Add help diag. for const = Enum missing braces around Enum

[JulianKnodt]

Previously it was not clear why this errored or if it was even supported, as there was no diagnostic that suggested wrapping it in braces.

Thus, add a simple diagnostic that suggests wrapping enum variants in braces.

Fixes #105927

[rustbot]

r? @cjgillot

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[cjgillot]

Why is this suggestion correct in general?
AFAIK, disambiguating using braces only works for equality associated constraints.
The suggestion needs to be restricted to this case, doesn't it?

[JulianKnodt]

Do you mean as opposed to other const generics? Disambiguating with braces also works for functions in generic const positions.
By this case, do you mean specifically for when the constraint is a const?

[cjgillot]

I mean as opposed to all the other places where one can put a type.
Does this suggestion fire with this?

fn foo() -> Mode::Cool { /* ... */ }

[JulianKnodt]

It does fire, I'll try to see where to change to make it not

[JulianKnodt]

I've changed it to be only for associated equality, but it's not so specific to enums.

[cjgillot]

@bors r+

[bors]

📌 Commit 077fae9 has been approved by cjgillot

It is now in the queue for this repository.

[bors]

⌛ Testing commit 077fae9 with merge d72b7d2...

[bors]

☀️ Test successful - checks-actions
Approved by: cjgillot
Pushing d72b7d2 to master...

[rust-timer]

Finished benchmarking commit (d72b7d2): comparison URL.

Overall result: ❌ regressions - 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)	1.3%	[1.3%, 1.3%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

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)	-	-	0
Improvements ✅ (primary)	-2.9%	[-2.9%, -2.9%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.9%	[-2.9%, -2.9%]	1

Cycles

This benchmark run did not return any relevant results for this metric.