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

   1 use clippy_utils::diagnostics::span_lint;
   2 use clippy_utils::SpanlessEq;
   3 use if_chain::if_chain;
   4 use rustc_hir::{BinOpKind, Expr, ExprKind, QPath};
   5 use rustc_lint::{LateContext, LateLintPass};
   6 use rustc_session::{declare_lint_pass, declare_tool_lint};
   7
   8 declare_clippy_lint! {
   9     /// ### What it does
  10     /// Detects classic underflow/overflow checks.
  11     ///
  12     /// ### Why is this bad?
  13     /// Most classic C underflow/overflow checks will fail in
  14     /// Rust. Users can use functions like `overflowing_*` and `wrapping_*` instead.
  15     ///
  16     /// ### Example
  17     /// ```rust
  18     /// # let a = 1;
  19     /// # let b = 2;
  20     /// a + b < a;
  21     /// ```
  22     pub OVERFLOW_CHECK_CONDITIONAL,
  23     complexity,
  24     "overflow checks inspired by C which are likely to panic"
  25 }
  26
  27 declare_lint_pass!(OverflowCheckConditional => [OVERFLOW_CHECK_CONDITIONAL]);
  28
  29 const OVERFLOW_MSG: &str = "you are trying to use classic C overflow conditions that will fail in Rust";
  30 const UNDERFLOW_MSG: &str = "you are trying to use classic C underflow conditions that will fail in Rust";
  31
  32 impl<'tcx> LateLintPass<'tcx> for OverflowCheckConditional {
  33     // a + b < a, a > a + b, a < a - b, a - b > a
  34     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  35         let eq = |l, r| SpanlessEq::new(cx).eq_path_segment(l, r);
  36         if_chain! {
  37             if let ExprKind::Binary(ref op, first, second) = expr.kind;
  38             if let ExprKind::Binary(ref op2, ident1, ident2) = first.kind;
  39             if let ExprKind::Path(QPath::Resolved(_, path1)) = ident1.kind;
  40             if let ExprKind::Path(QPath::Resolved(_, path2)) = ident2.kind;
  41             if let ExprKind::Path(QPath::Resolved(_, path3)) = second.kind;
  42             if eq(&path1.segments[0], &path3.segments[0]) || eq(&path2.segments[0], &path3.segments[0]);
  43             if cx.typeck_results().expr_ty(ident1).is_integral();
  44             if cx.typeck_results().expr_ty(ident2).is_integral();
  45             then {
  46                 if op.node == BinOpKind::Lt && op2.node == BinOpKind::Add {
  47                     span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span, OVERFLOW_MSG);
  48                 }
  49                 if op.node == BinOpKind::Gt && op2.node == BinOpKind::Sub {
  50                     span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span, UNDERFLOW_MSG);
  51                 }
  52             }
  53         }
  54
  55         if_chain! {
  56             if let ExprKind::Binary(ref op, first, second) = expr.kind;
  57             if let ExprKind::Binary(ref op2, ident1, ident2) = second.kind;
  58             if let ExprKind::Path(QPath::Resolved(_, path1)) = ident1.kind;
  59             if let ExprKind::Path(QPath::Resolved(_, path2)) = ident2.kind;
  60             if let ExprKind::Path(QPath::Resolved(_, path3)) = first.kind;
  61             if eq(&path1.segments[0], &path3.segments[0]) || eq(&path2.segments[0], &path3.segments[0]);
  62             if cx.typeck_results().expr_ty(ident1).is_integral();
  63             if cx.typeck_results().expr_ty(ident2).is_integral();
  64             then {
  65                 if op.node == BinOpKind::Gt && op2.node == BinOpKind::Add {
  66                     span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span, OVERFLOW_MSG);
  67                 }
  68                 if op.node == BinOpKind::Lt && op2.node == BinOpKind::Sub {
  69                     span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span, UNDERFLOW_MSG);
  70                 }
  71             }
  72         }
  73     }
  74 }