clippy_lints/src/casts/ptr_as_ptr.rs

   1 use std::borrow::Cow;
   2
   3 use clippy_utils::diagnostics::span_lint_and_sugg;
   4 use clippy_utils::meets_msrv;
   5 use clippy_utils::sugg::Sugg;
   6 use if_chain::if_chain;
   7 use rustc_errors::Applicability;
   8 use rustc_hir::{Expr, ExprKind, Mutability, TyKind};
   9 use rustc_lint::LateContext;
  10 use rustc_middle::ty::{self, TypeAndMut};
  11 use rustc_semver::RustcVersion;
  12
  13 use super::PTR_AS_PTR;
  14
  15 const PTR_AS_PTR_MSRV: RustcVersion = RustcVersion::new(1, 38, 0);
  16
  17 pub(super) fn check(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, msrv: &Option<RustcVersion>) {
  18     if !meets_msrv(msrv.as_ref(), &PTR_AS_PTR_MSRV) {
  19         return;
  20     }
  21
  22     if_chain! {
  23         if let ExprKind::Cast(cast_expr, cast_to_hir_ty) = expr.kind;
  24         let (cast_from, cast_to) = (cx.typeck_results().expr_ty(cast_expr), cx.typeck_results().expr_ty(expr));
  25         if let ty::RawPtr(TypeAndMut { mutbl: from_mutbl, .. }) = cast_from.kind();
  26         if let ty::RawPtr(TypeAndMut { ty: to_pointee_ty, mutbl: to_mutbl }) = cast_to.kind();
  27         if matches!((from_mutbl, to_mutbl),
  28             (Mutability::Not, Mutability::Not) | (Mutability::Mut, Mutability::Mut));
  29         // The `U` in `pointer::cast` have to be `Sized`
  30         // as explained here: https://github.com/rust-lang/rust/issues/60602.
  31         if to_pointee_ty.is_sized(cx.tcx.at(expr.span), cx.param_env);
  32         then {
  33             let mut applicability = Applicability::MachineApplicable;
  34             let cast_expr_sugg = Sugg::hir_with_applicability(cx, cast_expr, "_", &mut applicability);
  35             let turbofish = match &cast_to_hir_ty.kind {
  36                     TyKind::Infer => Cow::Borrowed(""),
  37                     TyKind::Ptr(mut_ty) if matches!(mut_ty.ty.kind, TyKind::Infer) => Cow::Borrowed(""),
  38                     _ => Cow::Owned(format!("::<{}>", to_pointee_ty)),
  39                 };
  40             span_lint_and_sugg(
  41                 cx,
  42                 PTR_AS_PTR,
  43                 expr.span,
  44                 "`as` casting between raw pointers without changing its mutability",
  45                 "try `pointer::cast`, a safer alternative",
  46                 format!("{}.cast{}()", cast_expr_sugg.maybe_par(), turbofish),
  47                 applicability,
  48             );
  49         }
  50     }
  51 }