Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1072 insertions, 0 deletions

diff --git a/compiler/rustc_typeck/src/check/cast.rs b/compiler/rustc_typeck/src/check/cast.rs
new file mode 100644
index 000000000..7aaddc2bd
--- /dev/null
+++ b/compiler/rustc_typeck/src/check/cast.rs
@@ -0,0 +1,1072 @@
+//! 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 super::FnCtxt;
+
+use crate::hir::def_id::DefId;
+use crate::type_error_struct;
+use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder, ErrorGuaranteed};
+use rustc_hir as hir;
+use rustc_hir::lang_items::LangItem;
+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::subst::SubstsRef;
+use rustc_middle::ty::{self, Ty, TypeAndMut, TypeVisitable};
+use rustc_session::lint;
+use rustc_session::Session;
+use rustc_span::symbol::sym;
+use rustc_span::Span;
+use rustc_trait_selection::infer::InferCtxtExt;
+use rustc_trait_selection::traits;
+use rustc_trait_selection::traits::error_reporting::report_object_safety_error;
+
+/// Reifies a cast check to be checked once we have full type information for
+/// a function context.
+#[derive(Debug)]
+pub struct CastCheck<'tcx> {
+    expr: &'tcx hir::Expr<'tcx>,
+    expr_ty: Ty<'tcx>,
+    expr_span: Span,
+    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 fat pointers if their metadata have the same
+/// kind.
+#[derive(Copy, Clone, PartialEq, Eq)]
+enum PointerKind<'tcx> {
+    /// No metadata attached, ie pointer to sized type or foreign type
+    Thin,
+    /// A trait object
+    VTable(Option<DefId>),
+    /// Slice
+    Length,
+    /// The unsize info of this projection
+    OfProjection(&'tcx ty::ProjectionTy<'tcx>),
+    /// The unsize info of this opaque ty
+    OfOpaque(DefId, SubstsRef<'tcx>),
+    /// The unsize info of this parameter
+    OfParam(&'tcx 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);
+
+        if let Some(reported) = t.error_reported() {
+            return Err(reported);
+        }
+
+        if self.type_is_known_to_be_sized_modulo_regions(t, span) {
+            return Ok(Some(PointerKind::Thin));
+        }
+
+        Ok(match *t.kind() {
+            ty::Slice(_) | ty::Str => Some(PointerKind::Length),
+            ty::Dynamic(ref tty, ..) => Some(PointerKind::VTable(tty.principal_def_id())),
+            ty::Adt(def, substs) if def.is_struct() => match def.non_enum_variant().fields.last() {
+                None => Some(PointerKind::Thin),
+                Some(f) => {
+                    let field_ty = self.field_ty(span, f, substs);
+                    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::Projection(ref pi) => Some(PointerKind::OfProjection(pi)),
+            ty::Opaque(def_id, substs) => Some(PointerKind::OfOpaque(def_id, substs)),
+            ty::Param(ref 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::GeneratorWitness(..)
+            | ty::RawPtr(_)
+            | ty::Ref(..)
+            | ty::FnDef(..)
+            | ty::FnPtr(..)
+            | ty::Closure(..)
+            | ty::Generator(..)
+            | ty::Adt(..)
+            | ty::Never
+            | ty::Error(_) => {
+                let reported = self
+                    .tcx
+                    .sess
+                    .delay_span_bug(span, &format!("`{:?}` should be sized but is not?", t));
+                return Err(reported);
+            }
+        })
+    }
+}
+
+#[derive(Copy, Clone)]
+pub enum CastError {
+    ErrorGuaranteed,
+
+    CastToBool,
+    CastToChar,
+    DifferingKinds,
+    /// Cast of thin to fat raw ptr (e.g., `*const () as *const [u8]`).
+    SizedUnsizedCast,
+    IllegalCast,
+    NeedDeref,
+    NeedViaPtr,
+    NeedViaThinPtr,
+    NeedViaInt,
+    NonScalar,
+    UnknownExprPtrKind,
+    UnknownCastPtrKind,
+    /// Cast of int to (possibly) fat 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.
