clippy_lints/src/identity_op.rs

   1 use rustc::hir::*;
   2 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   3 use rustc::ty;
   4 use rustc::{declare_lint_pass, declare_tool_lint};
   5 use syntax::source_map::Span;
   6
   7 use crate::consts::{constant_simple, Constant};
   8 use crate::utils::{clip, in_macro_or_desugar, 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     /// x / 1 + 0 * 1 - 0 | 0
  21     /// ```
  22     pub IDENTITY_OP,
  23     complexity,
  24     "using identity operations, e.g., `x + 0` or `y / 1`"
  25 }
  26
  27 declare_lint_pass!(IdentityOp => [IDENTITY_OP]);
  28
  29 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for IdentityOp {
  30     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
  31         if in_macro_or_desugar(e.span) {
  32             return;
  33         }
  34         if let ExprKind::Binary(ref cmp, ref left, ref right) = e.node {
  35             match cmp.node {
  36                 BinOpKind::Add | BinOpKind::BitOr | BinOpKind::BitXor => {
  37                     check(cx, left, 0, e.span, right.span);
  38                     check(cx, right, 0, e.span, left.span);
  39                 },
  40                 BinOpKind::Shl | BinOpKind::Shr | BinOpKind::Sub => check(cx, right, 0, e.span, left.span),
  41                 BinOpKind::Mul => {
  42                     check(cx, left, 1, e.span, right.span);
  43                     check(cx, right, 1, e.span, left.span);
  44                 },
  45                 BinOpKind::Div => check(cx, right, 1, e.span, left.span),
  46                 BinOpKind::BitAnd => {
  47                     check(cx, left, -1, e.span, right.span);
  48                     check(cx, right, -1, e.span, left.span);
  49                 },
  50                 _ => (),
  51             }
  52         }
  53     }
  54 }
  55
  56 #[allow(clippy::cast_possible_wrap)]
  57 fn check(cx: &LateContext<'_, '_>, e: &Expr, m: i8, span: Span, arg: Span) {
  58     if let Some(Constant::Int(v)) = constant_simple(cx, cx.tables, e) {
  59         let check = match cx.tables.expr_ty(e).sty {
  60             ty::Int(ity) => unsext(cx.tcx, -1_i128, ity),
  61             ty::Uint(uty) => clip(cx.tcx, !0, uty),
  62             _ => return,
  63         };
  64         if match m {
  65             0 => v == 0,
  66             -1 => v == check,
  67             1 => v == 1,
  68             _ => unreachable!(),
  69         } {
  70             span_lint(
  71                 cx,
  72                 IDENTITY_OP,
  73                 span,
  74                 &format!(
  75                     "the operation is ineffective. Consider reducing it to `{}`",
  76                     snippet(cx, arg, "..")
  77                 ),
  78             );
  79         }
  80     }
  81 }