648                    "consider casting to a reference instead",
649                    format!("&{mtstr}"),
650                    Applicability::MachineApplicable,
651                );
652            }
653            ty::Adt(def, ..) if def.is_box() => {
654                err.multipart_suggestion(
655                    "you can cast to a `Box` instead",
656                    vec![
657                        (self.cast_span.shrink_to_lo(), "Box<".to_string()),
658                        (self.cast_span.shrink_to_hi(), ">".to_string()),
659                    ],
660                    Applicability::MachineApplicable,
661                );
662            }
663            _ => {
664                err.span_help(self.expr_span, "consider using a box or reference as appropriate");
665            }
666        }
667        err.emit()
668    }
669
670    fn trivial_cast_lint(&self, fcx: &FnCtxt<'a, 'tcx>) {
671        let (numeric, lint) = if self.cast_ty.is_numeric() && self.expr_ty.is_numeric() {
672            (true, lint::builtin::TRIVIAL_NUMERIC_CASTS)
673        } else {
674            (false, lint::builtin::TRIVIAL_CASTS)
675        };
676        let expr_ty = fcx.resolve_vars_if_possible(self.expr_ty);
677        let cast_ty = fcx.resolve_vars_if_possible(self.cast_ty);
678        fcx.tcx.emit_node_span_lint(
679            lint,
680            self.expr.hir_id,
681            self.span,
682            errors::TrivialCast { numeric, expr_ty, cast_ty },
683        );
684    }
685
686    #[instrument(skip(fcx), level = "debug")]
687    pub(crate) fn check(mut self, fcx: &FnCtxt<'a, 'tcx>) {
688        self.expr_ty = fcx.structurally_resolve_type(self.expr_span, self.expr_ty);
689        self.cast_ty = fcx.structurally_resolve_type(self.cast_span, self.cast_ty);
690
691        debug!("check_cast({}, {:?} as {:?})", self.expr.hir_id, self.expr_ty, self.cast_ty);
692
693        if !fcx.type_is_sized_modulo_regions(fcx.param_env, self.cast_ty)
694            && !self.cast_ty.has_infer_types()
695        {
696            self.report_cast_to_unsized_type(fcx);
697        } else if self.expr_ty.references_error() || self.cast_ty.references_error() {
698            // No sense in giving duplicate error messages
699        } else {
700            match self.try_coercion_cast(fcx) {
701                Ok(()) => {
702                    if self.expr_ty.is_raw_ptr() && self.cast_ty.is_raw_ptr() {
703                        // When casting a raw pointer to another raw pointer, we cannot convert the cast into
704                        // a coercion because the pointee types might only differ in regions, which HIR typeck
705                        // cannot distinguish. This would cause us to erroneously discard a cast which will
706                        // lead to a borrowck error like #113257.
707                        // We still did a coercion above to unify inference variables for `ptr as _` casts.
708                        // This does cause us to miss some trivial casts in the trivial cast lint.
709                        debug!(" -> PointerCast");
710                    } else {
711                        self.trivial_cast_lint(fcx);
712                        debug!(" -> CoercionCast");
713                        fcx.typeck_results
714                            .borrow_mut()
715                            .set_coercion_cast(self.expr.hir_id.local_id);
716                    }
717                }
718                Err(_) => {
719                    match self.do_check(fcx) {
720                        Ok(k) => {
721                            debug!(" -> {:?}", k);
722                        }
723                        Err(e) => self.report_cast_error(fcx, e),
724                    };
725                }
726            };
727        }
728    }
729    /// Checks a cast, and report an error if one exists. In some cases, this
730    /// can return Ok and create type errors in the fcx rather than returning
731    /// directly. coercion-cast is handled in check instead of here.
732    fn do_check(&self, fcx: &FnCtxt<'a, 'tcx>) -> Result<CastKind, CastError<'tcx>> {
733        use rustc_middle::ty::cast::CastTy::*;
734        use rustc_middle::ty::cast::IntTy::*;
735
736        let (t_from, t_cast) = match (CastTy::from_ty(self.expr_ty), CastTy::from_ty(self.cast_ty))
737        {
738            (Some(t_from), Some(t_cast)) => (t_from, t_cast),
739            // Function item types may need to be reified before casts.
