clean-up and add comments

RE: comments: I quickly got lost in all the `op`s and `left`s and
`right`s, so I wrote down them down to help me. I imagine they could be
helpful to the next person that looks at this

Author: ada4a

clippy_lints/src/operators/bit_mask.rs

@@ -15,9 +15,12 @@ pub(super) fn check<'tcx>(
     right: &'tcx Expr<'_>,
 ) {
     if op.is_comparison() {
+        // `<left> <op> <const_right>`
         if let Some(cmp_opt) = fetch_int_literal(cx, right) {
             check_compare(cx, left, op, cmp_opt, e.span);
+        // `<const_left> <op> <right>`
         } else if let Some(cmp_val) = fetch_int_literal(cx, left) {
+            // turn into `<right> <inv(op)> <const_left>`
             check_compare(cx, right, invert_cmp(op), cmp_val, e.span);
         }
     }
@@ -37,13 +40,15 @@ fn invert_cmp(cmp: BinOpKind) -> BinOpKind {
 }
 
 fn check_compare<'a>(cx: &LateContext<'a>, bit_op: &Expr<'a>, cmp_op: BinOpKind, cmp_value: u128, span: Span) {
-    if let ExprKind::Binary(op, left, right) = &bit_op.kind {
-        if op.node != BinOpKind::BitAnd && op.node != BinOpKind::BitOr || is_from_proc_macro(cx, bit_op) {
-            return;
-        }
-        if let Some(mask) = fetch_int_literal(cx, right).or_else(|| fetch_int_literal(cx, left)) {
-            check_bit_mask(cx, op.node, cmp_op, mask, cmp_value, span);
-        }
+    // whether `<bit_op> <cmp_op> <cmp_value>`
+    // is `(<left> <op> <right>) <cmp_op> <cmp_value>`
+    // is `(<masked> <op> <mask>) <cmp_op> <cmp_value>` (either `left` or `right` is the `mask`)
+    if let ExprKind::Binary(op, left, right) = &bit_op.kind
+        && matches!(op.node, BinOpKind::BitAnd | BinOpKind::BitOr)
+        && !is_from_proc_macro(cx, bit_op)
+        && let Some(mask) = fetch_int_literal(cx, right).or_else(|| fetch_int_literal(cx, left))
+    {
+        check_bit_mask(cx, op.node, cmp_op, mask, cmp_value, span);
     }
 }
 

tests/ui/bit_masks.rs

@@ -1,13 +1,10 @@
+#![allow(clippy::identity_op, clippy::no_effect, clippy::unnecessary_operation)]
+
 const THREE_BITS: i64 = 7;
 const EVEN_MORE_REDIRECTION: i64 = THREE_BITS;
 
 #[warn(clippy::bad_bit_mask)]
-#[allow(
-    clippy::ineffective_bit_mask,
-    clippy::identity_op,
-    clippy::no_effect,
-    clippy::unnecessary_operation
-)]
+#[allow(clippy::ineffective_bit_mask)]
 fn main() {
     let x = 5;
 
@@ -68,7 +65,7 @@ fn main() {
 }
 
 #[warn(clippy::ineffective_bit_mask)]
-#[allow(clippy::bad_bit_mask, clippy::no_effect, clippy::unnecessary_operation)]
+#[allow(clippy::bad_bit_mask)]
 fn ineffective() {
     let x = 5;
 

tests/ui/bit_masks.stderr

@@ -1,5 +1,5 @@
 error: &-masking with zero
-  --> tests/ui/bit_masks.rs:14:5
+  --> tests/ui/bit_masks.rs:11:5
    |
 LL |     x & 0 == 0;
    |     ^^^^^^^^^^
@@ -8,81 +8,81 @@ LL |     x & 0 == 0;
    = help: to override `-D warnings` add `#[allow(clippy::bad_bit_mask)]`
 
 error: this operation will always return zero. This is likely not the intended outcome
-  --> tests/ui/bit_masks.rs:14:5
+  --> tests/ui/bit_masks.rs:11:5
    |
 LL |     x & 0 == 0;
    |     ^^^^^
    |
    = note: `#[deny(clippy::erasing_op)]` on by default
 
