clippy_lints/src/invalid_upcast_comparisons.rs

   1 use std::cmp::Ordering;
   2
   3 use rustc_hir::{Expr, ExprKind};
   4 use rustc_lint::{LateContext, LateLintPass};
   5 use rustc_middle::ty::{self, IntTy, UintTy};
   6 use rustc_session::{declare_lint_pass, declare_tool_lint};
   7 use rustc_span::Span;
   8 use rustc_target::abi::LayoutOf;
   9
  10 use crate::consts::{constant, Constant};
  11
  12 use clippy_utils::comparisons::Rel;
  13 use clippy_utils::diagnostics::span_lint;
  14 use clippy_utils::source::snippet;
  15 use clippy_utils::{comparisons, sext};
  16
  17 declare_clippy_lint! {
  18     /// **What it does:** Checks for comparisons where the relation is always either
  19     /// true or false, but where one side has been upcast so that the comparison is
  20     /// necessary. Only integer types are checked.
  21     ///
  22     /// **Why is this bad?** An expression like `let x : u8 = ...; (x as u32) > 300`
  23     /// will mistakenly imply that it is possible for `x` to be outside the range of
  24     /// `u8`.
  25     ///
  26     /// **Known problems:**
  27     /// https://github.com/rust-lang/rust-clippy/issues/886
  28     ///
  29     /// **Example:**
  30     /// ```rust
  31     /// let x: u8 = 1;
  32     /// (x as u32) > 300;
  33     /// ```
  34     pub INVALID_UPCAST_COMPARISONS,
  35     pedantic,
  36     "a comparison involving an upcast which is always true or false"
  37 }
  38
  39 declare_lint_pass!(InvalidUpcastComparisons => [INVALID_UPCAST_COMPARISONS]);
  40
  41 #[derive(Copy, Clone, Debug, Eq)]
  42 enum FullInt {
  43     S(i128),
  44     U(u128),
  45 }
  46
  47 impl FullInt {
  48     #[allow(clippy::cast_sign_loss)]
  49     #[must_use]
  50     fn cmp_s_u(s: i128, u: u128) -> Ordering {
  51         if s < 0 {
  52             Ordering::Less
  53         } else if u > (i128::MAX as u128) {
  54             Ordering::Greater
  55         } else {
  56             (s as u128).cmp(&u)
  57         }
  58     }
  59 }
  60
  61 impl PartialEq for FullInt {
  62     #[must_use]
  63     fn eq(&self, other: &Self) -> bool {
  64         self.partial_cmp(other).expect("`partial_cmp` only returns `Some(_)`") == Ordering::Equal
  65     }
  66 }
  67
  68 impl PartialOrd for FullInt {
  69     #[must_use]
  70     fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
  71         Some(match (self, other) {
  72             (&Self::S(s), &Self::S(o)) => s.cmp(&o),
  73             (&Self::U(s), &Self::U(o)) => s.cmp(&o),
  74             (&Self::S(s), &Self::U(o)) => Self::cmp_s_u(s, o),
  75             (&Self::U(s), &Self::S(o)) => Self::cmp_s_u(o, s).reverse(),
  76         })
  77     }
  78 }
  79
  80 impl Ord for FullInt {
  81     #[must_use]
  82     fn cmp(&self, other: &Self) -> Ordering {
  83         self.partial_cmp(other)
  84             .expect("`partial_cmp` for FullInt can never return `None`")
  85     }
  86 }
  87
  88 fn numeric_cast_precast_bounds<'a>(cx: &LateContext<'_>, expr: &'a Expr<'_>) -> Option<(FullInt, FullInt)> {
  89     if let ExprKind::Cast(cast_exp, _) = expr.kind {
  90         let pre_cast_ty = cx.typeck_results().expr_ty(cast_exp);
  91         let cast_ty = cx.typeck_results().expr_ty(expr);
  92         // if it's a cast from i32 to u32 wrapping will invalidate all these checks
  93         if cx.layout_of(pre_cast_ty).ok().map(|l| l.size) == cx.layout_of(cast_ty).ok().map(|l| l.size) {
  94             return None;
  95         }
  96         match pre_cast_ty.kind() {
  97             ty::Int(int_ty) => Some(match int_ty {
  98                 IntTy::I8 => (FullInt::S(i128::from(i8::MIN)), FullInt::S(i128::from(i8::MAX))),
  99                 IntTy::I16 => (FullInt::S(i128::from(i16::MIN)), FullInt::S(i128::from(i16::MAX))),
 100                 IntTy::I32 => (FullInt::S(i128::from(i32::MIN)), FullInt::S(i128::from(i32::MAX))),
 101                 IntTy::I64 => (FullInt::S(i128::from(i64::MIN)), FullInt::S(i128::from(i64::MAX))),
 102                 IntTy::I128 => (FullInt::S(i128::MIN), FullInt::S(i128::MAX)),
 103                 IntTy::Isize => (FullInt::S(isize::MIN as i128), FullInt::S(isize::MAX as i128)),
 104             }),
 105             ty::Uint(uint_ty) => Some(match uint_ty {
 106                 UintTy::U8 => (FullInt::U(u128::from(u8::MIN)), FullInt::U(u128::from(u8::MAX))),
 107                 UintTy::U16 => (FullInt::U(u128::from(u16::MIN)), FullInt::U(u128::from(u16::MAX))),
 108                 UintTy::U32 => (FullInt::U(u128::from(u32::MIN)), FullInt::U(u128::from(u32::MAX))),
