rustdoc: write directly to buffer in inner_full_print

[notriddle]

This change avoids several temporary allocations for every argument.

[rust-highfive]

r? @CraftSpider

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[CraftSpider]

This looks fine, going to do a perf run and see if it has any impact. I think it's...
@bors try @rust-timer queue

[rust-timer]

Awaiting bors try build completion.

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

[bors]

⌛ Trying commit 41de685 with merge e22cfc7e9d1b50e293ac3caff191a248bd48c108...

[bors]

☀️ Try build successful - checks-actions
Build commit: e22cfc7e9d1b50e293ac3caff191a248bd48c108 (e22cfc7e9d1b50e293ac3caff191a248bd48c108)

[rust-timer]

Queued e22cfc7e9d1b50e293ac3caff191a248bd48c108 with parent 4566094, future comparison URL.

[rust-timer]

Finished benchmarking commit (e22cfc7e9d1b50e293ac3caff191a248bd48c108): comparison url.

Summary: This benchmark run shows 1 relevant improvement 🎉 but 1 relevant regression 😿 to instruction counts.

• Arithmetic mean of all relevant changes: 1.5%
• Largest improvement in instruction counts: -0.9% on full builds of externs doc
• Largest regression in instruction counts: 4.0% on incr-full builds of coercions debug

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

[CraftSpider]

I'm not 100% sure how perf handles doc changes, and whether these are relevant. I'm going to ask the perf team on Zulip.

[nnethercote]

The ones labelled doc measure rustdoc speed. The website filters uninteresting results by default, you can uncheck the "Show only significant changes" and "Filter out very small changes" boxes to see all the results.

In short, very little changed. The variations you do see are almost certainly noise. I think your changes are good -- they do avoid unnecessary allocations, and make the code easier to read -- but I suspect they happen on a code path that isn't hot.

[camelid]

The regression is spurious.

@rustbot label: +perf-regression-triaged

[CraftSpider]

@bors r+

[bors]

📌 Commit 41de685 has been approved by CraftSpider

[bors]

⌛ Testing commit 41de685 with merge f58d51b...

[bors]

☀️ Test successful - checks-actions
Approved by: CraftSpider
Pushing f58d51b to master...

[rust-timer]

Finished benchmarking commit (f58d51b): comparison url.

Summary: This benchmark run did not return any relevant results. 3 results were found to be statistically significant but too small to be relevant.

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

@rustbot label: -perf-regression