clippy_lints/src/overflow_check_conditional.rs

   1 use rustc::lint::*;
   2 use rustc::hir::*;
   3 use crate::utils::{span_lint, SpanlessEq};
   4
   5 /// **What it does:** Detects classic underflow/overflow checks.
   6 ///
   7 /// **Why is this bad?** Most classic C underflow/overflow checks will fail in
   8 /// Rust. Users can use functions like `overflowing_*` and `wrapping_*` instead.
   9 ///
  10 /// **Known problems:** None.
  11 ///
  12 /// **Example:**
  13 /// ```rust
  14 /// a + b < a
  15 /// ```
  16 declare_clippy_lint! {
  17     pub OVERFLOW_CHECK_CONDITIONAL,
  18     complexity,
  19     "overflow checks inspired by C which are likely to panic"
  20 }
  21
  22 #[derive(Copy, Clone)]
  23 pub struct OverflowCheckConditional;
  24
  25 impl LintPass for OverflowCheckConditional {
  26     fn get_lints(&self) -> LintArray {
  27         lint_array!(OVERFLOW_CHECK_CONDITIONAL)
  28     }
  29 }
  30
  31 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for OverflowCheckConditional {
  32     // a + b < a, a > a + b, a < a - b, a - b > a
  33     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  34         let eq = |l, r| SpanlessEq::new(cx).eq_path_segment(l, r);
  35         if_chain! {
  36             if let ExprKind::Binary(ref op, ref first, ref second) = expr.node;
  37             if let ExprKind::Binary(ref op2, ref ident1, ref ident2) = first.node;
  38             if let ExprKind::Path(QPath::Resolved(_, ref path1)) = ident1.node;
  39             if let ExprKind::Path(QPath::Resolved(_, ref path2)) = ident2.node;
  40             if let ExprKind::Path(QPath::Resolved(_, ref path3)) = second.node;
  41             if eq(&path1.segments[0], &path3.segments[0]) || eq(&path2.segments[0], &path3.segments[0]);
  42             if cx.tables.expr_ty(ident1).is_integral();
  43             if cx.tables.expr_ty(ident2).is_integral();
  44             then {
  45                 if let BinOpKind::Lt = op.node {
  46                     if let BinOpKindAdd = op2.node {
  47                         span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span,
  48                             "You are trying to use classic C overflow conditions that will fail in Rust.");
  49                     }
  50                 }
  51                 if let BinOpKind::Gt = op.node {
  52                     if let BinOpKind::Sub = op2.node {
  53                         span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span,
  54                             "You are trying to use classic C underflow conditions that will fail in Rust.");
  55                     }
  56                 }
  57             }
  58         }
  59
  60         if_chain! {
  61             if let ExprKind::Binary(ref op, ref first, ref second) = expr.node;
  62             if let ExprKind::Binary(ref op2, ref ident1, ref ident2) = second.node;
  63             if let ExprKind::Path(QPath::Resolved(_, ref path1)) = ident1.node;
  64             if let ExprKind::Path(QPath::Resolved(_, ref path2)) = ident2.node;
  65             if let ExprKind::Path(QPath::Resolved(_, ref path3)) = first.node;
  66             if eq(&path1.segments[0], &path3.segments[0]) || eq(&path2.segments[0], &path3.segments[0]);
  67             if cx.tables.expr_ty(ident1).is_integral();
  68             if cx.tables.expr_ty(ident2).is_integral();
  69             then {
  70                 if let BinOpKind::Gt = op.node {
  71                     if let BinOpKindAdd = op2.node {
  72                         span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span,
  73                             "You are trying to use classic C overflow conditions that will fail in Rust.");
  74                     }
  75                 }
  76                 if let BinOpKind::Lt = op.node {
  77                     if let BinOpKind::Sub = op2.node {
  78                         span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span,
  79                             "You are trying to use classic C underflow conditions that will fail in Rust.");
  80                     }
  81                 }
  82             }
  83         }
  84     }
  85 }