+    IntToFatCast(Option<&'static str>),
+}
+
+impl From<ErrorGuaranteed> for CastError {
+    fn from(_: ErrorGuaranteed) -> Self {
+        CastError::ErrorGuaranteed
+    }
+}
+
+fn make_invalid_casting_error<'a, 'tcx>(
+    sess: &'a Session,
+    span: Span,
+    expr_ty: Ty<'tcx>,
+    cast_ty: Ty<'tcx>,
+    fcx: &FnCtxt<'a, 'tcx>,
+) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
+    type_error_struct!(
+        sess,
+        span,
+        expr_ty,
+        E0606,
+        "casting `{}` as `{}` is invalid",
+        fcx.ty_to_string(expr_ty),
+        fcx.ty_to_string(cast_ty)
+    )
+}
+
+impl<'a, 'tcx> CastCheck<'tcx> {
+    pub 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::Slice(..) => {
+                let reported = check.report_cast_to_unsized_type(fcx);
+                Err(reported)
+            }
+            _ => Ok(check),
+        }
+    }
+
+    fn report_cast_error(&self, fcx: &FnCtxt<'a, 'tcx>, e: CastError) {
+        match e {
+            CastError::ErrorGuaranteed => {
+                // an error has already been reported
+            }
+            CastError::NeedDeref => {
+                let error_span = self.span;
+                let mut err = make_invalid_casting_error(
+                    fcx.tcx.sess,
+                    self.span,
+                    self.expr_ty,
+                    self.cast_ty,
+                    fcx,
+                );
+                let cast_ty = fcx.ty_to_string(self.cast_ty);
+                err.span_label(
+                    error_span,
+                    format!("cannot cast `{}` as `{}`", fcx.ty_to_string(self.expr_ty), cast_ty),
+                );
+                if let Ok(snippet) = fcx.sess().source_map().span_to_snippet(self.expr_span) {
+                    err.span_suggestion(
+                        self.expr_span,
+                        "dereference the expression",
+                        format!("*{}", snippet),
+                        Applicability::MaybeIncorrect,
+                    );
+                } else {
+                    err.span_help(self.expr_span, "dereference the expression with `*`");
+                }
+                err.emit();
+            }
+            CastError::NeedViaThinPtr | CastError::NeedViaPtr => {
+                let mut err = make_invalid_casting_error(
+                    fcx.tcx.sess,
+                    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",
+                            _ => bug!(),
+                        }
+                    ));
+                }
+                err.emit();
+            }
+            CastError::NeedViaInt => {
+                make_invalid_casting_error(
+                    fcx.tcx.sess,
+                    self.span,
+                    self.expr_ty,
+                    self.cast_ty,
+                    fcx,
+                )
+                .help(&format!(
+                    "cast through {} first",
+                    match e {
+                        CastError::NeedViaInt => "an integer",
+                        _ => bug!(),
+                    }
+                ))
+                .emit();
+            }
+            CastError::IllegalCast => {
+                make_invalid_casting_error(
+                    fcx.tcx.sess,
+                    self.span,
+                    self.expr_ty,
+                    self.cast_ty,
+                    fcx,
+                )
+                .emit();
+            }
+            CastError::DifferingKinds => {
+                make_invalid_casting_error(
+                    fcx.tcx.sess,
+                    self.span,
+                    self.expr_ty,
+                    self.cast_ty,
+                    fcx,
+                )
+                .note("vtable kinds may not match")
+                .emit();
+            }
+            CastError::CastToBool => {
+                let mut err =
+                    struct_span_err!(fcx.tcx.sess, self.span, E0054, "cannot cast as `bool`");
+
+                if self.expr_ty.is_numeric() {
+                    match fcx.tcx.sess.source_map().span_to_snippet(self.expr_span) {
+                        Ok(snippet) => {
+                            err.span_suggestion(
+                                self.span,
+                                "compare with zero instead",
+                                format!("{snippet} != 0"),
+                                Applicability::MachineApplicable,
+                            );
+                        }
+                        Err(_) => {
+                            err.span_help(self.span, "compare with zero instead");
+                        }
+                    }
+                } else {
+                    err.span_label(self.span, "unsupported cast");
+                }
+
+                err.emit();
+            }
+            CastError::CastToChar => {
+                let mut err = type_error_struct!(
