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use clippy_utils::diagnostics::span_lint;
use clippy_utils::SpanlessEq;
use if_chain::if_chain;
use rustc_hir::{BinOpKind, Expr, ExprKind, QPath};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
declare_clippy_lint! {
/// **What it does:** Detects classic underflow/overflow checks.
///
/// **Why is this bad?** Most classic C underflow/overflow checks will fail in
/// Rust. Users can use functions like `overflowing_*` and `wrapping_*` instead.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// # let a = 1;
/// # let b = 2;
/// a + b < a;
/// ```
pub OVERFLOW_CHECK_CONDITIONAL,
complexity,
"overflow checks inspired by C which are likely to panic"
}
declare_lint_pass!(OverflowCheckConditional => [OVERFLOW_CHECK_CONDITIONAL]);
impl<'tcx> LateLintPass<'tcx> for OverflowCheckConditional {
// a + b < a, a > a + b, a < a - b, a - b > a
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
let eq = |l, r| SpanlessEq::new(cx).eq_path_segment(l, r);
if_chain! {
if let ExprKind::Binary(ref op, first, second) = expr.kind;
if let ExprKind::Binary(ref op2, ident1, ident2) = first.kind;
if let ExprKind::Path(QPath::Resolved(_, path1)) = ident1.kind;
if let ExprKind::Path(QPath::Resolved(_, path2)) = ident2.kind;
if let ExprKind::Path(QPath::Resolved(_, path3)) = second.kind;
if eq(&path1.segments[0], &path3.segments[0]) || eq(&path2.segments[0], &path3.segments[0]);
if cx.typeck_results().expr_ty(ident1).is_integral();
if cx.typeck_results().expr_ty(ident2).is_integral();
then {
if let BinOpKind::Lt = op.node {
if let BinOpKind::Add = op2.node {
span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span,
"you are trying to use classic C overflow conditions that will fail in Rust");
}
}
if let BinOpKind::Gt = op.node {
if let BinOpKind::Sub = op2.node {
span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span,
"you are trying to use classic C underflow conditions that will fail in Rust");
}
}
}
}
if_chain! {
if let ExprKind::Binary(ref op, first, second) = expr.kind;
if let ExprKind::Binary(ref op2, ident1, ident2) = second.kind;
if let ExprKind::Path(QPath::Resolved(_, path1)) = ident1.kind;
if let ExprKind::Path(QPath::Resolved(_, path2)) = ident2.kind;
if let ExprKind::Path(QPath::Resolved(_, path3)) = first.kind;
if eq(&path1.segments[0], &path3.segments[0]) || eq(&path2.segments[0], &path3.segments[0]);
if cx.typeck_results().expr_ty(ident1).is_integral();
if cx.typeck_results().expr_ty(ident2).is_integral();
then {
if let BinOpKind::Gt = op.node {
if let BinOpKind::Add = op2.node {
span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span,
"you are trying to use classic C overflow conditions that will fail in Rust");
}
}
if let BinOpKind::Lt = op.node {
if let BinOpKind::Sub = op2.node {
span_lint(cx, OVERFLOW_CHECK_CONDITIONAL, expr.span,
"you are trying to use classic C underflow conditions that will fail in Rust");
}
}
}
}
}
}
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