rustc_hir_typeck/cast.rs
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//! Code for type-checking cast expressions.
//!
//! A cast `e as U` is valid if one of the following holds:
//! * `e` has type `T` and `T` coerces to `U`; *coercion-cast*
//! * `e` has type `*T`, `U` is `*U_0`, and either `U_0: Sized` or
//! pointer_kind(`T`) = pointer_kind(`U_0`); *ptr-ptr-cast*
//! * `e` has type `*T` and `U` is a numeric type, while `T: Sized`; *ptr-addr-cast*
//! * `e` is an integer and `U` is `*U_0`, while `U_0: Sized`; *addr-ptr-cast*
//! * `e` has type `T` and `T` and `U` are any numeric types; *numeric-cast*
//! * `e` is a C-like enum and `U` is an integer type; *enum-cast*
//! * `e` has type `bool` or `char` and `U` is an integer; *prim-int-cast*
//! * `e` has type `u8` and `U` is `char`; *u8-char-cast*
//! * `e` has type `&[T; n]` and `U` is `*const T`; *array-ptr-cast*
//! * `e` is a function pointer type and `U` has type `*T`,
//! while `T: Sized`; *fptr-ptr-cast*
//! * `e` is a function pointer type and `U` is an integer; *fptr-addr-cast*
//!
//! where `&.T` and `*T` are references of either mutability,
//! and where pointer_kind(`T`) is the kind of the unsize info
//! in `T` - the vtable for a trait definition (e.g., `fmt::Display` or
//! `Iterator`, not `Iterator<Item=u8>`) or a length (or `()` if `T: Sized`).
//!
//! Note that lengths are not adjusted when casting raw slices -
//! `T: *const [u16] as *const [u8]` creates a slice that only includes
//! half of the original memory.
//!
//! Casting is not transitive, that is, even if `e as U1 as U2` is a valid
//! expression, `e as U2` is not necessarily so (in fact it will only be valid if
//! `U1` coerces to `U2`).
use rustc_data_structures::fx::FxHashSet;
use rustc_errors::codes::*;
use rustc_errors::{Applicability, Diag, ErrorGuaranteed};
use rustc_hir::{self as hir, ExprKind};
use rustc_infer::infer::DefineOpaqueTypes;
use rustc_macros::{TypeFoldable, TypeVisitable};
use rustc_middle::mir::Mutability;
use rustc_middle::ty::adjustment::AllowTwoPhase;
use rustc_middle::ty::cast::{CastKind, CastTy};
use rustc_middle::ty::error::TypeError;
use rustc_middle::ty::{self, Ty, TyCtxt, TypeAndMut, TypeVisitableExt, VariantDef};
use rustc_middle::{bug, span_bug};
use rustc_session::lint;
use rustc_span::def_id::LOCAL_CRATE;
use rustc_span::symbol::sym;
use rustc_span::{DUMMY_SP, Span};
use rustc_trait_selection::infer::InferCtxtExt;
use tracing::{debug, instrument};
use super::FnCtxt;
use crate::{errors, type_error_struct};
/// Reifies a cast check to be checked once we have full type information for
/// a function context.
#[derive(Debug)]
pub(crate) struct CastCheck<'tcx> {
/// The expression whose value is being casted
expr: &'tcx hir::Expr<'tcx>,
/// The source type for the cast expression
expr_ty: Ty<'tcx>,
expr_span: Span,
/// The target type. That is, the type we are casting to.
cast_ty: Ty<'tcx>,
cast_span: Span,
span: Span,
}
/// The kind of pointer and associated metadata (thin, length or vtable) - we
/// only allow casts between wide pointers if their metadata have the same
/// kind.
#[derive(Debug, Copy, Clone, PartialEq, Eq, TypeVisitable, TypeFoldable)]
enum PointerKind<'tcx> {
/// No metadata attached, ie pointer to sized type or foreign type
Thin,
/// A trait object
VTable(&'tcx ty::List<ty::Binder<'tcx, ty::ExistentialPredicate<'tcx>>>),
/// Slice
Length,
/// The unsize info of this projection or opaque type
OfAlias(ty::AliasTy<'tcx>),
/// The unsize info of this parameter
OfParam(ty::ParamTy),
}
impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
/// Returns the kind of unsize information of t, or None
/// if t is unknown.
fn pointer_kind(
&self,
t: Ty<'tcx>,
span: Span,
) -> Result<Option<PointerKind<'tcx>>, ErrorGuaranteed> {
debug!("pointer_kind({:?}, {:?})", t, span);
let t = self.resolve_vars_if_possible(t);
t.error_reported()?;
if self.type_is_sized_modulo_regions(self.param_env, t) {
return Ok(Some(PointerKind::Thin));
}
let t = self.try_structurally_resolve_type(span, t);
Ok(match *t.kind() {
ty::Slice(_) | ty::Str => Some(PointerKind::Length),
ty::Dynamic(tty, _, ty::Dyn) => Some(PointerKind::VTable(tty)),
ty::Adt(def, args) if def.is_struct() => match def.non_enum_variant().tail_opt() {
None => Some(PointerKind::Thin),
Some(f) => {
let field_ty = self.field_ty(span, f, args);
self.pointer_kind(field_ty, span)?