+                    fcx.tcx.sess,
+                    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.tcx.sess,
+                    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(TypeAndMut { ty: expr_ty, .. }) = *self.expr_ty.kind()
+                        && fcx
+                            .try_coerce(
+                                self.expr,
+                                fcx.tcx.mk_ref(
+                                    fcx.tcx.lifetimes.re_erased,
+                                    TypeAndMut { ty: expr_ty, mutbl },
+                                ),
+                                self.cast_ty,
+                                AllowTwoPhase::No,
+                                None,
+                            )
+                            .is_ok()
+                    {
+                        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
+                            .try_coerce(
+                                self.expr,
+                                fcx.tcx.mk_ref(
+                                    expr_reg,
+                                    TypeAndMut { ty: expr_ty, mutbl: Mutability::Mut },
+                                ),
+                                self.cast_ty,
+                                AllowTwoPhase::No,
+                                None,
+                            )
+                            .is_ok()
+                    {
+                        sugg_mutref = true;
+                    }
+
+                    if !sugg_mutref
+                        && sugg == None
+                        && fcx
+                            .try_coerce(
+                                self.expr,
+                                fcx.tcx.mk_ref(reg, TypeAndMut { ty: self.expr_ty, mutbl }),
+                                self.cast_ty,
+                                AllowTwoPhase::No,
+                                None,
+                            )
+                            .is_ok()
+                    {
+                        sugg = Some((format!("&{}", mutbl.prefix_str()), false));
+                    }
+                } else if let ty::RawPtr(TypeAndMut { mutbl, .. }) = *self.cast_ty.kind()
+                    && fcx
+                        .try_coerce(
+                            self.expr,
+                            fcx.tcx.mk_ref(
+                                fcx.tcx.lifetimes.re_erased,
+                                TypeAndMut { ty: self.expr_ty, mutbl },
+                            ),
+                            self.cast_ty,
+                            AllowTwoPhase::No,
+                            None,
+                        )
+                        .is_ok()
+                {
+                    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)
+                        .map_or(false, |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);
+                        let ty_params = fcx.tcx.mk_substs_trait(expr_ty, &[]);
+                        if fcx
+                            .infcx
+                            .type_implements_trait(from_trait, ty, ty_params, 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 = "an `as` expression can only be used to convert between primitive \
+                               types or to coerce to a specific trait object";
+                    if label {
+                        err.span_label(self.span, msg);
+                    } else {
+                        err.note(msg);
+                    }
+                } else {
+                    err.span_label(self.span, "invalid cast");
+                }
+                err.emit();
+            }
+            CastError::SizedUnsizedCast => {
+                use crate::structured_errors::{SizedUnsizedCast, StructuredDiagnostic};
+
+                SizedUnsizedCast {
+                    sess: &fcx.tcx.sess,
+                    span: self.span,
+                    expr_ty: self.expr_ty,
+                    cast_ty: fcx.ty_to_string(self.cast_ty),
+                }
+                .diagnostic()
+                .emit();
+            }
+            CastError::IntToFatCast(known_metadata) => {
+                let mut err = struct_span_err!(
+                    fcx.tcx.sess,
+                    self.cast_span,
+                    E0606,
+                    "cannot cast `{}` to a pointer that {} wide",
+                    fcx.ty_to_string(self.expr_ty),
+                    if known_metadata.is_some() { "is" } else { "may be" }
+                );
+
+                err.span_label(
+                    self.cast_span,
+                    format!(
+                        "creating a `{}` requires both an address and {}",
+                        self.cast_ty,
+                        known_metadata.unwrap_or("type-specific metadata"),
+                    ),
+                );
+
+                if fcx.tcx.sess.is_nightly_build() {
+                    err.span_label(