 109                 UintTy::U64 => (FullInt::U(u128::from(u64::MIN)), FullInt::U(u128::from(u64::MAX))),
 110                 UintTy::U128 => (FullInt::U(u128::MIN), FullInt::U(u128::MAX)),
 111                 UintTy::Usize => (FullInt::U(usize::MIN as u128), FullInt::U(usize::MAX as u128)),
 112             }),
 113             _ => None,
 114         }
 115     } else {
 116         None
 117     }
 118 }
 119
 120 fn node_as_const_fullint<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<FullInt> {
 121     let val = constant(cx, cx.typeck_results(), expr)?.0;
 122     if let Constant::Int(const_int) = val {
 123         match *cx.typeck_results().expr_ty(expr).kind() {
 124             ty::Int(ity) => Some(FullInt::S(sext(cx.tcx, const_int, ity))),
 125             ty::Uint(_) => Some(FullInt::U(const_int)),
 126             _ => None,
 127         }
 128     } else {
 129         None
 130     }
 131 }
 132
 133 fn err_upcast_comparison(cx: &LateContext<'_>, span: Span, expr: &Expr<'_>, always: bool) {
 134     if let ExprKind::Cast(cast_val, _) = expr.kind {
 135         span_lint(
 136             cx,
 137             INVALID_UPCAST_COMPARISONS,
 138             span,
 139             &format!(
 140                 "because of the numeric bounds on `{}` prior to casting, this expression is always {}",
 141                 snippet(cx, cast_val.span, "the expression"),
 142                 if always { "true" } else { "false" },
 143             ),
 144         );
 145     }
 146 }
 147
 148 fn upcast_comparison_bounds_err<'tcx>(
 149     cx: &LateContext<'tcx>,
 150     span: Span,
 151     rel: comparisons::Rel,
 152     lhs_bounds: Option<(FullInt, FullInt)>,
 153     lhs: &'tcx Expr<'_>,
 154     rhs: &'tcx Expr<'_>,
 155     invert: bool,
 156 ) {
 157     if let Some((lb, ub)) = lhs_bounds {
 158         if let Some(norm_rhs_val) = node_as_const_fullint(cx, rhs) {
 159             if rel == Rel::Eq || rel == Rel::Ne {
 160                 if norm_rhs_val < lb || norm_rhs_val > ub {
 161                     err_upcast_comparison(cx, span, lhs, rel == Rel::Ne);
 162                 }
 163             } else if match rel {
 164                 Rel::Lt => {
 165                     if invert {
 166                         norm_rhs_val < lb
 167                     } else {
 168                         ub < norm_rhs_val
 169                     }
 170                 },
 171                 Rel::Le => {
 172                     if invert {
 173                         norm_rhs_val <= lb
 174                     } else {
 175                         ub <= norm_rhs_val
 176                     }
 177                 },
 178                 Rel::Eq | Rel::Ne => unreachable!(),
 179             } {
 180                 err_upcast_comparison(cx, span, lhs, true);
 181             } else if match rel {
 182                 Rel::Lt => {
 183                     if invert {
 184                         norm_rhs_val >= ub
 185                     } else {
 186                         lb >= norm_rhs_val
 187                     }
 188                 },
 189                 Rel::Le => {
 190                     if invert {
 191                         norm_rhs_val > ub
 192                     } else {
 193                         lb > norm_rhs_val
 194                     }
 195                 },
 196                 Rel::Eq | Rel::Ne => unreachable!(),
 197             } {
 198                 err_upcast_comparison(cx, span, lhs, false);
 199             }
 200         }
 201     }
 202 }
 203
 204 impl<'tcx> LateLintPass<'tcx> for InvalidUpcastComparisons {
 205     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
 206         if let ExprKind::Binary(ref cmp, lhs, rhs) = expr.kind {
 207             let normalized = comparisons::normalize_comparison(cmp.node, lhs, rhs);
 208             let (rel, normalized_lhs, normalized_rhs) = if let Some(val) = normalized {
 209                 val
 210             } else {
 211                 return;
 212             };
 213
 214             let lhs_bounds = numeric_cast_precast_bounds(cx, normalized_lhs);
 215             let rhs_bounds = numeric_cast_precast_bounds(cx, normalized_rhs);
 216
 217             upcast_comparison_bounds_err(cx, expr.span, rel, lhs_bounds, normalized_lhs, normalized_rhs, false);
 218             upcast_comparison_bounds_err(cx, expr.span, rel, rhs_bounds, normalized_rhs, normalized_lhs, true);
 219         }
 220     }
 221 }