}
},
ty::Tuple(fields) => match fields.last() {
None => Some(PointerKind::Thin),
Some(&f) => self.pointer_kind(f, span)?,
},
// Pointers to foreign types are thin, despite being unsized
ty::Foreign(..) => Some(PointerKind::Thin),
// We should really try to normalize here.
ty::Alias(_, pi) => Some(PointerKind::OfAlias(pi)),
ty::Param(p) => Some(PointerKind::OfParam(p)),
// Insufficient type information.
ty::Placeholder(..) | ty::Bound(..) | ty::Infer(_) => None,
ty::Bool
| ty::Char
| ty::Int(..)
| ty::Uint(..)
| ty::Float(_)
| ty::Array(..)
| ty::CoroutineWitness(..)
| ty::RawPtr(_, _)
| ty::Ref(..)
| ty::Pat(..)
| ty::FnDef(..)
| ty::FnPtr(..)
| ty::Closure(..)
| ty::CoroutineClosure(..)
| ty::Coroutine(..)
| ty::Adt(..)
| ty::Never
| ty::Dynamic(_, _, ty::DynStar)
| ty::Error(_) => {
let guar = self
.dcx()
.span_delayed_bug(span, format!("`{t:?}` should be sized but is not?"));
return Err(guar);
}
})
}
}
#[derive(Copy, Clone, Debug)]
enum CastError<'tcx> {
ErrorGuaranteed(ErrorGuaranteed),
CastToBool,
CastToChar,
DifferingKinds {
src_kind: PointerKind<'tcx>,
dst_kind: PointerKind<'tcx>,
},
/// Cast of thin to wide raw ptr (e.g., `*const () as *const [u8]`).
SizedUnsizedCast,
IllegalCast,
NeedDeref,
NeedViaPtr,
NeedViaThinPtr,
NeedViaInt,
NonScalar,
UnknownExprPtrKind,
UnknownCastPtrKind,
/// Cast of int to (possibly) wide raw pointer.
///
/// Argument is the specific name of the metadata in plain words, such as "a vtable"
/// or "a length". If this argument is None, then the metadata is unknown, for example,
/// when we're typechecking a type parameter with a ?Sized bound.
IntToWideCast(Option<&'static str>),
ForeignNonExhaustiveAdt,
}
impl From<ErrorGuaranteed> for CastError<'_> {
fn from(err: ErrorGuaranteed) -> Self {
CastError::ErrorGuaranteed(err)
}
}
fn make_invalid_casting_error<'a, 'tcx>(
span: Span,
expr_ty: Ty<'tcx>,
cast_ty: Ty<'tcx>,
fcx: &FnCtxt<'a, 'tcx>,
) -> Diag<'a> {
type_error_struct!(
fcx.dcx(),
span,
expr_ty,
E0606,
"casting `{}` as `{}` is invalid",
fcx.ty_to_string(expr_ty),
fcx.ty_to_string(cast_ty)
)
}
/// If a cast from `from_ty` to `to_ty` is valid, returns a `Some` containing the kind
/// of the cast.
///
/// This is a helper used from clippy.
pub fn check_cast<'tcx>(
tcx: TyCtxt<'tcx>,
param_env: ty::ParamEnv<'tcx>,
e: &'tcx hir::Expr<'tcx>,
from_ty: Ty<'tcx>,
to_ty: Ty<'tcx>,
) -> Option<CastKind> {
let hir_id = e.hir_id;
let local_def_id = hir_id.owner.def_id;
let root_ctxt = crate::TypeckRootCtxt::new(tcx, local_def_id);
let fn_ctxt = FnCtxt::new(&root_ctxt, param_env, local_def_id);
if let Ok(check) = CastCheck::new(
&fn_ctxt, e, from_ty, to_ty,
// We won't show any errors to the user, so the span is irrelevant here.
DUMMY_SP, DUMMY_SP,
) {
check.do_check(&fn_ctxt).ok()
} else {
None
}
}
impl<'a, 'tcx> CastCheck<'tcx> {
pub(crate) fn new(
fcx: &FnCtxt<'a, 'tcx>,
expr: &'tcx hir::Expr<'tcx>,
expr_ty: Ty<'tcx>,
cast_ty: Ty<'tcx>,
cast_span: Span,
span: Span,
) -> Result<CastCheck<'tcx>, ErrorGuaranteed> {
let expr_span = expr.span.find_ancestor_inside(span).unwrap_or(expr.span);
let check = CastCheck { expr, expr_ty, expr_span, cast_ty, cast_span, span };
// For better error messages, check for some obviously unsized
// cases now. We do a more thorough check at the end, once
// inference is more completely known.
