Lint singleton gaps after exclusive ranges

[Nadrieril]

In the discussion to stabilize exclusive range patterns (#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 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):

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.

[Nadrieril]

Let's see if this makes unicode_normalization sad.

@bors try @rust-timer queue

[bors]

⌛ Trying commit 89053d1 with merge 8b07d6f...

[bors]

💔 Test failed - checks-actions

[bors]

💔 Test failed - checks-actions

[Nadrieril]

@bors r=@estebank

[bors]

📌 Commit 8ac9a04 has been approved by estebank

It is now in the queue for this repository.

[bors]

⌛ Testing commit 8ac9a04 with merge 1b427b3...

[bors]

☀️ Test successful - checks-actions
Approved by: estebank
Pushing 1b427b3 to master...

[rust-timer]

Finished benchmarking commit (1b427b3): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	2.9%	[2.9%, 2.9%]	1
Regressions ❌ (secondary)	2.5%	[1.6%, 5.2%]	5
Improvements ✅ (primary)	-0.6%	[-0.6%, -0.6%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.2%	[-0.6%, 2.9%]	2

Cycles

This benchmark run did not return any relevant results for this metric.

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 650.25s -> 650.027s (-0.03%)
Artifact size: 172.57 MiB -> 172.57 MiB (-0.00%)