Pretty-print argument-position impl trait to name it.

[cjgillot]

This removes a corner case.

RPIT and TAIT keep having no name, and it would be wrong to use the one in HIR (Ident::empty), so I make this case ICE.

[rustbot]

r? @WaffleLapkin

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[WaffleLapkin]

I don't understand the reasons behind this change/the difference of RPIT/APIT in the case/implications, could you explain more? @cjgillot

[WaffleLapkin]

@rustbot author

[cjgillot]

impl-trait are currently given an anonymous def-path ImplTrait, which prints opaque with a number.

This is fine for stuff that are truly anonymous, like an RPIT or the opaques inside a TAIT. Those have an empty name in HIR.

APIT do have a name: themselves pretty-printed. So there is no real reason not to give them that name in their def-path, to be the user-facing impl MyTrait. This makes APIT behave exactly like a generic parameter named impl MyTrait, in the type namespace.

[WaffleLapkin]

@bors r+

[bors]

📌 Commit 832a2a1 has been approved by WaffleLapkin

It is now in the queue for this repository.

[bors]

⌛ Testing commit 832a2a1 with merge bdb0fa3...

[bors]

☀️ Test successful - checks-actions
Approved by: WaffleLapkin
Pushing bdb0fa3 to master...

[rust-timer]

Finished benchmarking commit (bdb0fa3): comparison URL.

Overall result: ✅ improvements - no action needed

@rustbot label: -perf-regression

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.7%	[-0.7%, -0.7%]	2
Improvements ✅ (secondary)	-0.3%	[-0.3%, -0.3%]	3
All ❌✅ (primary)	-0.7%	[-0.7%, -0.7%]	2

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
Regressions ❌ (secondary)	3.5%	[1.9%, 5.1%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

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)	-	-	0
Improvements ✅ (primary)	-1.0%	[-1.1%, -0.8%]	3
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-1.0%	[-1.1%, -0.8%]	3

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)	0.1%	[0.0%, 0.1%]	6
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Bootstrap: 631.689s -> 631.334s (-0.06%)
Artifact size: 317.88 MiB -> 317.85 MiB (-0.01%)