Replace usages of vec![].into_iter with [].into_iter

[rukai]

[].into_iter is idiomatic over vec![].into_iter because its simpler and faster (unless the vec is optimized away in which case it would be the same)

So we should change all the implementation, documentation and tests to use it.

I skipped:

• src/tools - Those are copied in from upstream
• src/test/ui - Hard to tell if vec![].into_iter was used intentionally or not here and not much benefit to changing it.
• any case where vec![].into_iter was used because we specifically needed a Vec::IntoIter<T>
• any case where it looked like we were intentionally using vec![].into_iter to test it.

[rust-highfive]

r? @Mark-Simulacrum

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

[rust-highfive]

⚠️ Warning ⚠️

• These commits modify compiler targets. (See the Target Tier Policy.)

[Mark-Simulacrum]

@bors try @rust-timer queue to confirm perf is not worse (I expect roughly neutral to slight improvement, most likely)

Thanks!

[rust-timer]

Awaiting bors try build completion.

@rustbot label: +S-waiting-on-perf

[bors]

⌛ Trying commit d04936a8a3d12e310d82d6cec02105b9b9712a65 with merge 321070819ae6a777a2fcf631205d23c330f693ad...

[rukai]

Thanks!
I'll investigate the test failures tomorrow, its a bit late over here.

[bors]

☀️ Try build successful - checks-actions
Build commit: 321070819ae6a777a2fcf631205d23c330f693ad (321070819ae6a777a2fcf631205d23c330f693ad)

[rust-timer]

Queued 321070819ae6a777a2fcf631205d23c330f693ad with parent d3f3004, future comparison URL.

[rust-timer]

Finished benchmarking commit (321070819ae6a777a2fcf631205d23c330f693ad): comparison url.

Summary: This change led to moderate relevant mixed results 🤷 in compiler performance.

• Moderate improvement in instruction counts (up to -0.9% on incr-unchanged builds of externs)
• Small regression in instruction counts (up to 1.8% on incr-patched: println builds of regression-31157)

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

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR led to changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please fix the regressions and do another perf run. If the next run shows neutral or positive results, the label will be automatically removed.

@bors rollup=never
@rustbot label: +S-waiting-on-review -S-waiting-on-perf +perf-regression

[rukai]

The build failures look like they will all be resolved by #92068 so i'll put this PR on hold until that lands.

Not sure how the benchmarks successfully ran when the PR doesnt even build.
Does it maybe not use the std/core from my PR?

[Mark-Simulacrum]

@bors try @rust-timer queue

mingw-check looks to be failing due to tests not building, which are not required to produce artifacts for try builds. Going to rerun the perf build since it looks like it might've been a little bit due to noise.

[rust-timer]

Awaiting bors try build completion.

@rustbot label: +S-waiting-on-perf

[bors]

⌛ Trying commit 988539835929405f9b233ab5b17ed149bc9ce6f3 with merge f5a08fefa57a109a7b8253b284666479011847b4...

[bors]

☀️ Try build successful - checks-actions
Build commit: f5a08fefa57a109a7b8253b284666479011847b4 (f5a08fefa57a109a7b8253b284666479011847b4)

[rust-timer]

Queued f5a08fefa57a109a7b8253b284666479011847b4 with parent 5883b87, future comparison URL.

[rust-timer]

Finished benchmarking commit (f5a08fefa57a109a7b8253b284666479011847b4): comparison url.

Summary: This benchmark run did not return any relevant changes.

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

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR led to changes in compiler perf.

@bors rollup=never
@rustbot label: +S-waiting-on-review -S-waiting-on-perf -perf-regression

[rukai]

Alright, this PR is ready for review again.

[Mark-Simulacrum]

Thanks -- this looks great to me now.

@bors r+

[bors]

📌 Commit 0882985 has been approved by Mark-Simulacrum

[klensy]

Is there clippy lint for this? If no, maybe you create suggestion to add it?

[bors]

⌛ Testing commit 0882985 with merge 2e2c86e...

[bors]

☀️ Test successful - checks-actions
Approved by: Mark-Simulacrum
Pushing 2e2c86e to master...

[rust-timer]

Finished benchmarking commit (2e2c86e): comparison url.

Summary: This benchmark run did not return any relevant changes.

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

@rustbot label: -perf-regression