+                        self.expr_span,
+                        "consider casting this expression to `*const ()`, \
+                        then using `core::ptr::from_raw_parts`",
+                    );
+                }
+
+                err.emit();
+            }
+            CastError::UnknownCastPtrKind | CastError::UnknownExprPtrKind => {
+                let unknown_cast_to = match e {
+                    CastError::UnknownCastPtrKind => true,
+                    CastError::UnknownExprPtrKind => false,
+                    _ => bug!(),
+                };
+                let mut err = struct_span_err!(
+                    fcx.tcx.sess,
+                    if unknown_cast_to { self.cast_span } else { self.span },
+                    E0641,
+                    "cannot cast {} a pointer of an unknown kind",
+                    if unknown_cast_to { "to" } else { "from" }
+                );
+                if unknown_cast_to {
+                    err.span_label(self.cast_span, "needs more type information");
+                    err.note(
+                        "the type information given here is insufficient to check whether \
+                        the pointer cast is valid",
+                    );
+                } else {
+                    err.span_label(
+                        self.span,
+                        "the type information given here is insufficient to check whether \
+                        the pointer cast is valid",
+                    );
+                }
+                err.emit();
+            }
+        }
+    }
+
+    fn report_cast_to_unsized_type(&self, fcx: &FnCtxt<'a, 'tcx>) -> ErrorGuaranteed {
+        if let Some(reported) =
+            self.cast_ty.error_reported().or_else(|| self.expr_ty.error_reported())
+        {
+            return reported;
+        }
+
+        let tstr = fcx.ty_to_string(self.cast_ty);
+        let mut err = type_error_struct!(
+            fcx.tcx.sess,
+            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();
+                if self.cast_ty.is_trait() {
+                    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);
+                        }
+                    }
+                } else {
+                    let msg =
+                        &format!("consider using an implicit coercion to `&{mtstr}{tstr}` instead");
+                    err.span_help(self.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 t_cast = self.cast_ty;
+        let t_expr = self.expr_ty;
+        let type_asc_or =
+            if fcx.tcx.features().type_ascription { "type ascription or " } else { "" };
+        let (adjective, lint) = if t_cast.is_numeric() && t_expr.is_numeric() {
+            ("numeric ", lint::builtin::TRIVIAL_NUMERIC_CASTS)
+        } else {
+            ("", lint::builtin::TRIVIAL_CASTS)
+        };
+        fcx.tcx.struct_span_lint_hir(lint, self.expr.hir_id, self.span, |err| {
+            err.build(&format!(
+                "trivial {}cast: `{}` as `{}`",
+                adjective,
+                fcx.ty_to_string(t_expr),
+                fcx.ty_to_string(t_cast)
+            ))
+            .help(&format!(
+                "cast can be replaced by coercion; this might \
+                                   require {type_asc_or}a temporary variable"
+            ))
+            .emit();
+        });
+    }
+
+    #[instrument(skip(fcx), level = "debug")]
+    pub fn check(mut self, fcx: &FnCtxt<'a, 'tcx>) {
+        self.expr_ty = fcx.structurally_resolved_type(self.expr_span, self.expr_ty);
+        self.cast_ty = fcx.structurally_resolved_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_known_to_be_sized_modulo_regions(self.cast_ty, self.span)
+            && !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(()) => {
+                    self.trivial_cast_lint(fcx);
+                    debug!(" -> CoercionCast");
+                    fcx.typeck_results.borrow_mut().set_coercion_cast(self.expr.hir_id.local_id);
+                }
+                Err(ty::error::TypeError::ObjectUnsafeCoercion(did)) => {
+                    self.report_object_unsafe_cast(&fcx, did);
+                }
+                Err(_) => {
+                    match self.do_check(fcx) {
+                        Ok(k) => {
+                            debug!(" -> {:?}", k);
+                        }
+                        Err(e) => self.report_cast_error(fcx, e),
+                    };
+                }
+            };
+        }
+    }
+
+    fn report_object_unsafe_cast(&self, fcx: &FnCtxt<'a, 'tcx>, did: DefId) {
+        let violations = fcx.tcx.object_safety_violations(did);
+        let mut err = report_object_safety_error(fcx.tcx, self.cast_span, did, violations);
+        err.note(&format!("required by cast to type '{}'", fcx.ty_to_string(self.cast_ty)));
+        err.emit();
+    }
+
+    /// 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.
