Auto merge of rust-lang#118879 - Nadrieril:lint-range-gap, r=estebank

Lint singleton gaps after exclusive ranges

In the discussion to stabilize exclusive range patterns (rust-lang#37854), it has often come up that they're likely to cause off-by-one mistakes. We already have the `overlapping_range_endpoints` lint, so I [proposed](rust-lang#37854 (comment)) a lint to catch the complementary mistake.

This PR adds a new `non_contiguous_range_endpoints` lint that catches likely off-by-one errors with exclusive range patterns. Here's the idea (see the test file for more examples):
```rust
match x {
    0..10 => ..., // WARN: this range doesn't match `10_u8` because `..` is an exclusive range
    11..20 => ..., // this could appear to continue range `0_u8..10_u8`, but `10_u8` isn't matched by either of them
    _ => ...,
}
// help: use an inclusive range instead: `0_u8..=10_u8`
```

More precisely: for any exclusive range `lo..hi`, if `hi+1` is matched by another range but `hi` isn't, we suggest writing an inclusive range `lo..=hi` instead. We also catch `lo..T::MAX`.

Author: bors

tests/ui/manual_range_patterns.fixed

@@ -1,4 +1,5 @@
 #![allow(unused)]
+#![allow(non_contiguous_range_endpoints)]
 #![warn(clippy::manual_range_patterns)]
 #![feature(exclusive_range_pattern)]
 

tests/ui/manual_range_patterns.rs

@@ -1,4 +1,5 @@
 #![allow(unused)]
+#![allow(non_contiguous_range_endpoints)]
 #![warn(clippy::manual_range_patterns)]
 #![feature(exclusive_range_pattern)]
 

tests/ui/manual_range_patterns.stderr

@@ -1,5 +1,5 @@
 error: this OR pattern can be rewritten using a range
-  --> tests/ui/manual_range_patterns.rs:8:25
+  --> tests/ui/manual_range_patterns.rs:9:25
    |
 LL |     let _ = matches!(f, 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10);
    |                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `1..=10`
@@ -8,109 +8,109 @@ LL |     let _ = matches!(f, 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10);
    = help: to override `-D warnings` add `#[allow(clippy::manual_range_patterns)]`
 
 error: this OR pattern can be rewritten using a range
-  --> tests/ui/manual_range_patterns.rs:9:25
+  --> tests/ui/manual_range_patterns.rs:10:25
    |
 LL |     let _ = matches!(f, 4 | 2 | 3 | 1 | 5 | 6 | 9 | 7 | 8 | 10);
    |                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `1..=10`
 
 error: this OR pattern can be rewritten using a range
-  --> tests/ui/manual_range_patterns.rs:16:25
+  --> tests/ui/manual_range_patterns.rs:17:25
    |
 LL |     let _ = matches!(f, 1 | (2..=4));
    |                         ^^^^^^^^^^^ help: try: `1..=4`
 
 error: this OR pattern can be rewritten using a range
-  --> tests/ui/manual_range_patterns.rs:17:25
+  --> tests/ui/manual_range_patterns.rs:18:25
    |
 LL |     let _ = matches!(f, 1 | (2..4));
    |                         ^^^^^^^^^^ help: try: `1..4`
 
 error: this OR pattern can be rewritten using a range
-  --> tests/ui/manual_range_patterns.rs:18:25
+  --> tests/ui/manual_range_patterns.rs:19:25
    |
 LL |     let _ = matches!(f, (1..=10) | (2..=13) | (14..=48324728) | 48324729);
    |                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `1..=48324729`
 
 error: this OR pattern can be rewritten using a range
-  --> tests/ui/manual_range_patterns.rs:19:25
+  --> tests/ui/manual_range_patterns.rs:20:25
    |
 LL |     let _ = matches!(f, 0 | (1..=10) | 48324730 | (2..=13) | (14..=48324728) | 48324729);
    |                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `0..=48324730`
 
