| use if_chain::if_chain; |
| use rustc_hir::{BinOp, BinOpKind, Expr, ExprKind}; |
| use rustc_lint::{LateContext, LateLintPass}; |
| use rustc_middle::ty; |
| use rustc_session::{declare_lint_pass, declare_tool_lint}; |
| use rustc_span::source_map::Span; |
| |
| use crate::consts::{constant_simple, Constant}; |
| use crate::utils::{clip, snippet, span_lint, unsext}; |
| |
| declare_clippy_lint! { |
| /// **What it does:** Checks for identity operations, e.g., `x + 0`. |
| /// |
| /// **Why is this bad?** This code can be removed without changing the |
| /// meaning. So it just obscures what's going on. Delete it mercilessly. |
| /// |
| /// **Known problems:** None. |
| /// |
| /// **Example:** |
| /// ```rust |
| /// # let x = 1; |
| /// x / 1 + 0 * 1 - 0 | 0; |
| /// ``` |
| pub IDENTITY_OP, |
| complexity, |
| "using identity operations, e.g., `x + 0` or `y / 1`" |
| } |
| |
| declare_lint_pass!(IdentityOp => [IDENTITY_OP]); |
| |
| impl<'tcx> LateLintPass<'tcx> for IdentityOp { |
| fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) { |
| if e.span.from_expansion() { |
| return; |
| } |
| if let ExprKind::Binary(cmp, ref left, ref right) = e.kind { |
| if is_allowed(cx, cmp, left, right) { |
| return; |
| } |
| match cmp.node { |
| BinOpKind::Add | BinOpKind::BitOr | BinOpKind::BitXor => { |
| check(cx, left, 0, e.span, right.span); |
| check(cx, right, 0, e.span, left.span); |
| }, |
| BinOpKind::Shl | BinOpKind::Shr | BinOpKind::Sub => check(cx, right, 0, e.span, left.span), |
| BinOpKind::Mul => { |
| check(cx, left, 1, e.span, right.span); |
| check(cx, right, 1, e.span, left.span); |
| }, |
| BinOpKind::Div => check(cx, right, 1, e.span, left.span), |
| BinOpKind::BitAnd => { |
| check(cx, left, -1, e.span, right.span); |
| check(cx, right, -1, e.span, left.span); |
| }, |
| _ => (), |
| } |
| } |
| } |
| } |
| |
| fn is_allowed(cx: &LateContext<'_>, cmp: BinOp, left: &Expr<'_>, right: &Expr<'_>) -> bool { |
| // `1 << 0` is a common pattern in bit manipulation code |
| if_chain! { |
| if let BinOpKind::Shl = cmp.node; |
| if let Some(Constant::Int(0)) = constant_simple(cx, cx.tables(), right); |
| if let Some(Constant::Int(1)) = constant_simple(cx, cx.tables(), left); |
| then { |
| return true; |
| } |
| } |
| |
| false |
| } |
| |
| #[allow(clippy::cast_possible_wrap)] |
| fn check(cx: &LateContext<'_>, e: &Expr<'_>, m: i8, span: Span, arg: Span) { |
| if let Some(Constant::Int(v)) = constant_simple(cx, cx.tables(), e) { |
| let check = match cx.tables().expr_ty(e).kind { |
| ty::Int(ity) => unsext(cx.tcx, -1_i128, ity), |
| ty::Uint(uty) => clip(cx.tcx, !0, uty), |
| _ => return, |
| }; |
| if match m { |
| 0 => v == 0, |
| -1 => v == check, |
| 1 => v == 1, |
| _ => unreachable!(), |
| } { |
| span_lint( |
| cx, |
| IDENTITY_OP, |
| span, |
| &format!( |
| "the operation is ineffective. Consider reducing it to `{}`", |
| snippet(cx, arg, "..") |
| ), |
| ); |
| } |
| } |
| } |