clippy_lints/src/overflow_check_conditional.rs

   1 // Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution.
   3 //
   4 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   5 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   6 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   7 // option. This file may not be copied, modified, or distributed
   8 // except according to those terms.
   9
  10 use crate::utils::{span_lint, SpanlessEq};
  11 use if_chain::if_chain;
  12 use rustc::hir::*;
  13 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
  14 use rustc::{declare_tool_lint, lint_array};
  15
  16 /// **What it does:** Detects classic underflow/overflow checks.
  17 ///
  18 /// **Why is this bad?** Most classic C underflow/overflow checks will fail in
  19 /// Rust. Users can use functions like `overflowing_*` and `wrapping_*` instead.
  20 ///
  21 /// **Known problems:** None.
  22 ///
  23 /// **Example:**
  24 /// ```rust
  25 /// a + b < a
  26 /// ```
  27 declare_clippy_lint! {
  28     pub OVERFLOW_CHECK_CONDITIONAL,
  29     complexity,
  30     "overflow checks inspired by C which are likely to panic"
  31 }
  32
  33 #[derive(Copy, Clone)]
  34 pub struct OverflowCheckConditional;
  35
  36 impl LintPass for OverflowCheckConditional {
  37     fn get_lints(&self) -> LintArray {
  38         lint_array!(OVERFLOW_CHECK_CONDITIONAL)
  39     }
  40 }
  41
  42 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for OverflowCheckConditional {
  43     // a + b < a, a > a + b, a < a - b, a - b > a
  44     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  45         let eq = |l, r| SpanlessEq::new(cx).eq_path_segment(l, r);
  46         if_chain! {
  47             if let ExprKind::Binary(ref op, ref first, ref second) = expr.node;
  48             if let ExprKind::Binary(ref op2, ref ident1, ref ident2) = first.node;
  49             if let ExprKind::Path(QPath::Resolved(_, ref path1)) = ident1.node;
  50             if let ExprKind::Path(QPath::Resolved(_, ref path2)) = ident2.node;
  51             if let ExprKind::Path(QPath::Resolved(_, ref path3)) = second.node;
  52             if eq(&path1.segments[0], &path3.segments[0]) || eq(&path2.segments[0], &path3.segments[0]);
  53             if cx.tables.expr_ty(ident1).is_integral();
  54             if cx.tables.expr_ty(ident2).is_integral();
  55             then {
  56                 if let BinOpKind::Lt = op.node {
  57                     if let BinOpKind::Add = op2.node {
  58                         span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span,
  59                             "You are trying to use classic C overflow conditions that will fail in Rust.");
  60                     }
  61                 }
  62                 if let BinOpKind::Gt = op.node {
  63                     if let BinOpKind::Sub = op2.node {
  64                         span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span,
  65                             "You are trying to use classic C underflow conditions that will fail in Rust.");
  66                     }
  67                 }
  68             }
  69         }
  70
  71         if_chain! {
  72             if let ExprKind::Binary(ref op, ref first, ref second) = expr.node;
  73             if let ExprKind::Binary(ref op2, ref ident1, ref ident2) = second.node;
  74             if let ExprKind::Path(QPath::Resolved(_, ref path1)) = ident1.node;
  75             if let ExprKind::Path(QPath::Resolved(_, ref path2)) = ident2.node;
  76             if let ExprKind::Path(QPath::Resolved(_, ref path3)) = first.node;
  77             if eq(&path1.segments[0], &path3.segments[0]) || eq(&path2.segments[0], &path3.segments[0]);
  78             if cx.tables.expr_ty(ident1).is_integral();
  79             if cx.tables.expr_ty(ident2).is_integral();
  80             then {
  81                 if let BinOpKind::Gt = op.node {
  82                     if let BinOpKind::Add = op2.node {
  83                         span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span,
  84                             "You are trying to use classic C overflow conditions that will fail in Rust.");
  85                     }
  86                 }
  87                 if let BinOpKind::Lt = op.node {
  88                     if let BinOpKind::Sub = op2.node {
  89                         span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span,
  90                             "You are trying to use classic C underflow conditions that will fail in Rust.");
  91                     }
  92                 }
  93             }
  94         }
  95     }
  96 }