+    pub fn do_check(&self, fcx: &FnCtxt<'a, 'tcx>) -> Result<CastKind, CastError> {
+        use rustc_middle::ty::cast::CastTy::*;
+        use rustc_middle::ty::cast::IntTy::*;
+
+        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_associated_types_in(
+                            self.expr_span,
+                            self.expr_ty.fn_sig(fcx.tcx),
+                        );
+                        let res = fcx.try_coerce(
+                            self.expr,
+                            self.expr_ty,
+                            fcx.tcx.mk_fn_ptr(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) => {
+                                self.check_ref_cast(fcx, TypeAndMut { mutbl, ty: inner_ty }, mt)
+                            }
+                            _ => Err(CastError::NonScalar),
+                        };
+                    }
+                    _ => return Err(CastError::NonScalar),
+                }
+            }
+            _ => return Err(CastError::NonScalar),
+        };
+
+        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(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_expr: ty::TypeAndMut<'tcx>,
+        m_cast: ty::TypeAndMut<'tcx>,
+    ) -> Result<CastKind, CastError> {
+        debug!("check_ptr_ptr_cast m_expr={:?} m_cast={:?}", m_expr, m_cast);
+        // ptr-ptr cast. vtables must match.
+
+        let expr_kind = fcx.pointer_kind(m_expr.ty, self.span)?;
+        let cast_kind = fcx.pointer_kind(m_cast.ty, self.span)?;
+
+        let Some(cast_kind) = cast_kind else {
+            // We can't cast if target pointer kind is unknown
+            return Err(CastError::UnknownCastPtrKind);
+        };
+
+        // Cast to thin pointer is OK
+        if cast_kind == PointerKind::Thin {
+            return Ok(CastKind::PtrPtrCast);
+        }
+
+        let Some(expr_kind) = expr_kind else {
+            // We can't cast to fat pointer if source pointer kind is unknown
+            return Err(CastError::UnknownExprPtrKind);
+        };
+
+        // thin -> fat? report invalid cast (don't complain about vtable kinds)
+        if expr_kind == PointerKind::Thin {
+            return Err(CastError::SizedUnsizedCast);
+        }
+
+        // vtable kinds must match
+        if cast_kind == expr_kind {
+            Ok(CastKind::PtrPtrCast)
+        } else {
+            Err(CastError::DifferingKinds)
+        }
+    }
+
+    fn check_fptr_ptr_cast(
+        &self,
+        fcx: &FnCtxt<'a, 'tcx>,
+        m_cast: ty::TypeAndMut<'tcx>,
+    ) -> Result<CastKind, CastError> {
+        // 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> {
+        // 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> {
+        // array-ptr-cast: allow mut-to-mut, mut-to-const, const-to-const
+        if m_expr.mutbl == hir::Mutability::Mut || m_cast.mutbl == hir::Mutability::Not {
+            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 AddressOf in MIR.