match cast_ty.kind() {
ty::Dynamic(_, _, ty::Dyn) | ty::Slice(..) => {
Err(check.report_cast_to_unsized_type(fcx))
}
_ => Ok(check),
}
}
fn report_cast_error(&self, fcx: &FnCtxt<'a, 'tcx>, e: CastError<'tcx>) {
match e {
CastError::ErrorGuaranteed(_) => {
// an error has already been reported
}
CastError::NeedDeref => {
let mut err =
make_invalid_casting_error(self.span, self.expr_ty, self.cast_ty, fcx);
if matches!(self.expr.kind, ExprKind::AddrOf(..)) {
// get just the borrow part of the expression
let span = self.expr_span.with_hi(self.expr.peel_borrows().span.lo());
err.span_suggestion_verbose(
span,
"remove the unneeded borrow",
"",
Applicability::MachineApplicable,
);
} else {
err.span_suggestion_verbose(
self.expr_span.shrink_to_lo(),
"dereference the expression",
"*",
Applicability::MachineApplicable,
);
}
err.emit();
}
CastError::NeedViaThinPtr | CastError::NeedViaPtr => {
let mut err =
make_invalid_casting_error(self.span, self.expr_ty, self.cast_ty, fcx);
if self.cast_ty.is_integral() {
err.help(format!("cast through {} first", match e {
CastError::NeedViaPtr => "a raw pointer",
CastError::NeedViaThinPtr => "a thin pointer",
e => unreachable!("control flow means we should never encounter a {e:?}"),
}));
}
self.try_suggest_collection_to_bool(fcx, &mut err);
err.emit();
}
CastError::NeedViaInt => {
make_invalid_casting_error(self.span, self.expr_ty, self.cast_ty, fcx)
.with_help("cast through an integer first")
.emit();
}
CastError::IllegalCast => {
make_invalid_casting_error(self.span, self.expr_ty, self.cast_ty, fcx).emit();
}
CastError::DifferingKinds { src_kind, dst_kind } => {
let mut err =
make_invalid_casting_error(self.span, self.expr_ty, self.cast_ty, fcx);
match (src_kind, dst_kind) {
(PointerKind::VTable(_), PointerKind::VTable(_)) => {
err.note("the trait objects may have different vtables");
}
(
PointerKind::OfParam(_) | PointerKind::OfAlias(_),
PointerKind::OfParam(_)
| PointerKind::OfAlias(_)
| PointerKind::VTable(_)
| PointerKind::Length,
)
| (
PointerKind::VTable(_) | PointerKind::Length,
PointerKind::OfParam(_) | PointerKind::OfAlias(_),
) => {
err.note("the pointers may have different metadata");
}
(PointerKind::VTable(_), PointerKind::Length)
| (PointerKind::Length, PointerKind::VTable(_)) => {
err.note("the pointers have different metadata");
}
(
PointerKind::Thin,
PointerKind::Thin
| PointerKind::VTable(_)
| PointerKind::Length
| PointerKind::OfParam(_)
| PointerKind::OfAlias(_),
)
| (
PointerKind::VTable(_)
| PointerKind::Length
| PointerKind::OfParam(_)
| PointerKind::OfAlias(_),
PointerKind::Thin,
)
| (PointerKind::Length, PointerKind::Length) => {
span_bug!(self.span, "unexpected cast error: {e:?}")
}
}
err.emit();
}
CastError::CastToBool => {
let expr_ty = fcx.resolve_vars_if_possible(self.expr_ty);
let help = if self.expr_ty.is_numeric() {
errors::CannotCastToBoolHelp::Numeric(
self.expr_span.shrink_to_hi().with_hi(self.span.hi()),
)
} else {
errors::CannotCastToBoolHelp::Unsupported(self.span)
};
fcx.dcx().emit_err(errors::CannotCastToBool { span: self.span, expr_ty, help });
}
CastError::CastToChar => {
let mut err = type_error_struct!(
fcx.dcx(),
self.span,
self.expr_ty,
E0604,
"only `u8` can be cast as `char`, not `{}`",
self.expr_ty
);
err.span_label(self.span, "invalid cast");
if self.expr_ty.is_numeric() {
if self.expr_ty == fcx.tcx.types.u32 {
match fcx.tcx.sess.source_map().span_to_snippet(self.expr.span) {
Ok(snippet) => err.span_suggestion(
self.span,
"try `char::from_u32` instead",
format!("char::from_u32({snippet})"),
Applicability::MachineApplicable,
),
Err(_) => err.span_help(self.span, "try `char::from_u32` instead"),
};
} else if self.expr_ty == fcx.tcx.types.i8 {
err.span_help(self.span, "try casting from `u8` instead");
} else {
err.span_help(self.span, "try `char::from_u32` instead (via a `u32`)");
};
}
err.emit();
}
CastError::NonScalar => {
let mut err = type_error_struct!(
fcx.dcx(),
self.span,
self.expr_ty,
E0605,
"non-primitive cast: `{}` as `{}`",
self.expr_ty,
fcx.ty_to_string(self.cast_ty)
);
let mut sugg = None;
let mut sugg_mutref = false;
if let ty::Ref(reg, cast_ty, mutbl) = *self.cast_ty.kind() {
if let ty::RawPtr(expr_ty, _) = *self.expr_ty.kind()
&& fcx.may_coerce(
Ty::new_ref(fcx.tcx, fcx.tcx.lifetimes.re_erased, expr_ty, mutbl),
self.cast_ty,
)
{
sugg = Some((format!("&{}*", mutbl.prefix_str()), cast_ty == expr_ty));
} else if let ty::Ref(expr_reg, expr_ty, expr_mutbl) = *self.expr_ty.kind()
&& expr_mutbl == Mutability::Not
&& mutbl == Mutability::Mut
&& fcx.may_coerce(Ty::new_mut_ref(fcx.tcx, expr_reg, expr_ty), self.cast_ty)
{
sugg_mutref = true;
}
if !sugg_mutref
&& sugg == None
&& fcx.may_coerce(
Ty::new_ref(fcx.tcx, reg, self.expr_ty, mutbl),
self.cast_ty,
)
{
sugg = Some((format!("&{}", mutbl.prefix_str()), false));
}
} else if let ty::RawPtr(_, mutbl) = *self.cast_ty.kind()
&& fcx.may_coerce(
Ty::new_ref(fcx.tcx, fcx.tcx.lifetimes.re_erased, self.expr_ty, mutbl),
self.cast_ty,
)
{
sugg = Some((format!("&{}", mutbl.prefix_str()), false));
}
if sugg_mutref {
err.span_label(self.span, "invalid cast");
err.span_note(self.expr_span, "this reference is immutable");
err.span_note(self.cast_span, "trying to cast to a mutable reference type");
} else if let Some((sugg, remove_cast)) = sugg {
err.span_label(self.span, "invalid cast");
let has_parens = fcx
.tcx
.sess
.source_map()
.span_to_snippet(self.expr_span)
.is_ok_and(|snip| snip.starts_with('('));
// Very crude check to see whether the expression must be wrapped
// in parentheses for the suggestion to work (issue #89497).
