rustdoc: stop preloading Source Serif 4 Bold

[notriddle]

According to #91170, italic fonts are not preloaded because they're rarely used, but bold fonts are. This seems to be true of bold Source Code Pro and bold Fira Sans, but bold and italic Source Serif Pro seem to be equally heavily used.

This is, I assume, the result of using Fira Sans Bold and Source Code Bold headings, so you only get bold Serif text when the doc author uses strong ** emphasis (or within certain kinds of tooltip, which shouldn't be preloaded because they only show up long after the page is loaded).

To check this, run these two commands in the browser console to measure how much they're used. The measurement is extremely rough, but it gets the idea across: the two styles are about equally popular.

// count bold elements
Array.prototype.slice.call(document.querySelectorAll("*")).filter(x => { const y = document.defaultView.getComputedStyle(x); return y.fontFamily.indexOf("Source Serif 4") !== -1 && y.fontWeight > 400 }).length
// count italic elements
Array.prototype.slice.call(document.querySelectorAll("*")).filter(x => { const y = document.defaultView.getComputedStyle(x); return y.fontFamily.indexOf("Source Serif 4") !== -1 && y.fontStyle == "italic" }).length

URL	Bold	Italic
std	2	9
Vec	8	89
regex	33	17
test_suite	0	0

[rustbot]

r? @jsha

(rustbot has picked a reviewer for you, use r? to override)

[GuillaumeGomez]

Please re-assign to someone else @notriddle if the reviewer is not available. 😉

Thanks for this!

@bors r+ rollup

[bors]

📌 Commit 2a92981 has been approved by GuillaumeGomez

It is now in the queue for this repository.

[bors]

⌛ Testing commit 2a92981 with merge 9bd71af...

[bors]

☀️ Test successful - checks-actions
Approved by: GuillaumeGomez
Pushing 9bd71af to master...

[rust-timer]

Finished benchmarking commit (9bd71af): 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)	0.5%	[0.5%, 0.5%]	1
Regressions ❌ (secondary)	0.9%	[0.9%, 0.9%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.5%	[0.5%, 0.5%]	1

Cycles

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)	-	-	0
Regressions ❌ (secondary)	2.4%	[2.3%, 2.5%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.6%	[-0.6%, -0.6%]	1
All ❌✅ (primary)	-	-	0

Binary size

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)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.0%	[-0.0%, -0.0%]	3
Improvements ✅ (secondary)	-0.0%	[-0.0%, -0.0%]	1
All ❌✅ (primary)	-0.0%	[-0.0%, -0.0%]	3

Bootstrap: 663.805s -> 663.998s (0.03%)
Artifact size: 308.97 MiB -> 308.95 MiB (-0.01%)