740            (None, Some(t_cast)) => {
741                match *self.expr_ty.kind() {
742                    ty::FnDef(..) => {
743                        // Attempt a coercion to a fn pointer type.
744                        let f = fcx.normalize(self.expr_span, self.expr_ty.fn_sig(fcx.tcx));
745                        let res = fcx.coerce(
746                            self.expr,
747                            self.expr_ty,
748                            Ty::new_fn_ptr(fcx.tcx, f),
749                            AllowTwoPhase::No,
750                            None,
751                        );
752                        if let Err(TypeError::IntrinsicCast) = res {
753                            return Err(CastError::IllegalCast);
754                        }
755                        if res.is_err() {
756                            return Err(CastError::NonScalar);
757                        }
758                        (FnPtr, t_cast)
759                    }
760                    // Special case some errors for references, and check for
761                    // array-ptr-casts. `Ref` is not a CastTy because the cast
762                    // is split into a coercion to a pointer type, followed by
763                    // a cast.
764                    ty::Ref(_, inner_ty, mutbl) => {
765                        return match t_cast {
766                            Int(_) | Float => match *inner_ty.kind() {
767                                ty::Int(_)
768                                | ty::Uint(_)
769                                | ty::Float(_)
770                                | ty::Infer(ty::InferTy::IntVar(_) | ty::InferTy::FloatVar(_)) => {
771                                    Err(CastError::NeedDeref)
772                                }
773                                _ => Err(CastError::NeedViaPtr),
774                            },
775                            // array-ptr-cast
776                            Ptr(mt) => {
777                                if !fcx.type_is_sized_modulo_regions(fcx.param_env, mt.ty) {
778                                    return Err(CastError::IllegalCast);
779                                }
780                                self.check_ref_cast(fcx, TypeAndMut { mutbl, ty: inner_ty }, mt)
781                            }
782                            _ => Err(CastError::NonScalar),
783                        };
784                    }
785                    _ => return Err(CastError::NonScalar),
786                }
787            }
788            _ => return Err(CastError::NonScalar),
789        };
790        if let ty::Adt(adt_def, _) = *self.expr_ty.kind()
791            && !adt_def.did().is_local()
792            && adt_def.variants().iter().any(VariantDef::is_field_list_non_exhaustive)
793        {
794            return Err(CastError::ForeignNonExhaustiveAdt);
795        }
796        match (t_from, t_cast) {
797            // These types have invariants! can't cast into them.
798            (_, Int(CEnum) | FnPtr) => Err(CastError::NonScalar),
799
800            // * -> Bool
801            (_, Int(Bool)) => Err(CastError::CastToBool),
802
803            // * -> Char
804            (Int(U(ty::UintTy::U8)), Int(Char)) => Ok(CastKind::U8CharCast), // u8-char-cast
805            (_, Int(Char)) => Err(CastError::CastToChar),
806
807            // prim -> float,ptr
808            (Int(Bool) | Int(CEnum) | Int(Char), Float) => Err(CastError::NeedViaInt),
809
810            (Int(Bool) | Int(CEnum) | Int(Char) | Float, Ptr(_)) | (Ptr(_) | FnPtr, Float) => {
811                Err(CastError::IllegalCast)
812            }
813
814            // ptr -> ptr
815            (Ptr(m_e), Ptr(m_c)) => self.check_ptr_ptr_cast(fcx, m_e, m_c), // ptr-ptr-cast
816
817            // ptr-addr-cast
818            (Ptr(m_expr), Int(t_c)) => {
819                self.lossy_provenance_ptr2int_lint(fcx, t_c);
820                self.check_ptr_addr_cast(fcx, m_expr)
821            }
822            (FnPtr, Int(_)) => {
823                // FIXME(#95489): there should eventually be a lint for these casts
824                Ok(CastKind::FnPtrAddrCast)
825            }
826            // addr-ptr-cast
827            (Int(_), Ptr(mt)) => {
828                self.fuzzy_provenance_int2ptr_lint(fcx);
829                self.check_addr_ptr_cast(fcx, mt)
830            }
831            // fn-ptr-cast
832            (FnPtr, Ptr(mt)) => self.check_fptr_ptr_cast(fcx, mt),
833
834            // prim -> prim
835            (Int(CEnum), Int(_)) => {
836                self.err_if_cenum_impl_drop(fcx);
837                Ok(CastKind::EnumCast)
838            }
839            (Int(Char) | Int(Bool), Int(_)) => Ok(CastKind::PrimIntCast),
840
841            (Int(_) | Float, Int(_) | Float) => Ok(CastKind::NumericCast),
842        }
843    }
844
845    fn check_ptr_ptr_cast(
846        &self,
847        fcx: &FnCtxt<'a, 'tcx>,
848        m_src: ty::TypeAndMut<'tcx>,
849        m_dst: ty::TypeAndMut<'tcx>,
850    ) -> Result<CastKind, CastError<'tcx>> {
851        debug!("check_ptr_ptr_cast m_src={m_src:?} m_dst={m_dst:?}");
852        // ptr-ptr cast. metadata must match.
