clippy_lints/src/enum_clike.rs

   1 //! lint on C-like enums that are `repr(isize/usize)` and have values that
   2 //! don't fit into an `i32`
   3
   4 use rustc::lint::*;
   5 use rustc::middle::const_val::ConstVal;
   6 use rustc_const_math::*;
   7 use rustc::hir::*;
   8 use rustc::ty;
   9 use rustc::traits::Reveal;
  10 use rustc::ty::subst::Substs;
  11 use utils::span_lint;
  12
  13 /// **What it does:** Checks for C-like enumerations that are
  14 /// `repr(isize/usize)` and have values that don't fit into an `i32`.
  15 ///
  16 /// **Why is this bad?** This will truncate the variant value on 32 bit
  17 /// architectures, but works fine on 64 bit.
  18 ///
  19 /// **Known problems:** None.
  20 ///
  21 /// **Example:**
  22 /// ```rust
  23 /// #[repr(usize)]
  24 /// enum NonPortable {
  25 ///     X = 0x1_0000_0000,
  26 ///     Y = 0
  27 /// }
  28 /// ```
  29 declare_lint! {
  30     pub ENUM_CLIKE_UNPORTABLE_VARIANT,
  31     Warn,
  32     "C-like enums that are `repr(isize/usize)` and have values that don't fit into an `i32`"
  33 }
  34
  35 pub struct UnportableVariant;
  36
  37 impl LintPass for UnportableVariant {
  38     fn get_lints(&self) -> LintArray {
  39         lint_array!(ENUM_CLIKE_UNPORTABLE_VARIANT)
  40     }
  41 }
  42
  43 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnportableVariant {
  44     #[allow(cast_possible_truncation, cast_sign_loss)]
  45     fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx Item) {
  46         if let ItemEnum(ref def, _) = item.node {
  47             for var in &def.variants {
  48                 let variant = &var.node;
  49                 if let Some(body_id) = variant.disr_expr {
  50                     let expr = &cx.tcx.hir.body(body_id).value;
  51                     let did = cx.tcx.hir.body_owner_def_id(body_id);
  52                     let param_env = ty::ParamEnv::empty(Reveal::UserFacing);
  53                     let substs = Substs::identity_for_item(cx.tcx.global_tcx(), did);
  54                     let bad = match cx.tcx
  55                         .at(expr.span)
  56                         .const_eval(param_env.and((did, substs)))
  57                     {
  58                         Ok(&ty::Const {
  59                             val: ConstVal::Integral(Usize(Us64(i))),
  60                             ..
  61                         }) => u64::from(i as u32) != i,
  62                         Ok(&ty::Const {
  63                             val: ConstVal::Integral(Isize(Is64(i))),
  64                             ..
  65                         }) => i64::from(i as i32) != i,
  66                         _ => false,
  67                     };
  68                     if bad {
  69                         span_lint(
  70                             cx,
  71                             ENUM_CLIKE_UNPORTABLE_VARIANT,
  72                             var.span,
  73                             "Clike enum variant discriminant is not portable to 32-bit targets",
  74                         );
  75                     }
  76                 }
  77             }
  78         }
  79     }
  80 }