Suggest name value cfg when only value is used for check-cfg

[chenyukang]

Fixes #120427
r? @Nilstrieb

[Urgau]

I don't think this instability can be dismissed. It's possible that two or more different cfgs have the same value that we are searching for, in which case we should either suggest both or none.

@rustbot author

[chenyukang]

ah, we still need to keep #[allow(rustc::potential_query_instability)] to remove the warning because we use iter()...

[Urgau]

This is an unfortunate limitation of the lint, it doesn't detect the following sort() call. Can you add a comment explaining that this is fine since we sort the list just below.

[chenyukang]

I'm curious why keys() and values() don't have potential_query_instability, and into_keys(), into_values() have that property, according to the document, they are all in arbitrary order.

rust/library/std/src/collections/hash/map.rs

Lines 336 to 362 in 6351247

	/// An iterator visiting all keys in arbitrary order.
	/// The iterator element type is `&'a K`.
	///
	/// # Examples
	///
	/// ```
	/// use std::collections::HashMap;
	///
	/// let map = HashMap::from([
	/// ("a", 1),
	/// ("b", 2),
	/// ("c", 3),
	/// ]);
	///
	/// for key in map.keys() {
	/// println!("{key}");
	/// }
	/// ```
	///
	/// # Performance
	///
	/// In the current implementation, iterating over keys takes O(capacity) time
	/// instead of O(len) because it internally visits empty buckets too.
	#[stable(feature = "rust1", since = "1.0.0")]
	pub fn keys(&self) -> Keys<'_, K, V> {
	Keys { inner: self.iter() }
	}

[Urgau]

It's missing the custom rustc attribute #[rustc_lint_query_instability] like in the into_keys function:

rust/library/std/src/collections/hash/map.rs

Lines 484 to 486 in 6351247

	#[rustc_lint_query_instability]
	#[stable(feature = "map_into_keys_values", since = "1.54.0")]
	pub fn into_values(self) -> IntoValues<K, V> {

This could added in another PR.

[chenyukang]

yeah, I know it's missing #[rustc_lint_query_instability], I was wondering if there is any special reason here, but they are actually all iter in the inner.

I will create another pr later.

[Urgau]

This looks almost perfect :)

Just one last thing to improve.

[chenyukang]

@rustbot ready

[Noratrieb]

Thanks, and thanks @Urgau for the review!
One last thing: Could you add a test for the >3 case?
r=Urgau,Nilstrieb then

[Noratrieb]

@bors r=Urgau,Nilstrieb

[bors]

📌 Commit ca243e7 has been approved by Urgau,Nilstrieb

It is now in the queue for this repository.