rust-clippy/clippy_lints/src/identity_op.rs

88 lines
2.7 KiB
Rust
Raw Normal View History

2018-05-30 08:15:50 +00:00
use crate::consts::{constant_simple, Constant};
use rustc::hir::*;
2018-08-28 11:13:42 +00:00
use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
2018-07-29 09:04:40 +00:00
use rustc::{declare_tool_lint, lint_array};
use syntax::source_map::Span;
2018-05-30 08:15:50 +00:00
use crate::utils::{in_macro, snippet, span_lint, unsext, clip};
2018-03-13 10:38:11 +00:00
use rustc::ty;
/// **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.
///
2016-07-15 22:25:44 +00:00
/// **Example:**
/// ```rust
/// x / 1 + 0 * 1 - 0 | 0
/// ```
2018-03-28 13:24:26 +00:00
declare_clippy_lint! {
pub IDENTITY_OP,
2018-03-28 13:24:26 +00:00
complexity,
"using identity operations, e.g. `x + 0` or `y / 1`"
}
2017-08-09 07:30:56 +00:00
#[derive(Copy, Clone)]
pub struct IdentityOp;
impl LintPass for IdentityOp {
fn get_lints(&self) -> LintArray {
lint_array!(IDENTITY_OP)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for IdentityOp {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
if in_macro(e.span) {
2016-01-04 04:26:12 +00:00
return;
}
2018-07-12 07:30:57 +00:00
if let ExprKind::Binary(ref cmp, ref left, ref right) = e.node {
match cmp.node {
2018-07-12 07:50:09 +00:00
BinOpKind::Add | BinOpKind::BitOr | BinOpKind::BitXor => {
check(cx, left, 0, e.span, right.span);
check(cx, right, 0, e.span, left.span);
2016-12-20 17:21:30 +00:00
},
2018-07-12 07:50:09 +00:00
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);
2016-12-20 17:21:30 +00:00
},
2018-07-12 07:50:09 +00:00
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);
2016-12-20 17:21:30 +00:00
},
2016-01-04 04:26:12 +00:00
_ => (),
}
}
}
}
2017-06-11 04:46:26 +00:00
#[allow(cast_possible_wrap)]
2018-07-23 11:01:12 +00:00
fn check(cx: &LateContext<'_, '_>, e: &Expr, m: i8, span: Span, arg: Span) {
2018-05-13 11:16:31 +00:00
if let Some(Constant::Int(v)) = constant_simple(cx, cx.tables, e) {
2018-03-13 10:38:11 +00:00
let check = match cx.tables.expr_ty(e).sty {
ty::Int(ity) => unsext(cx.tcx, -1_i128, ity),
ty::Uint(uty) => clip(cx.tcx, !0, uty),
2018-03-13 10:38:11 +00:00
_ => return,
};
2015-09-06 08:53:55 +00:00
if match m {
2018-03-13 10:38:11 +00:00
0 => v == 0,
-1 => v == check,
1 => v == 1,
2015-09-06 08:53:55 +00:00
_ => unreachable!(),
2017-09-05 09:33:04 +00:00
} {
2017-08-09 07:30:56 +00:00
span_lint(
cx,
IDENTITY_OP,
span,
&format!(
"the operation is ineffective. Consider reducing it to `{}`",
snippet(cx, arg, "..")
),
);
}
}
}