853
854        let src_kind = fcx.tcx.erase_regions(fcx.pointer_kind(m_src.ty, self.span)?);
855        let dst_kind = fcx.tcx.erase_regions(fcx.pointer_kind(m_dst.ty, self.span)?);
856
857        // We can't cast if target pointer kind is unknown
858        let Some(dst_kind) = dst_kind else {
859            return Err(CastError::UnknownCastPtrKind);
860        };
861
862        // Cast to thin pointer is OK
863        if dst_kind == PointerKind::Thin {
864            return Ok(CastKind::PtrPtrCast);
865        }
866
867        // We can't cast to wide pointer if source pointer kind is unknown
868        let Some(src_kind) = src_kind else {
869            return Err(CastError::UnknownCastPtrKind);
870        };
871
872        match (src_kind, dst_kind) {
873            // thin -> fat? report invalid cast (don't complain about vtable kinds)
874            (PointerKind::Thin, _) => Err(CastError::SizedUnsizedCast),
875
876            // trait object -> trait object? need to do additional checks
877            (PointerKind::VTable(src_tty), PointerKind::VTable(dst_tty)) => {
878                match (src_tty.principal(), dst_tty.principal()) {
879                    // A<dyn Src<...> + SrcAuto> -> B<dyn Dst<...> + DstAuto>. need to make sure
880                    // - `Src` and `Dst` traits are the same
881                    // - traits have the same generic arguments
882                    // - projections are the same
883                    // - `SrcAuto` (+auto traits implied by `Src`) is a superset of `DstAuto`
884                    //
885                    // Note that trait upcasting goes through a different mechanism (`coerce_unsized`)
886                    // and is unaffected by this check.
887                    (Some(src_principal), Some(_)) => {
888                        let tcx = fcx.tcx;
889
890                        // We need to reconstruct trait object types.
891                        // `m_src` and `m_dst` won't work for us here because they will potentially
892                        // contain wrappers, which we do not care about.
893                        //
894                        // e.g. we want to allow `dyn T -> (dyn T,)`, etc.
895                        //
896                        // We also need to skip auto traits to emit an FCW and not an error.
897                        let src_obj = Ty::new_dynamic(
898                            tcx,
899                            tcx.mk_poly_existential_predicates(
900                                &src_tty.without_auto_traits().collect::<Vec<_>>(),
901                            ),
902                            tcx.lifetimes.re_erased,
903                            ty::Dyn,
904                        );
905                        let dst_obj = Ty::new_dynamic(
906                            tcx,
907                            tcx.mk_poly_existential_predicates(
908                                &dst_tty.without_auto_traits().collect::<Vec<_>>(),
909                            ),
910                            tcx.lifetimes.re_erased,
911                            ty::Dyn,
912                        );
913
914                        // `dyn Src = dyn Dst`, this checks for matching traits/generics/projections
915                        // This is `fcx.demand_eqtype`, but inlined to give a better error.
916                        let cause = fcx.misc(self.span);
917                        if fcx
918                            .at(&cause, fcx.param_env)
919                            .eq(DefineOpaqueTypes::Yes, src_obj, dst_obj)
920                            .map(|infer_ok| fcx.register_infer_ok_obligations(infer_ok))
921                            .is_err()
922                        {
923                            return Err(CastError::DifferingKinds { src_kind, dst_kind });
924                        }
925
926                        // Check that `SrcAuto` (+auto traits implied by `Src`) is a superset of `DstAuto`.
