rust-clippy/clippy_lints/src/identity_op.rs
2017-10-14 12:21:23 +03:00

97 lines
2.9 KiB
Rust

use consts::{constant_simple, Constant};
use rustc::hir::*;
use rustc::lint::*;
use rustc_const_math::ConstInt;
use syntax::codemap::Span;
use utils::{in_macro, snippet, span_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
/// x / 1 + 0 * 1 - 0 | 0
/// ```
declare_lint! {
pub IDENTITY_OP,
Warn,
"using identity operations, e.g. `x + 0` or `y / 1`"
}
#[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) {
return;
}
if let ExprBinary(ref cmp, ref left, ref right) = e.node {
match cmp.node {
BiAdd | BiBitOr | BiBitXor => {
check(cx, left, 0, e.span, right.span);
check(cx, right, 0, e.span, left.span);
},
BiShl | BiShr | BiSub => check(cx, right, 0, e.span, left.span),
BiMul => {
check(cx, left, 1, e.span, right.span);
check(cx, right, 1, e.span, left.span);
},
BiDiv => check(cx, right, 1, e.span, left.span),
BiBitAnd => {
check(cx, left, -1, e.span, right.span);
check(cx, right, -1, e.span, left.span);
},
_ => (),
}
}
}
}
fn no_zeros(v: &ConstInt) -> bool {
match *v {
ConstInt::I8(i) => i.count_zeros() == 0,
ConstInt::I16(i) => i.count_zeros() == 0,
ConstInt::I32(i) => i.count_zeros() == 0,
ConstInt::I64(i) => i.count_zeros() == 0,
ConstInt::I128(i) => i.count_zeros() == 0,
ConstInt::U8(i) => i.count_zeros() == 0,
ConstInt::U16(i) => i.count_zeros() == 0,
ConstInt::U32(i) => i.count_zeros() == 0,
ConstInt::U64(i) => i.count_zeros() == 0,
ConstInt::U128(i) => i.count_zeros() == 0,
_ => false
}
}
#[allow(cast_possible_wrap)]
fn check(cx: &LateContext, e: &Expr, m: i8, span: Span, arg: Span) {
if let Some(Constant::Int(v)) = constant_simple(cx, e) {
if match m {
0 => v.to_u128_unchecked() == 0,
-1 => no_zeros(&v),
1 => v.to_u128_unchecked() == 1,
_ => unreachable!(),
} {
span_lint(
cx,
IDENTITY_OP,
span,
&format!(
"the operation is ineffective. Consider reducing it to `{}`",
snippet(cx, arg, "..")
),
);
}
}
}