identity_op lint fix for '&' with unsigned types

Author: Yury Krivopalov

clippy_lints/src/identity_op.rs

@@ -1,9 +1,9 @@
 use consts::{constant_simple, Constant};
-use rustc::lint::*;
 use rustc::hir::*;
+use rustc::lint::*;
+use rustc_const_math::ConstInt;
 use syntax::codemap::Span;
 use utils::{in_macro, snippet, span_lint};
-use syntax::attr::IntType::{SignedInt, UnsignedInt};
 
 /// **What it does:** Checks for identity operations, e.g. `x + 0`.
 ///
@@ -58,15 +58,28 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for IdentityOp {
     }
 }
 
+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 => match v.int_type() {
-                SignedInt(_) => (v.to_u128_unchecked() as i128 == -1),
-                UnsignedInt(_) => false,
-            },
+            -1 => no_zeros(&v),
             1 => v.to_u128_unchecked() == 1,
             _ => unreachable!(),
         } {

tests/ui/identity_op.rs

@@ -27,4 +27,7 @@ fn main() {
 
     x & NEG_ONE;  //no error, as we skip lookups (for now)
     -1 & x;
+
+    let u : u8 = 0;
+    u & 255;
 }

tests/ui/identity_op.stderr

@@ -42,3 +42,9 @@ error: the operation is ineffective. Consider reducing it to `x`
 29 |     -1 & x;
    |     ^^^^^^
 
+error: the operation is ineffective. Consider reducing it to `u`
+  --> $DIR/identity_op.rs:32:5
+   |
+32 |     u & 255;
+   |     ^^^^^^^
+