927                        // Emit an FCW otherwise.
928                        let src_auto: FxHashSet<_> = src_tty
929                            .auto_traits()
930                            .chain(
931                                elaborate::supertrait_def_ids(tcx, src_principal.def_id())
932                                    .filter(|def_id| tcx.trait_is_auto(*def_id)),
933                            )
934                            .collect();
935
936                        let added = dst_tty
937                            .auto_traits()
938                            .filter(|trait_did| !src_auto.contains(trait_did))
939                            .collect::<Vec<_>>();
940
941                        if !added.is_empty() {
942                            return Err(CastError::PtrPtrAddingAutoTrait(added));
943                        }
944
945                        Ok(CastKind::PtrPtrCast)
946                    }
947
948                    // dyn Auto -> dyn Auto'? ok.
949                    (None, None) => Ok(CastKind::PtrPtrCast),
950
951                    // dyn Trait -> dyn Auto? not ok (for now).
952                    //
953                    // Although dropping the principal is already allowed for unsizing coercions
954                    // (e.g. `*const (dyn Trait + Auto)` to `*const dyn Auto`), dropping it is
955                    // currently **NOT** allowed for (non-coercion) ptr-to-ptr casts (e.g
956                    // `*const Foo` to `*const Bar` where `Foo` has a `dyn Trait + Auto` tail
957                    // and `Bar` has a `dyn Auto` tail), because the underlying MIR operations
958                    // currently work very differently:
959                    //
960                    // * A MIR unsizing coercion on raw pointers to trait objects (`*const dyn Src`
961                    //   to `*const dyn Dst`) is currently equivalent to downcasting the source to
962                    //   the concrete sized type that it was originally unsized from first (via a
963                    //   ptr-to-ptr cast from `*const Src` to `*const T` with `T: Sized`) and then
964                    //   unsizing this thin pointer to the target type (unsizing `*const T` to
965                    //   `*const Dst`). In particular, this means that the pointer's metadata
966                    //   (vtable) will semantically change, e.g. for const eval and miri, even
967                    //   though the vtables will always be merged for codegen.
968                    //
969                    // * A MIR ptr-to-ptr cast is currently equivalent to a transmute and does not
970                    //   change the pointer metadata (vtable) at all.
971                    //
972                    // In addition to this potentially surprising difference between coercion and
973                    // non-coercion casts, casting away the principal with a MIR ptr-to-ptr cast
974                    // is currently considered undefined behavior:
975                    //
976                    // As a validity invariant of pointers to trait objects, we currently require
977                    // that the principal of the vtable in the pointer metadata exactly matches
978                    // the principal of the pointee type, where "no principal" is also considered
979                    // a kind of principal.
980                    (Some(_), None) => Err(CastError::DifferingKinds { src_kind, dst_kind }),
981
982                    // dyn Auto -> dyn Trait? not ok.
