rust-clippy/clippy_lints/src/neg_multiply.rs
2020-02-21 11:14:18 +01:00

53 lines
1.8 KiB
Rust

use if_chain::if_chain;
use rustc_hir::{BinOpKind, Expr, ExprKind, UnOp};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::source_map::Span;
use crate::consts::{self, Constant};
use crate::utils::span_lint;
declare_clippy_lint! {
/// **What it does:** Checks for multiplication by -1 as a form of negation.
///
/// **Why is this bad?** It's more readable to just negate.
///
/// **Known problems:** This only catches integers (for now).
///
/// **Example:**
/// ```ignore
/// x * -1
/// ```
pub NEG_MULTIPLY,
style,
"multiplying integers with `-1`"
}
declare_lint_pass!(NegMultiply => [NEG_MULTIPLY]);
#[allow(clippy::match_same_arms)]
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NegMultiply {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr<'_>) {
if let ExprKind::Binary(ref op, ref left, ref right) = e.kind {
if BinOpKind::Mul == op.node {
match (&left.kind, &right.kind) {
(&ExprKind::Unary(..), &ExprKind::Unary(..)) => {},
(&ExprKind::Unary(UnOp::UnNeg, ref lit), _) => check_mul(cx, e.span, lit, right),
(_, &ExprKind::Unary(UnOp::UnNeg, ref lit)) => check_mul(cx, e.span, lit, left),
_ => {},
}
}
}
}
}
fn check_mul(cx: &LateContext<'_, '_>, span: Span, lit: &Expr<'_>, exp: &Expr<'_>) {
if_chain! {
if let ExprKind::Lit(ref l) = lit.kind;
if let Constant::Int(1) = consts::lit_to_constant(&l.node, cx.tables.expr_ty_opt(lit));
if cx.tables.expr_ty(exp).is_integral();
then {
span_lint(cx, NEG_MULTIPLY, span, "Negation by multiplying with `-1`");
}
}
}