 error: incompatible bit mask: `_ & 2` can never be equal to `1`
-  --> tests/ui/bit_masks.rs:20:5
+  --> tests/ui/bit_masks.rs:17:5
    |
 LL |     x & 2 == 1;
    |     ^^^^^^^^^^
 
 error: incompatible bit mask: `_ | 3` can never be equal to `2`
-  --> tests/ui/bit_masks.rs:26:5
+  --> tests/ui/bit_masks.rs:23:5
    |
 LL |     x | 3 == 2;
    |     ^^^^^^^^^^
 
 error: incompatible bit mask: `_ & 1` will never be higher than `1`
-  --> tests/ui/bit_masks.rs:29:5
+  --> tests/ui/bit_masks.rs:26:5
    |
 LL |     x & 1 > 1;
    |     ^^^^^^^^^
 
 error: incompatible bit mask: `_ | 2` will always be higher than `1`
-  --> tests/ui/bit_masks.rs:35:5
+  --> tests/ui/bit_masks.rs:32:5
    |
 LL |     x | 2 > 1;
    |     ^^^^^^^^^
 
 error: incompatible bit mask: `_ & 7` can never be equal to `8`
-  --> tests/ui/bit_masks.rs:44:5
+  --> tests/ui/bit_masks.rs:41:5
    |
 LL |     x & THREE_BITS == 8;
    |     ^^^^^^^^^^^^^^^^^^^
 
 error: incompatible bit mask: `_ | 7` will never be lower than `7`
-  --> tests/ui/bit_masks.rs:47:5
+  --> tests/ui/bit_masks.rs:44:5
    |
 LL |     x | EVEN_MORE_REDIRECTION < 7;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: &-masking with zero
-  --> tests/ui/bit_masks.rs:50:5
+  --> tests/ui/bit_masks.rs:47:5
    |
 LL |     0 & x == 0;
    |     ^^^^^^^^^^
 
 error: this operation will always return zero. This is likely not the intended outcome
-  --> tests/ui/bit_masks.rs:50:5
+  --> tests/ui/bit_masks.rs:47:5
    |
 LL |     0 & x == 0;
    |     ^^^^^
 
 error: incompatible bit mask: `_ | 2` will always be higher than `1`
-  --> tests/ui/bit_masks.rs:57:5
+  --> tests/ui/bit_masks.rs:54:5
    |
 LL |     1 < 2 | x;
    |     ^^^^^^^^^
 
 error: incompatible bit mask: `_ | 3` can never be equal to `2`
-  --> tests/ui/bit_masks.rs:60:5
+  --> tests/ui/bit_masks.rs:57:5
    |
 LL |     2 == 3 | x;
    |     ^^^^^^^^^^
 
 error: incompatible bit mask: `_ & 2` can never be equal to `1`
-  --> tests/ui/bit_masks.rs:63:5
+  --> tests/ui/bit_masks.rs:60:5
    |
 LL |     1 == x & 2;
    |     ^^^^^^^^^^
 
 error: ineffective bit mask: `x | 1` compared to `3`, is the same as x compared directly
-  --> tests/ui/bit_masks.rs:75:5
+  --> tests/ui/bit_masks.rs:72:5
    |
 LL |     x | 1 > 3;
    |     ^^^^^^^^^
@@ -91,19 +91,19 @@ LL |     x | 1 > 3;
    = help: to override `-D warnings` add `#[allow(clippy::ineffective_bit_mask)]`
 
 error: ineffective bit mask: `x | 1` compared to `4`, is the same as x compared directly
-  --> tests/ui/bit_masks.rs:78:5
+  --> tests/ui/bit_masks.rs:75:5
    |
 LL |     x | 1 < 4;
    |     ^^^^^^^^^
 
 error: ineffective bit mask: `x | 1` compared to `3`, is the same as x compared directly
-  --> tests/ui/bit_masks.rs:81:5
+  --> tests/ui/bit_masks.rs:78:5
    |
 LL |     x | 1 <= 3;
    |     ^^^^^^^^^^
 
 error: ineffective bit mask: `x | 1` compared to `8`, is the same as x compared directly
-  --> tests/ui/bit_masks.rs:84:5
+  --> tests/ui/bit_masks.rs:81:5
    |
 LL |     x | 1 >= 8;
    |     ^^^^^^^^^^