// Can/should be extended in the future.
let needs_parens =
!has_parens && matches!(self.expr.kind, hir::ExprKind::Cast(..));
let mut suggestion = vec![(self.expr_span.shrink_to_lo(), sugg)];
if needs_parens {
suggestion[0].1 += "(";
suggestion.push((self.expr_span.shrink_to_hi(), ")".to_string()));
}
if remove_cast {
suggestion.push((
self.expr_span.shrink_to_hi().to(self.cast_span),
String::new(),
));
}
err.multipart_suggestion_verbose(
"consider borrowing the value",
suggestion,
Applicability::MachineApplicable,
);
} else if !matches!(
self.cast_ty.kind(),
ty::FnDef(..) | ty::FnPtr(..) | ty::Closure(..)
) {
let mut label = true;
// Check `impl From<self.expr_ty> for self.cast_ty {}` for accurate suggestion:
if let Ok(snippet) = fcx.tcx.sess.source_map().span_to_snippet(self.expr_span)
&& let Some(from_trait) = fcx.tcx.get_diagnostic_item(sym::From)
{
let ty = fcx.resolve_vars_if_possible(self.cast_ty);
// Erase regions to avoid panic in `prove_value` when calling
// `type_implements_trait`.
let ty = fcx.tcx.erase_regions(ty);
let expr_ty = fcx.resolve_vars_if_possible(self.expr_ty);
let expr_ty = fcx.tcx.erase_regions(expr_ty);
if fcx
.infcx
.type_implements_trait(from_trait, [ty, expr_ty], fcx.param_env)
.must_apply_modulo_regions()
{
label = false;
err.span_suggestion(
self.span,
"consider using the `From` trait instead",
format!("{}::from({})", self.cast_ty, snippet),
Applicability::MaybeIncorrect,
);
}
}
let (msg, note) = if let ty::Adt(adt, _) = self.expr_ty.kind()
&& adt.is_enum()
&& self.cast_ty.is_numeric()
{
(
"an `as` expression can be used to convert enum types to numeric \
types only if the enum type is unit-only or field-less",
Some(
"see https://doc.rust-lang.org/reference/items/enumerations.html#casting for more information",
),
)
} else {
(
"an `as` expression can only be used to convert between primitive \
types or to coerce to a specific trait object",
None,
)
};
if label {
err.span_label(self.span, msg);
} else {
err.note(msg);
}
if let Some(note) = note {
err.note(note);
}
} else {
err.span_label(self.span, "invalid cast");
}
fcx.suggest_no_capture_closure(&mut err, self.cast_ty, self.expr_ty);
self.try_suggest_collection_to_bool(fcx, &mut err);
err.emit();
}
CastError::SizedUnsizedCast => {
fcx.dcx().emit_err(errors::CastThinPointerToWidePointer {
span: self.span,
expr_ty: self.expr_ty,
cast_ty: fcx.ty_to_string(self.cast_ty),
teach: fcx.tcx.sess.teach(E0607),
});
}
CastError::IntToWideCast(known_metadata) => {
let expr_if_nightly = fcx.tcx.sess.is_nightly_build().then_some(self.expr_span);
let cast_ty = fcx.resolve_vars_if_possible(self.cast_ty);
let expr_ty = fcx.ty_to_string(self.expr_ty);
let metadata = known_metadata.unwrap_or("type-specific metadata");
let known_wide = known_metadata.is_some();
let span = self.cast_span;
fcx.dcx().emit_err(errors::IntToWide {
span,
metadata,
expr_ty,
cast_ty,
expr_if_nightly,
known_wide,
});
}
CastError::UnknownCastPtrKind | CastError::UnknownExprPtrKind => {
let unknown_cast_to = match e {
CastError::UnknownCastPtrKind => true,
CastError::UnknownExprPtrKind => false,
e => unreachable!("control flow means we should never encounter a {e:?}"),
};
let (span, sub) = if unknown_cast_to {
(self.cast_span, errors::CastUnknownPointerSub::To(self.cast_span))
} else {
(self.cast_span, errors::CastUnknownPointerSub::From(self.span))
};
fcx.dcx().emit_err(errors::CastUnknownPointer { span, to: unknown_cast_to, sub });
}
CastError::ForeignNonExhaustiveAdt => {
make_invalid_casting_error(
self.span,
self.expr_ty,
self.cast_ty,
fcx,
)
.with_note("cannot cast an enum with a non-exhaustive variant when it's defined in another crate")
.emit();
}
}
}
fn report_cast_to_unsized_type(&self, fcx: &FnCtxt<'a, 'tcx>) -> ErrorGuaranteed {
if let Err(err) = self.cast_ty.error_reported() {
return err;
}
if let Err(err) = self.expr_ty.error_reported() {
return err;
}
let tstr = fcx.ty_to_string(self.cast_ty);
let mut err = type_error_struct!(
fcx.dcx(),
self.span,
self.expr_ty,
E0620,
"cast to unsized type: `{}` as `{}`",
fcx.resolve_vars_if_possible(self.expr_ty),
tstr
);
match self.expr_ty.kind() {
ty::Ref(_, _, mt) => {
let mtstr = mt.prefix_str();
match fcx.tcx.sess.source_map().span_to_snippet(self.cast_span) {
Ok(s) => {
err.span_suggestion(
self.cast_span,
"try casting to a reference instead",
format!("&{mtstr}{s}"),
Applicability::MachineApplicable,
);
}
Err(_) => {
let msg = format!("did you mean `&{mtstr}{tstr}`?");
err.span_help(self.cast_span, msg);
}
}
}
ty::Adt(def, ..) if def.is_box() => {
match fcx.tcx.sess.source_map().span_to_snippet(self.cast_span) {
Ok(s) => {
err.span_suggestion(
