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:** Detects classic underflow/overflow checks.
  10     ///
  11     /// **Why is this bad?** Most classic C underflow/overflow checks will fail in
  12     /// Rust. Users can use functions like `overflowing_*` and `wrapping_*` instead.
  13     ///
  14     /// **Known problems:** None.
  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 impl<'tcx> LateLintPass<'tcx> for OverflowCheckConditional {
  30     // a + b < a, a > a + b, a < a - b, a - b > a
  31     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  32         let eq = |l, r| SpanlessEq::new(cx).eq_path_segment(l, r);
  33         if_chain! {
  34             if let ExprKind::Binary(ref op, first, second) = expr.kind;
  35             if let ExprKind::Binary(ref op2, ident1, ident2) = first.kind;
  36             if let ExprKind::Path(QPath::Resolved(_, path1)) = ident1.kind;
  37             if let ExprKind::Path(QPath::Resolved(_, path2)) = ident2.kind;
  38             if let ExprKind::Path(QPath::Resolved(_, path3)) = second.kind;
  39             if eq(&path1.segments[0], &path3.segments[0]) || eq(&path2.segments[0], &path3.segments[0]);
  40             if cx.typeck_results().expr_ty(ident1).is_integral();
  41             if cx.typeck_results().expr_ty(ident2).is_integral();
  42             then {
  43                 if let BinOpKind::Lt = op.node {
  44                     if let BinOpKind::Add = op2.node {
  45                         span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span,
  46                             "you are trying to use classic C overflow conditions that will fail in Rust");
  47                     }
  48                 }
  49                 if let BinOpKind::Gt = op.node {
  50                     if let BinOpKind::Sub = op2.node {
  51                         span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span,
  52                             "you are trying to use classic C underflow conditions that will fail in Rust");
  53                     }
  54                 }
  55             }
  56         }
  57
  58         if_chain! {
  59             if let ExprKind::Binary(ref op, first, second) = expr.kind;
  60             if let ExprKind::Binary(ref op2, ident1, ident2) = second.kind;
  61             if let ExprKind::Path(QPath::Resolved(_, path1)) = ident1.kind;
  62             if let ExprKind::Path(QPath::Resolved(_, path2)) = ident2.kind;
  63             if let ExprKind::Path(QPath::Resolved(_, path3)) = first.kind;
  64             if eq(&path1.segments[0], &path3.segments[0]) || eq(&path2.segments[0], &path3.segments[0]);
  65             if cx.typeck_results().expr_ty(ident1).is_integral();
  66             if cx.typeck_results().expr_ty(ident2).is_integral();
  67             then {
  68                 if let BinOpKind::Gt = op.node {
  69                     if let BinOpKind::Add = op2.node {
  70                         span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span,
  71                             "you are trying to use classic C overflow conditions that will fail in Rust");
  72                     }
  73                 }
  74                 if let BinOpKind::Lt = op.node {
  75                     if let BinOpKind::Sub = op2.node {
  76                         span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span,
  77                             "you are trying to use classic C underflow conditions that will fail in Rust");
  78                     }
  79                 }
  80             }
  81         }
  82     }
  83 }