src/tools/clippy/clippy_lints/src/transmute/useless_transmute.rs

   1 use super::USELESS_TRANSMUTE;
   2 use clippy_utils::diagnostics::{span_lint, span_lint_and_then};
   3 use clippy_utils::sugg;
   4 use rustc_errors::Applicability;
   5 use rustc_hir::Expr;
   6 use rustc_lint::LateContext;
   7 use rustc_middle::ty::{self, Ty, TypeVisitable};
   8
   9 /// Checks for `useless_transmute` lint.
  10 /// Returns `true` if it's triggered, otherwise returns `false`.
  11 pub(super) fn check<'tcx>(
  12     cx: &LateContext<'tcx>,
  13     e: &'tcx Expr<'_>,
  14     from_ty: Ty<'tcx>,
  15     to_ty: Ty<'tcx>,
  16     arg: &'tcx Expr<'_>,
  17 ) -> bool {
  18     match (&from_ty.kind(), &to_ty.kind()) {
  19         _ if from_ty == to_ty && !from_ty.has_erased_regions() => {
  20             span_lint(
  21                 cx,
  22                 USELESS_TRANSMUTE,
  23                 e.span,
  24                 &format!("transmute from a type (`{}`) to itself", from_ty),
  25             );
  26             true
  27         },
  28         (ty::Ref(_, rty, rty_mutbl), ty::RawPtr(ptr_ty)) => {
  29             // No way to give the correct suggestion here. Avoid linting for now.
  30             if !rty.has_erased_regions() {
  31                 span_lint_and_then(
  32                     cx,
  33                     USELESS_TRANSMUTE,
  34                     e.span,
  35                     "transmute from a reference to a pointer",
  36                     |diag| {
  37                         if let Some(arg) = sugg::Sugg::hir_opt(cx, arg) {
  38                             let rty_and_mut = ty::TypeAndMut {
  39                                 ty: *rty,
  40                                 mutbl: *rty_mutbl,
  41                             };
  42
  43                             let sugg = if *ptr_ty == rty_and_mut {
  44                                 arg.as_ty(to_ty)
  45                             } else {
  46                                 arg.as_ty(cx.tcx.mk_ptr(rty_and_mut)).as_ty(to_ty)
  47                             };
  48
  49                             diag.span_suggestion(e.span, "try", sugg, Applicability::Unspecified);
  50                         }
  51                     },
  52                 );
  53             }
  54             true
  55         },
  56         (ty::Int(_) | ty::Uint(_), ty::RawPtr(_)) => {
  57             span_lint_and_then(
  58                 cx,
  59                 USELESS_TRANSMUTE,
  60                 e.span,
  61                 "transmute from an integer to a pointer",
  62                 |diag| {
  63                     if let Some(arg) = sugg::Sugg::hir_opt(cx, arg) {
  64                         diag.span_suggestion(e.span, "try", arg.as_ty(&to_ty.to_string()), Applicability::Unspecified);
  65                     }
  66                 },
  67             );
  68             true
  69         },
  70         _ => false,
  71     }
  72 }