self.cast_span,
"you can cast to a `Box` instead",
format!("Box<{s}>"),
Applicability::MachineApplicable,
);
}
Err(_) => {
err.span_help(
self.cast_span,
format!("you might have meant `Box<{tstr}>`"),
);
}
}
}
_ => {
err.span_help(self.expr_span, "consider using a box or reference as appropriate");
}
}
err.emit()
}
fn trivial_cast_lint(&self, fcx: &FnCtxt<'a, 'tcx>) {
let (numeric, lint) = if self.cast_ty.is_numeric() && self.expr_ty.is_numeric() {
(true, lint::builtin::TRIVIAL_NUMERIC_CASTS)
} else {
(false, lint::builtin::TRIVIAL_CASTS)
};
let expr_ty = fcx.resolve_vars_if_possible(self.expr_ty);
let cast_ty = fcx.resolve_vars_if_possible(self.cast_ty);
fcx.tcx.emit_node_span_lint(lint, self.expr.hir_id, self.span, errors::TrivialCast {
numeric,
expr_ty,
cast_ty,
});
}
#[instrument(skip(fcx), level = "debug")]
pub(crate) fn check(mut self, fcx: &FnCtxt<'a, 'tcx>) {
self.expr_ty = fcx.structurally_resolve_type(self.expr_span, self.expr_ty);
self.cast_ty = fcx.structurally_resolve_type(self.cast_span, self.cast_ty);
debug!("check_cast({}, {:?} as {:?})", self.expr.hir_id, self.expr_ty, self.cast_ty);
if !fcx.type_is_sized_modulo_regions(fcx.param_env, self.cast_ty)
&& !self.cast_ty.has_infer_types()
{
self.report_cast_to_unsized_type(fcx);
} else if self.expr_ty.references_error() || self.cast_ty.references_error() {
// No sense in giving duplicate error messages
} else {
match self.try_coercion_cast(fcx) {
Ok(()) => {
if self.expr_ty.is_unsafe_ptr() && self.cast_ty.is_unsafe_ptr() {
// When casting a raw pointer to another raw pointer, we cannot convert the cast into
// a coercion because the pointee types might only differ in regions, which HIR typeck
// cannot distinguish. This would cause us to erroneously discard a cast which will
// lead to a borrowck error like #113257.
// We still did a coercion above to unify inference variables for `ptr as _` casts.
// This does cause us to miss some trivial casts in the trivial cast lint.
debug!(" -> PointerCast");
} else {
self.trivial_cast_lint(fcx);
debug!(" -> CoercionCast");
fcx.typeck_results
.borrow_mut()
.set_coercion_cast(self.expr.hir_id.local_id);
}
}
Err(_) => {
match self.do_check(fcx) {
Ok(k) => {
debug!(" -> {:?}", k);
}
Err(e) => self.report_cast_error(fcx, e),
};
}
};
}
}
/// Checks a cast, and report an error if one exists. In some cases, this
/// can return Ok and create type errors in the fcx rather than returning
/// directly. coercion-cast is handled in check instead of here.
fn do_check(&self, fcx: &FnCtxt<'a, 'tcx>) -> Result<CastKind, CastError<'tcx>> {
use rustc_middle::ty::cast::CastTy::*;
use rustc_middle::ty::cast::IntTy::*;
if self.cast_ty.is_dyn_star() {
if fcx.tcx.features().dyn_star() {
span_bug!(self.span, "should be handled by `coerce`");
} else {
// Report "casting is invalid" rather than "non-primitive cast"
// if the feature is not enabled.
return Err(CastError::IllegalCast);
}
}
let (t_from, t_cast) = match (CastTy::from_ty(self.expr_ty), CastTy::from_ty(self.cast_ty))
{
(Some(t_from), Some(t_cast)) => (t_from, t_cast),
// Function item types may need to be reified before casts.
(None, Some(t_cast)) => {
match *self.expr_ty.kind() {
ty::FnDef(..) => {
// Attempt a coercion to a fn pointer type.
let f = fcx.normalize(self.expr_span, self.expr_ty.fn_sig(fcx.tcx));
let res = fcx.coerce(
self.expr,
self.expr_ty,
Ty::new_fn_ptr(fcx.tcx, f),
AllowTwoPhase::No,
None,
);
if let Err(TypeError::IntrinsicCast) = res {
return Err(CastError::IllegalCast);
}
if res.is_err() {
return Err(CastError::NonScalar);
}
(FnPtr, t_cast)
}
// Special case some errors for references, and check for
// array-ptr-casts. `Ref` is not a CastTy because the cast
// is split into a coercion to a pointer type, followed by
// a cast.
ty::Ref(_, inner_ty, mutbl) => {
return match t_cast {
Int(_) | Float => match *inner_ty.kind() {
ty::Int(_)
| ty::Uint(_)
| ty::Float(_)
| ty::Infer(ty::InferTy::IntVar(_) | ty::InferTy::FloatVar(_)) => {
Err(CastError::NeedDeref)
}
_ => Err(CastError::NeedViaPtr),
},
// array-ptr-cast
Ptr(mt) => {
if !fcx.type_is_sized_modulo_regions(fcx.param_env, mt.ty) {
return Err(CastError::IllegalCast);
}
self.check_ref_cast(fcx, TypeAndMut { mutbl, ty: inner_ty }, mt)
}
_ => Err(CastError::NonScalar),
};
}
_ => return Err(CastError::NonScalar),
}
}
_ => return Err(CastError::NonScalar),
};
if let ty::Adt(adt_def, _) = *self.expr_ty.kind()
&& adt_def.did().krate != LOCAL_CRATE
&& adt_def.variants().iter().any(VariantDef::is_field_list_non_exhaustive)
{
return Err(CastError::ForeignNonExhaustiveAdt);
}
match (t_from, t_cast) {
// These types have invariants! can't cast into them.
