src/tools/clippy/clippy_lints/src/overflow_check_conditional.rs

   1 use rustc::lint::*;
   2 use rustc::hir::*;
   3 use utils::span_lint;
   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_lint! {
  17     pub OVERFLOW_CHECK_CONDITIONAL,
  18     Warn,
  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         if_chain! {
  35             if let Expr_::ExprBinary(ref op, ref first, ref second) = expr.node;
  36             if let Expr_::ExprBinary(ref op2, ref ident1, ref ident2) = first.node;
  37             if let Expr_::ExprPath(QPath::Resolved(_, ref path1)) = ident1.node;
  38             if let Expr_::ExprPath(QPath::Resolved(_, ref path2)) = ident2.node;
  39             if let Expr_::ExprPath(QPath::Resolved(_, ref path3)) = second.node;
  40             if path1.segments[0] == path3.segments[0] || path2.segments[0] == path3.segments[0];
  41             if cx.tables.expr_ty(ident1).is_integral();
  42             if cx.tables.expr_ty(ident2).is_integral();
  43             then {
  44                 if let BinOp_::BiLt = op.node {
  45                     if let BinOp_::BiAdd = op2.node {
  46                         span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span,
  47                             "You are trying to use classic C overflow conditions that will fail in Rust.");
  48                     }
  49                 }
  50                 if let BinOp_::BiGt = op.node {
  51                     if let BinOp_::BiSub = op2.node {
  52                         span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span,
  53                             "You are trying to use classic C underflow conditions that will fail in Rust.");
  54                     }
  55                 }
  56             }
  57         }
  58
  59         if_chain! {
  60             if let Expr_::ExprBinary(ref op, ref first, ref second) = expr.node;
  61             if let Expr_::ExprBinary(ref op2, ref ident1, ref ident2) = second.node;
  62             if let Expr_::ExprPath(QPath::Resolved(_, ref path1)) = ident1.node;
  63             if let Expr_::ExprPath(QPath::Resolved(_, ref path2)) = ident2.node;
  64             if let Expr_::ExprPath(QPath::Resolved(_, ref path3)) = first.node;
  65             if path1.segments[0] == path3.segments[0] || path2.segments[0] == path3.segments[0];
  66             if cx.tables.expr_ty(ident1).is_integral();
  67             if cx.tables.expr_ty(ident2).is_integral();
  68             then {
  69                 if let BinOp_::BiGt = op.node {
  70                     if let BinOp_::BiAdd = op2.node {
  71                         span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span,
  72                             "You are trying to use classic C overflow conditions that will fail in Rust.");
  73                     }
  74                 }
  75                 if let BinOp_::BiLt = op.node {
  76                     if let BinOp_::BiSub = op2.node {
  77                         span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span,
  78                             "You are trying to use classic C underflow conditions that will fail in Rust.");
  79                     }
  80                 }
  81             }
  82         }
  83     }
  84 }