clippy_lints/src/overflow_check_conditional.rs

   1 use rustc::lint::*;
   2 use rustc::{declare_lint, lint_array};
   3 use if_chain::if_chain;
   4 use rustc::hir::*;
   5 use crate::utils::{span_lint, SpanlessEq};
   6
   7 /// **What it does:** Detects classic underflow/overflow checks.
   8 ///
   9 /// **Why is this bad?** Most classic C underflow/overflow checks will fail in
  10 /// Rust. Users can use functions like `overflowing_*` and `wrapping_*` instead.
  11 ///
  12 /// **Known problems:** None.
  13 ///
  14 /// **Example:**
  15 /// ```rust
  16 /// a + b < a
  17 /// ```
  18 declare_clippy_lint! {
  19     pub OVERFLOW_CHECK_CONDITIONAL,
  20     complexity,
  21     "overflow checks inspired by C which are likely to panic"
  22 }
  23
  24 #[derive(Copy, Clone)]
  25 pub struct OverflowCheckConditional;
  26
  27 impl LintPass for OverflowCheckConditional {
  28     fn get_lints(&self) -> LintArray {
  29         lint_array!(OVERFLOW_CHECK_CONDITIONAL)
  30     }
  31 }
  32
  33 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for OverflowCheckConditional {
  34     // a + b < a, a > a + b, a < a - b, a - b > a
  35     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  36         let eq = |l, r| SpanlessEq::new(cx).eq_path_segment(l, r);
  37         if_chain! {
  38             if let ExprKind::Binary(ref op, ref first, ref second) = expr.node;
  39             if let ExprKind::Binary(ref op2, ref ident1, ref ident2) = first.node;
  40             if let ExprKind::Path(QPath::Resolved(_, ref path1)) = ident1.node;
  41             if let ExprKind::Path(QPath::Resolved(_, ref path2)) = ident2.node;
  42             if let ExprKind::Path(QPath::Resolved(_, ref path3)) = second.node;
  43             if eq(&path1.segments[0], &path3.segments[0]) || eq(&path2.segments[0], &path3.segments[0]);
  44             if cx.tables.expr_ty(ident1).is_integral();
  45             if cx.tables.expr_ty(ident2).is_integral();
  46             then {
  47                 if let BinOpKind::Lt = op.node {
  48                     if let BinOpKind::Add = op2.node {
  49                         span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span,
  50                             "You are trying to use classic C overflow conditions that will fail in Rust.");
  51                     }
  52                 }
  53                 if let BinOpKind::Gt = op.node {
  54                     if let BinOpKind::Sub = op2.node {
  55                         span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span,
  56                             "You are trying to use classic C underflow conditions that will fail in Rust.");
  57                     }
  58                 }
  59             }
  60         }
  61
  62         if_chain! {
  63             if let ExprKind::Binary(ref op, ref first, ref second) = expr.node;
  64             if let ExprKind::Binary(ref op2, ref ident1, ref ident2) = second.node;
  65             if let ExprKind::Path(QPath::Resolved(_, ref path1)) = ident1.node;
  66             if let ExprKind::Path(QPath::Resolved(_, ref path2)) = ident2.node;
  67             if let ExprKind::Path(QPath::Resolved(_, ref path3)) = first.node;
  68             if eq(&path1.segments[0], &path3.segments[0]) || eq(&path2.segments[0], &path3.segments[0]);
  69             if cx.tables.expr_ty(ident1).is_integral();
  70             if cx.tables.expr_ty(ident2).is_integral();
  71             then {
  72                 if let BinOpKind::Gt = op.node {
  73                     if let BinOpKind::Add = op2.node {
  74                         span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span,
  75                             "You are trying to use classic C overflow conditions that will fail in Rust.");
  76                     }
  77                 }
  78                 if let BinOpKind::Lt = op.node {
  79                     if let BinOpKind::Sub = op2.node {
  80                         span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span,
  81                             "You are trying to use classic C underflow conditions that will fail in Rust.");
  82                     }
  83                 }
  84             }
  85         }
  86     }
  87 }