(_, Int(CEnum) | FnPtr) => Err(CastError::NonScalar),
// * -> Bool
(_, Int(Bool)) => Err(CastError::CastToBool),
// * -> Char
(Int(U(ty::UintTy::U8)), Int(Char)) => Ok(CastKind::U8CharCast), // u8-char-cast
(_, Int(Char)) => Err(CastError::CastToChar),
// prim -> float,ptr
(Int(Bool) | Int(CEnum) | Int(Char), Float) => Err(CastError::NeedViaInt),
(Int(Bool) | Int(CEnum) | Int(Char) | Float, Ptr(_)) | (Ptr(_) | FnPtr, Float) => {
Err(CastError::IllegalCast)
}
// ptr -> ptr
(Ptr(m_e), Ptr(m_c)) => self.check_ptr_ptr_cast(fcx, m_e, m_c), // ptr-ptr-cast
// ptr-addr-cast
(Ptr(m_expr), Int(t_c)) => {
self.lossy_provenance_ptr2int_lint(fcx, t_c);
self.check_ptr_addr_cast(fcx, m_expr)
}
(FnPtr, Int(_)) => {
// FIXME(#95489): there should eventually be a lint for these casts
Ok(CastKind::FnPtrAddrCast)
}
// addr-ptr-cast
(Int(_), Ptr(mt)) => {
self.fuzzy_provenance_int2ptr_lint(fcx);
self.check_addr_ptr_cast(fcx, mt)
}
// fn-ptr-cast
(FnPtr, Ptr(mt)) => self.check_fptr_ptr_cast(fcx, mt),
// prim -> prim
(Int(CEnum), Int(_)) => {
self.cenum_impl_drop_lint(fcx);
Ok(CastKind::EnumCast)
}
(Int(Char) | Int(Bool), Int(_)) => Ok(CastKind::PrimIntCast),
(Int(_) | Float, Int(_) | Float) => Ok(CastKind::NumericCast),
}
}
fn check_ptr_ptr_cast(
&self,
fcx: &FnCtxt<'a, 'tcx>,
m_src: ty::TypeAndMut<'tcx>,
m_dst: ty::TypeAndMut<'tcx>,
) -> Result<CastKind, CastError<'tcx>> {
debug!("check_ptr_ptr_cast m_src={m_src:?} m_dst={m_dst:?}");
// ptr-ptr cast. metadata must match.
let src_kind = fcx.tcx.erase_regions(fcx.pointer_kind(m_src.ty, self.span)?);
let dst_kind = fcx.tcx.erase_regions(fcx.pointer_kind(m_dst.ty, self.span)?);
// We can't cast if target pointer kind is unknown
let Some(dst_kind) = dst_kind else {
return Err(CastError::UnknownCastPtrKind);
};
// Cast to thin pointer is OK
if dst_kind == PointerKind::Thin {
return Ok(CastKind::PtrPtrCast);
}
// We can't cast to wide pointer if source pointer kind is unknown
let Some(src_kind) = src_kind else {
return Err(CastError::UnknownCastPtrKind);
};
match (src_kind, dst_kind) {
// thin -> fat? report invalid cast (don't complain about vtable kinds)
(PointerKind::Thin, _) => Err(CastError::SizedUnsizedCast),
// trait object -> trait object? need to do additional checks
(PointerKind::VTable(src_tty), PointerKind::VTable(dst_tty)) => {
match (src_tty.principal(), dst_tty.principal()) {
// A<dyn Src<...> + SrcAuto> -> B<dyn Dst<...> + DstAuto>. need to make sure
// - `Src` and `Dst` traits are the same
// - traits have the same generic arguments
// - projections are the same
// - `SrcAuto` (+auto traits implied by `Src`) is a superset of `DstAuto`
//
// Note that trait upcasting goes through a different mechanism (`coerce_unsized`)
// and is unaffected by this check.
(Some(src_principal), Some(_)) => {
let tcx = fcx.tcx;
// We need to reconstruct trait object types.
// `m_src` and `m_dst` won't work for us here because they will potentially
// contain wrappers, which we do not care about.
//
// e.g. we want to allow `dyn T -> (dyn T,)`, etc.
//
// We also need to skip auto traits to emit an FCW and not an error.
let src_obj = tcx.mk_ty_from_kind(ty::Dynamic(
tcx.mk_poly_existential_predicates(
&src_tty.without_auto_traits().collect::<Vec<_>>(),
),
tcx.lifetimes.re_erased,
ty::Dyn,
));
let dst_obj = tcx.mk_ty_from_kind(ty::Dynamic(
tcx.mk_poly_existential_predicates(
&dst_tty.without_auto_traits().collect::<Vec<_>>(),
),
tcx.lifetimes.re_erased,
ty::Dyn,
));
// `dyn Src = dyn Dst`, this checks for matching traits/generics/projections
// This is `fcx.demand_eqtype`, but inlined to give a better error.
let cause = fcx.misc(self.span);
if fcx
.at(&cause, fcx.param_env)
.eq(DefineOpaqueTypes::Yes, src_obj, dst_obj)
.map(|infer_ok| fcx.register_infer_ok_obligations(infer_ok))
.is_err()
{
return Err(CastError::DifferingKinds { src_kind, dst_kind });
}
// Check that `SrcAuto` (+auto traits implied by `Src`) is a superset of `DstAuto`.
