[rustdoc] Correctly handle intra-doc links on inlined same item with different names

[GuillaumeGomez]

Fixes #136777.

It works as follow: we keep the DefId indexing, but we add a new alternatives entry (same inlined items, but under a different path) which allows to pick the right entry.

So now, why this approach instead of changing the indexing (like (DefId, Symbol))? Because it's much less common to import a same item with different names, so increasing the size of the index seems unnecessary. That does make the code more noisy, which I'm not a big fan of, so if someone has ideas for improvements, definitely interested!

r? @lolbinarycat

[GuillaumeGomez]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: 99fb368 (99fb3688c36e7a0926fe47967953f64fb06a366a)
Base parent: 0fc1413 (0fc141305da7a8a222f65aef1f1acc739c46282b)

[rust-timer]

Finished benchmarking commit (99fb368): comparison URL.

Overall result: no relevant changes - no action needed

Benchmarking means the PR may be perf-sensitive. Consider adding rollup=never if this change is not fit for rolling up.

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

Instruction count

This perf run didn't have relevant results for this metric.

Max RSS (memory usage)

Results (primary -0.0%, secondary -1.1%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	0.7%	[0.5%, 1.1%]	3
Regressions ❌ (secondary)	3.9%	[3.9%, 3.9%]	1
Improvements ✅ (primary)	-0.6%	[-0.8%, -0.4%]	4
Improvements ✅ (secondary)	-6.0%	[-6.0%, -6.0%]	1
All ❌✅ (primary)	-0.0%	[-0.8%, 1.1%]	7

Cycles

Results (primary 0.1%, secondary 1.2%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	0.9%	[0.4%, 1.7%]	8
Regressions ❌ (secondary)	1.2%	[1.2%, 1.2%]	1
Improvements ✅ (primary)	-0.7%	[-1.0%, -0.5%]	7
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.1%	[-1.0%, 1.7%]	15

Binary size

Results (primary 0.0%, secondary 0.0%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	0.0%	[0.0%, 0.1%]	4
Regressions ❌ (secondary)	0.0%	[0.0%, 0.1%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.0%	[0.0%, 0.1%]	4

Bootstrap: 492.706s -> 494.246s (0.31%)
Artifact size: 406.91 MiB -> 406.92 MiB (0.00%)

[GuillaumeGomez]

That's an unexpected good surprise. =D