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
  11 use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
  12 use crate::rustc::{declare_tool_lint, lint_array};
  13 use if_chain::if_chain;
  14 use crate::rustc::hir::*;
  15 use crate::utils::{span_lint, SpanlessEq};
  16
  17 /// **What it does:** Detects classic underflow/overflow checks.
  18 ///
  19 /// **Why is this bad?** Most classic C underflow/overflow checks will fail in
  20 /// Rust. Users can use functions like `overflowing_*` and `wrapping_*` instead.
  21 ///
  22 /// **Known problems:** None.
  23 ///
  24 /// **Example:**
  25 /// ```rust
  26 /// a + b < a
  27 /// ```
  28 declare_clippy_lint! {
  29     pub OVERFLOW_CHECK_CONDITIONAL,
  30     complexity,
  31     "overflow checks inspired by C which are likely to panic"
  32 }
  33
  34 #[derive(Copy, Clone)]
  35 pub struct OverflowCheckConditional;
  36
  37 impl LintPass for OverflowCheckConditional {
  38     fn get_lints(&self) -> LintArray {
  39         lint_array!(OVERFLOW_CHECK_CONDITIONAL)
  40     }
  41 }
  42
  43 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for OverflowCheckConditional {
  44     // a + b < a, a > a + b, a < a - b, a - b > a
  45     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  46         let eq = |l, r| SpanlessEq::new(cx).eq_path_segment(l, r);
  47         if_chain! {
  48             if let ExprKind::Binary(ref op, ref first, ref second) = expr.node;
  49             if let ExprKind::Binary(ref op2, ref ident1, ref ident2) = first.node;
  50             if let ExprKind::Path(QPath::Resolved(_, ref path1)) = ident1.node;
  51             if let ExprKind::Path(QPath::Resolved(_, ref path2)) = ident2.node;
  52             if let ExprKind::Path(QPath::Resolved(_, ref path3)) = second.node;
  53             if eq(&path1.segments[0], &path3.segments[0]) || eq(&path2.segments[0], &path3.segments[0]);
  54             if cx.tables.expr_ty(ident1).is_integral();
  55             if cx.tables.expr_ty(ident2).is_integral();
  56             then {
  57                 if let BinOpKind::Lt = op.node {
  58                     if let BinOpKind::Add = op2.node {
  59                         span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span,
  60                             "You are trying to use classic C overflow conditions that will fail in Rust.");
  61                     }
  62                 }
  63                 if let BinOpKind::Gt = op.node {
  64                     if let BinOpKind::Sub = op2.node {
  65                         span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span,
  66                             "You are trying to use classic C underflow conditions that will fail in Rust.");
  67                     }
  68                 }
  69             }
  70         }
  71
  72         if_chain! {
  73             if let ExprKind::Binary(ref op, ref first, ref second) = expr.node;
  74             if let ExprKind::Binary(ref op2, ref ident1, ref ident2) = second.node;
  75             if let ExprKind::Path(QPath::Resolved(_, ref path1)) = ident1.node;
  76             if let ExprKind::Path(QPath::Resolved(_, ref path2)) = ident2.node;
  77             if let ExprKind::Path(QPath::Resolved(_, ref path3)) = first.node;
  78             if eq(&path1.segments[0], &path3.segments[0]) || eq(&path2.segments[0], &path3.segments[0]);
  79             if cx.tables.expr_ty(ident1).is_integral();
  80             if cx.tables.expr_ty(ident2).is_integral();
  81             then {
  82                 if let BinOpKind::Gt = op.node {
  83                     if let BinOpKind::Add = op2.node {
  84                         span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span,
  85                             "You are trying to use classic C overflow conditions that will fail in Rust.");
  86                     }
  87                 }
  88                 if let BinOpKind::Lt = op.node {
  89                     if let BinOpKind::Sub = op2.node {
  90                         span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span,
  91                             "You are trying to use classic C underflow conditions that will fail in Rust.");
  92                     }
  93                 }
  94             }
  95         }
  96     }
  97 }