src/tools/clippy/clippy_lints/src/identity_op.rs

   1 use rustc_hir::{BinOpKind, Expr, ExprKind};
   2 use rustc_lint::{LateContext, LateLintPass};
   3 use rustc_middle::ty;
   4 use rustc_session::{declare_lint_pass, declare_tool_lint};
   5 use rustc_span::source_map::Span;
   6
   7 use crate::consts::{constant_simple, Constant};
   8 use crate::utils::{clip, snippet, span_lint, unsext};
   9
  10 declare_clippy_lint! {
  11     /// **What it does:** Checks for identity operations, e.g., `x + 0`.
  12     ///
  13     /// **Why is this bad?** This code can be removed without changing the
  14     /// meaning. So it just obscures what's going on. Delete it mercilessly.
  15     ///
  16     /// **Known problems:** None.
  17     ///
  18     /// **Example:**
  19     /// ```rust
  20     /// # let x = 1;
  21     /// x / 1 + 0 * 1 - 0 | 0;
  22     /// ```
  23     pub IDENTITY_OP,
  24     complexity,
  25     "using identity operations, e.g., `x + 0` or `y / 1`"
  26 }
  27
  28 declare_lint_pass!(IdentityOp => [IDENTITY_OP]);
  29
  30 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for IdentityOp {
  31     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr<'_>) {
  32         if e.span.from_expansion() {
  33             return;
  34         }
  35         if let ExprKind::Binary(ref cmp, ref left, ref right) = e.kind {
  36             match cmp.node {
  37                 BinOpKind::Add | BinOpKind::BitOr | BinOpKind::BitXor => {
  38                     check(cx, left, 0, e.span, right.span);
  39                     check(cx, right, 0, e.span, left.span);
  40                 },
  41                 BinOpKind::Shl | BinOpKind::Shr | BinOpKind::Sub => check(cx, right, 0, e.span, left.span),
  42                 BinOpKind::Mul => {
  43                     check(cx, left, 1, e.span, right.span);
  44                     check(cx, right, 1, e.span, left.span);
  45                 },
  46                 BinOpKind::Div => check(cx, right, 1, e.span, left.span),
  47                 BinOpKind::BitAnd => {
  48                     check(cx, left, -1, e.span, right.span);
  49                     check(cx, right, -1, e.span, left.span);
  50                 },
  51                 _ => (),
  52             }
  53         }
  54     }
  55 }
  56
  57 #[allow(clippy::cast_possible_wrap)]
  58 fn check(cx: &LateContext<'_, '_>, e: &Expr<'_>, m: i8, span: Span, arg: Span) {
  59     if let Some(Constant::Int(v)) = constant_simple(cx, cx.tables, e) {
  60         let check = match cx.tables.expr_ty(e).kind {
  61             ty::Int(ity) => unsext(cx.tcx, -1_i128, ity),
  62             ty::Uint(uty) => clip(cx.tcx, !0, uty),
  63             _ => return,
  64         };
  65         if match m {
  66             0 => v == 0,
  67             -1 => v == check,
  68             1 => v == 1,
  69             _ => unreachable!(),
  70         } {
  71             span_lint(
  72                 cx,
  73                 IDENTITY_OP,
  74                 span,
  75                 &format!(
  76                     "the operation is ineffective. Consider reducing it to `{}`",
  77                     snippet(cx, arg, "..")
  78                 ),
  79             );
  80         }
  81     }
  82 }