983                    (None, Some(_)) => Err(CastError::DifferingKinds { src_kind, dst_kind }),
984                }
985            }
986
987            // fat -> fat? metadata kinds must match
988            (src_kind, dst_kind) if src_kind == dst_kind => Ok(CastKind::PtrPtrCast),
989
990            (_, _) => Err(CastError::DifferingKinds { src_kind, dst_kind }),
991        }
992    }
993
994    fn check_fptr_ptr_cast(
995        &self,
996        fcx: &FnCtxt<'a, 'tcx>,
997        m_cast: ty::TypeAndMut<'tcx>,
998    ) -> Result<CastKind, CastError<'tcx>> {
999        // fptr-ptr cast. must be to thin ptr
1000
1001        match fcx.pointer_kind(m_cast.ty, self.span)? {
1002            None => Err(CastError::UnknownCastPtrKind),
1003            Some(PointerKind::Thin) => Ok(CastKind::FnPtrPtrCast),
1004            _ => Err(CastError::IllegalCast),
1005        }
1006    }
1007
1008    fn check_ptr_addr_cast(
1009        &self,
1010        fcx: &FnCtxt<'a, 'tcx>,
1011        m_expr: ty::TypeAndMut<'tcx>,
1012    ) -> Result<CastKind, CastError<'tcx>> {
1013        // ptr-addr cast. must be from thin ptr
1014
1015        match fcx.pointer_kind(m_expr.ty, self.span)? {
1016            None => Err(CastError::UnknownExprPtrKind),
1017            Some(PointerKind::Thin) => Ok(CastKind::PtrAddrCast),
1018            _ => Err(CastError::NeedViaThinPtr),
1019        }
1020    }
1021
1022    fn check_ref_cast(
1023        &self,
1024        fcx: &FnCtxt<'a, 'tcx>,
1025        mut m_expr: ty::TypeAndMut<'tcx>,
1026        mut m_cast: ty::TypeAndMut<'tcx>,
1027    ) -> Result<CastKind, CastError<'tcx>> {
1028        // array-ptr-cast: allow mut-to-mut, mut-to-const, const-to-const
1029        m_expr.ty = fcx.try_structurally_resolve_type(self.expr_span, m_expr.ty);
1030        m_cast.ty = fcx.try_structurally_resolve_type(self.cast_span, m_cast.ty);
1031
1032        if m_expr.mutbl >= m_cast.mutbl
1033            && let ty::Array(ety, _) = m_expr.ty.kind()
1034            && fcx.can_eq(fcx.param_env, *ety, m_cast.ty)
1035        {
1036            // Due to historical reasons we allow directly casting references of
1037            // arrays into raw pointers of their element type.
1038
1039            // Coerce to a raw pointer so that we generate RawPtr in MIR.
1040            let array_ptr_type = Ty::new_ptr(fcx.tcx, m_expr.ty, m_expr.mutbl);
1041            fcx.coerce(self.expr, self.expr_ty, array_ptr_type, AllowTwoPhase::No, None)
1042                .unwrap_or_else(|_| {
1043                    bug!(
1044                        "could not cast from reference to array to pointer to array ({:?} to {:?})",
1045                        self.expr_ty,
1046                        array_ptr_type,
1047                    )
1048                });
1049
1050            // this will report a type mismatch if needed
1051            fcx.demand_eqtype(self.span, *ety, m_cast.ty);
1052            return Ok(CastKind::ArrayPtrCast);
1053        }
1054
1055        Err(CastError::IllegalCast)
1056    }
1057
1058    fn check_addr_ptr_cast(
1059        &self,
1060        fcx: &FnCtxt<'a, 'tcx>,
1061        m_cast: TypeAndMut<'tcx>,
1062    ) -> Result<CastKind, CastError<'tcx>> {
1063        // ptr-addr cast. pointer must be thin.
1064        match fcx.pointer_kind(m_cast.ty, self.span)? {
1065            None => Err(CastError::UnknownCastPtrKind),
1066            Some(PointerKind::Thin) => Ok(CastKind::AddrPtrCast),
1067            Some(PointerKind::VTable(_)) => Err(CastError::IntToWideCast(Some("a vtable"))),
1068            Some(PointerKind::Length) => Err(CastError::IntToWideCast(Some("a length"))),
1069            Some(PointerKind::OfAlias(_) | PointerKind::OfParam(_)) => {
1070                Err(CastError::IntToWideCast(None))
1071            }
1072        }
1073    }
1074
1075    fn try_coercion_cast(&self, fcx: &FnCtxt<'a, 'tcx>) -> Result<(), ty::error::TypeError<'tcx>> {
1076        match fcx.coerce(self.expr, self.expr_ty, self.cast_ty, AllowTwoPhase::No, None) {
1077            Ok(_) => Ok(()),
