rust-clippy/clippy_lints/src/neg_multiply.rs

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use clippy_utils::consts::{self, Constant};
use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::source::snippet_with_applicability;
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use if_chain::if_chain;
use rustc_errors::Applicability;
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use rustc_hir::{BinOpKind, Expr, ExprKind, UnOp};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::source_map::Span;
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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
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/// ```ignore
/// // Bad
/// let a = x * -1;
///
/// // Good
/// let b = -x;
/// ```
#[clippy::version = "pre 1.29.0"]
pub NEG_MULTIPLY,
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style,
"multiplying integers by `-1`"
}
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declare_lint_pass!(NegMultiply => [NEG_MULTIPLY]);
impl<'tcx> LateLintPass<'tcx> for NegMultiply {
fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
if let ExprKind::Binary(ref op, left, right) = e.kind {
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if BinOpKind::Mul == op.node {
match (&left.kind, &right.kind) {
(&ExprKind::Unary(..), &ExprKind::Unary(..)) => {},
(&ExprKind::Unary(UnOp::Neg, lit), _) => check_mul(cx, e.span, lit, right),
(_, &ExprKind::Unary(UnOp::Neg, lit)) => check_mul(cx, e.span, lit, left),
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_ => {},
}
}
}
}
}
fn check_mul(cx: &LateContext<'_>, span: Span, lit: &Expr<'_>, exp: &Expr<'_>) {
if_chain! {
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if let ExprKind::Lit(ref l) = lit.kind;
if consts::lit_to_mir_constant(&l.node, cx.typeck_results().expr_ty_opt(lit)) == Constant::Int(1);
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if cx.typeck_results().expr_ty(exp).is_integral();
then {
let mut applicability = Applicability::MachineApplicable;
let suggestion = format!("-{}", snippet_with_applicability(cx, exp.span, "..", &mut applicability));
span_lint_and_sugg(
cx,
NEG_MULTIPLY,
span,
"this multiplication by -1 can be written more succinctly",
"consider using",
suggestion,
applicability,
);
}
}
}