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use consts::{constant_simple, Constant};
use rustc::lint::*;
use rustc::hir::*;
use syntax::codemap::Span;
use utils::{span_lint, snippet, in_macro};
use rustc_const_math::ConstInt;
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(v @ Constant::Int(_)) = constant_simple(e) {
if match m {
0 => v == Constant::Int(ConstInt::Infer(0)),
-1 => v == Constant::Int(ConstInt::InferSigned(-1)),
1 => v == Constant::Int(ConstInt::Infer(1)),
_ => unreachable!(),
} {
span_lint(cx,
IDENTITY_OP,
span,
&format!("the operation is ineffective. Consider reducing it to `{}`",
snippet(cx, arg, "..")));
}
}
}