use clippy_utils::consts::{self, Constant};
-use clippy_utils::diagnostics::span_lint;
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::source::snippet_with_applicability;
use if_chain::if_chain;
+use rustc_errors::Applicability;
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;
declare_clippy_lint! {
- /// **What it does:** Checks for multiplication by -1 as a form of negation.
+ /// ### What it does
+ /// Checks for multiplication by -1 as a form of negation.
///
- /// **Why is this bad?** It's more readable to just negate.
+ /// ### Why is this bad?
+ /// It's more readable to just negate.
///
- /// **Known problems:** This only catches integers (for now).
+ /// ### Known problems
+ /// This only catches integers (for now).
///
- /// **Example:**
+ /// ### Example
/// ```ignore
- /// x * -1
+ /// // Bad
+ /// let a = x * -1;
+ ///
+ /// // Good
+ /// let b = -x;
/// ```
+ #[clippy::version = "pre 1.29.0"]
pub NEG_MULTIPLY,
style,
- "multiplying integers with `-1`"
+ "multiplying integers by `-1`"
}
declare_lint_pass!(NegMultiply => [NEG_MULTIPLY]);
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.typeck_results().expr_ty_opt(lit));
+ if consts::lit_to_constant(&l.node, cx.typeck_results().expr_ty_opt(lit)) == Constant::Int(1);
if cx.typeck_results().expr_ty(exp).is_integral();
+
then {
- span_lint(cx, NEG_MULTIPLY, span, "negation by multiplying with `-1`");
+ 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,
+ );
}
}
}