// Emit an FCW otherwise.
let src_auto: FxHashSet<_> = src_tty
.auto_traits()
.chain(
tcx.supertrait_def_ids(src_principal.def_id())
.filter(|def_id| tcx.trait_is_auto(*def_id)),
)
.collect();
let added = dst_tty
.auto_traits()
.filter(|trait_did| !src_auto.contains(trait_did))
.collect::<Vec<_>>();
if !added.is_empty() {
tcx.emit_node_span_lint(
lint::builtin::PTR_CAST_ADD_AUTO_TO_OBJECT,
self.expr.hir_id,
self.span,
errors::PtrCastAddAutoToObject {
traits_len: added.len(),
traits: {
let mut traits: Vec<_> = added
.into_iter()
.map(|trait_did| tcx.def_path_str(trait_did))
.collect();
traits.sort();
traits.into()
},
},
)
}
Ok(CastKind::PtrPtrCast)
}
// dyn Auto -> dyn Auto'? ok.
(None, None) => Ok(CastKind::PtrPtrCast),
// dyn Trait -> dyn Auto? not ok (for now).
//
// Although dropping the principal is already allowed for unsizing coercions
// (e.g. `*const (dyn Trait + Auto)` to `*const dyn Auto`), dropping it is
// currently **NOT** allowed for (non-coercion) ptr-to-ptr casts (e.g
// `*const Foo` to `*const Bar` where `Foo` has a `dyn Trait + Auto` tail
// and `Bar` has a `dyn Auto` tail), because the underlying MIR operations
// currently work very differently:
//
// * A MIR unsizing coercion on raw pointers to trait objects (`*const dyn Src`
// to `*const dyn Dst`) is currently equivalent to downcasting the source to
// the concrete sized type that it was originally unsized from first (via a
// ptr-to-ptr cast from `*const Src` to `*const T` with `T: Sized`) and then
// unsizing this thin pointer to the target type (unsizing `*const T` to
// `*const Dst`). In particular, this means that the pointer's metadata
// (vtable) will semantically change, e.g. for const eval and miri, even
// though the vtables will always be merged for codegen.
//
// * A MIR ptr-to-ptr cast is currently equivalent to a transmute and does not
// change the pointer metadata (vtable) at all.
//
// In addition to this potentially surprising difference between coercion and
// non-coercion casts, casting away the principal with a MIR ptr-to-ptr cast
// is currently considered undefined behavior:
//
// As a validity invariant of pointers to trait objects, we currently require
// that the principal of the vtable in the pointer metadata exactly matches
// the principal of the pointee type, where "no principal" is also considered
// a kind of principal.
(Some(_), None) => Err(CastError::DifferingKinds { src_kind, dst_kind }),
// dyn Auto -> dyn Trait? not ok.
(None, Some(_)) => Err(CastError::DifferingKinds { src_kind, dst_kind }),
}
}
// fat -> fat? metadata kinds must match
(src_kind, dst_kind) if src_kind == dst_kind => Ok(CastKind::PtrPtrCast),
(_, _) => Err(CastError::DifferingKinds { src_kind, dst_kind }),
}
}
fn check_fptr_ptr_cast(
&self,
fcx: &FnCtxt<'a, 'tcx>,
m_cast: ty::TypeAndMut<'tcx>,
) -> Result<CastKind, CastError<'tcx>> {
// fptr-ptr cast. must be to thin ptr
match fcx.pointer_kind(m_cast.ty, self.span)? {
None => Err(CastError::UnknownCastPtrKind),
Some(PointerKind::Thin) => Ok(CastKind::FnPtrPtrCast),
_ => Err(CastError::IllegalCast),
}
}
fn check_ptr_addr_cast(
&self,
fcx: &FnCtxt<'a, 'tcx>,
m_expr: ty::TypeAndMut<'tcx>,
) -> Result<CastKind, CastError<'tcx>> {
// ptr-addr cast. must be from thin ptr
match fcx.pointer_kind(m_expr.ty, self.span)? {
None => Err(CastError::UnknownExprPtrKind),
Some(PointerKind::Thin) => Ok(CastKind::PtrAddrCast),
_ => Err(CastError::NeedViaThinPtr),
}
}
fn check_ref_cast(
&self,
fcx: &FnCtxt<'a, 'tcx>,
m_expr: ty::TypeAndMut<'tcx>,
m_cast: ty::TypeAndMut<'tcx>,
) -> Result<CastKind, CastError<'tcx>> {
// array-ptr-cast: allow mut-to-mut, mut-to-const, const-to-const
if m_expr.mutbl >= m_cast.mutbl {
if let ty::Array(ety, _) = m_expr.ty.kind() {
// Due to the limitations of LLVM global constants,
// region pointers end up pointing at copies of
// vector elements instead of the original values.
// To allow raw pointers to work correctly, we
// need to special-case obtaining a raw pointer
// from a region pointer to a vector.
