fixed bad_bit_mask false positive

README.md

@@ -9,7 +9,7 @@ There are 55 lints included in this crate:
 name                                                                                                 | default | meaning
 -----------------------------------------------------------------------------------------------------|---------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 [approx_constant](https://github.com/Manishearth/rust-clippy/wiki#approx_constant)                   | warn    | the approximate of a known float constant (in `std::f64::consts` or `std::f32::consts`) is found; suggests to use the constant
-[bad_bit_mask](https://github.com/Manishearth/rust-clippy/wiki#bad_bit_mask)                         | deny    | expressions of the form `_ & mask == select` that will only ever return `true` or `false` (because in the example `select` containing bits that `mask` doesn't have)
+[bad_bit_mask](https://github.com/Manishearth/rust-clippy/wiki#bad_bit_mask)                         | warn    | expressions of the form `_ & mask == select` that will only ever return `true` or `false` (because in the example `select` containing bits that `mask` doesn't have)
 [box_vec](https://github.com/Manishearth/rust-clippy/wiki#box_vec)                                   | warn    | usage of `Box<Vec<T>>`, vector elements are already on the heap
 [cast_possible_truncation](https://github.com/Manishearth/rust-clippy/wiki#cast_possible_truncation) | allow   | casts that may cause truncation of the value, e.g `x as u8` where `x: u32`, or `x as i32` where `x: f32`
 [cast_possible_wrap](https://github.com/Manishearth/rust-clippy/wiki#cast_possible_wrap)             | allow   | casts that may cause wrapping around the value, e.g `x as i32` where `x: u32` and `x > i32::MAX`

src/bit_mask.rs

@@ -9,7 +9,7 @@ use utils::span_lint;
 
 declare_lint! {
     pub BAD_BIT_MASK,
-    Deny,
+    Warn,
     "expressions of the form `_ & mask == select` that will only ever return `true` or `false` \
      (because in the example `select` containing bits that `mask` doesn't have)"
 }
@@ -98,7 +98,7 @@ fn check_bit_mask(cx: &Context, bit_op: BinOp_, cmp_op: BinOp_,
                   mask_value: u64, cmp_value: u64, span: &Span) {
     match cmp_op {
         BiEq | BiNe => match bit_op {
-            BiBitAnd => if mask_value & cmp_value != mask_value {
+            BiBitAnd => if mask_value & cmp_value != cmp_value {
                 if cmp_value != 0 {
                     span_lint(cx, BAD_BIT_MASK, *span, &format!(
                         "incompatible bit mask: `_ & {}` can never be equal to `{}`",

tests/compile-fail/bit_masks.rs

@@ -25,6 +25,9 @@ fn main() {
     x | 2 > 1; //~ERROR incompatible bit mask
     x | 2 <= 2; // ok (if a bit silly), equals x <= 2
 
+    x & 192 == 128; // ok, tests for bit 7 and not bit 6
+    x & 0xffc0 == 0xfe80; // ok
+    
     // this also now works with constants
     x & THREE_BITS == 8; //~ERROR incompatible bit mask
     x | EVEN_MORE_REDIRECTION < 7; //~ERROR incompatible bit mask