Safer addition in computing length of bounds

If the `usize` is `128`, then this would have failed for (0..=u128::MAX).
We now just ignore this case.

clippy_lints/src/methods/map_with_unused_argument_over_ranges.rs

@@ -33,7 +33,7 @@ fn extract_count_with_applicability(
             let count = if upper_bound >= lower_bound {
                 match range.limits {
                     RangeLimits::HalfOpen => upper_bound - lower_bound,
-                    RangeLimits::Closed => upper_bound - lower_bound + 1,
+                    RangeLimits::Closed => (upper_bound - lower_bound).checked_add(1)?,
                 }
             } else {
                 0

tests/ui/map_with_unused_argument_over_ranges.fixed

@@ -53,6 +53,8 @@ fn main() {
     (lower_fn()..=upper_fn()).map(|_| do_something()); // Ranges not starting at zero not yet handled
     (0..10).map(|x| do_something_interesting(x, 4)); // Actual map over range
     "Foobar".chars().map(|_| do_something()); // Not a map over range
+    // i128::MAX == 340282366920938463463374607431768211455
+    (0..=340282366920938463463374607431768211455).map(|_: u128| do_something()); // Can't be replaced due to overflow
 }
 
 #[clippy::msrv = "1.27"]

tests/ui/map_with_unused_argument_over_ranges.rs

@@ -53,6 +53,8 @@ fn main() {
     (lower_fn()..=upper_fn()).map(|_| do_something()); // Ranges not starting at zero not yet handled
     (0..10).map(|x| do_something_interesting(x, 4)); // Actual map over range
     "Foobar".chars().map(|_| do_something()); // Not a map over range
+    // i128::MAX == 340282366920938463463374607431768211455
+    (0..=340282366920938463463374607431768211455).map(|_: u128| do_something()); // Can't be replaced due to overflow
 }
 
 #[clippy::msrv = "1.27"]

tests/ui/map_with_unused_argument_over_ranges.stderr

@@ -197,7 +197,7 @@ LL +     std::iter::repeat_with(|| do_something()).take((1 << 4) - 0);
    |
 
 error: map of a closure that does not depend on its parameter over a range
-  --> tests/ui/map_with_unused_argument_over_ranges.rs:65:5
+  --> tests/ui/map_with_unused_argument_over_ranges.rs:67:5
    |
 LL |     (0..10).map(|_| do_something());
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^