clippy_lints/src/overflow_check_conditional.rs

   1 use crate::utils::{span_lint, SpanlessEq};
   2 use if_chain::if_chain;
   3 use rustc_hir::{BinOpKind, Expr, ExprKind, QPath};
   4 use rustc_lint::{LateContext, LateLintPass};
   5 use rustc_session::{declare_lint_pass, declare_tool_lint};
   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     /// # let a = 1;
  18     /// # let b = 2;
  19     /// a + b < a;
  20     /// ```
  21     pub OVERFLOW_CHECK_CONDITIONAL,
  22     complexity,
  23     "overflow checks inspired by C which are likely to panic"
  24 }
  25
  26 declare_lint_pass!(OverflowCheckConditional => [OVERFLOW_CHECK_CONDITIONAL]);
  27
  28 impl<'tcx> LateLintPass<'tcx> for OverflowCheckConditional {
  29     // a + b < a, a > a + b, a < a - b, a - b > a
  30     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  31         let eq = |l, r| SpanlessEq::new(cx).eq_path_segment(l, r);
  32         if_chain! {
  33             if let ExprKind::Binary(ref op, ref first, ref second) = expr.kind;
  34             if let ExprKind::Binary(ref op2, ref ident1, ref ident2) = first.kind;
  35             if let ExprKind::Path(QPath::Resolved(_, ref path1)) = ident1.kind;
  36             if let ExprKind::Path(QPath::Resolved(_, ref path2)) = ident2.kind;
  37             if let ExprKind::Path(QPath::Resolved(_, ref path3)) = second.kind;
  38             if eq(&path1.segments[0], &path3.segments[0]) || eq(&path2.segments[0], &path3.segments[0]);
  39             if cx.typeck_results().expr_ty(ident1).is_integral();
  40             if cx.typeck_results().expr_ty(ident2).is_integral();
  41             then {
  42                 if let BinOpKind::Lt = op.node {
  43                     if let BinOpKind::Add = op2.node {
  44                         span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span,
  45                             "you are trying to use classic C overflow conditions that will fail in Rust");
  46                     }
  47                 }
  48                 if let BinOpKind::Gt = op.node {
  49                     if let BinOpKind::Sub = op2.node {
  50                         span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span,
  51                             "you are trying to use classic C underflow conditions that will fail in Rust");
  52                     }
  53                 }
  54             }
  55         }
  56
  57         if_chain! {
  58             if let ExprKind::Binary(ref op, ref first, ref second) = expr.kind;
  59             if let ExprKind::Binary(ref op2, ref ident1, ref ident2) = second.kind;
  60             if let ExprKind::Path(QPath::Resolved(_, ref path1)) = ident1.kind;
  61             if let ExprKind::Path(QPath::Resolved(_, ref path2)) = ident2.kind;
  62             if let ExprKind::Path(QPath::Resolved(_, ref path3)) = first.kind;
  63             if eq(&path1.segments[0], &path3.segments[0]) || eq(&path2.segments[0], &path3.segments[0]);
  64             if cx.typeck_results().expr_ty(ident1).is_integral();
  65             if cx.typeck_results().expr_ty(ident2).is_integral();
  66             then {
  67                 if let BinOpKind::Gt = op.node {
  68                     if let BinOpKind::Add = op2.node {
  69                         span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span,
  70                             "you are trying to use classic C overflow conditions that will fail in Rust");
  71                     }
  72                 }
  73                 if let BinOpKind::Lt = op.node {
  74                     if let BinOpKind::Sub = op2.node {
  75                         span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span,
  76                             "you are trying to use classic C underflow conditions that will fail in Rust");
  77                     }
  78                 }
  79             }
  80         }
  81     }
  82 }