1078            Err(err) => Err(err),
1079        }
1080    }
1081
1082    fn err_if_cenum_impl_drop(&self, fcx: &FnCtxt<'a, 'tcx>) {
1083        if let ty::Adt(d, _) = self.expr_ty.kind()
1084            && d.has_dtor(fcx.tcx)
1085        {
1086            let expr_ty = fcx.resolve_vars_if_possible(self.expr_ty);
1087            let cast_ty = fcx.resolve_vars_if_possible(self.cast_ty);
1088
1089            fcx.dcx().emit_err(errors::CastEnumDrop { span: self.span, expr_ty, cast_ty });
1090        }
1091    }
1092
1093    fn lossy_provenance_ptr2int_lint(&self, fcx: &FnCtxt<'a, 'tcx>, t_c: ty::cast::IntTy) {
1094        let expr_prec = fcx.precedence(self.expr);
1095        let needs_parens = expr_prec < ExprPrecedence::Unambiguous;
1096
1097        let needs_cast = !matches!(t_c, ty::cast::IntTy::U(ty::UintTy::Usize));
1098        let cast_span = self.expr_span.shrink_to_hi().to(self.cast_span);
1099        let expr_ty = fcx.resolve_vars_if_possible(self.expr_ty);
1100        let cast_ty = fcx.resolve_vars_if_possible(self.cast_ty);
1101        let expr_span = self.expr_span.shrink_to_lo();
1102        let sugg = match (needs_parens, needs_cast) {
1103            (true, true) => errors::LossyProvenancePtr2IntSuggestion::NeedsParensCast {
1104                expr_span,
1105                cast_span,
1106                cast_ty,
1107            },
1108            (true, false) => {
1109                errors::LossyProvenancePtr2IntSuggestion::NeedsParens { expr_span, cast_span }
1110            }
1111            (false, true) => {
1112                errors::LossyProvenancePtr2IntSuggestion::NeedsCast { cast_span, cast_ty }
1113            }
1114            (false, false) => errors::LossyProvenancePtr2IntSuggestion::Other { cast_span },
1115        };
1116
1117        let lint = errors::LossyProvenancePtr2Int { expr_ty, cast_ty, sugg };
1118        fcx.tcx.emit_node_span_lint(
1119            lint::builtin::LOSSY_PROVENANCE_CASTS,
1120            self.expr.hir_id,
1121            self.span,
1122            lint,
1123        );
1124    }
1125
1126    fn fuzzy_provenance_int2ptr_lint(&self, fcx: &FnCtxt<'a, 'tcx>) {
1127        let sugg = errors::LossyProvenanceInt2PtrSuggestion {
1128            lo: self.expr_span.shrink_to_lo(),
1129            hi: self.expr_span.shrink_to_hi().to(self.cast_span),
1130        };
1131        let expr_ty = fcx.resolve_vars_if_possible(self.expr_ty);
1132        let cast_ty = fcx.resolve_vars_if_possible(self.cast_ty);
1133        let lint = errors::LossyProvenanceInt2Ptr { expr_ty, cast_ty, sugg };
1134        fcx.tcx.emit_node_span_lint(
1135            lint::builtin::FUZZY_PROVENANCE_CASTS,
1136            self.expr.hir_id,
1137            self.span,
1138            lint,
1139        );
1140    }
1141
1142    /// Attempt to suggest using `.is_empty` when trying to cast from a
1143    /// collection type to a boolean.
1144    fn try_suggest_collection_to_bool(&self, fcx: &FnCtxt<'a, 'tcx>, err: &mut Diag<'_>) {
1145        if self.cast_ty.is_bool() {
1146            let derefed = fcx
1147                .autoderef(self.expr_span, self.expr_ty)
1148                .silence_errors()
1149                .find(|t| matches!(t.0.kind(), ty::Str | ty::Slice(..)));
1150
1151            if let Some((deref_ty, _)) = derefed {
1152                // Give a note about what the expr derefs to.
1153                if deref_ty != self.expr_ty.peel_refs() {
1154                    err.subdiagnostic(errors::DerefImplsIsEmpty { span: self.expr_span, deref_ty });
1155                }
1156
1157                // Create a multipart suggestion: add `!` and `.is_empty()` in
1158                // place of the cast.
1159                err.subdiagnostic(errors::UseIsEmpty {
1160                    lo: self.expr_span.shrink_to_lo(),
1161                    hi: self.span.with_lo(self.expr_span.hi()),
1162                    expr_ty: self.expr_ty,
1163                });
1164            }
1165        }
1166    }
1167}
rustc_hir_typeck/cast.rs

rustc_hir_typeck/
cast.rs