// Coerce to a raw pointer so that we generate RawPtr in MIR.
let array_ptr_type = Ty::new_ptr(fcx.tcx, m_expr.ty, m_expr.mutbl);
fcx.coerce(self.expr, self.expr_ty, array_ptr_type, AllowTwoPhase::No, None)
.unwrap_or_else(|_| {
bug!(
"could not cast from reference to array to pointer to array ({:?} to {:?})",
self.expr_ty,
array_ptr_type,
)
});
// this will report a type mismatch if needed
fcx.demand_eqtype(self.span, *ety, m_cast.ty);
return Ok(CastKind::ArrayPtrCast);
}
}
Err(CastError::IllegalCast)
}
fn check_addr_ptr_cast(
&self,
fcx: &FnCtxt<'a, 'tcx>,
m_cast: TypeAndMut<'tcx>,
) -> Result<CastKind, CastError<'tcx>> {
// ptr-addr cast. pointer must be thin.
match fcx.pointer_kind(m_cast.ty, self.span)? {
None => Err(CastError::UnknownCastPtrKind),
Some(PointerKind::Thin) => Ok(CastKind::AddrPtrCast),
Some(PointerKind::VTable(_)) => Err(CastError::IntToWideCast(Some("a vtable"))),
Some(PointerKind::Length) => Err(CastError::IntToWideCast(Some("a length"))),
Some(PointerKind::OfAlias(_) | PointerKind::OfParam(_)) => {
Err(CastError::IntToWideCast(None))
}
}
}
fn try_coercion_cast(&self, fcx: &FnCtxt<'a, 'tcx>) -> Result<(), ty::error::TypeError<'tcx>> {
match fcx.coerce(self.expr, self.expr_ty, self.cast_ty, AllowTwoPhase::No, None) {
Ok(_) => Ok(()),
Err(err) => Err(err),
}
}
fn cenum_impl_drop_lint(&self, fcx: &FnCtxt<'a, 'tcx>) {
if let ty::Adt(d, _) = self.expr_ty.kind()
&& d.has_dtor(fcx.tcx)
{
let expr_ty = fcx.resolve_vars_if_possible(self.expr_ty);
let cast_ty = fcx.resolve_vars_if_possible(self.cast_ty);
fcx.tcx.emit_node_span_lint(
lint::builtin::CENUM_IMPL_DROP_CAST,
self.expr.hir_id,
self.span,
errors::CastEnumDrop { expr_ty, cast_ty },
);
}
}
fn lossy_provenance_ptr2int_lint(&self, fcx: &FnCtxt<'a, 'tcx>, t_c: ty::cast::IntTy) {
let expr_prec = self.expr.precedence().order();
let needs_parens = expr_prec < rustc_ast::util::parser::PREC_UNAMBIGUOUS;
let needs_cast = !matches!(t_c, ty::cast::IntTy::U(ty::UintTy::Usize));
let cast_span = self.expr_span.shrink_to_hi().to(self.cast_span);
let expr_ty = fcx.resolve_vars_if_possible(self.expr_ty);
let cast_ty = fcx.resolve_vars_if_possible(self.cast_ty);
let expr_span = self.expr_span.shrink_to_lo();
let sugg = match (needs_parens, needs_cast) {
(true, true) => errors::LossyProvenancePtr2IntSuggestion::NeedsParensCast {
expr_span,
cast_span,
cast_ty,
},
(true, false) => {
errors::LossyProvenancePtr2IntSuggestion::NeedsParens { expr_span, cast_span }
}
(false, true) => {
errors::LossyProvenancePtr2IntSuggestion::NeedsCast { cast_span, cast_ty }
}
(false, false) => errors::LossyProvenancePtr2IntSuggestion::Other { cast_span },
};
let lint = errors::LossyProvenancePtr2Int { expr_ty, cast_ty, sugg };
fcx.tcx.emit_node_span_lint(
lint::builtin::LOSSY_PROVENANCE_CASTS,
self.expr.hir_id,
self.span,
lint,
);
}
fn fuzzy_provenance_int2ptr_lint(&self, fcx: &FnCtxt<'a, 'tcx>) {
let sugg = errors::LossyProvenanceInt2PtrSuggestion {
lo: self.expr_span.shrink_to_lo(),
hi: self.expr_span.shrink_to_hi().to(self.cast_span),
};
let expr_ty = fcx.resolve_vars_if_possible(self.expr_ty);
let cast_ty = fcx.resolve_vars_if_possible(self.cast_ty);
let lint = errors::LossyProvenanceInt2Ptr { expr_ty, cast_ty, sugg };
fcx.tcx.emit_node_span_lint(
lint::builtin::FUZZY_PROVENANCE_CASTS,
self.expr.hir_id,
self.span,
lint,
);
}
/// Attempt to suggest using `.is_empty` when trying to cast from a
/// collection type to a boolean.
fn try_suggest_collection_to_bool(&self, fcx: &FnCtxt<'a, 'tcx>, err: &mut Diag<'_>) {
if self.cast_ty.is_bool() {
let derefed = fcx
.autoderef(self.expr_span, self.expr_ty)
.silence_errors()
.find(|t| matches!(t.0.kind(), ty::Str | ty::Slice(..)));
if let Some((deref_ty, _)) = derefed {
// Give a note about what the expr derefs to.
if deref_ty != self.expr_ty.peel_refs() {
err.subdiagnostic(errors::DerefImplsIsEmpty {
span: self.expr_span,
deref_ty: fcx.ty_to_string(deref_ty),
});
}
// Create a multipart suggestion: add `!` and `.is_empty()` in
// place of the cast.
err.subdiagnostic(errors::UseIsEmpty {
lo: self.expr_span.shrink_to_lo(),
hi: self.span.with_lo(self.expr_span.hi()),
expr_ty: fcx.ty_to_string(self.expr_ty),
});
}
}
}
}