clippy_lints/src/overflow_check_conditional.rs

   1 use crate::utils::{span_lint, SpanlessEq};
   2 use if_chain::if_chain;
   3 use rustc::hir::*;
   4 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   5 use rustc::{declare_tool_lint, lint_array};
   6
   7 declare_clippy_lint! {
   8     /// **What it does:** Detects classic underflow/overflow checks.
   9     ///
  10     /// **Why is this bad?** Most classic C underflow/overflow checks will fail in
  11     /// Rust. Users can use functions like `overflowing_*` and `wrapping_*` instead.
  12     ///
  13     /// **Known problems:** None.
  14     ///
  15     /// **Example:**
  16     /// ```rust
  17     /// a + b < a
  18     /// ```
  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     fn name(&self) -> &'static str {
  33         "OverflowCheckConditional"
  34     }
  35 }
  36
  37 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for OverflowCheckConditional {
  38     // a + b < a, a > a + b, a < a - b, a - b > a
  39     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  40         let eq = |l, r| SpanlessEq::new(cx).eq_path_segment(l, r);
  41         if_chain! {
  42             if let ExprKind::Binary(ref op, ref first, ref second) = expr.node;
  43             if let ExprKind::Binary(ref op2, ref ident1, ref ident2) = first.node;
  44             if let ExprKind::Path(QPath::Resolved(_, ref path1)) = ident1.node;
  45             if let ExprKind::Path(QPath::Resolved(_, ref path2)) = ident2.node;
  46             if let ExprKind::Path(QPath::Resolved(_, ref path3)) = second.node;
  47             if eq(&path1.segments[0], &path3.segments[0]) || eq(&path2.segments[0], &path3.segments[0]);
  48             if cx.tables.expr_ty(ident1).is_integral();
  49             if cx.tables.expr_ty(ident2).is_integral();
  50             then {
  51                 if let BinOpKind::Lt = op.node {
  52                     if let BinOpKind::Add = op2.node {
  53                         span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span,
  54                             "You are trying to use classic C overflow conditions that will fail in Rust.");
  55                     }
  56                 }
  57                 if let BinOpKind::Gt = op.node {
  58                     if let BinOpKind::Sub = op2.node {
  59                         span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span,
  60                             "You are trying to use classic C underflow conditions that will fail in Rust.");
  61                     }
  62                 }
  63             }
  64         }
  65
  66         if_chain! {
  67             if let ExprKind::Binary(ref op, ref first, ref second) = expr.node;
  68             if let ExprKind::Binary(ref op2, ref ident1, ref ident2) = second.node;
  69             if let ExprKind::Path(QPath::Resolved(_, ref path1)) = ident1.node;
  70             if let ExprKind::Path(QPath::Resolved(_, ref path2)) = ident2.node;
  71             if let ExprKind::Path(QPath::Resolved(_, ref path3)) = first.node;
  72             if eq(&path1.segments[0], &path3.segments[0]) || eq(&path2.segments[0], &path3.segments[0]);
  73             if cx.tables.expr_ty(ident1).is_integral();
  74             if cx.tables.expr_ty(ident2).is_integral();
  75             then {
  76                 if let BinOpKind::Gt = op.node {
  77                     if let BinOpKind::Add = op2.node {
  78                         span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span,
  79                             "You are trying to use classic C overflow conditions that will fail in Rust.");
  80                     }
  81                 }
  82                 if let BinOpKind::Lt = op.node {
  83                     if let BinOpKind::Sub = op2.node {
  84                         span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span,
  85                             "You are trying to use classic C underflow conditions that will fail in Rust.");
  86                     }
  87                 }
  88             }
  89         }
  90     }
  91 }