+                let array_ptr_type = fcx.tcx.mk_ptr(m_expr);
+                fcx.try_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> {
+        // 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::IntToFatCast(Some("a vtable"))),
+            Some(PointerKind::Length) => Err(CastError::IntToFatCast(Some("a length"))),
+            Some(
+                PointerKind::OfProjection(_)
+                | PointerKind::OfOpaque(_, _)
+                | PointerKind::OfParam(_),
+            ) => Err(CastError::IntToFatCast(None)),
+        }
+    }
+
+    fn try_coercion_cast(&self, fcx: &FnCtxt<'a, 'tcx>) -> Result<(), ty::error::TypeError<'tcx>> {
+        match fcx.try_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)
+        {
+            fcx.tcx.struct_span_lint_hir(
+                lint::builtin::CENUM_IMPL_DROP_CAST,
+                self.expr.hir_id,
+                self.span,
+                |err| {
+                    err.build(&format!(
+                        "cannot cast enum `{}` into integer `{}` because it implements `Drop`",
+                        self.expr_ty, self.cast_ty
+                    ))
+                    .emit();
+                },
+            );
+        }
+    }
+
+    fn lossy_provenance_ptr2int_lint(&self, fcx: &FnCtxt<'a, 'tcx>, t_c: ty::cast::IntTy) {
+        fcx.tcx.struct_span_lint_hir(
+            lint::builtin::LOSSY_PROVENANCE_CASTS,
+            self.expr.hir_id,
+            self.span,
+            |err| {
+                let mut err = err.build(&format!(
+                    "under strict provenance it is considered bad style to cast pointer `{}` to integer `{}`",
+                    self.expr_ty, self.cast_ty
+                ));
+
+                let msg = "use `.addr()` to obtain the address of a pointer";
+
+                let expr_prec = self.expr.precedence().order();
+                let needs_parens = expr_prec < rustc_ast::util::parser::PREC_POSTFIX;
+
+                let scalar_cast = match t_c {
+                    ty::cast::IntTy::U(ty::UintTy::Usize) => String::new(),
+                    _ => format!(" as {}", self.cast_ty),
+                };
+
+                let cast_span = self.expr_span.shrink_to_hi().to(self.cast_span);
+
+                if needs_parens {
+                    let suggestions = vec![
+                        (self.expr_span.shrink_to_lo(), String::from("(")),
+                        (cast_span, format!(").addr(){scalar_cast}")),
+                    ];
+
+                    err.multipart_suggestion(msg, suggestions, Applicability::MaybeIncorrect);
+                } else {
+                    err.span_suggestion(
+                        cast_span,
+                        msg,
+                        format!(".addr(){scalar_cast}"),
+                        Applicability::MaybeIncorrect,
+                    );
+                }
+
+                err.help(
+                    "if you can't comply with strict provenance and need to expose the pointer \
+                    provenance you can use `.expose_addr()` instead"
+                );
+
+                err.emit();
+            },
+        );
+    }
+
+    fn fuzzy_provenance_int2ptr_lint(&self, fcx: &FnCtxt<'a, 'tcx>) {
+        fcx.tcx.struct_span_lint_hir(
+            lint::builtin::FUZZY_PROVENANCE_CASTS,
+            self.expr.hir_id,
+            self.span,
+            |err| {
+                let mut err = err.build(&format!(
+                    "strict provenance disallows casting integer `{}` to pointer `{}`",
+                    self.expr_ty, self.cast_ty
+                ));
+                let msg = "use `.with_addr()` to adjust a valid pointer in the same allocation, to this address";
+                let suggestions = vec![
+                    (self.expr_span.shrink_to_lo(), String::from("(...).with_addr(")),
+                    (self.expr_span.shrink_to_hi().to(self.cast_span), String::from(")")),
+                ];
+
+                err.multipart_suggestion(msg, suggestions, Applicability::MaybeIncorrect);
+                err.help(
+                    "if you can't comply with strict provenance and don't have a pointer with \
+                    the correct provenance you can use `std::ptr::from_exposed_addr()` instead"
+                 );
+
+                err.emit();
+            },
+        );
+    }
+}
+
+impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
+    fn type_is_known_to_be_sized_modulo_regions(&self, ty: Ty<'tcx>, span: Span) -> bool {
+        let lang_item = self.tcx.require_lang_item(LangItem::Sized, None);
+        traits::type_known_to_meet_bound_modulo_regions(self, self.param_env, ty, lang_item, span)
+    }
+}