 error: this OR pattern can be rewritten using a range
-  --> tests/ui/manual_range_patterns.rs:20:25
+  --> tests/ui/manual_range_patterns.rs:21:25
    |
 LL |     let _ = matches!(f, 0..=1 | 0..=2 | 0..=3);
    |                         ^^^^^^^^^^^^^^^^^^^^^ help: try: `0..=3`
 
 error: this OR pattern can be rewritten using a range
-  --> tests/ui/manual_range_patterns.rs:23:9
+  --> tests/ui/manual_range_patterns.rs:24:9
    |
 LL |         1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 => true,
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `1..=10`
 
 error: this OR pattern can be rewritten using a range
-  --> tests/ui/manual_range_patterns.rs:26:25
+  --> tests/ui/manual_range_patterns.rs:27:25
    |
 LL |     let _ = matches!(f, -1 | -5 | 3 | -2 | -4 | -3 | 0 | 1 | 2);
    |                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `-5..=3`
 
 error: this OR pattern can be rewritten using a range
-  --> tests/ui/manual_range_patterns.rs:28:25
+  --> tests/ui/manual_range_patterns.rs:29:25
    |
 LL |     let _ = matches!(f, -1_000_000..=1_000_000 | -1_000_001 | 1_000_001);
    |                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `-1_000_001..=1_000_001`
 
 error: this OR pattern can be rewritten using a range
-  --> tests/ui/manual_range_patterns.rs:31:17
+  --> tests/ui/manual_range_patterns.rs:32:17
    |
 LL |     matches!(f, 0x00 | 0x01 | 0x02 | 0x03);
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `0x00..=0x03`
 
 error: this OR pattern can be rewritten using a range
-  --> tests/ui/manual_range_patterns.rs:32:17
+  --> tests/ui/manual_range_patterns.rs:33:17
    |
 LL |     matches!(f, 0x00..=0x05 | 0x06 | 0x07);
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `0x00..=0x07`
 
 error: this OR pattern can be rewritten using a range
-  --> tests/ui/manual_range_patterns.rs:33:17
+  --> tests/ui/manual_range_patterns.rs:34:17
    |
 LL |     matches!(f, -0x09 | -0x08 | -0x07..=0x00);
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `-0x09..=0x00`
 
 error: this OR pattern can be rewritten using a range
-  --> tests/ui/manual_range_patterns.rs:35:17
+  --> tests/ui/manual_range_patterns.rs:36:17
    |
 LL |     matches!(f, 0..5 | 5);
    |                 ^^^^^^^^ help: try: `0..=5`
 
 error: this OR pattern can be rewritten using a range
-  --> tests/ui/manual_range_patterns.rs:36:17
+  --> tests/ui/manual_range_patterns.rs:37:17
    |
 LL |     matches!(f, 0 | 1..5);
    |                 ^^^^^^^^ help: try: `0..5`
 
 error: this OR pattern can be rewritten using a range
-  --> tests/ui/manual_range_patterns.rs:38:17
+  --> tests/ui/manual_range_patterns.rs:39:17
    |
 LL |     matches!(f, 0..=5 | 6..10);
    |                 ^^^^^^^^^^^^^ help: try: `0..10`
 
 error: this OR pattern can be rewritten using a range
-  --> tests/ui/manual_range_patterns.rs:39:17
+  --> tests/ui/manual_range_patterns.rs:40:17
    |
 LL |     matches!(f, 0..5 | 5..=10);
    |                 ^^^^^^^^^^^^^ help: try: `0..=10`
 
 error: this OR pattern can be rewritten using a range
-  --> tests/ui/manual_range_patterns.rs:40:17
+  --> tests/ui/manual_range_patterns.rs:41:17
    |
 LL |     matches!(f, 5..=10 | 0..5);
    |                 ^^^^^^^^^^^^^ help: try: `0..=10`
 
 error: this OR pattern can be rewritten using a range
-  --> tests/ui/manual_range_patterns.rs:44:26
+  --> tests/ui/manual_range_patterns.rs:45:26
    |
 LL |             matches!($e, 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10)
    |                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `1..=10`