rust-clippy/clippy_lints/src/identity_op.rs
Oliver Schneider 7bfa53f504 Almost there
2017-03-01 18:46:18 +01:00

80 lines
2.5 KiB
Rust

use consts::{constant_simple, Constant};
use rustc::lint::*;
use rustc::hir::*;
use syntax::codemap::Span;
use utils::{span_lint, snippet, in_macro};
use syntax::attr::IntType::{SignedInt, UnsignedInt};
/// **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(cx, 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 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 => match v.int_type() {
SignedInt(_) => (v.to_u128_unchecked() as i128 == -1),
UnsignedInt(_) => false
},
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, "..")));
}
}
}