Fix ICE in named_arguments_used_positionally lint

[compiler-errors]

Fixes #99261
Fixes #99289
Fixes #99284
Fixes #99273
Fixes #99297
Fixes #99271
Fixes #99327
Fixes #99330

This match pattern:

 FormatSpec { width: Count::CountIsName(s, _), .. }
| FormatSpec { precision: Count::CountIsName(s, _), .. }

does not account for when both width and precision are both Count::CountIsName, so split the check for these two fields into two separate if let.

Also, remove any future potential for ICEs by removing the index operator altogether.

---

It is still suspicious that this indexing was broken and caused the ICE, as opposed to just causing a spurious lint message.

cc @PrestonFrom, who may be familiar with this code because of implementing the lint this touches, perhaps you'd like to look into why named arguments in FormatSpec.precision seem to have indices that don't correspond to a span in Context.arg_spans?

Edit: Opened #99265 to track a (related?) incorrect argument indexing issue.

[rust-highfive]

r? @jackh726

(rust-highfive has picked a reviewer for you, use r? to override)

[PrestonFrom]

@compiler-errors Thank you for fixing this! Sorry I missed this case, but I have a slight suspicion of why the indices don't match. I'll look into that -- should I create an issue for it?

[compiler-errors]

Yeah, the more issues the merrier. I'll probably only be working on getting this ICE closed out, in case you want some follow-up work 😀

[PrestonFrom]

@compiler-errors Thank you! I have opened #99266 and will look into it.

[lqd]

There seems to be a few duplicates of #99261, so this fixes an issue that a number of projects are hitting on nightly (by depending on the popular crate time).

[HTGAzureX1212]

Just a heads up, #99271 is also a duplicate.

[jyn514]

@bors p=20 (should land before rollups)

[jyn514]

r=me unless you want approval from someone familiar with this specific lint

[compiler-errors]

Thanks @jyn514, I think this change is self-contained enough that your review is sufficient.

@bors r=jyn514

Anyways if someone else does have comments on the approach in this PR, happy to follow up, but I want to fix these ICEs given the number of bugs filed.

[bors]

📌 Commit 2902b92 has been approved by jyn514

It is now in the queue for this repository.

[bors]

⌛ Testing commit 2902b92 with merge 5635158...

[BlackDex]

All the dupes i could find (Including the one i just created my self, sorry).
Original: #99261
Duplicates: #99271, #99273, #99289, #99297, #99326, #99327 and #99330

[bors]

☀️ Test successful - checks-actions
Approved by: jyn514
Pushing 5635158 to master...

[rust-timer]

Finished benchmarking commit (5635158): comparison url.

Instruction count

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

Max RSS (memory usage)

Results

• Primary benchmarks: mixed results
• Secondary benchmarks: mixed results

	mean1	max	count2
Regressions 😿 (primary)	5.3%	5.3%	1
Regressions 😿 (secondary)	2.0%	2.0%	1
Improvements 🎉 (primary)	-2.4%	-2.4%	1
Improvements 🎉 (secondary)	-2.6%	-3.5%	2
All 😿🎉 (primary)	1.5%	5.3%	2

Cycles

Results

• Primary benchmarks: no relevant changes found
• Secondary benchmarks: mixed results

	mean1	max	count2
Regressions 😿 (primary)	N/A	N/A	0
Regressions 😿 (secondary)	3.7%	3.7%	1
Improvements 🎉 (primary)	N/A	N/A	0
Improvements 🎉 (secondary)	-4.5%	-4.5%	1
All 😿🎉 (primary)	N/A	N/A	0

If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf.

@rustbot label: -perf-regression

Footnotes

1. the arithmetic mean of the percent change ↩ ↩²

2. number of relevant changes ↩ ↩²